blue swimmer crab (portunus pelagicus) fishery · and 20.5% for sg for those crabs caught in...

Blue Swimmer Crab (Portunus pelagicus) Fishery Fishery Assessment Report to PIRSA for the

Blue Crab Fishery Management Committee 2004

SARDI Aqua

I. Svane and G. Hooper

tic Sciences Publication No: RD03/0274-2

Blue Swimmer Crab (Portunus pelagicus) Fishery

Fishery Assessment Report to PIRSA for the Blue Crab Fishery Management Committee

2004

I. Svane and G.E. Hooper

SARDI Aquatic Sciences Publication No: RD03/0274-2

This publication may be cited as: Svane, I. and Hooper, G.E. (2004), Blue Swimmer Crab (Portunus pelagicus) Fishery. Fishery Assessment Report to PIRSA for the Blue Crab Fishery Management Committee. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. RD 03/0274-2. South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5406 http://www.sardi.sa.gov.au Disclaimer. The authors warrant that they have taken all reasonable care in producing this report. The report has been through the SARDI Aquatic Sciences internal review process, and has been formally approved for release by the Chief Scientist. Although all reasonable efforts have been made to ensure quality, SARDI Aquatic Sciences does not warrant that the information in this report is free from errors or omissions. SARDI Aquatic Sciences does not accept any liability for the contents of this report or for any consequences arising from its use or any reliance placed upon it. © 2005 SARDI Aquatic Sciences This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the author. Printed in Adelaide March 2005 SARDI Aquatic Sciences Publication No RD03/0274-2 SARDI Research Report Series No 68 Author(s): Dr Ib Svane and Graham Hooper

Reviewers: Dr Adrian Linnane and Dr Yongshun Xiao

Approved by: Dr John Carragher

Signed:

Date: March 2005

Distribution: PIRSA Fisheries, Blue Crab Fishery Management Committee

SARDI Aquatic Sciences Library

Circulation: Public Domain

http://www.sardi.sa.gov.au/

Blue Crab Stock Assessment Svane and Hooper Page i _______________________________________________________________________________________________________________________________________________________________

Table of Contents ACKNOWLEDGEMENT...........................................................................................3

EXECUTIVE SUMMARY .........................................................................................4 PERFORMANCE OF THE FISHERY .................................................................................4 FISHERY INDEPENDENT SURVEYS ...............................................................................4 RECOMMENDATIONS...................................................................................................4

INTRODUCTION........................................................................................................5 HISTORY OF THE FISHERY ...........................................................................................5

Commercial Fishery...............................................................................................5 Recreational Fishery..............................................................................................6

MANAGEMENT ............................................................................................................7 Management Tools.................................................................................................7 Management Objectives.........................................................................................7 Management Strategies..........................................................................................7 Independent Research Review ...............................................................................8

FISHERIES BIOLOGY OF THE BLUE SWIMMER CRAB......................................................9 Taxonomy...............................................................................................................9 Description.............................................................................................................9 Distribution ............................................................................................................9 Population Genetics.............................................................................................10 Reproductive Cycle ..............................................................................................10 Ovarian Development ..........................................................................................10 Ovigerous Females ..............................................................................................12 Fecundity..............................................................................................................13 Multiple spawning................................................................................................13 Recruitment ..........................................................................................................14

PREVIOUS RELATED RESEARCH ................................................................................14 OTHER RELATED RESEARCH.....................................................................................14

FISHERY STATISTICS ...........................................................................................15

INTRODUCTION .........................................................................................................15 COMMERCIAL PRODUCTION......................................................................................15

Catch ....................................................................................................................15 Effort ....................................................................................................................16

POT FISHERY CATCH AND EFFORT............................................................................17 Catch ....................................................................................................................17 Effort ....................................................................................................................17 CPUE ...................................................................................................................18 Seasonal patterns .................................................................................................19 Spatial patterns ....................................................................................................21

MARINE SCALEFISH FISHERY CATCH AND EFFORT.................................................23 Catch ....................................................................................................................23 Effort ....................................................................................................................23 CPUE ...................................................................................................................23 Seasonal Patterns.................................................................................................24 Spatial Patterns....................................................................................................25

PERFORMANCE AGAINST INDICATORS – FISHERY STATISTICS...................................26 Catch ....................................................................................................................26

Blue Crab Stock Assessment Svane and Hooper Page ii _______________________________________________________________________________________________________________________________________________________________

Relative Exploitation Rate ...................................................................................26 Pre-Recruitment...................................................................................................26 Sex Ratio ..............................................................................................................26

FISHERY INDEPENDENT SURVEYS..................................................................28 INTRODUCTION .........................................................................................................28 METHODS..................................................................................................................28

Sampling ..............................................................................................................28 Statistical design ..................................................................................................30

RESULTS ...................................................................................................................30 Recruitment and Sex Distribution........................................................................30 Abundance of Crabs in Spencer Gulf...................................................................31 Abundance of Crabs in Gulf St Vincent ...............................................................36 Size Distributions .................................................................................................40

PERFORMANCE AGAINST INDICATORS – INDEPENDENT SURVEY......................44 Catch ....................................................................................................................44 Relative Exploitation Rate ...................................................................................44 Pre-Recruitment...................................................................................................44 Sex Ratio ..............................................................................................................44

BY-CATCH.................................................................................................................45

CONCLUSIONS ........................................................................................................48 FISHERY STATISTICS .................................................................................................48 FISHERY INDEPENDENT SURVEY...............................................................................48

RECOMMENDATIONS...........................................................................................49 RESEARCH NEEDS...............................................................................................49 ASSESSMENTS NEEDS........................................................................................49

REFERENCES...........................................................................................................50

APPENDIX.................................................................................................................52

Blue Crab Stock Assessment Svane and Hooper Page 3 ________________________________________________________________________________________________________________________________________________________________

ACKNOWLEDGEMENT SARDI research for this blue crab fishery assessment report was commissioned by PIRSA for the Blue Crab Fishery Management Committee. Mr Grant Barker, Mr Dennis Holder and Mr Mick Aston provided their crew and vessel for the 2004 fishery independent surveys. SARDI Aquatic Sciences provided substantial in-kind contributions to support this work.


EXECUTIVE SUMMARY

PERFORMANCE OF THE FISHERY

During the 2003/2004 season 95.28% of the TACC allocated was landed. This comprised 558.6 t taken by the pot sector and 38.6 t by the marine scalefish sector. This represents an overall 7.12% increase in catch from the previous year. The pre-recruitment indicators reported in the logbooks for the 2003/2004 season were 15.54% for Gulf St. Vincent (GSV) and 23.99% for Spencer Gulf (SG), and were within the target and limit reference values as set in the management plan (GSV: target 10%, limit 5%; SG: target 30%, limit 15%). However, some fishers do not report these data consistently and thereby increase the uncertainty of these estimates. The fishery independent survey showed pre-recruitment indicators of 12.2% for GSV and 20.5% for SG for those crabs caught in commercial pots. The female sex ratio (percentage of females in sample) reported in the logbooks was 44.91% (GSV) and 29.5% (SG). The fishery independent survey showed female sex ratios of 42.7% for GSV and 30.6% for SG. These values are above the target limit references in the management plan (target 30%, limit 15%). FISHERY INDEPENDENT SURVEYS

Three fishery independent surveys were conducted in both Spencer Gulf and Gulf St Vincent, one each year in July 2002, 2003 and 2004. A comparison between these three surveys is presented in this report. Detailed analyses of crab numbers per pot and their size distributions indicated a significant decline in the number of both legal and undersized crabs (<110 mm CW) entering into the fishery. This pattern was consistent in both gulfs and was reflected in both sexes. The decline in recruitment is further supported by a detailed analysis of the size-structure of the samples from both gulfs, showing that the mean crab size was larger in 2004 than in 2002 and 2003 due to fewer recruits and larger (=older) crabs in the populations. In general, the mean crab size in GSV is larger than in SG consistently across years and gender. However, this pattern varied slightly between years. RECOMMENDATIONS

It is recommended that • The BSCFMC note that recruitment was in 2003/04 observed to be lower in

both gulfs. • The BSCFMC note that the abundance of crabs has declined in SG.

Abundance of crabs in GSV was more variable with no statistical differences between years.


INTRODUCTION The first stock assessment report on the Blue crab fishery was published in 1998. This report is the second version of a “living” document that will be updated annually as part of SARDI Aquatic Sciences ongoing fishery assessment program for the South Australian Blue Crab Fishery. This assessment reports on the South Australian Blue crab fishery for the 2003/2004 financial year and summarises the information from previous reports and presents analyses of the information collected via commercial logbook returns and fishery independent surveys. Data collected from the blue crab catches in the West Coast region are not included. HISTORY OF THE FISHERY

Commercial Fishery

Blue crabs were first taken as by-catch in prawn and marine scale-fish fisheries in the 1970’s. In 1986, the sale of blue crabs, as by-catch from the prawn fishery was withdrawn. The South Australian Government issued twelve experimental fishing permits in the early 1980’s, four in the West Coast, six in Spencer Gulf (SG), and two in Gulf St Vincent (GSV). The West Coast fishery declined in 1986 and the four licence holders surrendered their entitlements. In June 1996, interim management arrangements for the Blue Swimmer Crab Fishery (BSCF) were established. An initial management strategy was implemented along with a core research program to support the development and maintenance of a sustainable and viable fishery. In 1997, PIRSA proposed a 3-year development strategy for the BSCF. During this period, the capacity for expansion of the fishery was to be determined through research and further fishing. A limited entry fishery was created with access based on historical catches. The fishery is based on the capture of a single species, Portunus pelagicus, although other crab species may also be landed, such as spider, velvet and rock crabs. The fishery is divided into two areas (Spencer Gulf and Gulf St Vincent, Figure 1) with two types of commercial fishery operating in each (pot and marine scale-fish). The South Australian BSCF has three major stakeholders: the commercial pot fishery, the commercial marine scale fishery (MSF) and the recreational fishery. In 2003-2004, there were 8 crab pot fishers with licences, five in SG and three in GSV. The marine scale fishers with access to the blue crab quota was made up of fourteen licences, one in SG and thirteen in GSV. Commercial pot fishers generally haul their gear every 24 hours using specifically designed crab pots covered with netting. Commercial marine scale-fish fishers use either hoop or drop nets hauled every 20-30 minutes. Crabs can be stored live in tanks, iced down uncooked or cooked before being landed in port. Most of the commercial catch is marketed in Australia, primarily in the Sydney and Melbourne fish markets. In 2002/03, the commercial landed value of blue crabs in South Australia was $3.57 million (Knight et al., 2004).


