Arresting the decline of the commercial and recreational
fisheries for mulloway (Argyrosomus japonicus)
Veronica Silberschneider & Charles A. Gray
NSW Department of Primary Industries
Cronulla Fisheries Research Centre of Excellence
P.O. Box 21, Cronulla, NSW, 2230
Australia
FRDC Project No. 2002/05
December 2005
NSW Department of Primary Industries Fisheries Final Report Series
No. 82
ISSN 1449-9967
Arresting the decline of the commercial and recreational fisheries for mulloway (Argyrosomus japonicus)
December 2005
Authors:
Silberschneider, V. and Gray, C.A.
Published By:
NSW Department of Primary Industries (now incorporating NSW Fisheries)
Postal Address:
Cronulla Fisheries Research Centre of Excellence, PO Box 21, NSW, 2230, Australia
Internet:
www.dpi.nsw.gov.au
NSW Department of Primary Industries and the Fisheries Research & Development Corporation
This work is copyright. Except as permitted under the Copyright Act, no part of this reproduction may be
reproduced by any process, electronic or otherwise, without the specific written permission of the copyright
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ISSN 1449-9967
(Note: Prior to July 2004, this report series was published as the ‘NSW Fisheries Final Report Series’ with ISSN
number 1440-3544)
Contents
i
TABLE OF CONTENTS
TABLE OF CONTENTS.................................................................................................................. I
LIST OF TABLES ......................................................................................................................... III
LIST OF FIGURES ....................................................................................................................... IV
LIST OF FIGURES ....................................................................................................................... IV
ACKNOWLEDGEMENTS.............................................................................................................V
NON-TECHNICAL SUMMARY ................................................................................................. VI
1.
INTRODUCTION ......................................................................................................................8
1.1. Background ...................................................................................................................8
1.2. Need...............................................................................................................................9
1.3. Objectives ......................................................................................................................9
2. A SYNOPSIS OF BIOLOGICAL, FISHERIES AND AQUACULTURE-RELATED INFORMATION ON
MULLOWAY ARGYROSOMUS JAPONICUS (PISCES: SCIAENIDAE), WITH PARTICULAR REFERENCE TO
AUSTRALIA ..................................................................................................................................10
2.1. Introduction.................................................................................................................11
2.2. Taxonomy ....................................................................................................................11
2.3. Distribution and stock structure..................................................................................11
2.4. Early life history..........................................................................................................13
2.5. Juvenile and adult distribution....................................................................................13
2.6. Movement ....................................................................................................................14
2.7. Age, growth and mortality...........................................................................................16
2.8. Reproduction ...............................................................................................................17
2.9. Diet..............................................................................................................................18
2.10.
Commercial and recreational fisheries ...................................................................18
2.11.
Bycatch and discarding...........................................................................................22
2.12.
Aquaculture .............................................................................................................23
2.13.
Enhancement of wild fish stocks..............................................................................25
2.14.
Conclusions and recommendations.........................................................................25
3. GROWTH AND REPRODUCTION OF MULLOWAY IN NSW .......................................................26
3.1. Introduction.................................................................................................................26
3.2. Methods .......................................................................................................................26
3.2.1.
Sampling procedure.............................................................................................26
3.2.2.
Estimation of age and growth..............................................................................27
3.2.3.
Size and age at maturity and timing of spawning................................................27
3.3. Results .........................................................................................................................28
3.3.1.
Age and growth ...................................................................................................28
3.3.2.
Timing of spawning and size at maturity ............................................................36
3.4. Discussion ...................................................................................................................38
4. ASPECTS OF THE COMMERCIAL FISHERY FOR MULLOWAY IN NSW ......................................41
4.1. Introduction.................................................................................................................41
4.2. Methods .......................................................................................................................41
4.2.1.
Trends in reported catch and effort .....................................................................41
4.2.2.
Length and age composition of commercial landings .........................................42
4.2.3.
Estimates of total, natural and fishing-associated mortality................................42
4.2.4.
Yield-per-recruit analyses ...................................................................................42
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
ii
Contents
4.3. Results ........................................................................................................................ 43
4.3.1.
Temporal trends in reported catch and effort ..................................................... 43
4.3.2.
Spatial trends in reported catch and effort.......................................................... 46
4.3.3.
Age Compositions of landings ........................................................................... 50
4.3.4.
Estimated total, natural and fishing-related mortality ........................................ 52
4.3.5.
Yield-per-recruit analyses .................................................................................. 52
4.4. Discussion .................................................................................................................. 56
4.4.1.
Management implications .................................................................................. 56
5. OUTCOMES AND RECOMMENDATIONS ................................................................................ 58
5.1. Benefits ....................................................................................................................... 58
5.2. Further Development ................................................................................................. 58
5.3. Planned Outcomes...................................................................................................... 58
5.4. Conclusions ................................................................................................................ 58
6. LITERATURE CITED ............................................................................................................. 60
7. APPENDICES........................................................................................................................ 66
7.1. Appendix 1 – Intellectual Property............................................................................. 66
7.2. Appendix 2 – Staff ...................................................................................................... 66
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
Contents
iii
LIST OF TABLES
Table 2.1.
Table 2.2.
Table 2.3.
Table 2.4.
Table 3.1.
Table 3.2.
Table 3.3.
Table 3.4.
Table 3.5.
Table 4.1.
Table 4.2.
Table 4.3.
Summaries of tag-recapture studies of mulloway showing numbers tagged and recaptured,
proportion showing no movement (< 10 km from tag location), greatest distances travelled
and maximum times at liberty. .............................................................................................16
Comparisons of estimated length (TL; cm) at age for mulloway.........................................17
Estimated commercial and recreational catches of mulloway in Australia in 2001. Data on
recreational catches are from the National Recreational and Indigenous Fishing Survey
(Henry & Lyle 2003)............................................................................................................19
The proportion of total reported commercial catch of mulloway taken in each fishery in
NSW for the years 1997/98 and 2002/03.............................................................................21
Macroscopic ovary and teste staging schedule used for mulloway......................................28
Age-length key for all mulloway sampled during the present study (2002-2005)...............29
Age-length-key for mulloway caught in estuaries throughout the study. ............................30
Age-length key for mulloway caught in ocean waters throughout the study. ......................31
Comparisons of estimated length (TL; cm) at age for mulloway from published growth
equations based on otolith-based age estimates. Lengths derived using the growth equation
and parameters given in the manuscript (Griffiths & Hecht 1995) and from the current
study. ....................................................................................................................................39
Number of commercial fishers that reported catching mulloway from 1984/85 to 2003/04.45
Mean proportion of total reported mulloway catch attributed to each fishery and the
proportion attributable to the main method within each separate fishery between 1997/98
and 2003/04..........................................................................................................................46
Optimum lengths at first capture (cm TL) for mulloway in relation to exploitation rate and
M/K. Linf = 131. ..................................................................................................................55
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
iv
Contents
LIST OF FIGURES
Figure 2.1.
Figure 2.2.
Figure 2.3.
Figure 2.4.
Figure 3.1.
Figure 3.2.
Figure 3.3.
Figure 3.4.
Figure 3.5.
Figure 3.6.
Figure 3.7.
Figure 3.8.
Figure 4.1.
Figure 4.2.
Figure 4.3.
Figure 4.4.
Figure 4.5.
Figure 4.6.
Figure 4.7.
Figure 4.8.
Figure 4.9.
Figure 4.10.
Figure 4.11.
Figure 4.12.
Figure 4.13.
Map of the world showing the known geographical distribution of mulloway. .................. 12
Map showing locations of release and recapture of tagged mulloway in New South Wales,
Australia............................................................................................................................... 15
Reported commercial catches of mulloway in NSW since 1940/41 and associated changes
in MLL, number of NSW fishers reporting catch of this species, and commercial catches
from South Australia............................................................................................................ 20
Estimated length compositions of retained fish from commercial catches of mulloway in
NSW for three periods between 1972 and 1999. ................................................................. 21
von Bertalanffy growth curve of mulloway sampled in NSW............................................. 32
Age – fish weight relationship of mulloway sampled in NSW............................................ 32
Length (mean ± se) at age of male and female mulloway sampled in NSW ....................... 33
Relationship between otolith weight and a) age, b) fish total length, and c) fish weight of
mulloway sampled in NSW. ................................................................................................ 34
Marginal increment analysis for a) 0+ (n = 317), b) 1+ (n = 133), c) 2+ (n = 1425), and d) 3+
or older (n = 682) aged fish for the 2002 - 2005 period. ..................................................... 35
Length-weight relationship of mulloway sampled in NSW................................................. 36
Estimated size at maturity of a) male and b) female mulloway based on 2 cm size classes 37
Estimated age at maturity of a) male and b) female mulloway based on yearly age classes38
Reported total commercial catches of mulloway in NSW between 1940/41 and 2003/04 and
associated changes in MLL.................................................................................................. 44
Total reported commercial landed catch (kg) and catch per unit of effort (kg per month) in
NSW from 1984/85 to 2003/04. .......................................................................................... 44
Total estimated landed catch (kg) by fishery in NSW from 1997/98. ................................. 45
CPUE (kg/day) of mulloway for the Estuary General and Ocean Trap & Line fisheries for
each year between 1997/98 and 2003/04............................................................................. 47
Total reported estuarine and coastal landings of mulloway by ocean zone for 2003/04.
Landings for ocean zones include estuarine landings from that area................................... 47
Mean (± standard errors) of reported landings by month for the Estuary General and Ocean
Trap & Line fisheries between 1997/98 and 2003/04.......................................................... 48
Length class distribution (1 cm size classes) of sampled commercial retained catches of
mulloway by region. Dotted line indicates 45 cm MLL. ..................................................... 49
Estimated length compositions of retained commercial catches of mulloway in NSW for
four periods between 1972 and 2005................................................................................... 49
Length composition of sampled estuarine and ocean commercial catches of mulloway
(pooled across regions). ....................................................................................................... 50
Estimated age compositions of samples of a) the total commercial catch (n = 2605), b) the
estuarine catch (n = 1681), and c) ocean retained commercial catches (n = 381) of
mulloway in NSW 2003 to 2005. ........................................................................................ 51
Linear regressions fitted to the natural logarithms (ln) of age composition for mulloway.. 52
Yield per recruit trajectories for mulloway calculated using the program B-H3 (Saila et al.
1988).................................................................................................................................... 53
Yield-per-recruit isopleths for mulloway for different scenarios of M/K............................ 54
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
Acknowledgments
v
ACKNOWLEDGEMENTS
This was a jointly funded study between the NSW Department of Primary Industries and the
Fisheries Research and Development Corporation.
We thank the many commercial fishers who assisted in the collection of samples and allowed us
access to their fish catches. In particular, Terry Haack provided insight into the fishery and
collected undersize individuals.
Numerous staff at the Cronulla Fisheries Research Centre provided assistance and advice during
the project. In particular, Paul Lokys helped process otolith and gonad samples, Kerrie Deguara, Jo
Fearman, James McLeod, Damian Young, Lachlan Barnes, James Mansfield and Victoria Andrews
provided technical assistance in the Sydney Fish Market and/or field, and John Stewart did the
yield-per-recruit analyses and advised on ageing procedures. The centre’s librarians, Carolyn Bland
and Kathy Bown, helped source many reference material for the review. Kevin Rowling provided
historical data from the Sydney Fish Markets.
Ian Potter and Bryn Farmer at Murdoch University in Western Australia provided discussions and
exchange of material.
Dr’s Kevin Rowling, John Stewart and Steve Kennelly provided constructive comments on the
report. We also thank the numerous researchers in the Wild Fisheries Program for discussions over
many aspects of the study and acknowledge the fruitful discussions and contributions of staff in the
Fisheries Management Branch and individual commercial and recreational fishers for their thoughts
concerning the biology and fisheries of mulloway.
Abbreviation of Title, Authors
FRDC Project No. 2002/005
vi
Non Technical Summary
NON-TECHNICAL SUMMARY
2002/005
Arresting the decline of the commercial and recreational fisheries for mulloway
(Argyrosomus japonicus)
PRINCIPAL INVESTIGATOR:
TECHNICAL OFFICER:
Charles A. Gray
Veronica Silberschneider
ADDRESS:
NSW Department of Primary Industries
Cronulla Fisheries Research Centre
PO Box 21
Cronulla, NSW, 2230
Telephone: 02 9527 8411 Fax: 02 9527 8576
OBJECTIVES:
(1)
Synthesize, write and publish a review of the biology and fisheries of mulloway (and other
relevant sciaenid species) in an international scientific journal and provide a layman’s
summary that can be given to stakeholders.
(2)
Reanalyse all existing tagging information on mulloway.
(3)
Describe the growth and age and reproductive biology of mulloway in NSW and do yieldper-recruit analyses.
(4)
Determine the length, sex and age compositions of commercial catches of mulloway and
assess how these vary between different gear types, industry sectors (e.g. estuary v ocean)
and regionally.
(5)
Advise the commercial and recreational fishing communities and other interest groups on
the biology of mulloway and provide recommendations on ways to stop the apparent
decline in populations and future management and assessment strategies for the species.
NON TECHNICAL SUMMARY:
Outcomes Achieved
This study provides the first description and analysis of the age, growth and aspects of the
reproductive biology and fisheries of mulloway in NSW. Collation of statistics on the commercial
fishery and sampling of catches for length and age composition were used to assess the current
status of mulloway. The data show that mulloway are growth overfished and changes in the
management of the species including greater protection to spawners and juvenile fish are required
for arresting the decline in populations in NSW. Proposed changes in the minimum legal length of
mulloway are currently being discussed with the commercial and recreational fishing industries.
For some time there has been concern over the status of the population of mulloway (Argyrosomus
japonicus) in NSW. This concern has primarily been driven by the continuing declines over the
past two decades in reported commercial catches, recreational fishers reporting reduced catches and
fewer large fish, and the identification that large numbers of juveniles are discarded as bycatch
from estuarine and coastal prawn trawlers.
Mulloway are distributed in estuarine and nearshore Pacific and Indian Ocean waters surrounding
Australia, Africa, India, Pakistan, China, Korea and Japan. Mulloway are commercially and
recreationally fished throughout their distribution and the species is also the basis of a growing
aquaculture industry in Australia. A review of the published scientific literature on mulloway
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
Non Technical Summary
vii
indicated a dearth of information concerning their biology and fisheries, except for southern Africa
where the biology of mulloway is relatively well studied. In South Africa, mulloway is a fast
growing fish that can live to a relatively old age (42+ years) and large size (> 175 cm TL). In South
Africa mulloway is considered recruitment overfished.
This current study in NSW identified that, like in South Africa, mulloway grow fast reaching, on
average, nearly 40 cm TL in 1 year and 95 cm TL in 5 years. Mulloway in NSW reach sexual
maturity at a size of approximately 68 and 51 cm TL for females and males respectively and at an
age of 2+ to 3+ years. These lengths and ages are significantly smaller and younger than
corresponding attributes for mulloway in South Africa, highlighting the need for local data to fully
understand the biological characteristics of a species for management considerations. Mulloway
appear to predominantly spawn in ocean waters between November and March in NSW.
In NSW, mulloway are primarily caught using mesh (gill) nets in estuaries and by line in ocean
waters. Analyses of the statistics of commercial fisheries of mulloway in NSW showed that
reported catches have been declining in both the ocean and estuary sectors. However reported
fishing effort has also declined and this may be the reason for the observed declines in total
landings. The sampling of catches for length and age composition showed that most (approximately
80%) mulloway were within 15 cm of the minimum legal length (MLL = 45 cm TL) and that very
few large (> 70 cm TL) fish contributed to commercial catches. Furthermore, commercial catches
were dominated (> 70%) by fish aged 2 years. These data are disturbing given that these fish can
potentially grow to > 175 cm TL and reach ages of 40+ years. Estimates of total mortality based on
catch-curve-analyses were relatively high (0.45 – 0.7) and yield-per-recruit analyses identified that
the MLL of mulloway needs to be increased greatly (to at least 70 cm TL) for optimal harvesting of
the species. The data presented are indicative of a species that is growth overfished.
Changes in the management arrangements of mulloway are required for their effective conservation
and sustainable harvesting. Greater protection to the spawning population and to juveniles in
estuaries from capture in the prawn trawl fisheries is required. Implementation of bycatch reduction
devices (BRD’s) in the estuarine prawn trawl fleet should help with the latter, but a significant
increase in MLL and possible seasonal and spatial closures to fishing may be required to protect the
spawning population.
KEYWORDS: Argyrosomus japonicus, Mulloway, Sciaenidae, Fishery analysis
Mulloway biology and fishery assessment, Silberschneider and Gray
Project No. 2002/05
8
NSW Dept of Primary Industries
1.
INTRODUCTION
1.1.
Background
For some time there has been considerable controversy surrounding the status and allocation of the
coastal and estuarine fisheries resources in NSW. For several of the major species, there is adequate
biological and fisheries-related data available to base many important management strategies (e.g.
appropriate legal lengths). Over the past 8 years NSW Fisheries has developed procedures for
sampling the biology and fisheries of several important species of estuarine and coastal fishes.
These procedures were primarily developed via funding from FRDC (e.g. FRDC 93/074, 94/042,
94/024, 95/151, 97/125). These initial studies have been rolled over into ongoing monitoring and
assessment of stocks of these species (e.g. snapper, sea mullet, bream, dusky flathead, yellowtail
scad). Whilst stock assessments are now being undertaken for some of our important fish species,
there is only rudimentary fishery and biological information available for many other major
species, including mulloway (Argyrosomus japonicus). The objective of this proposed study is to
redress this situation for mulloway, so to provide information essential to the sustainable
management of the species in NSW.
Mulloway are a relatively long-lived (> 40 years) species that can attain a large size (> 2 m) and
weight (> 40 kg) (Kailola et al. 1993, Griffiths & Hecht 1995). They are caught by commercial and
recreational fishers in all Australian states except Tasmania, and are also important to fisheries in
southern Africa, Japan and Taiwan. In NSW, mulloway are an important component of the Estuary
General and Ocean Trap and Line fisheries and are commonly caught as bycatch in estuarine and
coastal prawn fisheries. Mulloway are also highly sought after by recreational fishers throughout
Australia. An aquaculture industry is developing for mulloway in NSW and the species has been
the subject of stock enhancement trials (FRDC 95/148; Fielder et al. 1999).
