b4 1u

T JOliRlAL Of CRISI ALIAt- HIOLIJGY J02J 200-205 21llll

REPRODUCTIVE BIOLOGY OF PORTUNUS PELAGJCUS lN A SOuiH-EAST AUSTRALIAN ESTUARY

Daniel D Johnson Charles A Gray and William G Macbeth

(DJ correspo ndence Danieljohn$onindustrynswgobull au CG WM) Cronulla Fisheries Research Centre of Excellence PO Box 21 Cronulla NSW 2230 Australia

ABSTRACT

Ponwlltlt peloims (blu~ swimmer crab is widely diSirihuled and fished lhroughout th~ indo-we~ t Pacific but little known of ih hiology and ecology in southeas t Austruliu ln this studythe reproducti ve biology of P prlugims inhabiting Wallis Lake n lorg~ co1stal lah Ihal supports the 1Hr8cst reg ional commercial fishery for th~ species was inwsligated Males and females wilh mature gonad~ occur throughout the fis hing season (November to July) however ovigrous female~ are must prev~lcnt in Novembr and December The mean size at which 50 of females reRchcd matu rity is estimated at 46 mm carapace length (CLl Fecundity i ncrea~ed linearly wilh Cl md females arc capable of producing up to 3 broolls of ~ggs within the oblgtCrvcd spawning scuson with crabs of 60-69 mm CL producing approximately 76 of the estimatd tmal egg production Incrcusing 1he currenl minimum carapace lenglh above 60 nun CL

would potentially provide greater prOltClion to matun females and increase tottl tgg production but this would rduce total retain~ ca1chcs in the fisheries

KFY WoRns blue crab fecundity maturity Porcwws pelagicus reproduction

DOl 10165108-30761

]NTRODUCTJON

The blue swimmer crab Porcunus pelagicus (Linnaeus 1758) occurs in shallow tropical and temperate coastal and estuarine waters throughout the Indo-West Pacific from Africa to India southeast Asia and Aus tralia (Smith and Sumpton 1989 Chande and Mgaya 2003) Throughout its distribution it is important in many commercial and recreational fisheries (Sukumaran and Neelakantan 1997 Sumpton et al 2003) In Australia commercial and recreational fishers harvest approximately 3000 metric tons of P pelagicus each year (Henry and Lyle 2003)

Knowledge of the reproductive biology of a species is one of the most important aspects in evaluating the harvesting strategies of exploited populations (Campbell and Eagles 1982 Addison and Bennet I 992) Studies investigating aspects of the reproductive biology of P pelagicus have reported regional and area-specific differshyences in the timing and length of spawning season (4 to 9 months) size at sexual maturity (31 to 49 mm carapace length) and fecundity (270000 to 1880000 eggs per brood) (Sulrumaran and Neelakantan 1997 1998 de Lestang et al 2003a b Kumar et al 2003 Smith et al 2004 Xiao and Kumar 2004) There have been no studies on the reproductive biology of P pelagicus in southeastern Australia even though it supports substantial fisheries The life history of P pelagicus in southeastern Au st ralia may differ from populations elsewhere Local data pertaining to the reproductive biology of P pelagicus is therefore required to help determine appropriate management options for thi s species in southeast Australia

The specific aims of this study were to investigate I) length of spawning period 2) gonad and ovarian developshyment 3) size at sexual maturity 4) relationship between size and fecundity and 5) the relative contribution that each size class makes to total egg production for a

population of P pelagicus in southeastern Australia This work was done in Wallis Lake New South Wales (NSW) as it supports the largest (40 of total landings) P pelagicus fishery in NSW (NSW DPl unpublished data)

MATERIALS AhD METHODS

Study Site and Collection of Samples

Wallis Lake (3217S 15252E) is ~large (water surface arcu of 86 kmz) banmiddoticr e$UDry comprising a shallow ccntrol lagoon with three main und numerous smaller tributaric~ and with n single opening to the sea (Roy tt ul 2001 ) Much of the lagoon contHins ascas ofdense seagra~s (Posidonia ausrrais and z~mem mplicorni) as well os shallow unvegctated habitats ( lt 2m in depth)