Pt Pirie

Gulf St.Vincent

Adelaide

Streaky BayPt Augusta

South Australia’sBlue Crab Fishing Regions

West Coast

Australia

SpencerGulf

360 S

340 S

320 S

1380 E1360 E1340 E

Wallaroo

Pt Pirie

Gulf St.Vincent

Adelaide

Streaky BayPt Augusta

South Australia’sBlue Crab Fishing Regions

West Coast

Australia

SpencerGulf

360 S

340 S

320 S

1380 E1360 E1340 E

Wallaroo

Figure 1. Map showing the blue crab fishing zones.

Commercial quantities of blue crabs are also taken from bays on the west coast of South Australia, however they are included as part of the MSF and therefore, they are excluded in this report. However, in 2003/04, the landed catch from the West Coast fishery was 14.2 t from 227 boat days, a CPUE of 62.6 kg/day. This was a decrease in catch (25.2 t) and effort (418 boat days) from 2002/03, and an increase in CPUE from 60.25 kg/day. Recreational Fishery

There is no continuous assessment of the recreational harvest of the blue swimmer crab in South Australia. McGlennon & Kinloch (1997) estimated a total catch of 161.2 t per year, of which 115.8 t was taken in GSV and 45.4 t in SG. Thus, the recreational catch was estimated to be 32.9% in GSV, 10.8% in SG, and 20% overall. This estimate does not include the recreational shore-based fishery, which is considered to be significant. More recently, a National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003) was conducted between May 2000 and April 2001. The estimated annual catch taken by recreational fishers during this period for South Australia was 389.8 t. A further 31.7% of the total catch was released after capture (Anon, 2003). The release rate is based upon the crabs that were discarded under the legal size limit or


they were caught when the bag limit was exceeded. This indicates that the recreational harvest was 37.5% of the total catch during 2000/2001. The estimates of regional catches, release rates, fishing locations and fishing methods are yet to be analysed. MANAGEMENT

Management Tools

The fishery is managed under the Fisheries Act of 1982, the Fisheries (Blue Crab Fishery) regulations of 1998, and the Fisheries (Marine Scale-fish Fishery) regulations of 1991. The minimum legal size is 11cm in carapace width (measured at the posterior base of the first spine). No ovigerous females may be retained. The commercial pot fishers fish exclusively for blue crabs, whereas the marine scale-fish fishers may also target other species included in their MSF licences. The commercial fishery may only take crabs from the waters of GSV and SG. The commercial fishery is further regulated by equipment restrictions and seasonal closures in December and January in SG, and in November, December and half of January in GSV. In addition, output controls (catch quotas) were imposed on the BSCF by means of a Total Allowable Commercial Catch (TACC). The TACC was distributed as quota to individual operators, with different levels being allocated for pot fishers and marine scale-fish fishers. The TACC was initially set by PIRSA at 520 t for the 1996/97 fishing season, after which the Blue Crab Fisheries Management Committee (BCFMC) recommend to the Minister on the TACC. In 2003/04, the TACC was 626.8 t. The recreational fishery is subject to a daily bag limit of 40 blue crabs per person per day. When fishing from a boat, the personal bag limit applies up to a total of three people, after which a boat limit of 120 blue crabs per day applies.

Management Objectives

The primary objectives for the BSCF, as stated in the Management Plan for the BCFMC, are to:

1. Ensure sustainable harvests from the blue crab resource, 2. Ensure equitable allocation of the blue crab resource to the commercial and

recreational sectors, 3. Provide efficient and cost effective management of the fishery, 4. Provide for secure access to the resource for each sector, 5. Minimise the impact of blue crab fishing on the environment, and 6. Provide society with a return from the blue swimmer crab resource.

Management Strategies

To ensure a robust assessment of the fishery, performance is measured annually against the prescribed key indicators set by the BCFMC (Table I). On the basis of this assessment, the BCFMC recommends a TACC for the commercial industry on an annual basis.


Table I. Key indicators for the BSCF

Indicator Interim Target Reference

Interim Limit Reference

Catch TACC 80% of TACC Relative exploitation rate

Gulf St Vincent (% of 1994 level) Spencer Gulf (% of 1990 level)

50 40

100 80

Pre-recruit ( as % under-size in June and July) Gulf St Vincent Spencer Gulf

10 30

5 15

Sex Ratio ( % female in June and July) 30 15 Independent Research Review

Following the independent research review of the BSCF by Scandol and Kennelly (2001), a set of indicators was developed as a management tool using information collected during fishery independent surveys and the catch and effort logbook data (Table II). Table II. Likely response of key indices to recruitment indicators for the BSCF.

increase, clear increase, decrease, clear decrease, no signal Size Structure CPUE Sex Ratio Catch

Pre-recruit index Mean Size Fishery Survey Males Females

Decrease in recruitment

Constant recruitment

Increase in recruitment


FISHERIES BIOLOGY OF THE BLUE SWIMMER CRAB

Taxonomy

The blue swimmer crab (Portunus pelagicus, Linnaeus 1766) is a true crab (Brachyura) belonging to the family Portunidae. Description

The blue swimmer crab has five pairs of legs. The first pair are chelae or claws, the following three pairs are walking legs where the last pair of legs are modified as swimming paddles. The carapace is rough in texture, broad and has a prominent projection/spine on each side. Blue swimmer crabs are active swimmers, but during inactivity they bury in the sediment, with only eyes, antennae and gill chamber openings uncovered. Males are blue and have larger claws than females, which are green-brown in colour (Figure 2). A detailed description is provided by Stephenson (1972).

Figure 2. Male (left) and female (right) blue swimmer crab Portunus pelagicus (L.).

Distribution

Portunus pelagicus is distributed throughout the coastal waters of the tropical regions of the western Indian Ocean and the Eastern Pacific (Kailola et al. 1993); they are adapted to a life in warmer waters. In the relatively colder, temperate parts of Australia, the life cycle has evolved to complete growth and reproduction during the warmer part of the year when water temperatures are elevated to those similar to the tropical regions. For the rest of the year, blue crabs withstand the relatively lower temperatures in the southern Australian environment by being less active. P. pelagicus occurs in a wide range of algal and seagrass habitats and on both sandy and muddy substrata, from the intertidal zone to at least fifty metres of depth (Williams 1982, Edgar 1990). In coastal waters, smaller crabs are found in shallow waters, while adults are found in comparatively deeper waters. Juvenile crabs occur in mangrove creeks and mud flats for eight to twelve months by which time they attain a size of 80 to 100 mm in carapace width. Within South Australia, there is a distinct seasonal pattern of adult crab movements into shallow inshore waters during the warmer months of September to April and to deeper offshore waters during the colder months of May to August (Smith 1982).


Population Genetics

Using allozyme markers, Bryars and Adams (1999) determined that the populations of P. pelagicus within SG, GSV and the West Coast regions of South Australia, represented separate sub-populations with a limited gene flow. They also found that inter-regional larval dispersal is restricted, and each sub-population must be dependent on its own larval supply. Chaplin et al. (2001), using microsatellite markers, found that the assemblages of P. pelagicus in different embayments in South Australia often constitute genetically different meta-populations. The level of migration between these populations is probably limited and the dynamics of a population, in a given embayment, is likely to be determined by local factors. Reproductive Cycle

Male and female P. pelagicus generally reach sexual maturity at a size of 70 to 90 mm in carapace width, when they are approximately one year old. The male and female will form a pre-corpula for eight to ten days before ecdysis of the female. After female ecdysis, when the female is soft-shelled, copulation takes place over a six to eight hour period (Meagher 1971). The spawning season lasts for 3 to 4 months over the summer/autumn period. The duration of the growing season varies among individuals because those settling in early summer have a longer growing season than those settling in mid-to-late summer. In South Australian waters, crabs close to the minimum legal size (110 mm) are approximately 14 to 18 months old, sexually mature, and females have produced at least two batches of eggs within one season (Kumar et al. 2000, 2003). Ovarian Development

Development of the ovaries in females appears to be triggered by rising water temperatures in spring. During copulation, the spermatophore is transferred to the female spermatheca. The eggs are subsequently fertilised on extrusion (Smith 1982). Van Engel (1958) found that the sperm in the spematheca of female Callinectes sapidus could remain viable for at least 12 months. This is likely to also be the case for P. pelagicus. Egg extrusion is independent of the timing of copulation. The ovarian development can be classified by five visually distinguishable stages (see Sumpton et al. 1994 and Figure 3):

Stage 1(S1): Gonad immature, white or translucent Stage 2(S2): Gonad maturing, light yellow/orange, not extending into hepatic region Stage 3(S3): Gonad maturing, yellow/orange not extending into hepatic region Stage 4(S4): Gonad mature, dark yellow/orange extending into hepatic region Stage 5(S5): Ovigerus, female bearing fully matured eggs (pale to dark yellow eggs) externally.