Reported commercial catches of mulloway in NSW have declined dramatically over the past 15
years (1983/84 to 2003/04) from approx. 117 to 21 tonnes in ocean waters and from approx. 45 to
41 tonnes in estuarine waters. Hence, there is considerable concern over the status of the stock and,
whilst there has been much discussion whether this reported commercial catch data is indicative of
stock abundance (highlighted in the NSW Fisheries Catch and Effort Working Group report), there
is virtually no other biological or fisheries-related data available on which to base current and
future management strategies for the species. In NSW, mulloway are currently managed through a
combination of gear restrictions, minimum legal length and bag limits and spatial and temporal
closures. Information on the age, growth and demographic characteristics of commercial and
recreational catches is required to make more informed management decisions concerning the
species. The proposed study aims to collect this very important information for this species and to
synthesise this and all other available information to advise fisheries managers and other relevant
groups of the status of the fishery and future management strategies for stopping the apparent
decline in the populations of this species.
At present, there is only limited published information concerning the biology and ecology of
mulloway in the wild in Australia (e.g. Hall 1984, Gray & McDonall 1993, West 1993), and not all
of the data collected on mulloway have been analysed. For example, mulloway have been tagged in
NSW but only very preliminary analyses have been made of the data (West 1993). Further, the
only detailed description of a fishery for mulloway is that by Hall (1986) in South Australia.
Elsewhere, there are generally fragmented pieces of information concerning commercial and
recreational catches. For example, several discrete surveys of recreational fishing have been done
in NSW that include data on mulloway. All available data on mulloway needs to be collated and
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
NSW Dept of Primary Industries
9
synthesised to provide a concise critique of the biology, ecology and fisheries of the species. This
will provide the foundation for discussions and decisions on future research and management
options for the species.
1.2.
Need
There is a need to synthesize all existing information and to obtain new basic biological and
fisheries-related information on mulloway to be able to make informed management decisions
concerning the continued sustainable harvesting of the species in NSW waters and elsewhere and to
arrest the apparent decline in populations. Most importantly, the growth and age of mulloway
needs to be accurately described and data on the length, sex and age compositions of catches and
how these vary between different fishing sectors and gear types needs to be collected and analysed
to provide us with even the most basic understanding of the potential effects of fishing on this very
important species. Yield-per-recruit analyses need to be done to aid discussions on appropriate
legal lengths.
1.3.
Objectives
1 Synthesize, write and publish a review of the biology and fisheries of mulloway (and other
relevant sciaenid species) in an international scientific journal and provide a layman’s summary
that can be given to stakeholders (Chapter 2).
2 Reanalyse all existing tagging information on mulloway (Chapters 2 and 3).
3 Describe the growth and age and reproductive biology of mulloway in NSW and do yield-perrecruit analyses (Chapter 3).
4 Determine the length, sex and age compositions of commercial catches of mulloway and assess
how these vary between different gear types, industry sectors (e.g. estuary v ocean) and regionally
(Chapter 4).
5 Advise the commercial and recreational fishing communities and other interest groups on the
biology of mulloway and provide recommendations on ways to stop the apparent decline in
populations and future management and assessment strategies for the species (ongoing).
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
10
2.
NSW Dept of Primary Industries
A
SYNOPSIS
OF
BIOLOGICAL,
AQUACULTURE-RELATED
MULLOWAY
ARGYROSOMUS
FISHERIES
INFORMATION
JAPONICUS
AND
ON
(PISCES:
SCIAENIDAE), WITH PARTICULAR REFERENCE TO
AUSTRALIA
Abstract
Argyrosomus japonicus (mulloway) is a member of the family Sciaenidae, which are commonly
known as drums and croakers. Mulloway occur in estuarine and nearshore Pacific and Indian
Ocean waters surrounding Australia, Africa, India, Pakistan, China, Korea and Japan. The biology
of mulloway is relatively well studied in South Africa but little elsewhere. Juveniles and adults are
prevalent in estuaries and nearshore coastal waters, but there may be differences in the early life
history distribution of the species between different regions, with their distribution in estuaries
linked to salinity, turbidity, freshwater flows and depth of water. Studies in South Africa found that
juvenile fish grow rapidly, attaining 35 cm TL in 1 year and 90 cm TL in 5 years, but sexual
maturity is not attained until at least 5 - 6 years of age and > 80 cm TL. The maximum reported
length and age of mulloway is 175 cm and 42 years, respectively. Spawning most likely occurs in
nearshore coastal waters, but the time of spawning varies between different geographic localities
and is probably linked to water temperature and oceanography. Juvenile fish (< 2 years) appear to
be relatively sedentary, but sub-adults and adults can move relatively large distances (> 200 km)
and such movements may be linked to pre-spawning migrations.
Mulloway is important in many recreational and commercial fisheries, but like other sciaenids, it is
prone to overfishing. In South Africa the species is classified as recruitment overfished, and
Australian commercial fisheries are generally characterised by declining catches. The levels of
discarding of juveniles in prawn-trawl fisheries are a concern and much research has been done to
minimize their capture. An aquaculture industry is developing for mulloway in Australia and
preliminary research on the impacts and success of replenishing wild populations has begun.
Greater information on rates of growth, size and age at attainment of sexual maturity, length and
age compositions of commercial and recreational harvests and exploitation rates in Australia is
required to provide better advice concerning management of Australian fisheries. Greater
protection of spawners and improved fishing practices to enhance survival of discarded juveniles
may be required to arrest the apparent decline in Australian populations.
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
NSW Dept of Primary Industries
2.1.
11
Introduction
Argyrosomus japonicus (mulloway) is a member of the family Sciaenidae, commonly referred to as
croakers and drums. Sciaenids are mostly demersal fishes found in fresh, estuarine and coastal
marine waters in subtropical to temperate regions of the Atlantic, Indian and Pacific Oceans. The
family contains approximately 70 genera and up to 270 species worldwide, with 28 species
restricted to freshwater (Paxton & Eschmeyer 1994, Froese & Pauly 2003). Twenty species from
nine genera have been recorded from Australia, with only two species occurring in temperate
waters - Argyrosomus japonicus (Temminck & Schlegel 1843) and Attractoscion aequidens
(Cuvier, 1830) (Steffe & Neira 1998).
Sciaenids, including mulloway, are important in many commercial and recreational fisheries and
form the basis of aquaculture industries in many regions of the world. Thus there has been
significant biological, fisheries and aquaculture-related research done on many species. This review
encompasses biological, fisheries and aquaculture related studies done on mulloway.
2.2.
Taxonomy
The taxonomic relationships among sciaenids have undergone much revision in recent years.
Griffiths & Heemstra (1995) report that mulloway has been known by at least 13 other synonyms
and, until 1995, was previously misidentified as A. hololepidotus in some areas, notably Australia
and South Africa (Lin 1940, Trewavas 1977, Griffiths & Heemstra 1995). A full description of the
morphological characteristics of mulloway is given in Griffiths & Heemstra (1995). In this review,
we therefore include relevant information on A. hololepidotus from Australia that was published
prior to the most recent change in species name (i.e. to A. japonicus). In contrast, we do not include
several earlier studies done on A. hololepidotus in South Africa because they most likely represent
another previously misidentified species, A. inodorus (see Griffiths 1996).
2.3.
Distribution and stock structure
Mulloway is a nearshore coastal (< 100 m depth) species that also occurs in estuaries and is found
in Pacific and Indian Ocean waters surrounding Australia, Africa, India, Pakistan, China, Korea
and Japan (Fig. 2.1). In Australia, it is distributed along the eastern, southern and western
seaboards from the Burnett River in Queensland to North West Cape in Western Australia (Kailola
et al. 1993). It is found along the African south-east coast from the Cape of Good Hope to southern
Mozambique, and, in the northern Indian Ocean, it occurs off Pakistan and the northwest coast of
India. In the Northern Pacific it has been reported from Hong Kong, northwards along the Chinese
coast, to southern Korea and Japan (Griffiths & Heemstra 1995).
There is limited information available on the stock structure of mulloway. Genetic-based studies
have been done only in Australia and the conclusions from these studies are limited as they were
based on samples comprising very few individual fish from only a few locations. Black & Dixon
(1992) provided some electrophoresis-based evidence that a separate sub-population of mulloway
occurs in Western Australia compared to the southern (South Australia and Victoria) and eastern
(NSW and Queensland) seaboards. They further hypothesised that there may be additional
population sub-structuring between fish in South Australia and New South Wales, but preliminary
data based on mitochondrial DNA (mtDNA) did not appear to support this. There are no other
reported genetic studies done elsewhere on the species and therefore the degree of genetic division
among populations along different seaboards and oceans is not known.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
12
NSW Dept of Primary Industries
Sea of
Okhotsk
Sea of
Japan
South
China
Sea
Arabian
Sea
South
Atlantic
Ocean
North
Pacific
Ocean
Philippine
Sea
Indian
Ocean
South
Pacific
Ocean
Tasman
Sea
Figure 2.1.
Map of the world showing the known geographical distribution of mulloway.
We suggest that future studies to assess the genetic structuring of the species be approached using
mtDNA analyses of fish collected via a stratified sampling program that incorporates several
replicate samples taken in predetermined regions along and between coastlines so that within and
between population variation in genetic structure can be assessed. A good example of the utility
and strength of such an experimental design in a genetic study is that provided by Gold et al.
(2002) on Cynoscion nebulosus.
Tag-recapture studies shed no further light on the stock structure of the species. Most tagging
studies have been limited in scope (see below) and were not designed to answer questions
regarding stock structure. Nevertheless, the data presented from these studies (Griffiths 1996, West
1993, and see Fig. 2.2) show relatively small-scale (< 400 km) movements of mulloway along a
coastline and between estuaries. Whilst limited movements could be used to support stock
separation along a coastline, no definitive conclusions can be made regarding the population
structure of the species. Despite this, Griffiths & Hecht (1995) suggest that the population of
mulloway in South Africa (called dusky kob) is a single genetic stock.
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2.4.
13
Early life history
Steffe & Neira (1998) give a full description of the larval development of mulloway based on
reared and wild caught larvae. The previous description by Beckley (1990) of the larval
development of A. hololepidotus is most likely that of A. inodorus. The eggs of mulloway are
pelagic, approximately 938 ± 24 µm in diameter and under laboratory conditions, hatch in 28 – 30
hours (at 23°C) after spawning, with the larvae being 2.2 – 2.3 mm TL upon hatching (Battaglene
& Talbot 1994).
Eggs have been collected near the surface in coastal waters off south-eastern Africa (Griffiths
1996) and larvae (up to 10 mm TL) have been caught in estuarine and coastal waters (out to 100 m
depth contour) off south-eastern Australia between February and April (Miskiewicz 1987, Steffe
1991, Gray & Miskiewicz 2000). During daytime sampling in coastal waters of NSW, mulloway
larvae (predominantly early pre-flexion stage) were caught in subsurface waters, with greatest
concentrations below 30 m depth (Gray 1995). Similarly, most larvae captured in towed plankton
nets in a coastal embayment (Botany Bay) in NSW, were close to the substratum (Steffe 1991),
suggesting that larval mulloway may prefer deeper parts of the water column.
2.5.
Juvenile and adult distribution
Small (< 30 cm TL) juveniles are found in estuaries and nearshore coastal environments, including
surf zones (Hall 1986, Lenanton & Potter 1987, Gray & McDonall 1993, Griffiths 1996, West &
Walford 2000). Some ambiguity exists however, concerning the timing, age and length that
individuals recruit to estuaries. Several authors suggest that early development of mulloway
primarily takes place at sea and juveniles enter estuaries at a length between 10 - 20 cm TL and up
to 1 year after birth (Hall 1986, Potter et al. 1990, Anon 1993). In contrast, Griffiths (1996)
reported that mulloway recruit to estuaries in South Africa at 2 - 3 cm TL approximately 4 weeks
after hatching. Given this latter study in South Africa, and the fact that larvae and small juveniles
(2 - 10 cm TL) have been caught in estuaries in NSW (Anon 1981a, Gray & McDonall 1993, Steffe
1991, West & Walford 2000), we suggest that small mulloway are present in estuaries from a very
early age, but are probably not susceptible to capture in most common research sampling methods
(i.e. larger meshed trawls, gillnets and seines) until they reach a larger length (see also Griffiths
1996). We thus propose that previous conclusions that young mulloway do not occur in estuaries
until a later age may be a result of inappropriate sampling regimes for catching small fish. We
acknowledge however, that some individuals probably develop at sea and recruit to estuaries at a
latter age and larger length and that reported differences in the early life history distribution of
mulloway between estuaries in Western and South Australia (Hall 1986, Potter et al. 1990, Anon
1993) compared to eastern Australia (Anon 1981a, Gray & McDonall 1993, Steffe 1991, West &
Walford 2000) and eastern Africa (Griffiths 1996) may be related to differing environmental and
oceanographic conditions in these regions (see Potter et al. 1990). Standardised sampling of small
juveniles using nets with small mesh across several estuaries and coastal areas in different regions
of Australia is required to test whether the distribution of young juveniles during their first year
varies between seaboards.
In estuaries, juveniles (including early post-settlement stages) may favour deeper waters and not
the shallow littoral fringes where most sampling for juvenile fishes has traditionally taken place
(see below). For example, in a study in two estuaries in northern NSW (West & Walford 2000)
most small mulloway (2 – 40 cm TL) were captured by trawling in the deeper waters of the main
river channels, particularly where prawn abundances were high. None were caught in shallow
waters or small tributaries (using small seine nets). Further, relatively few small juveniles have
been caught along the shallow (< 2 m depth) vegetated (e.g. seagrass and mangrove) and nonvegetated fringes of estuaries, despite the extensive sampling of these habitats in south-eastern
Mulloway biology and fishery assessment, Silberschneider & Gray
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14
NSW Dept of Primary Industries
Australia and southern Africa (Anon 1981a, Potter et al. 1990, Ferrell et al. 1993, Connolly 1994,
Paterson & Whitfield 2000). We conclude therefore, that unlike many other species, mulloway is
not dependent on shallow vegetated habitats as a juvenile nursery habitat, which is in direct
contrast to several other scianenids, including Cynoscion nebulosus (see Rutherford et al. 1982).
The horizontal distribution of mulloway in estuaries can vary substantially and is probably linked
to environmental factors including salinity, freshwater flows, turbidity and life history stage.
Griffiths (1996) reported that fish < 15 cm predominantly recruit to the upper regions of estuaries
where salinities are < 5 ppt. Gray & McDonall (1993) found that most juvenile fish (10 – 20 cm
TL) occurred at locations in an estuary where the salinity was 15 to 20 ppt. However, some
juvenile fish were caught in upstream locations where salinity was < 5 ppt and also near the estuary
mouth where salinity was > 25 ppt. Griffiths (1996) also found that juveniles were more prevalent
in turbid versus non-turbid estuaries and hypothesised that juveniles may be more abundant in
estuaries with significant freshwater flows. This may also be true in NSW where juveniles appear
to be more prevalent in the deeper riverine type estuaries compared to the shallower barrier (coastal
lagoon) estuaries. Both Hall (1984) and Griffiths (1996) further suggested that freshwater flow
promoted recruitment of larval and juvenile mulloway to estuaries.
Sub-adult and adult mulloway occur in estuarine and ocean waters (Griffiths 1996). In estuaries,
larger juveniles and sub-adult fish (> 40 cm TL) appear to be more abundant in the lower reaches
where salinities are nearer to seawater (Anon 1993, Griffiths 1996). The distribution of these larger
individuals may be related to particular hydrographic conditions. For example, Anon (1993)
reported that larger fish moved from estuaries to the ocean in Western Australia in winter when
estuarine salinity levels dropped. Large individuals are caught around the mouths of estuaries, in
surf zones and around rocky reefs and ridges in offshore waters.
2.6.
Movement
Several tag-recapture studies have been done on mulloway, although the objectives and scales of
the studies, and the data published, have been variable and in some cases, unclear. In Australia,
separate tag-recapture studies have been done on mulloway in NSW (Thomson 1959, West 1993,
NSW Fisheries unpublished data), South Australia (Hall 1984) and Western Australia (Anon
1993), while in southern Africa there has been one published study (Griffiths 1996).
The data concerning movements of tagged mulloway show that some fish appear to be relatively
sedentary (predominantly juveniles), whereas others move significant distances along a coastline
and from one estuary to another (Table 2.1). For example, in South Africa, Griffiths (1996) found
that 83% of the 263 recaptures (primarily juvenile and sub adult fish < 120 cm) were found < 10
km from where they were tagged even though these fish recorded long periods of liberty (> 1400
days). Only 15 fish were recaptured > 30 km from the initial tag location. Similarly, in NSW, most
tagged mulloway were recaptured in the estuary where they were originally tagged (83 %, n =
519), but 70 fish (13.5 % of recaptured fish) moved between estuaries both north and south from
the estuary where they were tagged (Fig. 2.2). The greatest distance migrated was approximately
400 km southward from the Clarence River to Wallis Lake with the fish at liberty for 176 days
(Table 2.1 and Fig. 2.2). The greatest northward migration was approximately 300 km from the
Clarence River to the Brisbane River with the fish at liberty for 851 days. To date, the longest
period at liberty for a recaptured mulloway in NSW has been 1954 days, with the fish recaptured
approximately 375 km south of where it was tagged. Some tagged mulloway have moved relatively
large distances in opposing directions elsewhere. In South Australia, Hall (1984, 1986) reported 7
fish were recaptured about 200 km from the tagging site and that these occurred in both north and
south directions. Northward and southward movements of mulloway have been observed in South
Africa, with fish being recaptured up to approximately 260 km north and 190 km south from the
place of tagging (see Fig 12 in Griffiths 1996). We note that caution needs to be exercised in the
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NSW Dept of Primary Industries
15
interpretation of the release-recapture data provided. Much more information (e.g. distribution of
sampling or fishing effort) than presently available is required to assess rates of movements in
different directions, between different estuaries and regions of a coastline.