Samples of P pelu~icus from Wallis Lake md adjacent in~hore coastal waters were obtained via three differenl sources Crabs were collected from commercial trtp c~tcbes each month helwecn November 2002 and July 2003 after which time the trJgt-Iishing season had ended The commercial trap fishlt) for P pdagicus is managed by spatial closures gear re~trictions aud 11 minimum lcpoundal size for retained crabs (cnropace length [Cl) of 60 mm) This size limit was introduced withoul quantitlltive dnta from NSW P pelagimt populations Fishers operat ing in Wallis Lllk~ are permitted to set a maximum of 30 crab traps per day Commercial fishers are permitted to trap in all months however greatest reported landings and effort predominately occur between late summer and autumn (January to April each year Low ca1ches during the winter period prevent commercial fishers from tosgetin crohs

Cr~hs were also collected from commcrciol prawn-seim (see Macbeth and Gray 2008) and research beam-trawl catches (see Rotherham et al 2008 for a description of gear during February 11ntl Mnrch 2003 All crtbs wen melttbllred for carapace length (Cl nearc~t mm) weighed (nearest g) and sexed Samples were also rel ained for further examination in the laboratOT)

Gonad and Ovarian D~velopmcnt

Ea~h munth a totaJ of 70 crnbs lt35 males and 35 fema les) were randomly selectd from com mercial trap catches and monooCopically examined to determine the ir slage of gonad development Si stages were used to clas~ify females and three s1ages to classify male~ bced on the reproductive staging lritcria deeloped by Sukumardn and Ncelakantan (1998 (Tallie 1)

200

JllHgtSON ET AL R~IROIJIJ(IIV~ HIOLOG UF PVR7US1i~ PfL4DICUS 20 1

Table I Sag~s of f~male ovary md male jltgtnuJ development (based on Sukumaran and Nedakanlan 199~j

MucrOSltmiddotopk uppc orunce of fcmule ovury

I Colourless ovary lhread like in appearance II lmmcdiuely after ovulation the owary returns 10 the immature

stngc before remoturation The oary is yellow brown in colour and thick und translucent

Ill The ovruy is imry or yellow in coluur and slighlly enlnrgcd IV The colour of I he ovary varies from yellow to orHngc The ovary

al this stage i wollcn with prnnnunccd Jnhulati om v Malurc nvuries are deep ordnge in colour and the swollen lohes

obcurc he underlying h(patopancreas VI The ovary is ivory or yellow orange in colour and very fla(cid

Macroscopic appearonee of male ~onad

Testes and vasu deferentia not clearly differemialed vas deferentia are 1hin translucent slraighl lubes

II Testes and vasa deferentia well developed testes urc a large coiled Lube spreading lalcrally and posleriorly in the ~lomach Vasa deferentia opaque or while coiled mass extending lo both sides of the heart

111 Testes further enlarged VIIS deferentia are thick and while milky mass extending to fill most of the body cavity

Si1e a1 MaUrily

Juvenile and adult female crahs collcct~d from the benm trawl (159 individuals) and prawn seine (283 individuals) were used 10 examine size nt maturity Compared wi1h trap catches these relatively less size-selecti ve fishing methods provide n wider size range of crabs and lhcrefore a potentially unbiased eslimale of size al mmurily (Smilh e1 ol 2004) We used 1he definition of Smitl1 et al (2004) to determine if a female crab was malurc A female crab wu~ deemed mature when the oval shuped pleonal nap could be separated from the carapace During the pubertal moult the plecnal flap of he femal e portunid species chunges from triangular to oval shape and becomes loosely fixed to the carapoc c The size at whkh 50 (150) of fernal~ were sexually mature walt estimated by finin~ a logistic regresbullion curve tn the pmponion ofmatnre P pliagicus for each sequential 1-mm CL size class as described by King ( 1995) and Oh and Jeong (2003)