The fourth stage of ovarian development was observed in late October to November in conjunction with rising seawater temperatures. Kumar et al. (2000) demonstrated that during November, more than 40% of crabs were in advanced Stage 4, and 80%


caught were between Stages 3-4. Figure 4 shows the seasonal ovarian developmental stages in the blue swimmer crab.

Stage 1 Stage 2

Stage 3 Stage 4

Stage 5

Figure 3. Ovarian stages of the blue swimmer crab (from Kumar et al. 2000).


0

10

20

30

40

50

60

70

80

90

100

F M A M J J A S O N D J F M A M J J A S O N D

Month/Year

Perc

enta

ge o

f ova

ry s

tage

S1 S2 S3 S4

1997 1998

Figure 4. Ovarian development of the blue swimmer crab samples collected in South Australia during 1997 and 1998. Colour codes for the various reproductive stages shown above (from Kumar et al., 2000).

Ovigerous Females

In tropical waters, female blue swimmer crabs are found to carry eggs throughout the year. However, during a particular period in any year, a seasonal variation in the number of egg-bearing females can be observed (see Kumar et al. 2000). During embryonic development (Stage 5), the colour of the eggs changes from yellow to a dark grey (Figure 3). In South Australian waters, egg-bearing females have been observed throughout the year, however in late spring there is a substantial increase in the proportion of berried females. Data from the commercial fishery logbooks during season 2001/2002 shows the proportion of berried females caught in GSV from July 1997 to June 2004 (Figure 5). In SG, a larger proportion of berried females appeared in the catch slightly later than in GSV. This pattern was consistent between years.


Year

1997 1998 1999 2000 2001 2002 2003 2004

Ber

ried

Fem

ales

(%)

0

10

20

30

40

50

60

70

80

90

100GSVSPG

Figure 5. Abundance of berried females in the commercial catches from 2001/2002 to 2003/2004. GSV=Gulf St Vincent; SPG=Spencer Gulf.

Fecundity

Fecundity is calculated as the number of eggs carried externally by the female. Kumar et al. (2003) found that the fecundity of female crabs is size-dependent and increases up to a carapace width of 134 mm and decrease thereafter. Fecundity increased by 83.9% with an increase of carapace width from 105 mm to 125 mm, implying that a single large female could produce as many eggs as two small females. Kumar et al. (2000) found that a female blue crab can produce between 650,000 to 1,760,000 eggs per spawning. Multiple spawning

P. pelagicus can spawn more than one batch of eggs in a season. Eight to ten days after spawning the first batch of eggs, the female may ovulate and fertilise a second batch (Meagher 1971). On examination of berried females, some carried developing oocytes at stages 2 and 3 in the ovary whilst also carrying an external egg mass (Kumar et al. 2003). While blue crabs are capable of producing more than one batch of eggs in a season, successive ovulations do not always occur (Meagher 1971).


Recruitment

Recruitment to the fishery is defined as those crabs entering the fishery, which are susceptible to being caught by the fishing gear. Recruits have a carapace width (measured from the posterior base of the spine) of less than 110 mm. Recruitment to the fishery has been found to take place during the winter months of the year, i.e. June and July (Kumar et al. 2000). PREVIOUS RELATED RESEARCH

The first report on the South Australian blue crab fishery was published in 1987 by the South Australian Department of Fisheries (Grove-Jones, 1987). In 1994, a review of the blue crab fishery by SARDI was published (Baker and Kumar, 1994). SARDI completed the first stock assessment report for the BSCF in 1998, and has since provided annual reports (Kumar, et al. 1998, Kumar, et al. 1999a, Kumar, et al. 1999b, Boxshall, et al. 2000, Boxshall, et al. 2001, Hooper and Svane 2003, Svane and Hooper 2004). The Proceeding of the First National Workshop on Blue Swimmer Crab was published in 1997 (Kumar et al. 1997). OTHER RELATED RESEARCH

Initiated by the Fisheries Research and Development Corporation (FRDC), the Centre of Research on Ecological Impacts of Coastal Cities at the University of Sydney completed an independent review into the research needs of the fishery in February 2001. This report, which was done in consultation with stakeholders, includes comments on the sampling issues for Ecological Sustainable Development (ESD) outcomes and provides a research review, short term monitoring advice, and recommendations for a 5-year research program (Scandol & Kennelly 2001).


FISHERY STATISTICS INTRODUCTION

SARDI maintains a comprehensive catch and effort database for the BSCF using data collected from the compulsory fishing logbook system. The logbook system is also used to collect biological data, including the number of undersized crabs and the sex ratio of the catch. Each gulf has been divided into administrative fishery blocks to aid in identifying catch areas (Appendix I & II). The data presented in this report are necessarily limited to ensure the confidentiality for individual fishers (Fisheries Act 1982). Since the implementation of the TACC in the South Australian BSCF, there has been a transfer of commercial effort from the MSF to the Pot fishery sectors. Figure 6 shows the number of licence holders in the fishery from 1996/97 to 2004/05, indicating an increase in the number of pot licences at the expense of the number of MSF licences. There was no change in the number of licences in either sector in the

Figure 6. Num

last season.

ber of licence holders for both sectors of the blue crab fishery (source:

OMMERCIAL PRODUCTION

/04, the allocated TACC for the BSCF was 626.8 t (source: PIRSA), the same

Year

1996/97 1997/98 1998/99 1999/00 2000/01 2001/02 2002/03 2003/04 2004/05

Lic

ence

num

bers

0

5

10

15

20

25

30

35

Pot Licence MSF Licence

PIRSA Fisheries).

C

Catch

In 2003TACC as for the previous three fishing seasons. The landed catch in 2003/04 from both commercial fisheries was 95.28% of the TACC, represented by 93.53% taken by


the pot fishery and 6.47% by the MSF, constituting a 7.12% increase in catch from 2002/03. The highest catch in a season occurred in the year 1996/97, prior to the commencement of the quota allocation, when 651.26 t was landed. In the following years catches decreased to 462.39 t, but have since increased steadily. In 2003/04, the highest catch after the TACC introduction was 597.25 t. Figure 7 shows the total commercial production of blue crabs since 1983/84 and the allocated TACC. Since the implementation of the TACC in 1996/97, it has never been fully taken.

Year

1983

/84

1984

/85

1985

/86

1986

/87

1987

/88

1988

/89

1989

/90

1990

/91

1991

/92

1992

/93

1993

/94

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/95

1995

/96

1996

/97

1997

/98

1998

/99

1999

/00

2000

/01

2001

/02

2002

/03

2003

/04

Cat

ch (t

)

0

100

200

300

400

500

600

700

Figure 7. Total commercial catch (vertical bars) and TACC (dots) for the BSCF from 1983/84 to 2003/04.

Effort

8 shows the effort (boat days) of the blue crab fishery since 1983/84. In Figure 1996/97 effort, in terms of boat days, was 2213, rising to a maximum (post TACC) of 2458 boat days in 1999/00. In 2003/04, effort decreased from 2154 (2002/03) boat days to 2121.


Year

1983

/84

1984

/85

1985

/86

1986

/87

1987

/88

1988

/89

1989

/90

1990

/91

1991

/92

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/97

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/98

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/99

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/00

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/02

2002

/03

2003

/04

Eff

ort (

boa

t day

s)

0

500

1000

1500

2000

2500

3000

3500

4000

Figure 8. Total commercial effort (dots) and the introduction of TACC (line) for the BSCF from 1983/84 to 2003/04.

POT FISHERY CATCH AND EFFORT

Catch

The pot fishery in 2003/04 was allocated 580.8 t of the TACC (source: PIRSA) of which 558.6 was landed, a 8.48% increase compared to 2002/03, and the highest total catch (95.43% of the TACC) since the implementation of quota in 1996/97. The catch in this sector has steadily increased since 1998/99 when 437.52 t were landed. Effort

Historical catch and effort is shown in Figure 9. Effort (boat days) has remained relatively constant during the first 6 years of the TACC with an average of 1517 days fished. In 2002/03, two new licences were issued by PIRSA and effort increased. In 2003/04, effort again increased from 1772 to 1808 boat days. The number of pot lifts in 1997/98 was recorded at 151,899. Effort has then continually increased during the next few years and in 2002/03 reached 196,646 potlifts/day. In 2003/04, there was a further increase of 2.7%, represented by 201,979 potlifts/day.


Year

1983

/84

1984

/85

1985

/86

1986

/87

1987

/88

1988

/89

1989

/90

1990

/91

1991

/92

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/93

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/94

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/96

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/97

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/99

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/00

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/01

2001

/02

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/03

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/04

Cat

ch (t

)

0

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600

Eff

ort (

days

)

0

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600

800

1000

1200

1400

1600

1800

2000

Figure 9. Historical catch (columns) and effort (dots) for the BSCF (pot fishery). The black vertical line indicates the time when quota was implemented.

CPUE

To analyse the catch per unit of effort (CPUE) for the pot fishery, two calculations can be applied:

catchCPUDboatdays

= .catchCPUL

no potlifts=

With the implementation of the TACC in 1996/97, pot fishers were allocated equal quota and effort, in terms of the number of pots to be used within the BSCF. Catch per unit of boat day (CPUD) was used to analyse this effort. Over time, this effort has become unequal with some fishers having a larger number of pots to catch their quota in the same amount of days. Catch per unit of pot lift (CPUL) is the effort measured on individual pot rates. It is therefore being variable and more precise and thus will be used in this report. A summary of CPUL since 1997/98 is shown in Figure 10. In the season 2003/04, the fishers had an increase in CPUL from 2.62 kg/potlift (2002/03) to 2.77 kg/potlift, constituting an increase of 5.56%. The season 2001/02 produced the highest CPUL of 3.16kg/potlift whereas in 1998/99 the fishery attained 2.53 kg/pot lift, its lowest CPUL.