150
0
151
0
152
0
24
0
153 E
Maroochy R
0
27 S
Brisbane R
Logan R
Coomera R
1
Tweed R
Brunswick R
102
1
1
28
2
0
2
8
2
3
Richmond R
29
0
6
41
Clarence R
1
Wooli Wooli R
0
30
Bellinger R
2
2
Nambucca R
1
4
1
1
Macleay R
0
31
1
Hastings R
Manning R
1
1
32
0
Wallis L
33
0
Hawkesbury R
Botany B
34
0
2
1
265
Shoalhaven R
23
1
35
L Conjola
1 Burrill L
0
ESTUARY MULLOWAY
Figure 2.2.
Map showing locations of release and recapture of tagged mulloway in New South
Wales, Australia. Each line & number represents the fish that travelled between
locations and the number at each estuary represents how many were recaptured in
the same estuary where they were released.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
16
Table 2.1.
NSW Dept of Primary Industries
Summaries of tag-recapture studies of mulloway showing numbers tagged and
recaptured, proportion showing no movement (< 10 km from tag location), greatest
distances travelled and maximum times at liberty.
Study
Number
of fish
tagged
Number of
fish
recaptured
Proportion of
fish with no
movement
Days at
liberty of fish
with no
movement
Greatest
movement
Days at
liberty of fish
with greatest
movement
Thomson
(1959)
Hall
(1984)
Hall
(1986)
12
0
N/A
N/A
N/A
N/A
628
21 (3.3%)
Not reported
Not reported
~ 150 days
6000
180 (3%)
172 (95.4%)
remained
within the
Coorong
Not reported
Griffiths
(1996)
Not
reported
263
> 1400
NSW
Fisheries
(unpub)
2510
519 (20.7%)
Approx. 218
(83%)
recaptured <
10 km from
tag site
452 (87%)
recaptured
within the tag
estuary
1 fish ~ 200
km
7 fish up to ~
200 km. Other
fish moved
>10 km within
the Coorong
Approx 250
km. 5.7%
moved >30
km
2.7.
Age, growth and mortality
1060
406 km
Not reported
Approx 900
days
176 days.
Greatest days
at liberty =
1954 (fish
moved 375
km)
Age and growth of mulloway has been little studied except in South Africa where they grow to a
large size and are relatively long lived, with the maximum reported length being 181 cm TL,
weight of 75 kg (Griffiths & Heemstra 1995) and age of 42 years (Griffiths & Hecht 1995). A
length of > 200 cm has also been reported for this species (Kailola et al. 1993) but no evidence is
provided to supports this. Rates of natural mortality have only been estimated for fish in South
Africa, where it was estimated that M = 0.15 (Griffiths 1997c).
Griffiths & Hecht (1995) provide the most detailed and reliable estimate (validated otolith-based
study; fish 3 – 175 cm TL) of the growth of wild mulloway. Growth of both sexes is initially rapid
and similar for the first 2 years, after which the rate of growth declines (see Table 2.2), with
females growing faster to attain an overall greater length (165 – 170 cm) and age (42 years) than
males (140 – 145 cm and age 30 years). Griffiths & Hecht (1995) estimated growth curves (using
the generalised Von Bertalanffy model) for females as Lt = 147.3[1-e-0.228(t + 2.620)]2.468 and for males
as Lt = 137.2[1-e-0.260(t + 4.282)]4.619. Although the rates of growth differed between sexes, the
length/weight relationships for males and females did not differ significantly.
Much less has been published concerning the growth of mulloway in Australian waters and none
for elsewhere. Despite this, comparative estimates of published mean length at age of mulloway are
presented in Table 4.2, although we acknowledge there can be large variation in length at age (see
Fig. 6 in Griffith & Hecht 1995). Gray & McDonall (1993), by following juvenile cohorts caught
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NSW Dept of Primary Industries
17
in prawn trawls, estimated that juveniles grew from a mean length of 7 to 15 cm TL and 16 to 25
cm TL in 6 months between April and October and that fish 15 cm in length were 6 months old.
Based on tag-recapture data and scale readings, Hall (1984) estimated that mulloway grew to 46 cm
(1.5 kg) in 2 to 3 years and a length of 80 cm (8 kg) in 5 to 6 years. West (1993) analysed tagrecapture data and estimated that mulloway grew to 49 cm TL in 2 years and 56 cm TL in 3 years.
The available data suggests that growth of mulloway is variable and may vary greatly between
different geographic regions. Much greater and validated data is required on the growth of
mulloway outside southern Africa, however, to test this. Ages estimated from the current study are
given here and are discussed in detail in Chapter 3.
Table 2.2.
Comparisons of estimated length (TL; cm) at age for mulloway.
Age in
years
Wallace &
Schleyer (1979) a*
Hall (1986) b
1
2
3
4
5
6
7
8
9
10
11
12
15
20
25
23
44
62
77
90
102
112
120
128
134
139
144
8
24
41
53
65
81
96
107
114
Griffiths & Hecht
(1995)a+
Male
Female
35.6
50.3
64.6
77.6
89
98.6
106.6
113.1
118.3
122.4
35.5
51.1
66
79.5
91.3
101.5
110
117.1
122.9
127.7
133.1
136.1
136.9
140.8
145.2
146.6
West (1993) c
Current study
41
49
56
65
34.7
52.0
66.3
78.0
87.6
95.5
102.0
107.3
111.6
115.2
125.5
129.4
130.8
Age estimated by: a otolith interpretation, b scale interpretation, c release-recapture data.
*
Presumed to be A. japonicus
+
Lengths derived using the growth equation and parameters given in the manuscript
2.8.
Reproduction
The reproductive biology of mulloway has been little studied. Griffiths (1996) reported that 50% of
male and female mulloway in South Africa were mature at 92 and 107 cm TL respectively, and that
all males and females > 110 and 120 cm TL respectively, displayed mature gonads. The 50% and
100% maturity levels correspond to 5 and 7 years of age for males, and 6 and 8 years for females,
respectively. It is reported that mulloway in South and Western Australia do not become sexually
mature until they attain about 75 cm TL and are approximately 70 - 80 cm (approx. 4 kg) and 5 to 6
years old (Hall 1986, Anon 1993). A study in Botany Bay in eastern Australia collected mulloway
up to 64 cm and all had immature gonads (Anon 1981a). No estimates of the fecundity of wild
mulloway have been reported, but Battaglene & Talbot (1994) estimated that hatchery kept fish
around 10 kg could spawn approximately 1 million eggs. Batteglene (1996) further reported that
the spawning mode of mulloway is group synchronous.
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18
NSW Dept of Primary Industries
The time of spawning appears to vary between geographic regions and with latitude and is
probably related to water temperature and oceanography. For example, in southern Africa, Griffiths
(1996) found that spawning varied along the coast from August to November (winter to spring) in
the northern KwaZulu region (30 - 31°S), and from October to January (summer) in the southern
and south-east Cape regions (33 - 35°S). Similarly, along the West Australian coast, Penn (1977)
reported fish with mature gonads in September and October in Shark Bay (26°S), whereas Anon
(1993) reported that mature fish occurred between December and January in the Swan River
(32°S). In South Australia, mulloway appear to spawn throughout summer (November to February)
(Hall 1986). Based on the occurrence of larvae between February and April (Gray & Miskiewicz
2000) and small juveniles 2 - 8 cm TL between April and June (Anon 1981a), spawning in central
NSW (around 35°S) appears to take place in late summer and autumn (January to April). However,
West & Walford (2000) reported that juvenile mulloway (< 10 cm TL) were present year round in
two estuaries in northern NSW (between 28°50’ and 29°30’S). Further, both Broadhurst (1993) and
Gray & McDonall (1993) reported two distinct juvenile cohorts in an estuarine population within
the same region which suggests that not all spawning is synchronous within a region.
Several authors have hypothesised that mulloway spawn in nearshore coastal waters around the
mouths of estuaries and in surf zones. This is based on observations in South Africa (Griffiths
1996) and South and Western Australia (Hall 1984, 1986, Anon 1993) that fish with mature or
spent gonads have been caught only in ocean waters, whilst fish in estuaries did not show
development of mature gonads. Further, off the east coast of South Africa, eggs have only been
collected in nearshore waters and not in the offshore Agulhas Current (see Griffiths 1996) and
larvae (but not eggs) have only been collected in low numbers in estuaries. Hall (1984) suggested
spawning may take place near the mouths of estuaries as large fish (80 - 150 cm TL) in spawning
condition have been caught in the mouth of the Murray River in South Australia. Hall (1984)
further postulated that freshwater outflow during summer may promote aggregations of spawning
fish near the mouths of estuaries as peak freshwater discharge generally coincided with, or just
preceded, the spawning season. The spring/summer-spawning season in South Africa also
coincides with the highest periods of rainfall and river discharge in that region. Griffiths (1996)
hypothesised that mulloway may have adapted a river discharge-spawning relationship as an
evolutionary tactic to enhance recruitment of juveniles to estuaries.
2.9.
Diet
Mulloway has a relatively large mouth with caniniform teeth, sharp gill rakers and a short intestine
with a large distensible stomach (Anon 1981a). It is regarded as a benthic carnivore but can
apparently feed throughout the water column (Kialola et al. 1993). The importance of different
dietary components has varied between studies and for different life history stages. Overall,
crustaceans, notably penaeid, mysid and alpheid shrimp, and small teleost fish have been the
primary dietary items observed in the stomachs of juvenile mulloway (Anon 1981a, Marais 1984,
Hall 1986, Fielder et al. 1999). Crustaceans accounted for between 14% (Fielder et al. 1999) and
81% (Anon 1981a) of the reported diet of juveniles. The importance of crustaceans in the diet of
mulloway appears to decrease with increasing fish size, resulting in fish and squid being the prey of
greater relative importance in larger mulloway (see Marais 1984, Griffiths 1997a,b).
2.10.
Commercial and recreational fisheries
Estimates of total worldwide commercial and recreational harvests of mulloway are not possible to
ascertain, as the quantities landed in many countries are either unknown or not reported. Moreover,
regional estimates of catches are incomplete for many countries. Hence, data concerning
commercial and recreational catches for Australia only are presented (Table 2.3). The data show
that harvests vary spatially and between fishing sectors and that estimated recreational catches in
several states (NSW, Victoria and Western Australia) are of an equivalent or greater magnitude
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NSW Dept of Primary Industries
19
than reported commercial catches. Although there are no estimates of total commercial or
recreational catches available for South Africa or elsewhere, nearshore commercial line boat fishers
in South Africa caught an average of 197 tonnes/year of mulloway between 1988 and 1992
(Griffiths & Heemstra 1995).
Most Australian fisheries for mulloway are managed by spatial and temporal fishing restrictions,
gear regulations, minimum legal lengths (MLL) and recreational bag limits. The MLL regulations
and recreational bag limits for mulloway vary between state jurisdictions, with most MLL’s set
between 40 and 50 cm TL. This is comparable to South Africa where the current MLL is 40 cm
TL. These MLL’s are not set on any biological basis.
Table 2.3.
State
NSW
Victoria
Queensland
SA
WA**
Total
#
Estimated commercial and recreational catches of mulloway in Australia in 2001.
Data on recreational catches are from the National Recreational and Indigenous
Fishing Survey (Henry & Lyle 2003).
Commercial
catch
Total Reported
Weight (kg) #
73 800
98
na
113 000#
61 700
Recreational catch
Total
Estimated
No.
Standard error
Total Estimated
weight (kg)
Mean weight of
fish (kg)*
136 852
5 421
73 243**
27 004
62 928**
323 460
21 678
2 997
13 392
5 156
14 921
273 703
10 841
84 229**
39 885
359 699**
925 057
2
2
1.2
1.5
5.7
Commercial catch data are for the 2001/2002 financial year.
* The mean weight of mulloway used to calculate the estimated weight
** Other species of sciaenids most likely included in these data.
In Australia, reported commercial catches of mulloway are available from 1940 for NSW and
between 1950 and 1984 for South Australia. Catch per unit effort (CPUE) information is also
available from 1984/85 for NSW although, from 1997/98, new reporting regulations meant that
CPUE could be calculated as kg per fisher month (from 1984/85 onwards) or as kg per day (from
1997/98 onwards). Reported commercial catches in South Australia fluctuated between 30 and 215
tonnes per annum between 1950 and 1984 (Hall 1986). In NSW, reported commercial catches
fluctuated between 50 and 100 tonnes between 1940 and 1970, after which commercial landings
increased sharply to peak at 380 tonnes in 1973/74. This increase in catch corresponded with the
rise of otter trawling in coastal waters and the removal of the MLL in 1971 (Fig. 2.3). Reported
commercial estuarine and ocean catches have steadily declined since the peak in 1973/74 to a low
of 60 tonnes in 2003/04 which was valued at around $AUD 435000. The general decline in catch
since the mid 1970’s in NSW is reflected in catch statistics across all estuaries and ocean ports
throughout NSW (see also West & Gordon 1994). In NSW, CPUE has consistently fluctuated
between 40 and 55 kg/fisher month from 1984/85 onwards and has fluctuated between 3.5 and 4.3
kg/day from 1997/98 onwards. Thus, despite a decrease in commercial landings (kgs) CPUE has
remained fairly stable. This suggests that the decrease in catch may be due to a reduction in the
number of commercial fishers targeting mulloway. However, reported CPUE for mulloway in
South Australia declined from approximately 15 kg/day in 1976/77 to about 5 kg/day in 1982/83
(Hall 1986). No current CPUE data for South Australia is available.
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NSW Dept of Primary Industries
MLL 18" (45.7 cm)
400
No MLL
MLL 15" (38.1 cm)
MLL 45 cm
1200
350
1000
900
300
800
250
700
600
200
500
150
400
300
100
200
50
Number of fishers reporting catch
Total estimated landings (tonnes)
1100
100
0
1940/41
1941/42
1944/45
1945/46
1946/47
1947/48
1948/49
1949/50
1950/51
1951/52
1952/53
1953/54
1954/55
1955/56
1956/57
1957/58
1958/59
1959/60
1960/61
1961/62
1962/63
1963/64
1964/65
1965/66
1966/67
1967/68
1968/69
1969/70
1970/71
1971/72
1972/73
1973/74
1974/75
1975/76
1976/77
1977/78
1978/79
1979/80
1980/81
1981/82
1982/83
1983/84
1984/85
1985/86
1986/87
1987/88
1988/89
1989/90
1990/91
1991/92
1992/93
1993/94
1994/95
1995/96
1996/97
1997/98
1998/99
1999/00
2000/01
2001/02
2002/03
2003/04
0
Financial year
Figure 2.3.
Reported commercial catches of mulloway in NSW since 1940/41 and associated
changes in MLL, number of NSW fishers reporting catch of this species, and
commercial catches from South Australia. Filled circles – NSW estimated landed
catch; open triangles – SA landed catch (reproduced from Hall 1986); filled
squares – number of NSW fishers reporting mulloway.
Reported commercial catches of mulloway throughout the past decade in NSW have generally been
greatest in estuaries (52 – 65% of reported annual production) compared to ocean waters (26 40%) (Table 4.4). Fish are mostly caught using gillnets in estuaries and by hook and line in ocean
waters. Reported estuarine commercial catches are generally greatest in the deeper coastal rivers
that experience high freshwater flows (Hawkesbury, Clarence and Shoalhaven rivers). In South
Australia, approximately 80% of the mulloway commercial fishery centres on one large estuary
(the Coorong) and 20% from waters immediately adjacent to the Coorong (Hall 1986). Within the
Coorong, the main fishing methods are gillnets and beach-seine nets, but in contrast to NSW,
gillnets and seine nets as well as hook and line are the main capture methods in ocean waters (Hall
1986). Commercial catches are generally greatest between December and June in NSW and
between December and March in South Australia.
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The proportion of total reported commercial catch of mulloway taken in each
fishery in NSW for the years 1997/98 and 2002/03.
Table 2.4.
Fishery
Main gear type used to
catch mulloway
Estuary General
Ocean trap & Line
Fish Trawl
Ocean Haul
Ocean Prawn Trawl
Estuary Prawn Trawl
Proportion of mulloway caught in each fishery
(%)
2003/04 (total est.
1997/98 (total est.
landed weight = 60129
landed weight = 93380
kg)
kg)
Mesh net
Handline
Fish trawl net
Beach haul net
Prawn trawl net
Prawn trawl net
51.63
39.66
4.04
3.94
0.70
0.03
65.23
26.51
2.80
4.85
0.51
0.10
The length composition of commercial catches in NSW has changed considerably over the past 3
decades (Fig. 2.4), corresponding to changes in MLL, with the modal length of fish harvested
increasing as MLL increased. The majority of fish landed were < 10cm TL above the MLL (when
in existence).
5
1972-75 (n=1606)
1987-90 (n=2334)
1996-99 (n=5842)
% Frequency
4
3
2
1
0
10
20
30
40
50
60
70
80
90
100 110 120 130 140 150
Fish total length (cm)
Figure 2.4.
Estimated length compositions of retained fish from commercial catches of
mulloway in NSW for three periods between 1972 and 1999.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
22
NSW Dept of Primary Industries
Estimates of total recreational catches of mulloway are available only for 2001 (Henry & Lyle
2003). This study estimated that recreational anglers retained approximately 323000 and released
approximately 276000 mulloway nationwide during 2001. Table 2.3 provides a breakdown of
catches on a regional basis. In NSW, fishers retained approximately 137000 and discarded a further
36000 individuals, whereas between 30000 and 40000 individuals were retained by recreational
anglers in South Australia and Western Australia. No time series of estimated recreational catches
of mulloway are available for any region.
Most other surveys of recreational harvests in Australia have been done at smaller spatial scales,
which have generally covered one catchment or a restricted area of coastline. Nevertheless, these
studies further document the importance of this species to recreational fishers. Steffe et al. (1996)
estimated that recreational offshore trailer boat anglers in NSW retained between 2800 and 5100
mulloway per annum, with the species ranking between 15th and 20th by weight and 40th and 44th by
number in total catches throughout the survey. By weight, mulloway ranked in the top ten fish
species caught by recreational fishers in northern NSW estuaries (West & Gordon 1994, Gartside et
al. 1999) and ranked 11th by weight and 20th by number in an earlier survey of recreational fishers
in Botany Bay (Anon 1981b). In South Africa, recreational boat fishers are estimated to catch a
similar quantity to commercial fishers (Griffiths & Heemstra 1995) and, amongst shore anglers,
Argyrosomus spp ranked in the top four of the preferred recreational target species and ranked in
the top five (by weight) for recreational catches in the Eastern Cape and KwaZulu-Natal coast
(Brouwer et al. 1997). Although relatively high numbers of mulloway are caught by recreational
fishers, estimated recreational catch rates for the species in Australia are generally low: < 0.12 fish
per angler per trip and 0.01 fish per angler per hour (West & Gordon 1994, Gartside et al. 1999).