Fecundity

We (Oilected a tolal of 30 ovigerous female crdbs with undamaged egg bnlches from trdp catches in November 2002 and February 2003 Prior to the removal of the egg batch and plconal flap the stage of egg development was determined and the whole weighl of the crab (nearest Olgl and it~ CL (nearest 01 mm) were mea~ured Only crabs with stage I eggs (bright yellow egg bltch Svanc and Cheshire 2005) were included in the analysis of batch fecu ndity

The tntal egg hatch (including he pleonal nap) was removed from the crab and immersed in 400 ml of I M KOH for l 2 h to dissolve the funiculae that anach the eggs 10 the setae Following the separation process the pleonal nap was removed the pleopods scraped clean and all setae removed from the separated egg balch The wet weight of the total separmed egg batch was recorded and five replicate 002 g sob-samples wen taken The average number of eggs per suh-sarnple was then scaled up lo estimate the total n umber of eggs per egg batch The relationship between size of crab (CL) and fecundity was estimated separately for each month by filling linear regressions for CL vs fecundity To investigate whether fecundity varied between different sample momhs the slopes and y-intercepts of the regressions for November and February were compared using analysis o f mvarianee ltANCOVA)

Multiple Batches

The pOlemial lolal number of egg hatches produced by malnre females during a single breeding sea~on was estimoted by lim determining the proport ion or ovigerous females within each 5 mm size class Using lhese data und estimates of spawning period (number of days thai gt 5 of mature females are ovigerou~) and brood ~riod (number of days carrying

an egg balch s~ Meagh~r IY71) lh~ CL v~ n umber o f batche relationship wa~ determined by filfinpound a modified lot islic curve ranging from one bmch 10 ~ m~Jlt i mum of I + numbe r (Nb) m~ximum hatch es a~ do~cribed by de Letang cl al 12003b)

Index o f Rcproduni v( Potent ial

To determine he rela1ive contribution hal eltJth size class mad e 10 lo tal egg production of the entire popu lalion an indeJlt or reproductive potenti ~l (IRP) was developed according to the methods of Kanciruk 11nd Hmnkind (1976) und Sukumartn and Neelakanlan ( l 997) We estimated the reproductive potential for each size class using he size-fecundity rclatior1~hip proportion of females th1t are ovilerous in each size class and the size-frequency disuibution of the po pulation (based on trap catches Johnson and Gray submiued) The da~s index of the newly mature females (54-59 mm CL) was stundardised at o value of 100

RESULTS

Gonad and Ovarian Development

Female crabs representative of all gonad stages were present during each month of the sampling period (Fig I a) The monthly mean CL for male crabs increased from 64 16 ( 028) mm in November to 6962 ( 036) mm in April Similarly the mean size of females increased from 6278 ( 034) to 6467 ( 094) mm in CL during the sampling period The highest proportion of female crabs with mature (stage V) ovaries was during November (49) while during all the other months crabs with stage V ovaries accounted for 17-25 of all individuals sampled Female crabs with spent (stage Vl) ovaries were most common in December (31) and July (29 ) The primary spawning period was concluded to be between November and February as at least 5 of mature crnbs were ovigerous during this period (Fig 2) Male crabs displayed no distinct changes in development stage throughout the sampling period with 25-40 of crabs reproductively mature (stage III gonads) each month (Fig lb)

Female Size at Maturity

The smallest mature female recorded from seine and beamshytrawl catches was 34 mm CL The size at which 50 of female P pelagicus were mature was estimated to be 46 mm CL (Fig 3) while 95 were estimated to be mature at 56 mm CL Overall 85 of female crabs (33-80 mm CL) in seine and beam-trawl catches were mature

Fecundity

The estimated fecundity for individual crabs varied from approximately 463000 ( t 13200) to I 751 000 ( 32300) eggs per batch during November and between 620 000 ( t 23500) and I 78 I 000 ( t 40200) eggs per batch during February There was no significant difference (P gt 005) between the slopes (P = 046) and y-intercepts (P = 066) of the fecundity vs CL regression lines fitted for November and February Consequently these data were combined providing an overall fecundity vs CL regression relationship of Fecundity = (04056 CL- 16116) X 104

(Fig 4) The mean fecundity estimates for crabs in each 5 rnm CL size class (months combined) is given in Table 2