Year

1997/98 1998/99 1999/00 2000/01 2001/02 2002/03 2003/04

CPU

L (k

g/po

tlift

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Figure 10. Estimated CPUL (kg/potlift) in the BSCF (pot fishery) since 1997/1998.

Seasonal patterns Catch

Fishing was conducted in most of the year, except in the closed season in GSV (November, December and the first half of January) and in SG during December and January. Catches are highly seasonal and may vary depending on water temperature and in some cases the participation of licensed fishers in the independent fishing surveys. In 1998, 2000 and 2002 catches in July were all below 40 t, and remained about this level until the closure (Fig. 11). When fishing recommenced catches increased dramatically with the coinciding warmer weather before declining as individual fishers drew close to their TACC. In 2003/04, a larger proportion of catch was taken prior to the closure. Similar to previous years the March yield was the highest catch for the season. Catches are always lower in November, as fewer fishers operate during this period.


1997/98

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

Cat

ch (t

)

0

20

40

60

80 1998/99


1999/00


Cat

ch (t

)

0

20

40

60

80 2000/01


2001/02


Cat

ch (t

)

0

20

40

60

80 2002/03

Month


2003/04

Month


Cat

ch (t

)

0

20

40

60

80

Figure 11. Monthly catch (vertical bars) for the BSCF pot fishery 1997-2004. November (prior to 2001) and January have been omitted for confidentiality reasons.


Effort

The effort by fishing month from July 1997 to June 2004 for the pot fishery is shown in Figure 12. The number of potlifts by month has varied considerably over the last six years seasons. Over the last two seasons, there has been an increase in the number of potlifts primarily due to the increase in pot fishers. During 2003/04, an increase in the number of potlifts prior to the closure is reflected by the larger catches in this season (Figure 11 and Figure 12).

CPUL The CPUL by fishing month from July 1997 to June 2004 for the pot fishery is shown in Figure 12. The catch per unit of potlift is generally similar from 1998/99 to 2003/04 with an increase in CPUL at the start of each season before decreasing in October and November. Since 97/98, CPUL has generally ranged between 2-4 kg per potlift. When the fishery reopens after the annual closure, there is a clear increase in CPUL during February and March and a clear decrease as the winter months approach. From February 2001 to April 2002, the CPUL was consistently above the average with most months recording over 3.0 kg/potlift. In 2003/04, the CPUL followed a similar trend. Spatial patterns

Spatial data for the pot fishery cannot be reported for confidentiality reasons.


1997/98


Pot L

ifts

0

5000

10000

15000

20000

25000

1998/99


CPU

L (k

g/po

tlift

s)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

1999/00


Pot L

ifts

0

5000

10000

15000

20000

25000

2000/01


CPU

L (k

g/po

tlift

s)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

2001/02


Pot L

ifts

0

5000

10000

15000

20000

25000

2002/03

Month


CPU

L (k

g/po

tlift

s)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

2003/04

Month


Pot L

ifts

0

5000

10000

15000

20000

25000

CPU

L (k

g/po

tlift

s)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Figure 12. Monthly effort – pot lifts (blue line) and CPUL (black dots) for the BSCF pot fishery 1997-2004. November (prior to 2001) and January have been omitted for confidentiality reasons.


MARINE SCALEFISH FISHERY CATCH AND EFFORT

Catch

In 2003/04, the MSF was allocated 45.96 t of the TACC, a reduction of 31.34 t from the previous season. Since the implementation of the TACC in 1996/97, the MSF sector has had a reduction of TACC from a peak of 114.6 t in 2000/01. The MSF landed 38.6 t of crabs in the 03/04 season, representing 84.07% of their TACC allocation. Effort

The historical catch and effort is shown in Figure 13. Effort, described in this fishery as boat days, has decreased from 382 boat days in 2002/03 to 313 boat days in 2003/04. One reason for this reduction is the decline in the number of licensed fishers.

Year

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

Cat

ch (t

)

0

100

200

300

400

500

600

Eff

ort (

days

)

200

400

600

800

1000

1200

1400

1600

1800

2000

Figure 13. Annual catch (columns) and effort (dotted line) for the blue crab MSF from 1983/84 to 2003/04. Black line indicates the year when the TACC was implemented.

CPUE

A summary of CPUE from 1983 to 2004 is shown in Figure 14. Catch per unit of effort (CPUE) for the MSF has reached its highest level since 1983. In season 2003/04, the CPUE increased from 111.62 kg/boat day to 123.5 kg/boat day (10.84%).


Year

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

CPU

E (k

g/bo

at d

ay)

0102030405060708090

100110120130140150160

Figure 14. Estimated values of CPUE in the BSCF (Marine Scalefish Fishery) since 1983/84. Black line indicates the year when TACC was introduced.

Seasonal Patterns Catch

The catch by month from July 2001 to June 2004 for the marine scale-fish fishery is shown in Figure 15. November has been omitted for confidentiality reasons. The largest part of the catch in the MSF fishery is landed in the warmer months February and March. In 2003/04, 94.8% of the landed catch was taken during this period, similar to the 95.2% caught in 2002/03.

Effort The effort by fishing month from July 2001 to June 2004 for the marine scale-fish fishery is shown in Figure 16. In the 2003/04 season, 88.3% of effort occurred after the closure period, compared with 90.3% in 2002/03. In 2001/2002, the increase in fishing effort prior to the closure resulted in the larger catches at this time, which corresponds to the larger recorded catch levels in the pot fishery.

CPUE The CPUE was at its highest in January this season, with some catches being in excess of 150 kg/per day. The high catch rate in August is due to a very low number of days fished, at this time.


The CPUE by fishing month from July 2001 to June 2004 for the marine scale-fish fishery is shown in Figure 16. Spatial Patterns

Spatial data for the marine scale-fish fishery cannot be reported for confidentiality reasons.

2 001 /02

Ju l A u g S ep O ct N ov D ec Jan Feb M ar A p r M ay Ju n

Cat

ch (t

)

0

5

1 0

1 5

2 0

20 03 /0 4

M on th


Cat

ch (t

)

0

5

1 0

1 5

2 0

20 02 /0 3


Figure 15. Monthly catch (blue columns) for the BSCF (MSF) 2001-2004.

20 01 /02


Boa

t day

s

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

20 02 /03


CPU

E (k

g/da

ys)

0

20

40

60

80

10 0

12 0

14 0

16 0

200 3 /0 4


Boa

t day

s

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

CPU

E (k

g/da

ys)

0

20

40

60

80

100

120

140

160

M o n th

M on th

Figure 16. Monthly effort (line) and CPUE (dots) for the BSCF MSF fishery 2001-2004.


PERFORMANCE AGAINST INDICATORS – FISHERY STATISTICS

The biological reference points and performance indicators stated in the BSCF Management Plan are:

• Catch • Relative Exploitation Rate • Pre-recruitment • Sex ratio.

The performance against the reference points and indicators of the fishery for the last six fishing seasons is shown in Table III. Catch

The catch for 2003/04 was well within the limit reference of 80% with 95.28% caught this season. This was the largest catch (t) since the implementation of the TACC in 1996/97. Relative Exploitation Rate

A prerequisite for calculating the performance indicator “Relative Exploitation Rate” is that modelling and a necessary sampling program be implemented by the BCFMC. In the absence of this, the Relative Exploitation Rate cannot be reported. Pre-Recruitment

The performance indicator “Pre-recruitment” (the relative number of undersized crabs - CW<110mm) is not consistently reported in the logbooks, and hence the commercial data cannot be analysed statistically. However, the pre-recruit index showed a decline in the number of recruits in both Gulf St Vincent and Spencer Gulf from the previous season. Nevertheless, the GSV fishery performed above and the SG within the target and limit reference. Sex Ratio

The performance indicator “ Sex ratio”, the relative number of females in comparison to the relative number of males in the commercial catch, is not consistently reported in the logbooks and cannot be statistically analysed. There was an increase in females in the catch in both GSV and SG. Nevertheless, the GSV fishery performed above and the SG within the target and limit reference.

Blue Crab Stock Assessment Svane and Hooper Page 27 _______________________________________________________________________________________________________________________________________________________________

All Figures were extracted from previous stock assessment reports

Table III. Biological reference points and performances for the BSCF from 1997/98 to 2003/04. (NA: not available, TACC: Total Allowable Commercial Catch

Indicator Target Limit 1998/99 1999/00 2000/01 2001/02 2002/03 2003/04

Catch TACC 80% of TACC 79.9 86.4 87.19 85.33 88.95 95.28

Relative Exploitation Rate GSV (% of 1994 level) SG (% of 1990 level)

50 40

100 80

36.2 15.6

NA

NA

NA

NA

NA

Pre recruit index GSV SG

10 30

5 15

10 32

18

NA NA

42.1 22.9

20.26 34.46

15.54 23.99

Sex Ratio GSV SG

30 30

15 15

30

NA

42

NA NA

22.9 26.9

40.9 21.6

44.91 29.5


FISHERY INDEPENDENT SURVEYS INTRODUCTION

In the South Australian blue crab fishery, fishery independent surveys have been conducted on three occasions in July 2002, July 2003 and July 2004, respectively. An additional survey was conducted in December 2002 and restricted to a few blocks to determine the reproductive stage of female crabs. The primary aim of the June/July fishery independent survey was to collect information on the spatial abundance and size composition of blue crabs in SG and GSV during winter, when juvenile crabs recruit to the fishery. The information can be used to determine a Recruitment Index – a quantitative measure of the small crabs (pre-recruits) recruiting to the fishery. In this report, a comparison of the three surveys is made.