Several studies have shown that the proportion of the total catch of mulloway taken by recreational
and commercial sectors can vary greatly across relatively small spatial scales. For example, the
recreational daytime catch of mulloway in Port Jackson was estimated at 8924 kg (6716 fish) in
1981, which was approximately ten times greater than the reported commercial catch in that estuary
(~726 kg) (Henry 1984). In contrast, the estimated recreational harvest of mulloway in Botany Bay
was about one third of the reported commercial catch (930 kg compared to 2960 kg) (Anon 1981b).
Griffiths (1997c) states that the stock of mulloway in South Africa is depleted and recruitment
overfished. This is based on sound knowledge of the species biology and estimates of growth, and
natural, fishing and total mortality. This may also be true for stocks in Australia, particularly for
NSW given that commercial catches have declined over the past decade.
2.11.
Bycatch and discarding
Juvenile mulloway are a significant component of the discarded bycatch in several fisheries,
particularly estuarine and oceanic prawn trawl fisheries (Gray et al. 1990, Broadhurst & Kennelly
1994, 1995, Liggins & Kennelly 1996, Liggins et al. 1996, Kennelly et al. 1998). Kennelly et al.
(1998) estimated that up to 97% of mulloway caught in the NSW oceanic prawn trawl fishery were
discarded and that approximately 48000 fish were discarded over two years from prawn trawlers
operating out of the 4 major ports in NSW in 1990-92. Miller (2002) further reported very high
discarding rates of small mulloway from the oceanic prawn-trawl fleet following floods, where
small fish were flushed from estuaries. Liggins & Kennelly (1996) estimated that approximately
120000 mulloway were discarded from the prawn trawl fishery in the Clarence River for the 3
years 1989 to 1991. These fish were predominantly < 20 cm TL (see also Gray et al. 1990). Similar
sized fish are also discarded in the estuarine prawn seine fishery in NSW, but in greatly reduced
quantities than the trawl fisheries (generally < 15 individuals were caught per fisher per day fished)
(Gray et al. 2003).
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
NSW Dept of Primary Industries
23
Mulloway also occur as minor bycatch in the estuarine gillnet (Gray 2002) and beach-seine
fisheries (Gray & Kennelly 2003, Gray et al., 2003), and the coastal protective shark-meshing
program (Krogh & Reid 1996) in NSW. Mulloway comprised only 0.7% of the discards from the
NSW estuarine gillnet fishery (Gray 2002) and only 282 fish were caught in the coastal shark
meshing nets in NSW between 1950 and 1993 (Krogh & Reid 1996).
Because of the high discarding rates of juvenile mulloway in the prawn trawl fisheries, and the fact
that the species is relatively sensitive to handling and stress, culminating in high mortality upon
interaction with fishing gears (Gray 2002), much research has been done on developing Bycatch
Reduction Devices (BRD’s) to exclude small mulloway from capture in these fisheries (see
Broadhurst 2000 for a review). Alternative codend designs showed that the mean number of
mulloway caught in the estuarine prawn trawl fishery could be reduced by 95%, but these designs
were not acceptable to industry as they also significantly reduced catches of retained prawns
(Broadhurst & Kennelly 1994). Consequently, other alternative cod ends that did not significantly
reduce prawn catches, but reduced the catch of mulloway by between 34 and 54% (Broadhurst &
Kennelly 1994, 1995), have been introduced in the estuarine prawn-trawl fisheries in NSW. The
potential benefits of these changes in fishing gears on stocks of mulloway have not been assessed.
Henry & Lyle (2003) estimated recreational anglers discarded approximately 50000 individuals
during each year. The condition of these released fish was not reported and thus the impacts of
recreational and commercial hook and release on survival remains largely unknown for mulloway,
particularly from deeper waters where fish may suffer barotrauma stress. Broadhurst & Barker
(2000) showed that juvenile mulloway hooked in the mouth from a relatively shallow (< 2m) depth
and then released, had minimal effect on their overall condition and no mortalities were recorded
over the 25-day holding time in experimental pond conditions. However, studies incorporating a
range of fish hooks, hooking location (i.e. mouth v gut hooked), capture times, and exposure to air
need to be done to assess mortality rates and to help identify fishing and handling practices that
may enhance survival of released fish.
2.12.
Aquaculture
Sciaenids are generally considered good aquaculture species because they are widely distributed,
euryhaline, highly fecund, fast growing with good food conversion ratios (FCRs). Several species
of scianeids are widely used in aquaculture and in the year 2000 an estimated 2220 tonnes of
scianeids were produced in aquaculture throughout the world (FAO 2002). Sciaenids are not only
reared for human consumption, but for enhancement of wild fish stocks. For example, in Texas, red
drum (Sciaenops ocellatus) is mainly reared to enhance wild stocks and to improve catches in
recreational fisheries (McEachron et al. 1995).
Unlike the vast amount of research into the aquaculture potential and actual aquaculture production
of sciaenids throughout the world (Arnold et al. 1988, Chamberlain et al. 1990), only over the past
decade has there been a developing aquaculture industry based on mulloway in Australia (Gooley
et al. 2000). Reported commercial aquaculture production of mulloway in Australia in 1997/98 was
6.8 tonnes and in 1998/99 0.1 tonnes (O’Sullivan & Roberts 2000, O’Sullivan & Dobson (2001).
There are no reported aquaculture initiatives for mulloway elsewhere. Mulloway shows a high
degree of similarity in its ontogenetic development with other cultured sciaenids, including S.
ocellatus and A. nobilis, and these similarities have assisted the development of hatchery
techniques for mulloway.
Initial research done in NSW developed the methodology to induce captive adults to spawn, rear
the larvae and grow out fish to a marketable size in controlled experimental ponds (Battaglene &
Talbot 1994, Fielder & Bardsley 1999, O’Sullivan & Ryan 2001). Mulloway broodstock can be
held in aquarium facilities and induced to spawn in tanks after injection with hormones and pellet
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
24
NSW Dept of Primary Industries
implants (Thomas & Boyd 1988, Battaglene & Talbot 1994). Like other sciaenids, mulloway
generally spawn approximately 30 to 35 hours after induction, with spawning occurring in
salinities between 30 and 35 ppt and at temperatures around 25oC (Battaglene & Talbot 1994).
Larval mulloway require a salinity between 5 to 35 ppt and temperatures of 18 to 25°C, although
they can tolerate temperatures up to 30°C. Optimum salinity for growth and survival in juvenile
rearing is approximately 5 to 12.5 ppt, where disease problems have been found to be least (Fielder
& Bardsley 1999). Larvae that are 2 - 3 mm TL at hatching begin to feed and inflate their swim
bladders 3 days after hatching, with metamorphosis complete after day 34 when larvae are 15 - 26
mm TL (Battaglene & Talbot 1994). Because mulloway can tolerate low salinities, current research
is assessing the feasibility of farming fish in ponds filled with extracted saline ground water and
underground aquifers (i.e. inland saline ponds).
In controlled aquaculture conditions, initial growth of mulloway is dependent upon the type of
technique used, with growth varying from 0.3 – 0.5 mm/day in intensive tank systems to 1.2 – 1.7
mm/day in extensive ponds (Fielder et al. 1999). These authors further reported that captive fish
with a mean length of 15 cm TL were 5 months old and that they could maintain a growth rate of
approximately 1 mm/day and reach 45 cm TL in 500 days.
Mulloway can be stocked into grow out operations at about 40 mm (~30 to 40 days old), where
they have been grown in sea cages to a legal size of 45 cm (~ 1.1 kg) within 26 months. To date,
stocking rates of 15 kg/m3 have been assessed but further research is needed to determine optimal
stocking densities. The feeding schedules used for mulloway are comparable with those of other
cultured sciaenids, including S. ocellatus (Robinson 1988, Battaglene & Talbot 1994). Enriched
rotifers and brine shrimp can be fed to larvae while juveniles can be fed a variety of foods
including adult brine shrimp, fishmeal and a 50% protein pellet.
The need for low culture densities to avoid cannibalism, coupled with the fast growing attributes of
juvenile mulloway, suggests that production of large quantities of the species may be best achieved
by larval rearing in intensive tanks, followed by extensive larval culture methods in ponds, similar
to that practiced with S. ocellatus (see McCarty et al. 1986). The relative ease of larval rearing
enhances the suitability of mulloway for aquaculture however the reliable supply of mature
broodstock has been highlighted as a problem (Battaglene 1996). Mulloway matures at a larger size
(and age) than most other cultured sciaenids and therefore the broodstock may have to be kept for
longer periods than other cultured sciaenids before they spawn in captivity (Battaglene & Talbot
1994).
The technology of rearing and raising mulloway in Australia has recently been transferred to
industry and they are successfully being grown out in sea cages for a small domestic market (500
kg produced in 2001/02 in NSW). In NSW, permits currently exist for 25 farms of which 7 have
hatchery permits and 1 for growout. For 2001/02, NSW aquaculture produced 120600 fingerlings
(NSW Fisheries 2003). Currently, there are commercial mulloway aquaculture operations using sea
cages in Botany Bay (NSW), Port Stephens (NSW) and Port Lincoln (South Australia). Site
availability of sea cages (due to conflicts with other waterway users) may limit the expansion of
this industry.
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
NSW Dept of Primary Industries
2.13.
25
Enhancement of wild fish stocks
Because of declining recreational and commercial catches, the potential to enhance wild stocks of
mulloway is being assessed in eastern Australia. The first experimental release of small hatcheryreared mulloway was done in three intermittently opening-closing lagoons in NSW, with
approximately 25000 juveniles (chemically marked with oxytetracycline) stocked in each lagoon
(Fielder et al. 1999). Commercial fishers recaptured many (100’s) of released fish in one lagoon,
but none were recaptured in the two other lagoons, probably because the fish were flushed into
ocean waters as the lagoons opened to the sea due to flooding soon after being stocked (Fielder et
al. 1999). As part of a larger environmental assessment of stock enhancement, a second experiment
has recently begun with more than 100000 small fish released into two estuaries in NSW. This
study aims to assess the potential negative ecological impacts of stocking and determine the best
strategy for enhancing wild populations and fisheries.
2.14.
Conclusions and recommendations
The biology of mulloway is has been well studied in South Africa. It is a relatively fast growing
and long-lived species (maximum age 42 years), but does not mature until 6-8 years old. Sciaenids
are prone to overfishing (Sadovy & Cheung 2003, Piner & Jones 2004) and mulloway has been
declared recruitment overfished in South Africa (Griffiths 1997c). It appears that populations of
mulloway have been declining in Australia since the mid 1970’s. To make more informed
decisions concerning the future management of the fisheries and wild populations of mulloway
throughout Australia, more detailed information on rates of growth, size and age at sexual maturity,
length and age structure of populations and estimates of exploitation and mortality rates, as
determined for this species in South Africa (Griffiths 1997c), are required. A greater understanding
of the impacts of hook and release fisheries and of potential positive impacts of BRD’s in
commercial prawn trawl fisheries would assist fisheries impact studies. Greater protection of
juveniles from bycatch associated mortality and spawning aggregations from fishing may be
required to arrest the apparent decline in Australian populations.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
26
NSW Dept of Primary Industries
3.
GROWTH AND REPRODUCTION OF MULLOWAY IN
NSW
3.1.
Introduction
The assessment of the exploitation status of many fish stocks is often dependent on the knowledge
of the age and growth characteristics of a species and how this varies spatially and temporally. This
together with information on the reproductive dynamics of a species can be beneficial in
determining the effects of fishing and management changes on populations. Although basic
information concerning the age, growth and reproductive dynamics of several key species of fish
inhabiting south-eastern Australia is known, little information is available for many important
species, including mulloway.
Mulloway (Argyrosomus japonicus) are distributed throughout coastal and estuarine waters in
Pacific and Indian Ocean waters surrounding Australia, Africa, India, Pakistan, China, Korea and
Japan (Griffiths & Heemstra 1995). Despite the importance of this species in many commercial and
recreational fisheries throughout its distribution (see Chapter 2), there is very little information
concerning its life history in many areas. Basic biological information concerning the age, growth,
reproduction and movements of mulloway exists for South Africa (Griffiths & Hecht 1995,
Griffiths 1996), but comparable information does not exist in Australia. This is surprising given
that mulloway are caught in commercial quantities in at least three Australian states and are
regarded as a trophy fish amongst recreational anglers. There is also a paucity of information on
stock structure and the demographic characteristics of harvested populations in different regions,
including their length, sex and age compositions. Consequently, there is little fisheries-related
biological data to assess stocks of mulloway, the effects of fishing on stocks and thus little
information to aid future options concerning the management of the species.
In this chapter we redress the current lack of information concerning age determination, growth and
reproduction of mulloway in south-eastern Australia. We specifically document: (1) age and
growth characteristics, and (2) size and age at sexual maturity, for the species in NSW. These data
are later used to assess the exploitation status of the species (Chapter 4).
3.2.
Methods
3.2.1.
Sampling procedure
Samples of mulloway for age and reproductive determination were primarily sought from
commercial catches from estuarine and ocean waters throughout NSW. Commercial landings of
mulloway caught throughout NSW were sampled on a regular basis between November 2002 and
February 2005. Sampling was primarily done at the Sydney Fish Market (SFM) but also at several
ports of landings (fishing co-operatives). Some fish were also sampled from catches of selected
individual commercial and recreational fishers. Fish below the minimum legal length (MLL) of 45
cm were collected from catches obtained by other scientific research programs and also by a
commercial fisher who was issued with a special permit.
All fish sampled were measured to the nearest millimetre and weighed to either the nearest: (1)
gram (fish < 0.7 kg), (2) 10 g (fish 0.7 - 5 kg), (3) 25 g (fish 5 - 10 kg) and (4) 50 g (fish 10 - 25
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
NSW Dept of Primary Industries
27
kg). When possible, each fish was also sexed, gonads weighed (nearest gram) and the sagittal
otoliths removed for age estimation.
3.2.2.
Estimation of age and growth
Sectioned sagittal otoliths were used to estimate the age of mulloway. One whole sagittae from
each fish was weighed to the nearest 0.001 g. This otolith was then embedded in clear resin and
sectioned transversely through the otolith core using a low-speed saw fitted with two diamond
blades. Both sides of the resulting thin section were polished with 9 µm lapping film after which
the section was mounted on a standard glass slide with glue and a cover slip. Age was estimated by
viewing the section under a binocular microscope (6 – 12x) with reflected light against a black
background. Opaque bands were evident in sections of otoliths viewed in this way and were scored
as annual marks. Otolith weight was compared to fish age, total length and whole weight to
determine if otolith weight could be used as a predictor for these parameters. To determine the
periodicity of increment formation by marginal increment analysis, measurements were taken
between the otolith core and first opaque band, last opaque band to the otolith edge, and from the
last to second last opaque band. If age was recorded as 0+, then the measurement was from the core
to the otolith edge. If the age was recorded as 1+, then the distance from the opaque band to the
otolith edge was compared, as a proportion, to the distance from the core to the band. If the age was
recorded as 2+ or greater, the distance from the last band to the edge was compared to the distance
between the last and second last bands. A random sample of otolith images was sent to Western
Australia for verification of ageing procedure.
Growth was estimated by fitting the size-at-age data to the von Bertalanffy growth function:
Lt = L∞ [l-e-k(t-t0)], where Lt is the length at age t; L∞ is asymptotic length; k is the rate at which the
curve approaches the L∞ and t0 is the hypothetical age at zero length.
Growth was also attempted to be modelled using available tag-recapture data for mulloway.
Previous tagging studies carried out by the NSW DPI (previously NSW Fisheries) were reanalysed
using GROTAG, a maximum likelihood approach (Francis 1988), to estimate growth rate of
mulloway. However, only 58 of the 477 fish (12%) were at liberty for more than one year and only
15 fish (3%) were at liberty for greater than two years. Of these fish, the recapture size was
comparatively small (79% of the fish recaptured were <55 cm TL) given the large size that
mulloway can attain (181 cm TL, Griffiths & Heemstra 1995). Consequently, estimates of growth
provided by GROTAG using the available data were unrealistic.
The length-weight relationship for mulloway was calculated using the equation:
y = axb, where y = fish weight (kg), x = fish length (cm), and a and b are constants.
3.2.3.
Size and age at maturity and timing of spawning
Macroscopic examination of gonads was used to determine the sex of the fish and the stage of
gonad development. A reproductive stage was assigned to each gonad for male and female fish
according to the developmental criteria based on size, colour and visibility of oocytes outlined in
Table 3.1.
Size at sexual maturity was estimated for males and females using assigned reproductive stages.
Fish staged 4, 5 and 6 were assumed to be reproductively mature and capable of spawning in the
ensuing season. The proportion of female and male fish assigned being mature in each 2 cm length
class was calculated and logistic curves were fitted to the data for each sex using a non-linear least
squares procedure.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
28
NSW Dept of Primary Industries
Macroscopic ovary and teste staging schedule used for mulloway.
Table 3.1.
Stage
I/II
Classification
Virgin and Immature/resting
III
Developing
IV
Maturing
V/VI
Mature/Spawning
VII
Spent
VIII
Recovering spent
3.3.
Results
3.3.1.
Age and growth
Macroscopic characteristics
Ovaries small and translucent, pink or orange in colour. Oocytes
not visible through ovarian wall. Testes very thin and flat, light
pink in colour.
Ovaries slightly larger. Oocytes visible through ovarian wall.
Testes slightly larger, triangular in cross-section, beige in colour.
Sperm present in main sperm duct.
Ovaries larger, opaque, yellow or orange in colour. Yolk granule
oocytes visible through ovarian wall. Testes larger, mottled beige
and cream in colour. Softer texture, sperm present in tissue. Testes
rupture when pinched.
Ovaries larger than stage IV, orange in colour. Testes larger, cream
in colour, ruptures under slight pressure.
Ovaries and testes far smaller than stage V/VI. Ovaries flaccid.
Some yolk granule oocytes still visible through ovarian wall.