(a) I

-~ t=J bullII

-~middotHO cJStbullrbull l -)1~middotCIJ ml 5urf 1 01

60 c CIJ ~ Q) 0 40

20

()

(b) I

80

CIJ 01 60 c Q)

~ CIJ 40

0

20

0 Nov Dec Jan Feb Mar Apr May Jun Jul

Month

Fig I The proportion of each gonad maturity stage for (a) femnlc and (b) male P pelagicus

Multiple Batches

Fifty-three percent of ovigerous female crabs (n = 69) had stage IV to stage V ovaries indicating they were capable of producing multiple batches from a single mating per spawning season The estimated number of batches produced (NBj) by female crabs in each size class ranged from approximately one in crabs of 50-54 mm CL to approximately three in crabs 75-79 mm CL (Fig 5) The estimated CL-batch relationship is NBj = I + 2(1 + 0810 exp (CLj - 57)) where the spawning and brood periods were estimated as 120 and I 9 days respectively

40

35

5 30 ~ 01 25

middot 0 20 ~

15

10

5

0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul

Month

JOURNAL O F C RUSTACfiN lltULOGY VUL )II Nltl ~ 70 10 202

Fig 2 The proportion of ovigcrou~ female~ obltrved in conuncrcial trap catches

100

Q) - shy

2 ro 075 E c 0 t 0500 a 0 L

a 025

000 -1-=--___---r------r-------r------ 0 10 20 30 40 50 60 70 BO 90

Carapace length (mm)

Fig J Logistic curve showing the p roponion of mature female P pflugicus in each size category

Index of Rep roductive Potential

Females in the size class immediately below the current legal minimum CL of 60 mm (55-59 mm) represented 2 I 9 of all fema les yet produced onl y 135 of estimated total egg production and had an estimated reproductivity of 062 (Table 3) The estimated reproducshytivity of crabs was greatest (I 56) in the 65-69 mm size class while for larger crabs (ie 75-79 mm CL) it was considerably lower (032) Crabs measuring 60-69 mm CL represented 64 of the observed population and produced 76 of the estimated total egg production

DISCUSSION

TI1e reproductive biology of P pelalicus sampled in Wallis Lake was sufficiently different to that of P pelagicus from other parts of the world to support the hypothesis of strong regional differences in biology of P pelaRicus (Table 4) More specifically our es timates of fecundity differed to other studies in several ways despite similar methods For example our estimates of batch fecundity (463000shy1781000) were greater than that reported for individuals

20 0 0 0 18 ci 0 16

gtlt 14 c a 12 c 1 0 10 ~ ~ B IIgt 6

middotE

4 Ul

2 9080

Carapace length (mm)

Fig 4 Carapace lengt h-fecundity re lnt io nship for fcmnle P prlu~ims

pooled acro~s months (November and February)

50

bull

60 70

I JOHNSil-1 Fl AI REIROOl(TlgtE BIOLOGY Of POII TUNUS ftL~iCl1 20~

Table 2 Mtgtan carapace length CCI) wri~ht egg b~tch weigh t and estimates of fecundity of P pliagirus for elt~rh 5 mm size cla~s I I SE J Data plgtolcd for lovemhltr and February

nrllJt JmTrl Sumhcr of JldllduOJI - -

Me n Cl hnm l ----shy

W~middot1ch1 Ipound ) FJiJ ml~ OoC lJhl (~) Tnc al of crt~ pmiddott iOOivaLJ l

55middot 59 60-64 65-69 70-74 75-79 ---shy - - -

15 17 12 10 6 -

569 (042) 619 (039) 666 1060) 719 (0 39) 766 (027)

132 9 (336) 17558 (~60) 2939 (590) 2 7l82 (461) 33370 (286)

416 (3 6) 50 15 (350)

591 (240) 746(731) 942 (801)

731188 (25 943 ) 66468 (24520)