METHODS

Sampling

The survey area covered waters with depths ranging from 3 m to 22 m northwards from Semaphore to Port Vincent in GSV and northwards from Bird Island (Wallaroo) to Victoria Point (Cowell) in SG.

Commercial fishermen determined the sampling sites based on their fishing experience and their historical catch and effort data. From these recommendations, four sites were selected in each fishing block to be surveyed. In SG, the survey blocks were 3, 4, 6, 7, 9, 10, 11, 12, 13, 14, 15, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 30, 31, 33, 36, 37, 42 (total 27 blocks) with 1080 pot lifts. In GSV, the survey blocks were 3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 21, 23, 26, 27, 33, 35, 89 (total 23 blocks) with 920 pot lifts. Appendix I and II show the locations of the fishing blocks. For statistical purposes, the data from each block were grouped into three areas for each gulf. In SG, blocks 1-12 constitute area A (north), blocks 13-26 area B (centre), and the remaining blocks area C (south). In GSV, blocks 1-11 plus block 37 constitute area A (north), blocks 12-21 plus blocks 39, 40 and 36 area B (centre), and the remaining blocks area C (south).

At each site, commercial crab pots and research pots were set and hauled on a daily basis. Commercial pots (Figure 17) have a diameter of 1.2-1.4 m, a height of 50 cm, and are covered with a 90 mm mesh. Research pots (Figure 18), used specifically for surveys only, have a diameter of 1.4 m, a height of 50 cm, and a smaller mesh covering of 55 mm.

At each pot survey site, five sets of gear were deployed along a line, each comprising of one commercial and one research pot. Each pot was separated by 40 m of rope and each set of gear spaced 150 m apart. Pots were baited with fresh Australian salmon or striped trumpeter, and were hauled at dawn.

A global positioning system (GPS, model Garmin GPS 72) was used to locate the gear, and depth sounder readings were recorded for each site. Blue crabs were measured using Vernier callipers (carapace width), sexed (male or female), and their condition (dead, soft, berried) recorded. The abundance of other species was also recorded.


Figure 17. Commercial crab pot used by the fishery with a mesh size of 90 mm.

Figure 18. Research crab pot with a mesh size of 55 mm.


Statistical design

The purpose of the statistical analyses was to compare the abundance, size and sex distributions between years and areas to provide biological data to determine the TACC. The continuous variables selected for the fishery independent survey were crab number and size (mm CW). The analyses of these two variables were performed individually. The nominal variables were sex (F, M), size (L=legal size, CW>=110mm; U=undersize, CW<110mm), pot type (C, R), block and year. An Analysis of Variance (ANOVA) design will accordingly be size (pot)*sex (pot)*pot*area*year, with “size” and “sex” nested within “pot”. The nominal variables for size (mm CW) were sex (F, M), pot type (C, R), area and year. An ANOVA design will accordingly be sex (pot)*pot*area*year, with “sex” nested within “pot”. The use of ANOVA requires that the data are normally distributed and that variances are homogeneous. The continuous variables “number of crabs” were not normally distributed and the variances were not homogeneous because of a large number of zeros (pots where no crabs were caught) and successively fewer pots with increasing numbers of crabs caught. It was not possible to correct this problem by transformation. The continuous variable “crab size” was found to be normally distributed but the variances were not homogeneous. Transformations did not prove suitable, but because an ANOVA is fairly robust in relation to these requirements, factorial analyses were performed on the sub-sets of nominal variables and further substantiated by a series of non-parametric tests. A Dunnett C test, which does not require homogeneous variances, was used to separate homogeneous sub-sets. Size distributions were analysed using non-parametric tests for comparisons between years for each sex and year. RESULTS

Recruitment and Sex Distribution

The proportion and numbers of undersized crabs (<110mm) caught during the three fishery-independent surveys are shown in Table IV. As expected, the research pots, due to their smaller mesh size, caught larger numbers of undersized (recruits) crabs. In both gulfs and irrespective of pot type, there is a decline from 2002 to 2004 in the proportion of undersized crabs caught. This implies that the number of recruits entering into the fishery has declined since 2002. The proportion of females in GSV has increased, whereas the number in SG remains stable. However, these generalised data does not take into account the spatial variability, which is analysed further below. Table IV. Proportion (%) and numbers of undersized (<110mm) crabs and the total percentages of females caught in both pot types in the survey samples. C=commercial pot, R=research pot. Area Year

GSV July 2002

GSV July 2003

GSV July 2004

SG July 2002

SG July 2003

SG July 2004

Pot C R C R C R C R C R C R % 49.3 61.5 23.2 41.6 12.2 21.2 36.2 51.6 29.4 49.5 20.5 31.6 No. 464 664 364 790 101 133 1363 2548 1016 2225 828 1255 % 26.5 34.1 42.7 28.8 26.9 30.6


Abundance of Crabs in Spencer Gulf Effects of Year and Area

The number of crabs caught per pot as a function of year and area is shown in Figure 19. A significant effect of year and area was found (mixed model ANOVA, p<0.05). A post hoc test (SNK) revealed that 2002 was significantly different from year 2003 and 2004, showing that irrespective of area, significantly fewer crabs were caught in 2003 and 2004 than in 2002. Year 2003 and 2004 were not statistically different. A significant effect of area was also evident and a Dunnett C test separated all three areas. The number of crabs caught declined from north to south. However, this pattern was not consistent for year 2002, which caused significant statistical interactions. Considering the non-homogenous variances, two Kruskal-Wallis tests were performed for year and area separately. The result confirmed the results of the ANOVA, showing a significant effect of year (χ2=462.976, df=2, p<0.05), indicating that 2002>(2003=2004) and area (χ2=707.118, df=2, p<0.05), indicating that A>B>C.

Effects of Pot Type

The number of crabs caught per pot type as a function of year and area and pot type is shown in Figures 20 and 21. In addition to year and area, a significant effect of pot was found (mixed model ANOVA, p<0.05). A pattern of more crabs being caught in research pots than in commercial pots is evident. A Dunnett C test separated year 2003 and 2004 from year 2002. A mean of 2.3±0.08 CI crabs was caught per research pot compared with 1.93±0.08 CI per commercial pot. A Kruskal-Wallis test confirmed this result (χ2=50.577, df=1, p<0.05), indicating that larger numbers of crabs were caught in research pots than in commercial pots.

2002 2003 2004

Mea

n nu

mbe

rs p

er p

ot

0

1

2

3

4

Area A mean B mean C

YearFigure 19. Mean numbers of crabs caught per pot in Spencer Gulf as a function of year and area. Values are mean ± 95% confidence interval. Area A = north, area B= middle and area C South.


Year

2002 2003 2004

Mea

n nu

mbe

rs p

er r

esea

rch

pot

0

1

2

3

4

5

Area A Area B Area C

Figure 20. Mean numbers of crabs caught per research pot in Spencer Gulf as a function of year and area. Values are mean ± 95% confidence interval.

Year

2002 2003 2004

Mea

n nu

mbe

rs p

er c

omm

erci

al p

ot

0

1

2

3

4


Figure 21. Mean numbers of crabs caught in commercial pots in Spencer Gulf as a function of year and area. Values are mean ± 95% confidence interval.


Effects of Sex

The mean numbers of females and males caught per pot as a function of year and area are shown in Figures 22 and 23. The mixed model ANOVA, in addition to year and area, showed a significant effect of gender. In general, significantly more males (mean = 3.01) than females (mean = 1.22) were caught. The pattern follows a trend that most crabs (both females and males) were caught in area A (north) with declining numbers towards south. This pattern is consistent between years, with the exception of males in 2002 (Dunnett C test: ((2003=2004)≠2002). This pattern was confirmed by a Kruskal-Wallis test (χ2=1021.892, df=1, p<0.05). The mean number of females caught per pot in area A (north) in 2004 (mean 1.95±0.17 CI) was significantly larger than in 2003 (mean 1.33±0.21 CI) (Mann-Whitney U-test, Z=-4.609, p=0.00).

Year

2002 2003 2004

Mea

n nu

mbe

rs o

f fem

ales

per

pot

0

1

2

3

4


Year

2002 2003 2004

Mea

n nu

mbe

rs o

f fem

ales

per

pot

0

1

2

3

4


Figure 22. Mean numbers of female crabs caught per pot in Spencer Gulf as a function of year and area. Values are mean ± 95% confidence interval.


Year

2002 2003 2004

Mea

n nu

mbe

rs o

f mal

es p

er p

ot

0

1

2

3

4

5

6


Figure 23. Mean numbers of male crabs caught per pot in Spencer Gulf as a function of year and area. Values are mean ± 95% confidence interval.

Effect of Size

The numbers of legal (>110 mm) and undersized (<110 mm) crabs caught per pot is shown in Figures 24 and 25, respectively. The pattern between years and areas is similar to that described above for the total number of crabs caught. A significant effect of size was evident, showing that in general more legal sized than undersized crabs were caught (Kruskal-Wallis test, χ2=273.918, df=1, p<0.05). However, a statistically significant declining trend in the numbers of undersized crabs caught in year 2002 to 2004 is evident (Kruskal-Wallis Test, χ2=448.842, df=2, p<0.05). A Dunnett C test showed that all three years are significantly different. This pattern was consistent for all areas. The mean values were 2.51±0.15 CI, 1.53±0.11 CI, and 0.96 ±0.07 CI for 2002, 2003 and 2004, respectively.