Testes mottled-beige and cream in colour. Some sperm present in
main duct and tissue.
Ovaries and testes were small. Similar to stage II, but ovaries red
in colour.
Mulloway aged in this study were estimated to be between 0 and 24+ years old (Table 3.2). Fish
aged 0 and 1 were primarily observed in samples caught in estuaries, whereas a greater proportion
of older fish (> 6 years) were sampled in ocean catches (Tables 3.3 and 3.4). The mulloway
estimated to be 24 years old was 120 cm TL. The largest fish sampled was 169 cm TL and it was
estimated to be 14 years old. We acknowledge that our ageing procedure has not been validated.
We assumed that the banding observed on sectioned otoliths were annual marks and that the first
observed ring was actually 1 year old.
There was considerable variation in the length of mulloway at any given age (Table 3.2, Fig. 3.1),
and similarly for the weight of mulloway at any given age (Fig. 3.2). The von Bertalanffy growth
parameters were calculated to be as follows: t0 = -0.552, k = 0.197, L∞ = 131.7. Growth could not
be modelled for each sex separately as sample sizes were small (the majority of fish sampled from
commercial catches were sold whole or were cleaned prior to sampling and thus could not be
sexed). Nevertheless, mulloway grew rapidly in the first 4 years, reaching approximately 80 cm
TL, after which the rate of growth slowed (Fig. 3.1). Mean length at age data based on fish that
could be sexed indicated that males and females grew at the same rate until about 5 years of age
(Fig. 3.3). After this age, females appear to grow more rapidly although no definitive result can be
obtained due to small sample sizes for older fish.
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
Age-length key for all mulloway sampled during the present study (2002-2005).
Table 3.2.
Length
class
(cm, TL)
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
85-89
90-94
95-99
100-104
105-109
110-114
115-119
120-124
125-129
130-134
135-139
140-144
145-149
150-154
155-159
160-164
165-169
n
0
23
188
75
31
15
3
1
2
3
34
50
13
23
11
23
1
2
4
17
43
737
673
237
81
30
8
3
3
4
39
64
70
44
26
14
3
7
6
1
4
4
22
40
30
34
30
21
27
15
9
2
5
1
4
6
9
10
8
9
18
9
7
2
6
5
2
2
4
3
3
2
8
5
1
7
3
3
4
4
4
2
3
5
4
1
8
1
2
1
1
6
5
Ages (years)
10 11 12
9
1
1
2
1
1
Total
13
1
1
3
4
1
2
2
1
1
1
1
2
2
1
2
1
1
1
158
1835
278
234
85
35
32
18
17
18
19
20
21
22
23
24
1
2
1
1
1
1
3
3
1
1
1
1
1
1
2
1
1
1
335
16
1
1
1
15
3
1
1
1
14
11
8
9
Mulloway biology and fishery assessment, Silberschneider & Gray, Project No. 2002/005
11
4
1
1
1
14
5
0
0
2
0
0
2
0
0
1
23
188
78
65
67
20
40
54
764
712
306
173
115
73
62
54
48
52
30
37
20
28
27
15
8
5
7
2
3
1
3077
Page 29
Age-length-key for mulloway caught in estuaries throughout the study.
Table 3.3.
Length
class
(cm, TL)
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
85-89
90-94
95-99
100-104
105-109
110-114
115-119
120-124
125-129
130-134
135-139
140-144
n
Ages (years)
0
3
182
75
31
15
3
1
2
2
34
50
13
23
9
15
1
309
147
2
1
3
19
444
477
167
48
19
5
3
1188
3
3
32
63
69
43
25
12
2
2
5
256
4
2
19
33
18
16
21
8
13
5
2
1
138
5
6
1
2
2
3
4
5
4
7
7
1
36
1
1
1
2
3
7
8
9
10
11
12
2
2
2
Total
13
14
15
16
17
18
19
20
21
22
23
24
2
1
1
2
2
1
1
3
13
11
1
2
1
2
3
2
1
1
1
0
3
Mulloway biology and fishery assessment, Silberschneider & Gray, Project No. 2002/005
1
1
5
1
0
0
1
0
0
0
0
0
0
0
0
1
3
182
77
65
67
17
26
28
462
509
233
136
96
51
34
31
18
28
9
10
9
5
8
6
1
1
0
1
2113
Page 30
Age-length key for mulloway caught in ocean waters throughout the study.
Table 3.4.
Length
class
(cm, TL)
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
85-89
90-94
95-99
100-104
105-109
110-114
115-119
120-124
125-129
130-134
135-139
140-144
145-149
150-154
155-159
160-164
165-169
n
0
1
2
2
3
51
38
25
12
4
2
3
6
1
1
1
1
1
5
1
1
4
1
3
6
11
16
6
10
12
10
5
1
5
2
2
5
5
2
4
11
2
6
1
6
3
1
1
2
3
2
5
3
7
3
1
2
2
3
2
2
1
3
1
8
1
2
1
1
5
2
9
1
10
1
2
1
Ages (years)
11
12
13
1
Total
14
15
16
17
18
19
20
21
22
23
24
1
3
53
44
27
16
11
18
23
19
26
21
20
24
11
22
16
6
7
4
6
1
3
4
1
382
1
1
1
1
1
2
1
1
3
2
1
2
1
1
2
1
1
1
1
1
1
1
1
1
2
3
1
1
1
1
1
2
1
1
0
2
135
18
81
42
20
19
14
8
8
1
1
4
1
13
6
Mulloway biology and fishery assessment, Silberschneider & Gray, Project No. 2002/005
4
0
0
2
0
0
2
0
0
0
Page 31
32
NSW Dept of Primary Industries
180
160
Fish total length (cm)
140
120
100
80
60
40
20
0
0
2
4
6
8
10
12
14
16
18
20
22
24
Age+ (years)
von Bertalanffy growth curve of mulloway sampled in NSW (n = 3077).
Figure 3.1.
26
24
22
20
Weight (kg)
18
16
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
18
20
22
Age+ (years)
Figure 3.2.
Age – fish weight relationship of mulloway sampled in NSW (n = 1386).
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33
140
Females
Males
130
Total Length (cm)
120
110
100
90
80
70
60
50
40
2
4
6
8
10
12
14
16
18
20
Age+ (years)
Figure 3.3.
Length (mean ± se) at age of male and female mulloway sampled in NSW (n = 91
males and n = 162 females).
A good relationship was found between fish age and otolith weight (Fig. 3.4a; adj r2 = 0.88).
However, otolith weight was not considered a practical predictor of fish age, as any particular
otolith weight could correspond to a range of ages. For example, a 1 g otolith could indicate that a
fish was between 2 – 4 years old, while a 3 g otolith could indicate that a fish was between 7 – 14
years old. Although there was a strong relationship between fish length/weight and otolith weight
(Figs 3.4b,c; adj. r2 = 0.93 and 0.94 respectively), otolith weight was still spread across a wide
range of fish lengths and weights. For example, a 1 g otolith could correspond to fish of total length
around 50 – 70 cm and a fish weight of 1 – 3 kg, while a 3 g otolith could correspond to fish of
about 90 – 140 cm in length and 8 – 23 kg in weight.
Results from the marginal increment analysis suggest that opaque bands on otoliths are formed
between late spring and early summer for 1+, 2+ and 3+/older fish in each year (Fig. 3.5). Sampling
of 0+ year old fish was not extensive enough to determine timing of first ring formation.
The length-weight relationship for mulloway fitted well to the regression equation (Fig 3.6, adj r2 =
0.97) with the constants estimated at a = 0.00001679 and b = 2.869.
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34
NSW Dept of Primary Industries
Otolith weight (g)
7
a)
6
5
4
3
2
1
0
0
2
4
6
8
10
12
14
16
18
20
22
24
Age+ (years)
Otolith weight (g)
7
b)
6
5
4
3
2
1
0
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180
Fish total length (cm)
Otolith weight (g)
6
c)
5
4
3
2
1
0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36
Fish weight (kg)
Figure 3.4.
Relationship between otolith weight and a) age (n = 3030), b) fish total length (n =
3028), and c) fish weight (n = 1372) of mulloway sampled in NSW.
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1.2
35
a)
Millimetres
1.0
0.8
0.6
0.4
0.2
0.0
1.6
1.4
b)
1.2
1.0
0.8
0.6
0.4
0.2
Proportion
0.0
0.9
c)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1.2
d)
1.0
0.8
0.6
0.4
0.2
Au
g
Se
p
Oc
No t
Dev
c
Ja
n
Fe
b
M
ar
Ap
M r
ay
Ju
n
Ju
Au l
g
Se
p
Oc
No t
Dev
c
Ja
n
Fe
b
M
ar
Ap
M r
ay
Ju
n
Ju
Au l
g
Se
p
Oc
No t
Dev
c
Ja
n
Fe
b
0.0
Month
Figure 3.5.
Marginal increment analysis for a) 0+ (n = 317), b) 1+ (n = 133), c) 2+ (n = 1425),
and d) 3+ or older (n = 682) aged fish for the 2002 - 2005 period. Mean ± standard
errors are presented. Dotted lines indicate annual cycle. Note difference in y-axis
scales.
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Project No. 2002/005
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NSW Dept of Primary Industries
32
30
28
26
Total weight (kg)
24
22
20
18
16
14
12
10
8
6
4
2
0
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150 160
Total length (cm)
Figure 3.6.
3.3.2.
Length-weight relationship of mulloway sampled in NSW (n = 2865).
Timing of spawning and size at maturity
Size at sexual maturity (L50) was estimated to be 51.26 ± 1.35 cm TL for male and 67.86 ± 1.05 cm
TL for female mulloway (Fig 3.7a,b). This is equivalent to the 51.0 - 52.9 cm size class for males
and the 67.0 - 68.9 cm size class for females. All males sampled in the 63.0 - 64.9 cm size class or
greater were mature and all females were mature at 79.0 - 80.9 cm or greater. Approximate age at
maturity was estimated to be 2+ and 3+ years for males and females respectively (Fig 3.8a,b).
Spawning may take place in estuaries as well as ocean waters as 53% of mature male and 33% of
mature female mulloway sampled were observed in estuarine catches. Fish in spawning condition
(macroscopic staged 5, 6 and 7 fish) were mostly observed between November and March.
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100
37
a)
90
80
70
60
50
40
30
% Maturity
20
10
0
100
b)
90
80
70
60
50
40
30
20
10
0
40
50
60
70
80
90
100
110
120
130
Fish total length (cm)
Figure 3.7.
Estimated size at maturity of a) male and b) female mulloway based on 2 cm size
classes (n = 91 males and 162 females).
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Project No. 2002/005
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NSW Dept of Primary Industries
100
a)
90
80
70
60
50
40
30
% Maturity
20
10
0
100
b)
90
80
70
60
50
40
30
20
10
0
0
2
4
6
8
10
12
14
16
18
20
22
Age (years)
Figure 3.8.
3.4.
Estimated age at maturity of a) male and b) female mulloway based on yearly age
classes (n = 91 males and 162 females).
Discussion
The oldest mulloway we aged in this study (24 years) was much less than the maximum reported
age of 42 years (Griffith & Hecht 1995). This may have been due to limited sampling of large
individuals in the current study, or alternatively, mulloway in south-eastern Australia may not live
as long as those in southern Africa. Previously however, a mulloway caught in Port Stephens was
aged at 32 years (unpublished). As described for many species of fish, length at age of mulloway
was variable, but the patterns and rates of growth of mulloway observed in the current study were
similar to those described for mulloway in southern Africa by Griffith & Hecht (1995). In both
these studies, otolith-based age estimation was used and mulloway were estimated to reach
approximately 35 - 40 cm TL in 1 year and about 100 cm TL in 6 years (Table 3.5). Growth is
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Mulloway biology & fishery, Silberschneider & Gray
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39
particularly rapid in the first 5 years of life. Griffiths & Hecht (1995) showed that after about the
second year of life, females grew faster to attain an overall greater length (165 - 170 cm) and age
(42 years) than males (140 - 145 cm and age 30 years). Although we could not validate our ageing
procedure, the similarity of our results and those of Griffith & Hecht (1995) add weight that our
ageing was correct.
Comparisons of estimates of age and growth of populations of mulloway elsewhere in Australia
could not generally be made. Previously, Gray & McDonall (1993) followed juvenile cohorts of
mulloway in estuaries and estimated that juveniles grew from a mean length of 7 to 15 cm TL and
16 to 25 cm TL in 6 months between April and October and that fish 15 cm in length were 6
months old. Based on tag-recapture data and scale readings, Hall (1984) estimated that mulloway
grew to 46 cm (1.5 kg) in 2 to 3 years and a length of 80 cm (8 kg) in 5 to 6 years. West (1993)
analysed tag-recapture data for mulloway off south-eastern Australia and estimated that they grew
to 49 cm TL in 2 years and 56 cm TL in 3 years, which is smaller than we estimated.
Table 3.5.
Comparisons of estimated length (TL; cm) at age for mulloway from published
growth equations based on otolith-based age estimates. Lengths derived using the
growth equation and parameters given in the manuscript (Griffiths & Hecht 1995)
and from the current study.
Age in
years
1
2
3
4
5
6
7
8
9
10
15
20
25
Griffiths & Hecht
(1995)
Male
Female
35.6
50.3
64.6
77.6
89
98.6
106.6
113.1
118.3
122.4
133.1
136.1
136.9
Current study
35.5
51.1
66
79.5
91.3
101.5
110
117.1
122.9
127.7
140.8
145.2
146.6
34.7
52.0
66.3
78.0
87.6
95.5
102.0
107.3
111.6
115.2
125.5
129.4
130.8
Our estimates of length at maturity were considerably less than those reported for mulloway in
southern Africa by Griffiths (1996). We found that 50% of female and male mulloway matured at
68 and 51 cm TL respectively, compared to 107 and 92 cm TL respectively, by Griffiths (1996).
Our data also suggest that mulloway in NSW spawn at a much younger age than elsewhere. For
example, the 50% maturity levels observed in our study corresponded to fish aged approximately 2
and 3 years, whereas it was 5 to 6 years in southern Africa. Hall (1986) and Anon (1993) estimated
that mulloway in South and Western Australia do not become sexually mature until they attain
about 75 cm TL and are approximately 4 kg and 5 to 6 years old. Clearly, the length and age that
mulloway mature varies between and among regions and, as such, local data may be required for
determining best management options for conserving stocks.
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NSW Dept of Primary Industries
The time of spawning appears to vary between geographic regions and with latitude and is
probably related to water temperature and oceanography. Although not definitive, our data
concerning the prevalence of fish with mature gonads suggests that mulloway primarily spawn
between November and March in NSW waters. This conclusion is further corroborated by reported
larval occurrence between February and April in coastal waters off NSW (Gray & Miskiewicz
2000) and that small juveniles 2 - 8 cm TL occur in estuaries between April and June (Anon
1981a). West & Walford (2000) however, reported that juvenile mulloway (< 10 cm TL) were
present year round in two estuaries in northern NSW (between 28°50’ and 29°30’S). Further, both
Broadhurst (1993) and Gray & McDonall (1993) reported two distinct 0+ juvenile cohorts in an
estuarine population which suggests that not all spawning is synchronous within a region. The
protracted summer spawning season observed for mulloway in NSW is comparable to that
described for mulloway elsewhere. For example, in southern Africa, Griffiths (1996) found that
spawning varied along the coast from August to November (winter to spring) in the northern
KwaZulu region (30 - 31°S), and from October to January (summer) in the southern and south-east
Cape regions (33 - 35°S). Similarly, along the Western Australian coast, Penn (1977) reported fish
with mature gonads in September and October in Shark Bay (26°S), whereas Anon (1993) reported
that mature fish occurred between December and January in the Swan River (32°S). In South
Australia, mulloway appear to spawn throughout summer (November to February) (Hall 1986).
Several authors have hypothesised that mulloway spawn in nearshore coastal waters around the
mouths of estuaries and in surf zones. This is based on observations in South Africa (Griffiths
1996) and South and Western Australia (Hall 1984, 1986, Anon 1993) that fish with mature or
spent gonads have been caught only in ocean waters, whilst fish in estuaries did not show
development of mature gonads. Further, off the east coast of South Africa, eggs have only been
collected in nearshore waters and not in the offshore Agulhas Current (see Griffiths 1996) and
larvae (but not eggs) have only been collected in low numbers in estuaries. This is also
corroborated by a study in Botany Bay (central NSW) in which all mulloway collected (< 64 cm
TL) had immature gonads (Anon 1981a) although timing of capture may have been inconsistent
with spawning period. Our work shows that about half the mature males and one third of the
mature females sampled came from the estuary, indicating that mulloway throughout NSW spawn
predominantly at sea but may spawn in the estuary or move between these two areas. It is unclear
whether mature fish in the estuary will then travel to ocean waters to spawn or remain in the
estuary. Hall (1984) suggested spawning might take place near the mouths of estuaries as large fish
(80 - 150 cm TL) in spawning condition have been caught in the mouth of the Murray River in
South Australia. A separate population of mulloway is thought to occur in South Australia in
western waters in the Great Australian Bight (Jones et al. 1990). Location and timing of spawning
is unknown for this suspected population and further research is needed. Hall (1984) further
postulated that freshwater outflow during summer may promote aggregations of spawning fish near
the mouths of estuaries as peak freshwater discharge generally coincided with, or just preceded, the
spawning season. The spring/summer-spawning season in South Africa also coincides with the
highest periods of rainfall and river discharge in that region. Griffiths (1996) hypothesised that
mulloway may have adapted a river discharge-spawning relationship as an evolutionary tactic to
enhance recruitment of juveniles to estuaries.
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4.
ASPECTS
41
OF
THE
COMMERCIAL
FISHERY
FOR
MULLOWAY IN NSW
4.1.
Introduction
Commercial and recreational fisheries for mulloway occur in estuarine and coastal waters of NSW.
Mulloway is a key secondary species in the Estuary General and Ocean Trap & Line fisheries in
NSW. The Fishery Management Strategy (Anon 2003, OT&L in prep) for each of these fisheries
list the exploitation status of mulloway as “unknown” and “undefined” respectively. This is
primarily due to the limited biological and fishery-related information available for mulloway in
south-eastern Australia.