1081701 (15 120) I 237001 (41 401) 15790 I I cl8260)

of similar sizes in Western Australia (75000-325000 de Lcstang et al 2003b) and India (20000-750000 Sukumaran and Neelakantan 1997) but comparahle to estimates of fecundity for P pela~ icus in Queensland (Shields and Wood 1993) We also found that individual fecundity increased with increasing CL over the size range examined (55-79 mm CL) with the greatest number of eggs per batch carried on the largest female- an observation shared by Sukumaran and Neelakantan (1997) with respect to P pela~icus off the coast of India _ In contrast Kumar et al (2003) and de J-estang et al (2003b) reported that fecundity peaked at approximately 61 mm and 71 mm CL respectively then declined with further increase in size Finally we found no significant temporal difference in the relationship between size of crab (CL) and fecundity while Kumar et al (2003) reported that fecundity increased from October to December after which it declined

Although we can not isolate mechanisms for each of the observed differences in fecundity li sted above biotic and abiotic factors such as water temperature fluctuations growth rate (Prager et al 1990) and the population density and size-structure can influence fecundity in crustaceans (Mohan 1997 DeMartini et al 2003) For example the fecundity of the blue crab Callincctes sapidus (Rathbun 1896) in Chesapeake Bay was estimated to be greater in 1987 than in 1986 an observation attributed to favourable climatic conditions coupled with increased growth rates (Prager et al 1990)

Our estimate for the size at which 50 of female P pelagicus attain maturity in Wallis Lake (i e 46 mm CL)

35

30

~

r

i 25

0 y ~ 20 ~ c 1l 15 E ii

middot~

10

60 70 ec 90

Cosapll(c Jcn~th (mm)

Fig 5 Es1imatcd number o f egg ha1chcs produced during the ob~rved spawning period

was similar to corresponding estimates for females in Shark Bay (45 mm CL Smith et al 2004) and the Peel Harvey and Leschenault estuaries (43 mm CL de Lestang et al 2003b) in Western Australia but much greater than for females in Spencer Gulf South Australia (29 mm CL Xiao and Kumar 2004) This difference may simply reflect inter-regional differences in the biology ofP p elagic-us but may also be attributable to differences in th e selectivitv of the gears used to obtain samples Trap catches are often biased towards large sexually mature crabs resulting in an overestimation of the proportion of mature crabs in each size class and therefore an underestimation of the mean size at maturity (Smith et al 2004) Our estimaJcd mean size at 50 maturity was derived using samples from seine and beam trawls whereas that of Xiau and Kumar (2004) was derived using samples from trap catches Similarly place of capture (eg estuary vs ocean) may bias the estimation of mean size a t maturity of female P pelagicus (de Lestang et al 2003b) For example cmigralion of mature females from estuaries to the ocean might increase the proportion of immature crabs in each size class in the estuary leading to an over estimation of the overall mean size at 50 maturity for estuary-based samples (de Lestang et at 2003b) For this reason crabs used to estimate mean size at 50 maturity during our study were collected in February and March prior to emigration to ocean waters by sexually mature females

Despite the apparent inter-regional differences in feshycundity and size at maturity other aspects of the reproductive biology of P p elagicus in Wallis Lake appear similar to that reported elsewhere For example length of spawning period of P pelagicus appears to be influenced by water temperature with extended spawning observed in waters with higher temperatures (de Lestang et al 2003b) Reproductively mature P pelaRicus of both sexes (includshying ovigerous females) were found in Wallis Lake in all of the 9 months sampled demonstrating their capability for having a lengthy spawning period in south-eastern

Table 3 Index of reproductive potential of P prlagicmiddotus for each 5 mm si ze cla~s from commercial trap catclJCs

~~-~9

Siu cu t CL mm)

~ M-tV 1()14 75-79

of total female catch (A) 2186 329 1 3084 1208 231 ovigerous 1649 1908 2113 855 2 60 Estimated total potenlial

fecundily ( X 100000) 1462 1732 2867 3711 4737 Index of reproductive potential 10000 20637 35454 7273 539 of total egg production B) 1353 2792 4797 984 073 ReprodUlli~ity (BA) 0 62 084 156 081 032