Year

2002 2003 2004

Mea

n nu

mbe

rs o

f leg

al c

rabs

per

pot

0

1

2

3

4

5


Figure 24. Mean numbers of legal crabs (>110 mm) caught per pot in Spencer Gulf as a function of year and area. Values are mean ± 95% confidence interval.

Year

2002 2003 2004

Mea

n nu

mbe

rs o

f und

ersi

zed

crab

s per

pot

0

1

2

3

4


Figure 25. Mean numbers of undersized crabs (<110 mm) per pot caught in Spencer Gulf as a function of year and area. Values are mean ± 95% confidence interval.


Abundance of Crabs in Gulf St Vincent

Effects of Year and Area

The number of crabs per pot as a function of year and area is shown in Figure 26. A significant effect of year and area was found (mixed-model ANOVA, p<0.05). A Dunnett C test separated statistically years ((2002=2003)≠2004), and area A≠B≠C. A significant interaction was evident indicating that the pattern of area was not consistent between years, as given by the comparatively larger value in area A in 2002. Because the variances were not homogeneous, additional tests were performed. A Kruskal-Wallis test confirmed the significant effect of year (χ2=283.426, df=2, p<0.05) and area (χ2=239.943, df=2, p<0.05). In general, the result showed that more crabs were caught in 2002 (mean=0.86±0.09 CI) and 2003 (mean=0.95±0.09 CI) than in 2004 (mean =0.40±0.05). The number of crabs caught in 2004 was consequently 42% of the numbers caught in 2003.

Effects of Pot Type

The numbers of blue crabs per commercial and research pots as a function of year and area are shown in Figures 27 and 28, respectively. The ANOVA showed that there was no significant difference between numbers of crabs caught in the two types of pot. A non-parametric Kruskal-Wallis test confirmed this result (χ2=0.943, df=1, p=3.32).

Year

2002 2003 2004

Mea

n nu

mbe

rs p

er c

omm

erci

al p

ot

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Figure 27. Mean numbers of crabs per commercial pot caught in Gulf St. Vincent as a function of year and area. Values are mean ± 95% confidence interval.


ts of Sex

The of females and males caught per pot as a function of year and area

Year

2002 2003 2004

Mea

n nu

mbe

rs p

er r

esea

rch

pot

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Figure 28. Mean numbers of crabs per research pot caught in Gulf St. Vincent as a function of year and area. Values are mean ± 95% confidence interval.

Effec

mean numbersare shown in Figures 29 and 30. The mixed model ANOVA, in addition to year and area, showed a significant effect of sex. In general, significantly more males (mean=0.95±0.07) than females (mean=0.49±0.05) per pot were caught. This pattern was confirmed by a Kruskal-Wallis test (χ2=194.55, df=1, p<0.05). A Dunnett C test revealed that for both sexes the difference was between year 2003 and 2004, with no difference between years 2002 and 2003 (2002=2003≠2004). The difference between areas observed for all crabs (A≠B≠C) was the same for both sexes. Accordingly, the general trend of a decline in crab numbers between the years 2002 and 2003 compared to 2004 was reflected in both females and males.


Year

2002 2003 2004

Mea

n nu

mbe

rs o

f fem

ales

per

pot

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Figure 29. Mean numbers of female crabs per pot caught in Gulf St. Vincent as a function of year and area. Values are mean ± 95% confidence interval.

Year

2002 2003 2004

Mea

n nu

mbe

rs o

f mal

es p

er p

ot

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Figure 30. Mean numbers of male crabs per pot caught in Gulf St. Vincent as a function of year and area. Values are mean ± 95% confidence interval.


Effect of Size

The numbers of legal (>110 mm) and undersized (<110 mm) crabs caught per pot are shown in Figure 31 and 32, respectively. The pattern between years and areas is similar to that described above for the total number of crabs caught. A significant effect of size was evident, showing that in general more legal sized (mean=0.97±0.07 CI) than undersized crabs (mean=0.47±0.04 CI) were caught (Mann-Whitney U test, Z=-11.794, df=1, p<0.05).

The numbers of legal sized crabs caught were significantly different between years (Kruskal-Wallis test, χ2=54.307, df=2, p<0.05). This difference was between year 2002 and 2003 and years 2003 and 2004, but with no significant difference between years 2002 and 2004 (Mann-Whitney U test, Z=-0.365, df=1, p=0.715). The mean numbers of legal sized crabs caught were 0.77±0.11 CI, 1.41±0.15 CI and 0.67±0.10 CI for 2002, 2003 and 2004, respectively, showing a statistically significant decline in the numbers of legal sized crabs between years 2003 and 2004.

A statistically significant decline in the number of undersized crabs caught from year 2002 to 2004 is evident (Kruskal-Wallis Test, χ2=84.421, df=2, p<0.05). A Dunnett C test showed that all years were statistically different. This pattern was consistent for all areas. The mean values were 0.96±0.14 CI, 0.49±0.07 CI, and 0.13 ±0.03 CI for 2002, 2003 and 2004, respectively.

Accordingly, the general trend observed for all crabs that (2002=2003) ≠2004 is not consistent with size. For legal sized crabs the difference is (2002=2004)≠2003 and for undersized crabs, the difference is 2002≠2003≠2004.

Year

2002 2003 2004

Mea

n nu

mbe

rs o

f leg

al c

rabs

per

pot

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Area AArea B Area C

Figure 31. Mean numbers of legal sized crabs (>110mm) per pot caught in Gulf St. Vincent as a function of year and area. Values are mean ± 95% confidence interval.


Year

2002 2003 2004

Mea

n nu

mbe

rs o

f und

ersi

ze c

rabs

per

pot

0.0

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Figure 32. Mean numbers of under sized crabs (<110mm) per pot caught in Gulf St. Vincent as a function of year and area. Values are mean ± 95% confidence interval.

Size Distributions

Effects of Gulf and Sex

A significant effect of year and sex was found but with significant interactions (ANOVA, p<0.05). The interactions are caused by the interference from the shift in size distributions between years. The variances were not homogeneous and transformations did not rectify the problem. For both sexes and all years, with the exception of year 2002, crabs from GSV were larger than those from SG (females GSV: mean 113.80 mm±0.44 CI; females SG: mean 111.23 mm±0.30 CI; males GSV: mean 114.85 mm ±0.32 CI; males SG: 113.36 mm±0.18 CI). The statistically significant difference was confirmed by Mann-Whitney U test’s (females: Z= -7.833, p<0.00; males: Z=-5.664, p<0.00).

Effects of Year, Females SG

Figure 33 shows the accumulative size frequencies for female crabs caught in commercial and research pots combined during the three surveys in July 2002, 2003 and 2004 in Spencer Gulf. However, a Dunnett C test showed that all years were different (2002≠2003≠2004). A non-parametric Kruskal-Wallis test confirmed a statistically significant difference between years (χ2=176.655, df=2, p<0.05). The overall results showed that the mean female crab size (mm CW) was larger in 2004 than in 2002 and 2003 (2002: mean =111.32 mm±0.53 CI; 2003: mean = 108.21 mm±0.60 CI; 2004: mean 113.76 mm±0.40 CI).


Carapace width (mm)

70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100

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SG 2002 F SG 2003 F SG 2004 F

Figure 33. The accumulative size distributions of the female blue crabs caught in Spencer Gulf (SG) in both commercial and research pots during the surveys in July 2002, 2003 and 2004.

Carapace width (mm)

70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100

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SG 2002 M SG 2003 MSG 2004 M

Figure 34. The accumulative size distributions of the male blue crabs caught in Spencer Gulf (SG) in both commercial and research pots during the surveys in July 2002, 2003 and 2004.


Effects of Year, Males SG

Figure 34 shows the accumulative size frequencies for male crabs caught in commercial and research pots combined during the three surveys in July 2002, 2003 and 2004 in Spencer Gulf. The statistical patterns of males were similar to those of females. A Dunnett C test showed that all years were different (2002≠2003≠2004). A non-parametric Kruskal-Wallis test confirmed a statistically significant difference between years (χ2=418.137, df=2, p<0.05). However, separate Mann-Whithey U tests did not statistically separate year 2002 from year 2003 (Z = -0.496, p=0.621). Nevertheless, the overall results showed that the mean male crab size (mm CW) was larger in 2004 than in 2002 and 2003 (2002: mean =112.46 mm±0.33 CI; 2003: mean = 111.68 mm±0.33 CI; 2004: mean 116.10 mm±0.27 CI).

Effects of Year, Females GSV

Figure 35 shows the accumulative size frequencies for the female crabs caught in commercial and research pots combined during the three surveys in July 2002, 2003 and 2004 in Gulf St Vincent. A Dunnett C test showed that all years were different (2002≠2003≠2004). A non-parametric Kruskal-Wallis test confirmed a statistically significant difference between years (χ2=302.111, df=2, p<0.05). However, a non-parametric Mann-Whitney U test failed to separate year 2003 from 2004 (Z=-1.926, p=0.054). Accordingly, the overall results showed that the mean female crab size (mm CW) was smaller in 2002 than in 2003 and 2004 (2002: mean =106.97 mm±0.97 CI; 2003: mean = 115.38 mm±0.57 CI; 2004: mean 116.65 mm±0.70 CI).

Carapace width (mm)

72 74 76 78 80 82 84 86 88 90 92 94 96 98 100

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Figure 35. The accumulative size distributions of the female blue crabs caught in Gulf St Vincent (GSV) in both commercial and research pots during the surveys in July 2002, 2003 and 2004.