There is little description of the fisheries for mulloway in NSW and how catches vary between
fishing sectors, fishing gears and regions. Information of the relative changes in catch and effort
can provide indices of changes in populations and potential effects of fishing and changes in
targeting on populations. In Chapter 3, we described the growth and reproductive characteristics of
mulloway in NSW. More detailed analyses of the length, sex and age compositions of catches and
how these vary spatially and temporally can be used to help assess the status of fish populations
and is often fundamental to determining the status of exploited fish stocks (Megrey 1989, Richards
et al. 1997). Such information is known for many coastal and estuarine species of fish in NSW, but
similar information is unavailable for mulloway.
In this chapter we explore the commercial fishery for mulloway in NSW. Specifically, we
document and describe trends in reported commercial catch and effort of mulloway and assess the
length and age composition of landed catches. We then estimate rates of total mortality and provide
yield-per-recruit analyses to assess the exploitation status of mulloway in NSW. We conclude by
using these data to provide future management options to help conserve and sustain the mulloway
stocks in NSW.
4.2.
Methods
4.2.1.
Trends in reported catch and effort
Commercial fishers in NSW are required to submit monthly forms detailing their catch and effort.
The information recorded on these forms has changed since their inception. Reporting forms are
customised for each commercial fishery and currently provide information on the areas fished, the
number of days each method of fishing was used and the quantity of each species landed by that
method in that month. These current forms were implemented in 1997 and provide the best
information on reported catch and effort to date. Forms used between 1990 and 1996 did not
associate species catch with days of effort or fishing method and, prior to 1990, it was only
possible to determine species catch per month.
The quality of this self-reported information is difficult to ascertain but is probably more reliable
since 1997. Misreporting, either deliberately or unintentionally, may be a problem. For example, it
is common for ocean and estuary hauling skippers and their crew to report the same total quantities
of landing on their individual catch returns thereby multiplying the true amount taken by the
number of crew members. Identifying this form of misreporting usual requires the contacting of
individual fishers. Many fishers report small quantities of mulloway each year (i.e. <5 kg). Errors
Mulloway biology and fishery assessment, Silberschneider & Gray
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42
NSW Dept of Primary Industries
in catch statistics, either by multiple reporting, misreporting species, or data entry errors were
identified during examination of catch statistics and such errors have been corrected. While some
errors have been amended, we assume that there may be others and that there is a constant error
rate through time. We have used these catch statistics to describe temporal and spatial patterns in
estimated reported landings, and to make inferences about the relative abundance of mulloway.
Reported landings were obtained from the March 2005 extraction of Comcatch (the commercial
fisheries catch records database at NSW DPI). Distributions of mulloway landings were divided
into fisheries, ocean zones (and the estuaries that are bound by these zones) and two regions (north
and south of Sydney). Data from 1940 were used to show long-term trends in reported catches and,
where possible, catch statistics from 1984/85 to 2003/04 or from 1997/98 to 2003/04 were used to
gain a more comprehensive description of the commercial fishery.
4.2.2.
Length and age composition of commercial landings
Commercial landings of mulloway caught in estuaries and ocean waters throughout NSW were
sampled for length and age composition on a regular basis between November 2002 and February
2005. Sampling was primarily done at the Sydney Fish Market (SFM) but also at several ports of
landings (fishing co-operatives), notably from the Clarence River, Coffs Harbour, Hawkesbury
River and Shoalhaven River. These ports signify areas where large quantities of mulloway are
caught. Data concerning method and location of capture were obtained for each catch. The length
composition of commercial catches was assessed by region with Region 1 comprising waters from
Newcastle to the Queensland border and Region 2 was defined as waters south of Newcastle to the
Victorian border. Ages of fish were estimated as described in Chapter 2. Age composition of
landed catches was determined by applying age-length keys to relevant length composition data of
commercial landings. This was done separately for estuary and ocean caught fish, and for all
landings.
4.2.3.
Estimates of total, natural and fishing-associated mortality
Estimates of the instantaneous rate of total annual mortality (Z) were made from age-based catch
curve analysis (Ricker 1975). We used the total age frequency in commercial landings so as to
include both the estuary and ocean components of the fishery. Linear regressions were fitted to the
plot of natural logarithm of the frequency of fish in each age class against age for ages 2 to 10 and
2 to 15 years. Age 2 was chosen because it was the most abundant age class present (see Figure
4.10), despite mulloway not being fully recruited to the fishery until age 3 (see Figure 3.1 and
Table 3.2). This approach will have resulted in slightly low estimates of Z, however we consider it
more precautionary than estimating Z from age 3 onwards. We did not include ages 16 to 24
because of the low numbers (< 5 fish in total) observed in these age classes. Natural mortality (M)
was estimated using the method of Hoenig (1983) based on maximum age and the assumption that
either 5 or 1% of fish attain it. Maximum age was set at 42 years (Griffith & Hecht 1995). Fishing
mortality (F) was estimated by subtracting M from Z. These analyses assumed that recruitment and
growth of mulloway was constant across years and that the species displayed asymptotic growth
patterns.
4.2.4.
Yield-per-recruit analyses
Two approaches were used to model the relative yield per recruit (YPR) for mulloway. Firstly, the
Beverton-Holt YPR model (Beverton & Holt, 1957) was used to calculate yield per recruit curves
for a range of values of natural mortality (M) using the computer program B-H3 (Saila et al. 1988).
Input parameters were based on the von Bertalanffy growth model and the length-weight
relationship, both described in Chapter 3. Mortality rates were varied between M = 0.05, 1.0 and
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Mulloway biology & fishery, Silberschneider & Gray
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43
1.5 and F ranged between 0.35 and 0.6 (see below). Estimates of age at capture were converted to
weight at capture using the von Bertalanffy growth function parameters.
Yield per recruit analyses were also done using the program “YPER” (Ault et al., 1996). YPER
calculates relative YPR isopleths using the Beverton & Holt model. Input parameters included a
range of ratios of M/K, Lc/Linf and Exploitation rate, and a range of values for F and M.
4.3.
Results
4.3.1.
Temporal trends in reported catch and effort
Between 1940/41 and 1970/71 reported catches of mulloway varied between approximately 50 and
150 tonnes per annum (Fig. 4.1). During the early 1970’s catches greatly increased to peak at
approximately 400 tonnes in 1973/74. Since 1973/74 reported catches have continued to decline to
the current 60 tonnes per annum. The peak in catches in 1970’s coincided with the abolition of a
size limit on mulloway and with the development of the ocean demersal fish trawl fishery.
Despite the recent declining levels of reported commercial catch, CPUE of all commercial fisheries
combined (kg/fisher month) has remained fairly stable between 1984/85 and 2003/04 and this is
mirrored by the more recent CPUE of kg/day (Fig. 4.2). Thus, the recent decline in reported
commercial catch of mulloway may largely be due to the decline in the number of fishers reporting
landings of this species (Table 4.1).
Better reporting of commercial catches of fish since 1997/98 has allowed this harvest to be assessed
on a fishery basis. Since 1997/98, both the Estuary General and Ocean Trap & Line fisheries have
been the largest harvesters of mulloway (Fig 4.3). Opportunistic catches of this species by fishers
in the Ocean Hauling Fishery can manifest itself as small peaks in catch through time as occurred
in 2000/01. Catches of mulloway are still within historic levels although catches will still need to
be monitored to examine whether the recent declines seen in the Ocean Trap & Line fishery
continue.
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44
NSW Dept of Primary Industries
MLL 18" (45.7 cm)
400
No MLL
MLL 15" (38.1 cm)
MLL 45 cm
1200
350
1000
900
300
800
250
700
600
200
500
150
400
300
100
200
50
Number of fishers reporting catch
Total estimated landings (tonnes)
1100
100
0
1940/41
1941/42
1944/45
1945/46
1946/47
1947/48
1948/49
1949/50
1950/51
1951/52
1952/53
1953/54
1954/55
1955/56
1956/57
1957/58
1958/59
1959/60
1960/61
1961/62
1962/63
1963/64
1964/65
1965/66
1966/67
1967/68
1968/69
1969/70
1970/71
1971/72
1972/73
1973/74
1974/75
1975/76
1976/77
1977/78
1978/79
1979/80
1980/81
1981/82
1982/83
1983/84
1984/85
1985/86
1986/87
1987/88
1988/89
1989/90
1990/91
1991/92
1992/93
1993/94
1994/95
1995/96
1996/97
1997/98
1998/99
1999/00
2000/01
2001/02
2002/03
2003/04
0
Financial year
Figure 4.1.
Reported total commercial catches of mulloway in NSW between 1940/41 and
2003/04 and associated changes in MLL.
55
50
180
45
160
40
140
5
120
4
100
80
CPUE
Total estimated landings (tonnes)
200
3
60
2
40
Total catch
CPUE kg / day
CPUE kg / fisher month
20
0
1
0
/85 /86 /87 /88 /89 /90 /91 /92 /93 /94 /95 /96 /97 /98 /99 /00 /01 /02 /03 /04
84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03
19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 20 20 20 20
Financial year
Figure 4.2.
Total reported commercial landed catch (kg) and catch per unit of effort (kg per
month) in NSW from 1984/85 to 2003/04.
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Mulloway biology & fishery, Silberschneider & Gray
NSW Dept of Primary Industries
45
Number of commercial fishers that reported catching mulloway from 1984/85 to
2003/04.
Table 4.1.
Financial year
Number of fishers
1984/85
1985/86
1986/87
1987/88
1988/89
1989/90
1990/91
1991/92
1992/93
1993/94
1994/95
1995/96
1996/97
1997/98
1998/99
1999/00
2000/01
2001/02
2002/03
2003/04
978
1054
918
842
878
929
963
840
807
737
686
642
633
605
574
546
503
478
428
380
60000
Ocean Prawn trawl
Ocean Fish trawl
Ocean Trap & Line
Ocean Haul
Estuary General
Estuary Prawn Trawl
Estimated landed catch (kg)
55000
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
0
1997/98 1998/99 1999/00 2000/01 2001/02 2002/03 2003/04
Financial year
Figure 4.3.
Total estimated landed catch (kg) by fishery in NSW from 1997/98.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
46
4.3.2.
NSW Dept of Primary Industries
Spatial trends in reported catch and effort
Table 4.2 shows the proportion of the reported mulloway catch attributed to each commercial
fishery between 1997/98 and 2003/04, and clearly shows that the Estuary General and Ocean Trap
& Line fisheries catch the majority of fish (by weight). It also highlights that the majority of fish
caught within each fishery is by one method.
Table 4.2.
Mean proportion of total reported mulloway catch attributed to each fishery and the
proportion attributable to the main method within each separate fishery between
1997/98 and 2003/04.
Fishery
Ocean Prawn Trawl
Ocean Fish Trawl
Ocean Trap & Line
Ocean Hauling
Estuary General
Estuary Prawn Trawl
Percent contribution to
total commercial catch
Main method
0.6
3.1
37.3
4.7
54.1
0.1
Prawn trawl net
Fish trawl net
Handline
Beach haul net
Mesh net
Prawn trawl net
Despite the declines in catch shown above, CPUE (kg/day) for mulloway has remained stable since
1997/98 in the two main fisheries for this species (Fig. 4.4). CPUE in the Ocean Trap & Line
fishery was consistently between 6 and 7 kg/day between 1997/98 and 2003/04 with a sharp
increase in 1999/00 of closer to 10 kg/day. During this same period, CPUE in the Estuary General
fishery was typically between 3 and 4 kg/day. The higher CPUE in the Ocean Trap & Line fishery
is probably due to larger fish being caught in ocean waters compared to estuaries.
Commercial reported landings for mulloway from 2003/04 show that ocean zones 6, 5 and 2, and
the catches from estuaries that are bound by these zones, land the majority of mulloway in NSW
(Fig. 4.5). Estuaries that contribute much of the catch within each of these three primary ocean
zones are the Hawkesbury River (12.4 tonnes) in zone 6, Hunter River (6 tonnes) in zone 5 and
Clarence River (8.3 tonnes) in zone 2. The catch of mulloway in the Shoalhaven River is
comparable to these estuaries (6.2 tonnes) however the weight of fish caught in ocean zone 7 is
negligible (0.2 tonnes). The 2003/04 financial year is the most recent year for which data is
predominantly complete (85%) and is the first entire financial year after the buy-out of commercial
fishing businesses for the creation of recreational fishing havens was completed.
Project No. 2005/05
Mulloway biology & fishery, Silberschneider & Gray
NSW Dept of Primary Industries
47
10
Ocean Trap & Line
Estuary General
9
8
CPUE (kg/day)
7
6
5
4
3
2
1
0
1997/98 1998/99 1999/00 2000/01 2001/02 2002/03 2003/04
Financial year
CPUE (kg/day) of mulloway for the Estuary General and Ocean Trap & Line
fisheries for each year between 1997/98 and 2003/04.
Figure 4.4.
18
Reported landings (tonnes)
16
14
12
10
8
6
4
2
0
1
2
3
4
5
6
7
8
9
10
NSW Ocean zone
Figure 4.5.
Total reported estuarine and coastal landings of mulloway by ocean zone for
2003/04. Landings for ocean zones include estuarine landings from that area.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
48
NSW Dept of Primary Industries
Catches of mulloway differ both among months and between the Ocean Trap & Line and Estuary
General fisheries (Fig. 4.6). The greatest reported landings of mulloway harvested in the OT&L
fishery occurs in the summer months when the fishery targets those fish that have aggregated in
ocean waters to spawn. The greatest reported landings of fish harvested in the Estuary General
fishery occurs during autumn and winter.
Estuary General
Ocean Trap and Line
7000
Reported landings (kg)
6000
5000
4000
3000
2000
1000
0
r
r
r
r
y
ly
st
ry
ch
ar
be
be
be
be
Ju ugu
ua
ar
ru
m
to
m
m
n
M
c
b
e
e
e
a
A
v
c
J
O
pt
Fe
No
De
Se
r
Ap
il
M
ay
Ju
ne
Month
Figure 4.6.
Mean (± standard errors) of reported landings by month for the Estuary General
and Ocean Trap & Line fisheries between 1997/98 and 2003/04.
The estimated length composition of mulloway retained in commercial catches between 2003 and
2005 is given in Fig. 4.7. Region 2 had a higher frequency of smaller fish and a lower frequency of
larger fish than Region 1. The majority of fish caught (83%) were within 15 cm of the minimum
legal length (MLL = 45 cm) in all regions.
The estimated length compositions of retained commercial catches of mulloway have changed
through time and reflect changes in the MLL (Fig. 4.8). Between 1972 and 1990 fish between 30
and 40 cm TL dominated catches when there was no MLL. Since then, larger fish have dominated
catches because of the increased MLL to 45cm TL. A greater proportion of smaller fish between 45
and 60 cm were measured in catches in 2003 - 05 than in 1996 - 99.
Project No. 2005/05
Mulloway biology & fishery, Silberschneider & Gray
NSW Dept of Primary Industries
49
13
Region 1 (n=2896)
Region 2 (n=7119)
12
11
10
% Frequency
9
8
7
6
5
4
3
2
1
0
30
40
50
60
70
80
90
100 110 120 130 140 150 160 170
Size class (cm)
Length class distribution (1 cm size classes) of sampled commercial retained
catches of mulloway by region. Dotted line indicates 45 cm MLL.
Figure 4.7.
11
1972-75 (n=1606)
1987-90 (n=2334)
1996-99 (n=5842)
2003-05 (n=10020)
10
9
% Frequency
8
7
6
5
4
3
2
1
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150 160 170
Fish total length (cm)
Figure 4.8.
Estimated length compositions of retained commercial catches of mulloway in
NSW for four periods between 1972 and 2005.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
50
NSW Dept of Primary Industries
The length composition of sampled catches of mulloway taken in estuaries and ocean waters was
very similar (Fig. 4.9). A greater proportion of larger (> 70 cm TL) individuals were caught in
ocean waters. It is also interesting to note that, when converting fish lengths to weights using the
equation in Chapter 3, approximately 69% of fish measured were caught in estuaries compared to
31% caught in the ocean. This corresponds to the total weight of mulloway caught in each class of
water in 2003/04 where 65% of mulloway landed were caught in estuaries and 35% were caught in
ocean waters.
14
Estuary (n=7269)
Ocean (n=2143)
12
% Frequency
10
8
6
4
2
0
40
50
60
70
80
90
100 110 120 130 140 150 160 170 180
Length class (cm)
Figure 4.9.
4.3.3.
Length composition of sampled estuarine and ocean commercial catches of
mulloway (pooled across regions).
Age Compositions of landings
The age composition of commercial landings was estimated using the age-length key (Table 3.2)
and the size composition in landings (Fig. 4.9). Retained commercial catches taken in estuarine and
coastal waters were dominated (> 70%) by 2-year-old fish (Fig. 4.10). Fish aged between 2 and 5
years contributed approximately 98% to total landings. Fifty-five fish older than 8 years were
sampled (Table 3.2), but because they contributed less than 0.3% in any age class they are not
visible in Fig. 4.10.
Project No. 2005/05
Mulloway biology & fishery, Silberschneider & Gray
NSW Dept of Primary Industries
100
51
a)
90
80
70
60
50
40
30
20
10
0
100
b)
90
% Frequency
80
70
60
50
40
30
20
10
0
100
c)
90
80
70
60
50
40
30
20
10
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Age (years)
Figure 4.10.
Estimated age compositions of samples of a) the total commercial catch (n = 2605),
b) the estuarine catch (n = 1681), and c) ocean retained commercial catches (n =
381) of mulloway in NSW 2003 to 2005. Note that 3 fish could not be assigned to
a class of water.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
52
NSW Dept of Primary Industries
4.3.4.
Estimated total, natural and fishing-related mortality
Estimates of total mortality from the slope of the descending limb of the catch curve were 0.7 for
ages 2 to 10 and 0.45 for ages 2 to 15 (Fig. 4.11).
5
2-10 year regression
2-15 year regression
4
ln (% frequency)
3
2
1
0
-1
-2
-3
-4
-5
0
2
4
6
8
10
12
14
16
18
20
22
24
Age+ (years)
Figure 4.11.
4.3.5.
Linear regressions fitted to the natural logarithms (ln) of age composition for
mulloway. Curves were fitted between the ages of 2 and 10 and 2 and 15 years.