204 JOLIRIgtAL O F CR l STA(FAIgt BIOU)(Y VOl gt11 NO ~ ~0111

Tnhlc 4 Comparative finding~ of the reproduc1 ivc biology of Porrunut pda11icus Location New Soul h Waks NSW) Weslern AusraliH (WA) Queensland (QLD) St)llh Aus1ralia (SA)

Scit utlll pCtdio ic Siu oil mUuri~v Si7c ot Jmuuri1~middot

Lola1ion CM in CL nmmiddot ( M u Cl nun) fcn1ollity IF_ggt- X Hf) 0 -0U)middot cooditiun ~- omiddoti~crous Soorcc

NSW 3H 56 046-178 Nov-Delt Nov -J an Pn~cn l ~ udy WA 38 43 de Lcsang cl al (2003b) WA 42 47 Smith ct al (2004 ) WA 28 37 027-085 Jan-Fch Pnllcr cl al ( 1983) QLD 34 49 024-188 Jun-Mar Aug-Mar Shields and Wood ( 1993) SA 28 49 048- 160 Oci-Apr Smith (19amp2) India 38 47 Sep-Mar Prnsad and T01mpi ( 1953) India 025-075 Jan-Apr Aug-Feh Sukum aran and Ncelakontan

(1997) Egyp1 31 44 075-081 Apr-Sep Mar-Aug RlZek (198)

Australia This concurs with observations indicating that P pelugicus can spawn over several months (up to 10) in other sub-tropical and temperate regions (Potter et al 1983 de Lestang et al 2003b) Further during our study ovigerous female s were most prevalent (36) in late springearly summer (November and December) which coincides with observations from estuaries and embayments in temperate south-western Australia (de Lestang et al 2003b)

Female P pelaricus can produce several batches of eggs from a single mating (Meagher 1971) and our estimates of the relationship between CL and number of batches of eggs produced were similar to that reported by de Lestang et at (2003b) Crabs lt 55 mm CL tended to produce only one batch whereas crabs gt 75 mm CL produced up to three batches The greater number of egg batches produced by larger crabs can be explained by their longer interrnolt period between copulation and egg extrusion (de Lestang et al 2003b)

Female P pelagicus in Wallis Lake attain sexual maturity below the current minimum legal CL for retention by commercial and rec1eational fishers of 60 mm The lower fecundity of newly matured females (55-59 mm CL) combined with the small proportion of ovigerous females observed in this size class (Johnson and Gray submitted) means that these sized crabs probably make only a small contribution to the total egg production of the entire population Similarly because of their low abundances the largest sized crabs (75-79 mm CL) probably do not contribute greatly to the estimated total egg production of the population despite their potentially greater overall total fecundity compared with other size classes Egg production in the Wallis Lake population appears to be heavily dependent on crabs between 60-69 mm CL which are subject to the highest level of fishing pressure (Johnson and Gray submitted) Increased fishing effort for or catchshyability of crabs in this size class could potentially result in large reductions in egg production and depending on environmental conditions could lead to reuced levels of recruitment

A possible mechanism to increase the total reproductive output of P pelagicus populations in Wallis Lake might be to increase the minimum legal CL Increasing the current minimum legal CL from 60 mm to 65-70 mm could potentially protect 55-86 of the estimated egg producing females from harvesting and increase total egg production

by 14-34 respectively A legal CL of 70 mm would potentially enable female crabs in the 65-70 mm size class to produce a greater number of egg batches prior to harvesting Such a change would however probably also result in a large reduction in total retained catches in the commercial trap fishery and would impact on the burgeoning recreational fishery in NSW Before any change in the legally retainable size of crabs is implemenshyted further information on growth and mortality and spawner-recruitment relationships would also be required to properly assess the statu s of the P pelagicus stocks of southeastern Australia and their susceptibility with respect to harvesting under s uch a regime

ACKNOWLEDGEMENTS

Professor Don Gartside (Sombern Cros s Univcrsily) provided assistance and guidance throughou the duration of his researc h Thi s study would noc huvc been po~sihle withou1 the ~upport of the commercial fishers in Wallis Llke Cluis Walsh provided cri1icnl comments on 1he d mft manuscript