Effects of Year, Males GSV

Figure 36 shows the accumulative size frequencies for the male crabs caught in commercial and research pots combined during the three surveys in July 2002, 2003 and 2004 in Gulf St Vincent. The statistical patterns of the males are different from those of the females. A Dunnett C test showed that all years were different (2002≠2003≠2004). A non-parametric Kruskal-Wallis test confirmed a statistically significant difference between years (χ2=643.727, df=2, p<0.05). The overall results showed that the mean male crab size (mm CW) was larger in 2004 than in 2002 and 2003 (2002: mean =109.57 mm±0.52 CI; 2003: mean = 116.24 mm±0.45 CI; 2004: mean 120.41 mm±0.67 CI).

Carapace width (mm)

72 74 76 78 80 82 84 86 88 90 92 94 96 98 100

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Figure 36. The accumulative size distributions of the male blue crabs caught in Gulf St Vincent (GSV) in both commercial and research pots during the surveys in July 2002, 2003 and 2004.


PERFORMANCE AGAINST INDICATORS – INDEPENDENT SURVEY

Catch

Not applicable

Relative Exploitation Rate

Not Applicable

Pre-Recruitment

The recruitment index (% undersized crabs caught in research pots) showed a continued decline in both gulfs (GSV 2002: 61.5%, 2003: 41.6% and 2004: 21.2%; SG 2002: 51.6%, 2003: 49.5% and 2004: 31.6%). The target values (biological reference points) in the Management Plan are 30% and the limit 15%. Accordingly, the values for GSV in 2004 are above the target value, while the values for SG are within the target value.

Sex Ratio

The sex ratios (% females) for GSV in 2004 were 42.7% compared with 34.1% in 2003 and 26.5% in 2002. The sex ratios for SG in 2004 were 28.8% compared to 26.9% in 2003 and 28.8% in 2002. The target values (biological reference points) in the Management Plan are 30% and the limit 15%. Accordingly, the values for GSV in 2004 are above the target value, while the values for SG are within the target value.


BY-CATCH

Information on by-catch was collected from the fishery independent surveys in 2002, 2003 and 2004. By-catch is defined as those species that are captured in pots or drop nets as incidental catch while targeting blue swimmer crabs (Roosenburg et al. 1997, Saila 1983).

During the three independent surveys, 41 species have been recorded as by-catch from the BSCF. Five species of crabs predominantly make up the by-catch representing 95% of the individuals caught. By-catch other than crabs made up 5.0%.

Of the five by-catch crab species caught, 88.83% of them were, on average, the rock crab, Nectocarcinus intigrifrons. Table V shows the relative abundance and the percentage distribution of the rock crabs that were caught during the surveys. Table VI gives the number of rock crabs per pot lift. All by-catch species that have been caught during surveys are listed in Table VII. Table V. Abundance and percentage distribution of the rock crab, Nectocarcinus intigrifrons, caught as by-catch in the blue crab pot fishery independent surveys 2002-2004 in Spencer Gulf (SG) and Gulf St Vincent (GSV). SG

Abundance

Percentage Distribution

GSV

Abundance

Percentage Distribution

Commercial 2002 2003 2004

158 422 268

11.99% 24.13% 12.63%

602 313 761

19.4% 7.8% 11.4%

Research 2002 2003 2004

1160 1327 1854

88.01% 75.87% 87.37%

2509 3681 5887

80.6% 92.2% 88.6%

Table VI. Number of rock crab, Nectocarcinus intigrifrons, per pot caught as by-catch in the blue crab pot fishery independent surveys 2002-2004 in Spencer Gulf (SG) and Gulf St Vincent (GSV). SG GSV Commercial 2002 2003 2004 Research 2002 2003 2004

0.18 0.4 0.25

1.29 1.25 1.72

0.75 0.34 0.83

3.11 4.03 6.40


Table VII. Number of pot lifts, abundance and percentage distribution of by-catch species caught in commercial and research pots during the July 2002 and 2003 fishery independent surveys in Spencer Gulf (SG) and Gulf St Vincent (GSV). 2002 SG GSV 2003 SG GSV 2004 SG GSV

Potlifts 898 808 1064 914 1080 920

Common Scientific % % % % % % Name Name No.s Distn No.s Distn No.s Distn No.s Distn No.s Distn No.s Distn

Crustacean Seaweed crab Naxia spp. 0 0.00% 1 0.03% 0 0.00% 0 0.00% 7 0.29% 0 0.00% Rock crab Nectocarcinus integrifrons 1318 95.92% 3111 85.42% 1749 93.38% 3994 84.07% 2122 89.23% 6648 84.97% Sand crab Ovalipes australiensis 0 0.00% 46 1.26% 3 0.16% 110 2.32% 0 0.00% 227 2.90% Spider crab Leptomithrax spp. 3 0.22% 423 11.61% 24 1.28% 307 6.46% 116 4.88% 440 5.62% Balmain Bug Ibacus peronii 5 0.36% 0 0.00% 2 0.11% 1 0.02% 4 0.17% 8 0.10% Prawn Melicertus latisulcatus 4 0.29% 0 0.00% 1 0.05% 0 0.00% 8 0.34% 0 0.00%Fishes Bullseye Vincentia conspersa 0 0.00% 0 0.00% 11 0.59% 22 0.46% 9 0.38% 4 0.05% Cowfish Aracana aurita 3 0.22% 0 0.00% 0 0.00% 0 0.00% 2 0.08% 0 0.00% Flathead unidentified 0 0.00% 1 0.03% 0 0.00% 6 0.13% 1 0.04% 23 0.29% Flounder unidentified 0 0.00% 1 0.03% 1 0.05% 0 0.00% 0 0.00% 0 0.00% Leatherjacket Acanthaluteres spilomelanurus 0 0.00% 0 0.00% 27 1.44% 83 1.75% 33 1.39% 368 4.70% Moonlighter Tilodon sexfasciatum 0 0.00% 0 0.00% 0 0.00% 0 0.00% 0 0.00% 0 0.00% Numb Fish Hypnos monopterygium 3 0.22% 0 0.00% 0 0.00% 0 0.00% 0 0.00% 0 0.00% Porcupine fish Diodon nicthemerus 0 0.00% 0 0.00% 1 0.05% 0 0.00% 1 0.04% 0 0.00% Puffer Fish Torguigener pleurogramma 1 0.07% 1 0.03% 1 0.05% 1 0.02% 4 0.17% 6 0.08% Red Mullet Upeneichthys vlamingii 13 0.95% 37 1.02% 9 0.48% 134 2.82% 6 0.25% 32 0.41% Rock ling Genypterus tigerinus 0 0.00% 0 0.00% 0 0.00% 5 0.11% 0 0.00% 8 0.10% Snapper Pagrus auratus 4 0.29% 0 0.00% 0 0.00% 0 0.00% 0 0.00% 0 0.00% Soldier Fish Gymnapistes marmoratus 1 0.07% 2 0.05% 2 0.11% 18 0.38% 1 0.04% 2 0.03% Stinkfish Foetoreepus calauropomus 0 0.00% 0 0.00% 0 0.00% 1 0.02% 0 0.00% 0 0.00% Trumpeter Pelates sexlineatus 0 0.00% 1 0.03% 3 0.16% 0 0.00% 7 0.29% 0 0.00% Weedy Whiting Haletta semifasciata 0 0.00% 2 0.05% 0 0.00% 1 0.02% 1 0.04% 0 0.00% KG Whiting Sillaginodes punctata 0 0.00% 0 0.00% 2 0.11% 0 0.00% 0 0.00% 1 0.01%


Table VII (continued). Number of pot lifts, abundance and percentage distribution of by-catch species caught in commercial and research pots during the July 2002 and 2003 fishery independent surveys in Spencer Gulf (SG) and Gulf St Vincent (GSV). 2002 SG GSV 2003 SG GSV 2004 SG GSV

Common Scientific % % % % % %

name name No.s Distn No.s Distn No.s Distn No.s Distn No.s Distn No.s Distn

Cephalopods Cuttlefish Sepia apama 2 0.15% 7 0.19% 3 0.16% 12 0.25% 23 0.97% 7 0.09% Octopus Octopus maorum 0 0.00% 0 0.00% 0 0.00% 1 0.02% 0 0.00% 0 0.00% Squid Sepioteuthis australis 0 0.00% 0 0.00% 0 0.00% 1 0.02% 0 0.00% 1 0.01%Elasmobranch Fiddler Trygonorhina fasciata 5 0.36% 4 0.11% 12 0.64% 31 0.65% 9 0.38% 16 0.20% Gummy shark Mustelus antarcticus 0 0.00% 0 0.00% 1 0.05% 0 0.00% 0 0.00% 0 0.00% Pt Jackson Heterodontus portusjacksoni 5 0.36% 0 0.00% 13 0.69% 7 0.15% 7 0.29% 5 0.06% Seven Gill shark Notorynchus cepedianus 0 0.00% 0 0.00% 0 0.00% 1 0.02% 0 0.00% 0 0.00% Skate unidentified 1 0.07% 1 0.03% 5 0.27% 2 0.04% 0 0.00% 0 0.00% Stingray unidentified 0 0.00% 0 0.00% 0 0.00% 0 0.00% 1 0.04% 0 0.00% Wobbegong 0 0.00% 0 0.00% 0 0.00% 0 0.00% 1 0.04% 0 0.00%Others Scallop Pecten fumatus 3 0.22% 0 0.00% 0 0.00% 0 0.00% 1 0.04% 1 0.01% Sea urchin unidentified 0 0.00% 0 0.00% 0 0.00% 3 0.06% 0 0.00% 2 0.03% Starfish unidentified 2 0.15% 0 0.00% 1 0.05% 4 0.08% 1 0.04% 12 0.15% Beche De Mer unidentified 1 0.07% 4 0.11% 2 0.11% 6 0.13% 13 0.55% 5 0.06% Abalone Haliotis laevigata 0 0.00% 0 0.00% 0 0.00% 0 0.00% 0 0.00% 2 0.03% Tunicate unidentified 0 0.00% 0 0.00% 0 0.00% 0 0.00% 0 0.00% 2 0.03% Conch unidentified 0 0.00% 0 0.00% 0 0.00% 0 0.00% 0 0.00% 3 0.04%TOTALS 1374 3642 1873 4751 2378 7824


CONCLUSIONS

FISHERY STATISTICS

• TACC has remained at the same level, 626.8 t, for the fourth consecutive year.