Yield-per-recruit analyses
Yield-per-recruit trajectories for a range of sizes at first capture at 3 different estimates of M are
presented in Fig. 4.13. Yield per recruit estimates at any given F were influenced by M, being
much greater at lower values of M. Despite this, the shape of the trajectories was similar in each
case. The analyses indicate that at present levels of F (0.35 to 0.6) and at the current MLL (45cm)
that mulloway are growth overfished. Substantial increases in yield-per-recruit are predicted with
increases in the length at first capture.
Yield per recruit isopleths for our best estimate of M/K (0.1/0.197 = 0.5) show that at the current
exploitation rate (E ranges from 0.77 to 0.85) that substantial increases in yield per recruit are
predicted by increasing the length at first capture (Fig. 4.14). At the most likely situation of M/K =
0.5 the model predicts, at current exploitation levels, an increase in yield per recruit of
approximately 40% by increasing the minimum legal length to 70cm. Any increase in minimum
legal length is likely to reduce overall exploitation rates resulting in even greater increases in yield
per recruit with increases in the minimum legal length. Scenarios for M/K = 0.25 and M/K = 0.75
are also presented in Figs. 4.14. Once the length at first capture increases to greater than around
70% of the maximum size (i.e. approximately 90 cm TL) exploitation rate has little affect on yield
per recruit.
Project No. 2005/05
Mulloway biology & fishery, Silberschneider & Gray
NSW Dept of Primary Industries
53
Predicted optimum lengths at first capture are provided in Table 4.3. These data indicate that the
smallest optimum length to harvest mulloway would be 76 cm TL at an exploitation rate of 0.4 and
M/K ratio of 0.7. The optimum exploitable length at an exploitation rate of between 0.77 and 0.85
and at the best estimate of M/K of 0.5, is between 98 to 103cm.
M = 0.05
8
7
YPR
6
No MLL
45 cm
50 cm
60 cm
70 cm
80 cm
90 cm
5
4
3
2
1
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
F
M = 0.1
5
No MLL
45 cm
50 cm
60 cm
70 cm
80 cm
100 cm
YPR
4
3
2
1
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
F
M = 0.15
3.5
3.0
No MLL
45 cm
50 cm
60 cm
70 cm
80 cm
90 cm
110 cm
YPR
2.5
2.0
1.5
1.0
0.5
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
F
Figure 4.12.
Yield per recruit trajectories for mulloway calculated using the program B-H3
(Saila et al. 1988). Note different scales on the y-axes at different values of M.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
54
NSW Dept of Primary Industries
M/K = 0.25
0.7
18000
18000
18000
20000
20000
20000
22000
22000
22000
24000
24000
26000
26000
20000
22000
24000
24000
26000
28000
28000
0.6
260
280
00
30000
300
00
32000
Hypothetical 70 cm MLL
0.5
0
32
340
00
30
00
0
00
36
00
0
30
00
0
32
00
0
34
00
0
36
00
0
0.4
0.5
0
00
26
00
240 000
22 000
20
0.7
0
00 6000
28
2
0.3
0
00
26
0
00
28
0.4
0.3
00
280
00
Lc/Linf
18000
0.6
0
00
Hypothetical 50 cm MLL
24
00
220
00
200 Current 45 cm MLL
0
1800 000
16
0.8
0.9
Exploitation rate F/Z
M/K = 0.5
0.7
12000
12000
13000
13000
14000
14000
18
00
0
20000
16000
1900
0
15
00
0
00
0
00
17
19000
160
17000
18000
1400
0
15000
16000
17000
Lc/Linf
13000
15000
16000
0.6
12000
0.3
0.4
0
00
14
0
00
13
0
00
12
16
00
0
15
00
0
0
0
00 0 0
16 1 5
0.5
17
00
0
19000
18
00
0
17
00
0
210
00
20
00
19
0
00
0
0
00
23000
0.3
00
220
0.4
20
210
00
18000
0.5
0.6
0
00
14 000
13 000
12
0.7
15
00
0
0
1200
0
0
130
0
1400
15000
0
00
11 000
10 000
9 000
8
0.8
Hypothetical 70 cm MLL
Hypothetical 50 cm MLL
Current 45 cm MLL
0.9
Exploitation rate F/Z
Figure 4.13.
Yield-per-recruit isopleths for mulloway for different scenarios of M/K.
Project No. 2005/05
Mulloway biology & fishery, Silberschneider & Gray
NSW Dept of Primary Industries
55
M/K = 0.75
8000
0
800
9000
10000
1200
0
00
120
130
10
00
0
1100
0
11000
Lc/Linf
11000
00
13
00
0
0.5
00
90
10
00
0
11
00
0
14000
00
80
90
00
0
0.4
0.5
0.6
00
Current 45 cm MLL
70
00
60
00
50
00
80
10
00
00
0
11
0.3
0.3
Hypothetical 50 cm MLL
12
00
0
130
1400
0
00
0.4
150
00
Hypothetical 70 cm MLL
1200
0
0
00
11
10000
10
00
0
0
00
10
0.6
9000
9000
0
900
0.7
8000
0.7
0.8
0.9
Exploitation rate F/Z
Figure 4.13 (cont).
Table 4.3.
Yield-per-recruit isopleths for mulloway for different scenarios of M/K.
Optimum lengths at first capture (cm TL) for mulloway in relation to exploitation
rate and M/K. Linf = 131.
Exploitation rate E
M/K
0.3
0.4
0.5
0.6
0.7
0.4
86.06
83.33
80.73
78.26
76.05
0.5
92.95
90.09
87.36
84.76
82.42
0.6
99.06
96.07
93.21
90.48
88.01
Mulloway biology and fishery assessment, Silberschneider & Gray
0.7
104.52
101.4
98.41
95.68
92.95
0.8
109.46
106.21
103.22
100.23
97.50
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56
4.4.
NSW Dept of Primary Industries
Discussion
Mulloway has been commercially harvested in significant quantities in NSW since at least the
1940’s. There was a significant increase and peak in reported total catches in the early to mid
1970’s, after which total reported catches have declined. This decline may be indicative of
population abundance but may in part be due to the reduced levels of fishing effort, as the available
CPUE data have been relatively stable since the late 1980’s. Unfortunately, there are no
comparable data concerning the recreational fishery for mulloway in NSW, which in recent years
has been estimated to be at least three times greater than the corresponding commercial fishery
(Henry & Lyle 2003).
The commercial fishery for mulloway varies spatially and temporally. Mulloway are mostly caught
in estuaries during winter when mesh nets can be set overnight. In contrast, mulloway are
predominantly caught in ocean waters between summer and autumn when fish aggregate to spawn.
Greatest estuarine catches of mulloway are reported in the large riverine systems, which have
significant depth and catchments that allow for large freshwater discharge, notably the Clarence
and Hawkesbury rivers. In coastal waters, greatest quantities of mulloway are taken in ocean
fishing zones 5 and 6, between 32 and 34° S (Crowdy Head to Botany Bay).
The estimated length and age compositions of the estuarine and coastal catches of mulloway were
very similar, being dominated by fish very close to the minimum legal length (MLL) of 45 cm and
age of 2 years. The relatively small proportion of fish aged > 2 years in landings, despite having the
potential to live for more than 40 years, is indicative of a fishery that is heavily exploited. Our
estimates of F are between 3 and 6 times greater than our best estimate of M, a situation that is
likely to be unsustainable. Estimates of total mortality (0.45 to 0.7) are high and indicate that
between 36 and 50 % of mulloway die each year. This estimate of Z is more than 5 times greater
than that estimated for black drum (Pogonias cromis) in the USA (Jones & Wells 1998), but is
similar to that estimated for inshore mulloway (A. japonicus) in South Africa (Griffiths 1997c).
These high mortality rates, in conjunction with spawner biomass-per-recruit analyses, led to the
conclusion that this species in South Africa has been severely depleted and is recruitment
overfished (Griffiths 1997c). Sciaenids, in general, are prone to overfishing (Sadovy & Cheung
2003, Piner & Jones 2004). The data presented in this report show that mulloway in NSW are
growth overfished and, if similar to the South African stock, possibly recruitment overfished.
Further work to assess the current spawner biomass-per-recruit levels and any spawner biomassrecruitment relationship should be done as a priority for mulloway in NSW.
4.4.1.
Management implications
Because sciaenids are prone to overfishing, it has been recommended that the spawning stock,
particularly identifiable spawning aggregations, be protected from harvesting to sustain wild
populations of some species (Sadovy & Cheung 2003). This report indicates that mulloway in
NSW are currently being exploited at unsustainable levels and are in urgent need of greater
protection. This could potentially be achieved by (1) increasing the minimum legal length of the
species to at least 70 cm TL, (2) introducing spatial and temporal fishing closures around spawning
aggregations or on prohibiting the taking of mulloway during the summer-autumn spawning season
as it is during this time that fish are most vulnerable to capture in the coastal line fishery, (3)
introducing a mandatory bycatch reduction device (see Broadhurst & Kennelly 1994, 1995) in the
estuarine and coastal prawn trawl fleet, and (4) reducing the bag-limit for recreational anglers in
conjunction with research into release mortality (5) using a combination of all of these options.
All such options will create negative economic impacts on estuary and coastal commercial fishers
that catch mulloway in significant numbers, impact on the recreational fishery and may be hard to
Project No. 2005/05
Mulloway biology & fishery, Silberschneider & Gray
NSW Dept of Primary Industries
57
regulate. Specifically, the introduction of a significant increase in the MLL of mulloway would
virtually eliminate the estuary fishery for mulloway. Since 2000/01, 32% of all commercial fishers
reporting mulloway harvest 90% of the total commercial catch. During this time, between 31 and
35% of estuary fishers harvested 90% of the estuary mulloway catch and this is a significant part of
their fishing income. In the ocean, 30 – 37% of fishers in this sector harvested 90% of the ocean
mulloway caught since 2000/01. Such a size limit increase would also negatively impact many
coastal fishers as most mulloway caught in ocean waters are also < 70 cm TL. Such an impact may
only be short-term (< 5 years) since growth from 45 cm to 70 cm will take less than 5 years, and
the yield-per-recruit analyses indicated that the total weight of harvests should be significantly
greater once fish grow to a larger size. However, any potential benefits to protect the stock may be
negated if mulloway are still caught and subsequently discarded in poor condition in significant
quantities in these fisheries. For example, mulloway will still be caught in mesh nets in estuaries
unless the minimum mesh size is increased greatly (but this would affect retained catches of most
other species) and the effects of the capture and discarding of mulloway in these nets is not known.
Current studies on survival of mulloway following hook and release show mortalities can be high
dependent on hooking location, exposure to air and handling practices, but this work has only been
done in estuaries. The additional effects of barotrauma on the survival of mulloway caught and
released in coastal waters is unknown. This information would be needed prior to any such fishing
closures and increases in MLL. Nonetheless, management interventions such as those discussed
above are required to adequately conserve the population of wild mulloway in NSW.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
58
NSW Dept of Primary Industries
5.
OUTCOMES AND RECOMMENDATIONS
5.1.
Benefits
This project has provided valuable biological information on the growth, size and age at maturity
and fisheries-related data on length and age compositions of commercial catches for mulloway in
NSW. Such information will benefit fisheries managers, conservation agencies and the commercial
and recreational fishing industries in determining future management arrangements for the
conservation and sustainable harvesting of the species.
5.2.
Further Development
Further work is required to determine the size and demographic characteristics of the recreational
fishery of mulloway in NSW. The data contained in the National Survey of Recreational and
Indigenous Fishing suggests that the recreational catch of mulloway in NSW is larger than the
commercial sector. A long-term strategy to monitor and assess the population and fisheries of
mulloway and to assess impacts of any changes in management regimes on the species is required.
The effects of the current experimental stock enhancements of mulloway and their potential to
rebuild the mulloway population need to be assessed. The conclusions and recommendations of this
study and their potential impacts on the fisheries for mulloway need to be discussed with industry.
5.3.
Planned Outcomes
The planned outcomes of this project were:
(1) The publication of a review of the biology and fishery of mulloway in an international
scientific journal: - A scientific manuscript has been submitted to an international journal
for consideration for publication.
(2) A synthesis and assessment of the commercial fishery of mulloway in NSW: - This was
achieved (Chapter 4).
(3) A description of the reproductive biology, growth and age and yield-per-recruit analyses of
mulloway: - This was achieved (Chapters 3 and 4)
(4) Provide advice and recommendations concerning the biology and fisheries of mulloway in
NSW to the relevant fisheries managers, MACs and industry in general: - This has been
done throughout the project and is ongoing.
5.4.
Conclusions
The key objectives of assessing the age, growth and reproductive biology of mulloway in NSW
have been achieved. A review of the scientific literature revealed a dearth of information on
mulloway, except for southern Africa. Our studies show that mulloway grow relatively fast, attain
sexual maturity at a reasonable size (approximately 68 cm and 51 cm TL for female and male
respectively) but at a relatively young age (2 – 4 years) and that the current minimum legal length
of 45 cm TL is too small to protect the spawning population of mulloway in NSW. Mulloway are
growth overfished and changes in the management arrangements of the species are required for the
conservation and sustainable harvesting of the species. In particular:
•
The spawning stock requires greater protection. This will be achieved partially through the
formation of a series of marine parks along the NSW coast. There will also be some flow-on
benefits to mulloway from fishing closures on highly productive reefs in order to protect grey
nurse sharks. These changes will probably suffice in providing protection to the spawning stock
in the short term.
Project No. 2005/05
Mulloway biology & fishery, Silberschneider & Gray
NSW Dept of Primary Industries
•
59
Fishing mortality needs to be reduced in order to achieve optimal yield. This will impact both
commercial and recreational fishers. The bag limit for recreational fishers may need to be
reduced and an increase in the MLL to 70 cm will (1) protect juveniles and give them the
chance to spawn before being recruited to the fishery; (2) increase egg production; (3) increase
the yield per recruit by more than 40%, and (4) increase the number of trophy fish for
recreational anglers.
The effectiveness of the proposed increase in MLL will be determined, in part, by the discard
mortality rates of mulloway from both commercial and recreational fishing gears. Therefore
research to assess rates of mortality of discarded juvenile mulloway would be necessary before
such an increase in MLL is implemented.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
60
6.
NSW Dept of Primary Industries
LITERATURE CITED
Anon. 1981a. The ecology of fish in Botany Bay – Biology of commercially and recreationally
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7.
APPENDICES
7.1.
Appendix 1 – Intellectual Property
No patentable inventions or processes were developed as part of this research project. The work
presented in this report remains the intellectual property of the authors. The authors should be
acknowledged when citing this work.
7.2.
Appendix 2 – Staff
Staff employed to work on this project by NSW DPI were:
Charles Gray – Principal Investigator
Veronica Silberschneider – Fisheries Technician
Paul Lokys – Fisheries Technician
Glen Cuthbert – Fisheries Technician
Damian Young – Fisheries Technician
Victoria Andrews – Fisheries Technician
James McLeod - Fisheries Technician
Project No. 2005/05
Mulloway biology & fishery, Silberschneider & Gray
Other Titles in the Series
67
Other titles in this series:
ISSN 1440-3544 (NSW Fisheries Final Report Series)
No. 1
Andrew, N.L., Graham, K.J., Hodgson, K.E. and Gordon, G.N.G., 1998. Changes after 20 years in
relative abundance and size composition of commercial fishes caught during fishery independent
surveys on SEF trawl grounds. Final Report to Fisheries Research and Development Corporation.
Project No. 96/139.
No. 2
Virgona, J.L., Deguara, K.L., Sullings, D.J., Halliday, I. and Kelly, K., 1998. Assessment of the
stocks of sea mullet in New South Wales and Queensland waters. Final Report to Fisheries Research
and Development Corporation. Project No. 94/024.
No. 3
Stewart, J., Ferrell, D.J. and Andrew, N.L., 1998. Ageing Yellowtail (Trachurus novaezelandiae) and
Blue Mackerel (Scomber australasicus) in New South Wales. Final Report to Fisheries Research and
Development Corporation. Project No. 95/151.
No. 4
Pethebridge, R., Lugg, A. and Harris, J., 1998. Obstructions to fish passage in New South Wales
South Coast streams. Final report to Cooperative Research Centre for Freshwater Ecology. 70pp.
No. 5
Kennelly, S.J. and Broadhurst, M.K., 1998. Development of by-catch reducing prawn-trawls and
fishing practices in NSW's prawn-trawl fisheries (and incorporating an assessment of the effect of
increasing mesh size in fish trawl gear). Final Report to Fisheries Research and Development
Corporation. Project No. 93/180. 18pp + appendices.
No. 6
Allan, G.L. and Rowland, S.J., 1998. Fish meal replacement in aquaculture feeds for silver perch.
Final Report to Fisheries Research and Development Corporation. Project No. 93/120-03. 237pp +
appendices.
No. 7
Allan, G.L., 1998. Fish meal replacement in aquaculture feeds: subprogram administration. Final
Report to Fisheries Research and Development Corporation. Project No. 93/120. 54pp + appendices.
No. 8
Heasman, M.P., O'Connor, W.A. and O'Connor, S.J., 1998. Enhancement and farming of scallops in
NSW using hatchery produced seedstock. Final Report to Fisheries Research and Development
Corporation. Project No. 94/083. 146pp.
No. 9
Nell, J.A., McMahon, G.A. and Hand, R.E., 1998. Tetraploidy induction in Sydney rock oysters.
Final Report to Cooperative Research Centre for Aquaculture. Project No. D.4.2. 25pp.
No. 10
Nell, J.A. and Maguire, G.B., 1998. Commercialisation of triploid Sydney rock and Pacific oysters.
Part 1: Sydney rock oysters. Final Report to Fisheries Research and Development Corporation.
Project No. 93/151. 122pp.
No. 11
Watford, F.A. and Williams, R.J., 1998. Inventory of estuarine vegetation in Botany Bay, with special
reference to changes in the distribution of seagrass. Final Report to Fishcare Australia. Project No.
97/003741. 51pp.
No. 12
Andrew, N.L., Worthington D.G., Brett, P.A. and Bentley N., 1998. Interactions between the abalone
fishery and sea urchins in New South Wales. Final Report to Fisheries Research and Development
Corporation. Project No. 93/102.
No. 13
Jackson, K.L. and Ogburn, D.M., 1999. Review of depuration and its role in shellfish quality
assurance. Final Report to Fisheries Research and Development Corporation. Project No. 96/355.
77pp.
No. 14
Fielder, D.S., Bardsley, W.J. and Allan, G.L., 1999. Enhancement of Mulloway (Argyrosomus
japonicus) in intermittently opening lagoons. Final Report to Fisheries Research and Development
Corporation. Project No. 95/148. 50pp + appendices.
No. 15
Otway, N.M. and Macbeth, W.G., 1999. The physical effects of hauling on seagrass beds. Final
Report to Fisheries Research and Development Corporation. Project No. 95/149 and 96/286. 86pp.
No. 16
Gibbs, P., McVea, T. and Louden, B., 1999. Utilisation of restored wetlands by fish and invertebrates.
Final Report to Fisheries Research and Development Corporation. Project No. 95/150. 142pp.
No. 17
Ogburn, D. and Ruello, N., 1999. Waterproof labelling and identification systems suitable for
shellfish and other seafood and aquaculture products. Whose oyster is that? Final Report to Fisheries
Research and Development Corporation. Project No. 95/360. 50pp.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
68
Other Titles in the Series
No. 18
Gray, C.A., Pease, B.C., Stringfellow, S.L., Raines, L.P. and Walford, T.R., 2000. Sampling estuarine
fish species for stock assessment. Includes appendices by D.J. Ferrell, B.C. Pease, T.R. Walford,
G.N.G. Gordon, C.A. Gray and G.W. Liggins. Final Report to Fisheries Research and Development
Corporation. Project No. 94/042. 194pp.
No. 19
Otway, N.M. and Parker, P.C., 2000. The biology, ecology, distribution, abundance and identification
of marine protected areas for the conservation of threatened Grey Nurse Sharks in south east
Australian waters. Final Report to Environment Australia. 101pp.
No. 20
Allan, G.L. and Rowland, S.J., 2000. Consumer sensory evaluation of silver perch cultured in ponds
on meat meal based diets. Final Report to Meat & Livestock Australia. Project No. PRCOP.009. 21pp
+ appendices.
No. 21
Kennelly, S.J. and Scandol, J. P., 2000. Relative abundances of spanner crabs and the development of
a population model for managing the NSW spanner crab fishery. Final Report to Fisheries Research
and Development Corporation. Project No. 96/135. 43pp + appendices.
No. 22
Williams, R.J., Watford, F.A. and Balashov, V., 2000. Kooragang Wetland Rehabilitation Project:
History of changes to estuarine wetlands of the lower Hunter River. Final Report to Kooragang
Wetland Rehabilitation Project Steering Committee. 82pp.
No. 23
Survey Development Working Group, 2000. Development of the National Recreational and
Indigenous Fishing Survey. Final Report to Fisheries Research and Development Corporation. Project
No. 98/169. (Volume 1 – 36pp + Volume 2 – attachments).
No.24
Rowling, K.R and Raines, L.P., 2000. Description of the biology and an assessment of the fishery of
Silver Trevally Pseudocaranx dentex off New South Wales. Final Report to Fisheries Research and
Development Corporation. Project No. 97/125. 69pp.
No. 25
Allan, G.L., Jantrarotai, W., Rowland, S., Kosuturak, P. and Booth, M., 2000. Replacing fishmeal in
aquaculture diets. Final Report to the Australian Centre for International Agricultural Research.
Project No. 9207. 13pp.
No. 26
Gehrke, P.C., Gilligan, D.M. and Barwick, M., 2001. Fish communities and migration in the
Shoalhaven River – Before construction of a fishway. Final Report to Sydney Catchment Authority.
126pp.
No. 27
Rowling, K.R. and Makin, D.L., 2001. Monitoring of the fishery for Gemfish Rexea solandri, 1996 to
2000. Final Report to the Australian Fisheries Management Authority. 44pp.
No. 28
Otway, N.M., 1999. Identification of candidate sites for declaration of aquatic reserves for the
conservation of rocky intertidal communities in the Hawkesbury Shelf and Batemans Shelf
Bioregions. Final Report to Environment Australia for the Marine Protected Areas Program. Project
No. OR22. 88pp.
No. 29
Heasman, M.P., Goard, L., Diemar, J. and Callinan, R., 2000. Improved Early Survival of Molluscs:
Sydney Rock Oyster (Saccostrea glomerata). Final report to the Aquaculture Cooperative Research
Centre. Project No. A.2.1. 63pp.
No. 30
Allan, G.L., Dignam, A and Fielder, S., 2001. Developing Commercial Inland Saline Aquaculture in
Australia: Part 1. R&D Plan. Final Report to Fisheries Research and Development Corporation.
Project No. 1998/335.
No. 31
Allan, G.L., Banens, B. and Fielder, S., 2001. Developing Commercial Inland Saline Aquaculture in
Australia: Part 2. Resource Inventory and Assessment. Final report to Fisheries Research and
Development Corporation. Project No. 1998/335. 33pp.
No. 32
Bruce, A., Growns, I. and Gehrke, P., 2001. Woronora River Macquarie Perch Survey. Final report to
Sydney Catchment Authority, April 2001. 116pp.
No. 33
Morris, S.A., Pollard, D.A., Gehrke, P.C. and Pogonoski, J.J., 2001. Threatened and Potentially
Threatened Freshwater Fishes of Coastal New South Wales and the Murray-Darling Basin. Report to
Fisheries Action Program and World Wide Fund for Nature. Project No. AA 0959.98. 177pp.
No. 34
Heasman, M.P., Sushames, T.M., Diemar, J.A., O’Connor, W.A. and Foulkes, L.A., 2001. Production
of Micro-algal Concentrates for Aquaculture Part 2: Development and Evaluation of Harvesting,
Preservation, Storage and Feeding Technology. Final Report to Fisheries Research and Development
Corporation. Project No. 1993/123 and 1996/342. 150pp + appendices.
Project No. 2002/005
Mulloway biology and fishery assessment, Silberschneider & Gray
Other Titles in the Series
69
No. 35
Stewart, J. and Ferrell, D.J., 2001. Mesh selectivity in the NSW demersal trap fishery. Final Report to
Fisheries Research and Development Corporation. Project No. 1998/138. 86pp.
No. 36
Stewart, J., Ferrell, D.J., van der Walt, B., Johnson, D. and Lowry, M., 2001. Assessment of length
and age composition of commercial kingfish landings. Final Report to Fisheries Research and
Development Corporation. Project No. 1997/126. 49pp.
No. 37
Gray, C.A. and Kennelly, S.J., 2001. Development of discard-reducing gears and practices in the
estuarine prawn and fish haul fisheries of NSW. Final Report to Fisheries Research and Development
Corporation. Project No. 1997/207. 151pp.
No. 38
Murphy, J.J., Lowry, M.B., Henry, G.W. and Chapman, D., 2002. The Gamefish Tournament
Monitoring Program – 1993 to 2000. Final report to Australian Fisheries Management Authority.
93pp.
No. 39
Kennelly, S.J. and McVea, T.A. (Ed), 2002. Scientific reports on the recovery of the Richmond and
Macleay Rivers following fish kills in February and March 2001. 325pp.
No. 40
Pollard, D.A. and Pethebridge, R.L., 2002. Report on Port of Botany Bay Introduced Marine Pest
Species Survey. Final Report to Sydney Ports Corporation. 69pp.
No. 41
Pollard, D.A. and Pethebridge, R.L., 2002. Report on Port Kembla Introduced Marine Pest Species
Survey. Final Report to Port Kembla Port Corporation. 72pp.
No. 42
O’Connor, W.A, Lawler, N.F. and Heasman, M.P., 2003. Trial farming the akoya pearl oyster,
Pinctada imbricata, in Port Stephens, NSW. Final Report to Australian Radiata Pty. Ltd. 170pp.
No. 43
Fielder, D.S. and Allan, G.L., 2003. Improving fingerling production and evaluating inland saline
water culture of snapper, Pagrus auratus. Final Report to the Aquaculture Cooperative Research
Centre. Project No. C4.2. 62pp.
No. 44
Astles, K.L., Winstanley, R.K., Harris, J.H. and Gehrke, P.C., 2003. Experimental study of the effects
of cold water pollution on native fish. A Final Report for the Regulated Rivers and Fisheries
Restoration Project. 55pp.
No. 45
Gilligan, D.M., Harris, J.H. and Mallen-Cooper, M., 2003. Monitoring changes in the Crawford River
fish community following replacement of an effective fishway with a vertical-slot fishway design:
Results of an eight year monitoring program. Final Report to the Cooperative Research Centre for
Freshwater Ecology. 80pp.
No. 46
Pollard, D.A. and Rankin, B.K., 2003. Port of Eden Introduced Marine Pest Species Survey. Final
Report to Coasts & Clean Seas Program. 67pp.
No. 47
Otway, N.M., Burke, A.L., Morrison, NS. and Parker, P.C., 2003. Monitoring and identification of
NSW Critical Habitat Sites for conservation of Grey Nurse Sharks. Final Report to Environment
Australia. Project No. 22499. 62pp.
No. 48
Henry, G.W. and Lyle, J.M. (Ed), 2003. The National Recreational and Indigenous Fishing Survey.
Final Report to Fisheries Research and Development Corporation. Project No. 1999/158. 188 pp.
No. 49
Nell, J.A., 2003. Selective breeding for disease resistance and fast growth in Sydney rock oysters.
Final Report to Fisheries Research and Development Corporation. Project No. 1996/357. 44pp. (Also
available - a CD-Rom published in March 2004 containing a collection of selected manuscripts
published over the last decade in peer-reviewed journals).
No. 50
Gilligan, D. and Schiller, S., 2003. Downstream transport of larval and juvenile fish. A final report for
the Natural Resources Management Strategy. Project No. NRMS R7019. 66pp.
No. 51
Liggins, G.W., Scandol, J.P. and Kennelly, S.J., 2003. Recruitment of Population Dynamacist. Final
Report to Fisheries Research and Development Corporation. Project No. 1993/214.05. 44pp.
No. 52
Steffe, A.S. and Chapman, J.P., 2003. A survey of daytime recreational fishing during the annual
period, March 1999 to February 2000, in Lake Macquarie, New South Wales. NSW Fisheries Final
Report. 124pp.
No. 53
Barker, D. and Otway, N., 2003. Environmental assessment of zinc coated wire mesh sea cages in
Botany Bay NSW. Final Report to OneSteel Limited. 36pp.
No. 54
Growns, I., Astles, A. and Gehrke, P., 2003. Spatial and temporal variation in composition of riverine
fish communities. Final Report to Water Management Fund. Project No. SW1 part 2. 24pp.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005
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Other Titles in the Series
No. 55
Gray, C. A., Johnson, D.D., Young, D.J. and Broadhurst, M. K., 2003. Bycatch assessment of the
Estuarine Commercial Gill Net Fishery in NSW. Final Report to Fisheries Research and Development
Corporation. Project No. 2000/172. 58pp.
No. 56
Worthington, D.G. and Blount, C., 2003. Research to develop and manage the sea urchin fisheries of
NSW and eastern Victoria. Final Report to Fisheries Research and Development Corporation. Project
No. 1999/128. 182pp.
No. 57
Baumgartner, L.J., 2003. Fish passage through a Deelder lock on the Murrumbidgee River, Australia.
NSW Fisheries Final Report. 34pp.
No. 58
Allan, G.L., Booth, M.A., David A.J. Stone, D.A.J. and Anderson, A..J., 2004. Aquaculture Diet
Development Subprogram: Ingredient Evaluation. Final Report to Fisheries Research and
Development Corporation. Project No. 1996/391. 171pp.
No. 59
Smith, D.M., Allan, G.L. and Booth, M.A., 2004. Aquaculture Diet Development Subprogram:
Nutrient Requirements of Aquaculture Species. Final Report to Fisheries Research and Development
Corporation. Project No. 1996/392. 220pp.
No. 60
Barlow, C.G., Allan, G.L., Williams, K.C., Rowland, S.J. and Smith, D.M., 2004. Aquaculture Diet
Development Subprogram: Diet Validation and Feeding Strategies. Final Report to Fisheries Research
and Development Corporation. Project No. 1996/393. 197pp.
No. 61
Heasman, M.H., 2004. Sydney Rock Oyster Hatchery Workshop 8-9 August 2002, Port Stephens,
NSW. Final Report to Fisheries Research and Development Corporation. Project No. 2002/206.
115pp.
No. 62
Heasman, M., Chick, R., Savva, N., Worthington, D., Brand, C., Gibson, P. and Diemar, J., 2004.
Enhancement of populations of abalone in NSW using hatchery-produced seed. Final Report to
Fisheries Research and Development Corporation. Project No. 1998/219. 269pp.
No. 63
Otway, N.M. and Burke, A.L., 2004. Mark-recapture population estimate and movements of Grey
Nurse Sharks. Final Report to Environment Australia. Project No. 30786/87. 53pp.
No. 64
Creese, R.G., Davis, A.R. and Glasby, T.M., 2004. Eradicating and preventing the spread of the
invasive alga Caulerpa taxifolia in NSW. Final Report to the Natural Heritage Trust’s Coasts and
Clean Seas Introduced Marine Pests Program. Project No. 35593. 110pp.
No. 65
Baumgartner, L.J., 2004. The effects of Balranald Weir on spatial and temporal distributions of lower
Murrumbidgee River fish assemblages. Final Report to the Department of Agriculture, Fisheries &
Forestry - Australia (National Heritage Trust MD2001 Fishrehab Program). 30pp.
No. 66
Heasman, M., Diggles, B.K., Hurwood, D., Mather, P., Pirozzi, I. and Dworjanyn, S., 2004. Paving
the way for continued rapid development of the flat (angasi) oyster (Ostrea angasi) farming in New
South Wales. Final Report to the Department of Transport & Regional Services. Project No.
NT002/0195. 40pp.
ISSN 1449-9967 (NSW Department of Primary Industries - Fisheries Final Report Series)
No. 67
Kroon, F.J., Bruce, A.M., Housefield, G.P. and Creese, R.G., 2004. Coastal floodplain management
in eastern Australia: barriers to fish and invertebrate recruitment in acid sulphate soil catchments.
Final Report to Fisheries Research and Development Corporation. Project No. 1998/215. 212pp.
No. 68
Walsh, S., Copeland, C. and Westlake, M., 2004. Major fish kills in the northern rivers of NSW in
2001: Causes, Impacts & Responses. NSW Department of Primary Industries - Fisheries Final Report.
55pp.
No. 69
Pease, B.C. (Ed), 2004. Description of the biology and an assessment of the fishery for adult
longfinned eels in NSW. Final Report to Fisheries Research and Development Corporation. Project
No. 1998/127. 168pp.
No. 70
West, G., Williams, R.J. and Laird, R., 2004. Distribution of estuarine vegetation in the Parramatta
River and Sydney Harbour, 2000. Final Report to NSW Maritime and the Australian Maritime Safety
Authority. 37pp.
No. 71
Broadhurst, M.K., Macbeth, W.G. and Wooden, M.E.L., 2005. Reducing the discarding of small
prawns in NSW's commercial and recreational prawn fisheries. Final Report to the Fisheries Research
Project No. 2002/005
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71
& Development Corporation. Project No. 2001/031. NSW Department of Primary Industries Fisheries Final Report Series No. 71. 202pp.
No. 72.
Graham, K.J., Lowry, M.B. and Walford, T.R., 2005. Carp in NSW: Assessment of distribution,
fishery and fishing methods. NSW Department of Primary Industries - Fisheries Final Report Series
No. 72. 88pp.
No. 73
Stewart, J., Hughes, J.M., Gray, C.A. and Walsh, C., 2005. Life history, reproductive biology, habitat
use and fishery status of eastern sea garfish (Hyporhamphus australis) and river garfish (H. regularis
ardelio) in NSW waters. Final report on the Fisheries Research & Development Corporation Project
No. 2001/027. 180pp.
No. 74
Growns, I. and Gehrke, P., 2005. Integrated Monitoring of Environmental Flows: Assessment of
predictive modelling for river flows and fish. NSW Department of Primary Industries - Fisheries Final
Report Series No. 74. 33pp.
No. 75
Gilligan, D., 2005. Fish communities of the Murrumbidgee catchment: Status and trends. Final report
to the Murrumbidgee Catchment Management Authority. Project No. BG4_03. 138pp.
No. 76
Ferrell, D.J., 2005. Biological information for appropriate management of endemic fish species at
Lord Howe Island. NSW Department of Primary Industries - Fisheries Final Report Series No. 76. 18
pp.
No. 77
Gilligan, D., Gehrke, P. and Schiller, C., 2005. Testing methods and ecological consequences of
large-scale removal of common carp. Final report to the Water Management Fund - Programs MFW6
and MUR5. 46pp.
No. 78
Boys, C.A., Esslemont, G.and Thoms, M.C., 2005. Fish habitat and protection in the Barwon-Darling
and Paroo Rivers. Final report to the Department of Agriculture, Fisheries and Forestry – Australia
(AFFA). 118pp.
No. 79
Steffe, A.S., Murphy, J.J., Chapman, D.J. and Gray, C.C., 2005. An assessment of changes in the
daytime recreational fishery of Lake Macquarie following the establishment of a ‘Recreational
Fishing Haven’. NSW Department of Primary Industries - Fisheries Final Report Series No. 79.
103pp.
No. 80
Gannassin, C. and Gibbs, P., 2005. Broad-Scale Interactions Between Fishing and Mammals, Reptiles
and Birds in NSW Marine Waters. Final Report for a project undertaken for the NSW Biodiversity
Strategy. 171pp.
No. 81
Steffe, A.S., Murphy, J.J., Chapman, D.J., Barrett, G.P. and Gray, C.A., 2005. An assessment of
changes in the daytime, boat-based, recreational fishery of the Tuross Lake estuary following the
establishment of a 'Recreational Fishing Haven'. NSW Department of Primary Industries - Fisheries
Final Report Series No. 81. 70pp.
No. 82
Silberschnieder, V. and Gray, C.A., 2005. Arresting the decline of the commercial and recreational
fisheries for mulloway (Argyrosomus japonicus). Final report on the Fisheries Research &
Development Corporation Project No. 2001/027. 72pp.
Mulloway biology and fishery assessment, Silberschneider & Gray
Project No. 2002/005