• TACC was not achieved across the fishery. • Commercial Catch in the fishery increased by 7.12% compared to previous

year. • Pot sector

o Landed 95.43% of the TACC allocation o Number of potlifts increased from 196,646 to 201,979 o CPUL increased from 2.62 kg/potlift to 2.77 kg/potlift

• MSF sector o Landed 84.07% of their TACC allocation.; o Fishing effort decreased from 382 to 313 boat days; o CPUE increased from 111.62 kg/day to 123.5 kg/day (highest

recorded level) • Pre-recruit index showed a decline in the numbers of recruits into both GSV

(20.26% to 15.54%) and SG (34.46% to 23.99%), but remain within the performance limits.

• Sex ratio index showed that females in the GSV catch are at their highest level (44.91%) in the history of the quota fishery. SG remained within the target and limit reference points (29.5%).

FISHERY INDEPENDENT SURVEY

• Blue crab abundance was consistently higher in the northern areas of both gulfs and declined towards south in all three years surveys have been conducted.

• Generally more males than females were caught. • A general decline in crab abundance between years was observed with the

lower numbers caught in 2004 than in the surveys in 2002 and 2003. • A decline in the proportion of undersized crabs (<110 mm) in both gulfs

was observed. • The decline in crab abundance is reflected in both females and males. • The mean crab size in GSV is larger than in SG consistently across years

and gender. • In SG, the mean crab size for both females and males was larger in 2004

than in 2002 and 2003. • In GSV, the mean crab size of females was larger in 2003 and 2004 than in

2002 while the mean crab size of males was larger in 2004 than in 2002 and 2003.


RECOMMENDATIONS

It is recommended that the BCFMC

o note that a general decline in crab abundance has been observed,

o note that a general decline in the number of undersized crabs (recruits) that enter into the fishery has been observed,

RESEARCH NEEDS

o Recruitment surveys into nursery areas may be needed to establish stock-recruitment relationships. This information is needed to allow a better long-term determination of the TACC and sustainability of the fishery

ASSESSMENTS NEEDS

o Continuation of the fishery independent surveys to ensure that adequate information is available to allow determination of TACC and to ensure a sustainable utilisation of the resource.

o To obtain accurate data on the recreational catches for better determination of TACC.


REFERENCES Anonymous (2003) Interim results of the National Recreational & Indigenous Fishing

Survey. Southern Fisheries Magazine, Autumn 2003.

Baker, J.L. and Kumar, M. (1994) Review of the Blue Crab (Portunus pelagicus) Fishery in South Australia. SARDI Research Report Series. No. 9.

Boxshall, S., Hooper, G. and Williams, H. (2000). Blue Crab. Fishery Assessment Report to PIRSA for the Blue Crab Fishery Management Committee. South Australian Fisheries Assessment Series 00/01.

Boxshall, S., Hooper, G. and Williams, H. (2001). Blue Crab. Fishery Assessment Report to PIRSA for the Blue Crab Fishery Management Committee. South Australian Fisheries Assessment Series 01/02.

Bryars, S. & Adams, M. (1999). An allozyme study of the blue swimmer crab, Portunus pelagicus (Crustacea: Portunidae), in Australia: stock delineation in southern Australia and evidence for a cryptic species in northern waters. Marine and Freshwater Research; 50, p 15-26.

Chaplin, J., Yap, E.S., Sezmis, E., and Potter, I.C. (2001). Genetic (microsatellite) determination of the stock structure of the blue swimmer crab in Australia. FRDC project 98/118.

Edgar, G.J., (1990). Predator-prey interactions in seagrass beds. II. Distribution and diet of the blue manna crab Portunus pelagicus Linnaeus at Cliff Head, Western Australia. J. Exp. Mar. Bio. Ecol., Vol 139, pp. 23-32.

Francis, R.I.C.C., (1988). Maximum likelihood estimation of growth and growth variability from tagging data. New Zealand Journal of Marine and Freshwater Research, Vol. 22; p 42-51.

Grove-Jones, R. (1987). Catch and effort in the South Australian blue crab (Portunus pelagicus) fishery. South Australian Department of Fisheries

Henry, E. W. and Lyle, J. M. ( 2003). The National Recreational and Indigenous Fishing Survey. FRDC project No.99/158.

Hooper, G., and Svane, I. (2003). South Australian Blue Crab (Portunus pelagicus) Fishery. South Australian Fisheries Assessment Series 02/02.

Kailola, P.J., Williams, M.J., Stewart, P.C., Reichelt, R.E., McNee, A. and Grieve, C. (1993) Australian Fisheries Resources. Bureau of Resources and the Fisheries Research and Development Corporation, Canberra, Australia, 422p.3

Knight, M.A., Tsolos, A and Doonan, AM. (2004). South Australian Fisheries and Aquaculture Information and Statistics Report. SARDI Research Report Series No. 60, pp2.

Kumar, M. (1997). Proceedings of the First National Workshop on Blue Swimmer Crab Portunus pelagicus. SARDI Research Report Series No.16, ISSN 1324-2083.

Kumar, M.S., Ferguson, G. and Boxall, V. (1998). Blue Crabs. South Australian Fisheries Assessment Series 98/1.


Kumar, M.S., Xiao, Y., Williams, H., Ferguson, G., Hooper, G. and Venema, S. (1999a). Blue Crab fishery, South Australian Fishery Assessment Series 99/02. SARDI

Kumar, M.S., Xiao, Y., Williams, H., Ferguson. G., and Venema, S. (1999b). Blue crab – Assessment Update and Review of Biological Indicators and Reference Points, South Australian Fishery Assessment Series 99/02-2. SARDI

Kumar, M.S., Ferguson, G Xiao, Y., Hooper, G. and Venema, S (2000). Studies on reproductive biology and distribution of the blue swimmer crab (Portunus pelagicus) in South Australian waters. SARDI Research Report Series No. 47.

Kumar, M.S., Xiao, Y., Venema, S. and Hooper, G. 2003. Reproductive cycle of the blue swimmer crab, Portunus pelagicus, off southern Australia. J. Mar. Biol. Ass. UK 83: 983-994.

McGlennon, D. and Kinloch, M.A. (1997). Resource allocation in the South Australian Marine Scalefish Fishery. FRDC project 93/249.

Meagher, T.D. (1971). Ecology of the crab Portunus pelagicus (Crustacea: Portunidae) in South Western Australia. Unpublished. PhD Thesis, Univ. W.A., Australia.

Roosenburg, W.M., Cresko, W., Modesitte, M., and Robbins, M.B. (1997). Diamondback terrapin (Malaclemys terrapin) mortality in crab pots. Conservation Biology 11: 1166-1172.

Saila, S.B. (1983). Importance and assessment of discards in commercial fisheries. FAO Fisheries Circular 765: 1-62.

Scandol, J.P. and Kennelly, S.J. (2001). Blue Crab Fishery Biological Research Review. Centre for Research on Ecological Impacts of Coastal Cities. University of Sydney.

Smith, H. (1982). Blue swimmer crabs in South Australia- their status, potential and biology. Safic. 6(5): 6-9.

Stephenson W., 1972. An annotated check list and key to the Indo-West-Pacific swimming crabs (Crustacea: Decapoda: Portunidae). Bulletin of the Royal Society of New Zealand, 10: 1-64.

Sumpton, W.D., Potter, M.A. and Smith, G.S. (1994). Reproduction and growth of the commercial sand crab, Portunus pelagicus (L.) in Moreton Bay, Queensland. Asian Fisheries Science 7:103-113.

Van Engel, W.A. (1958). The blue swimmer crab and its fishery in Chesapeake Bay, Part 1. Reproductions, early development, growth and migration. Comm. Fish. Rev. 20: 6-17.

Williams, M.J. (1982). Natural food and feeding in the commercial sand crab Portunus pelagicus Linneaus, 1766 (Crustacea: Decapoda: Portunidae) in Moreton Bay, Queensland. J. Exp. Mar. Biol. Ecol. 59: 165 - 176.


APPENDIX

ApSP

pendix I: THE COMMERCIAL FISHING BLOCKS FOR THE BLUE CRAB FISHERY IN ENCER GULF


89

!+

!+

E#

NO!+

!+

0

3 4

76

98

21

5

10

35

13 1514

17 19 20 2118

25 26 272423

29 31 32 3330

4443 4745 46

56535150 5452

59 61 646260 63

42

7170 72696867

7976 8078777574

83 84 85 8682 87

66

11

1612

57

48

28

36

88

34

38

58 65

73

22

37

49

81

41

4039

AD LAIDE

ARDROSSAN

PORT VINCENT

RTH ARM

PORT ADELAIDE

LegendGeneral Towns

Ports of Landing

#

!+

Blue Crab Fishing Blocks

Secondary RoadsHighways

0 10 205Kilometres

®

Appendix II: THE COMMERCIAL FISHING BLOCKS FOR THE BLUE CRAB FISHERY IN GULF.ST VINCENT

blue swimmer crab (portunus pelagicus) fishery · and 20.5% for sg for those crabs caught in...

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