REFERENCES

Addison J T and D B Bennett 1992 Assessm ent of minimum landing sizes ofthe edible crab Cancer pagurtts L on the east coast of England Fisheries Research 13 67-88

Campbell A aud MD Eagles 1982 Size at maturity and fec undity of rock crabs CalCmiddotebullmiddot irroratus from he Bay of Fundy ~nd souhwestern Nova Scotia Fishery Bullftin 81 357-362

Chande A 1 andY D Mgaya 003 The Fishery of Portunus ptiagitus and ~~cies diversity of portunid cmbs along he coasl of Dar es Salaam Tanzania Western lndiln Ocean Journal of Marine Sci~nce 2 75-84

de-Lestang S bull N Hall and I C Poner 2003a Changes in d ensity age composition lind growth rn1e of Pormnus pelagicus in a large embayment in which fis hing pressunS and environmental conditions hnvc been nltcred Journal of Crustacean Biology 23 908-919

-- --- - - middot middot - 2003b Reproductive biology of the blu~ swimmer crab (Ponunus pelagilttS Decapodt Portunidac) in live bodies of water on the west coas1 of Auslralia Fishery Bulletin 101 745-757

DeMartini E E G T D iNardo and H A Williams 2003 Tempornl changes in population density fecundity und egg size o f th~ Hawaiian spiny lobster (Pamtlirumiddot mr1rJ1itwtus) nt Necker Bank north-western Hawa iian Islands Fishery Bulletin 101 22-3 1

Hcruy G W and J M Lyle 2003 The national recreational and Indigenous Fishing Survey Final R eport to the Fisheries research and development Corpornlion and the Fisheries aclion Program Projecc No 1999158 188 pp

I JOHNSil-1 Fl AI REIROOl(TlgtE BIOLOGY Of POII TUNUS ftL~iCl1 20~

Table 2 Mtgtan carapace length CCI) wri~ht egg b~tch weigh t and estimates of fecundity of P pliagirus for elt~rh 5 mm size cla~s I I SE J Data plgtolcd for lovemhltr and February

nrllJt JmTrl Sumhcr of JldllduOJI - -

Me n Cl hnm l ----shy

W~middot1ch1 Ipound ) FJiJ ml~ OoC lJhl (~) Tnc al of crt~ pmiddott iOOivaLJ l

55middot 59 60-64 65-69 70-74 75-79 ---shy - - -

15 17 12 10 6 -

569 (042) 619 (039) 666 1060) 719 (0 39) 766 (027)

132 9 (336) 17558 (~60) 2939 (590) 2 7l82 (461) 33370 (286)

416 (3 6) 50 15 (350)

591 (240) 746(731) 942 (801)

731188 (25 943 ) 66468 (24520)

1081701 (15 120) I 237001 (41 401) 15790 I I cl8260)

of similar sizes in Western Australia (75000-325000 de Lcstang et al 2003b) and India (20000-750000 Sukumaran and Neelakantan 1997) but comparahle to estimates of fecundity for P pela~ icus in Queensland (Shields and Wood 1993) We also found that individual fecundity increased with increasing CL over the size range examined (55-79 mm CL) with the greatest number of eggs per batch carried on the largest female- an observation shared by Sukumaran and Neelakantan (1997) with respect to P pela~icus off the coast of India _ In contrast Kumar et al (2003) and de J-estang et al (2003b) reported that fecundity peaked at approximately 61 mm and 71 mm CL respectively then declined with further increase in size Finally we found no significant temporal difference in the relationship between size of crab (CL) and fecundity while Kumar et al (2003) reported that fecundity increased from October to December after which it declined

Although we can not isolate mechanisms for each of the observed differences in fecundity li sted above biotic and abiotic factors such as water temperature fluctuations growth rate (Prager et al 1990) and the population density and size-structure can influence fecundity in crustaceans (Mohan 1997 DeMartini et al 2003) For example the fecundity of the blue crab Callincctes sapidus (Rathbun 1896) in Chesapeake Bay was estimated to be greater in 1987 than in 1986 an observation attributed to favourable climatic conditions coupled with increased growth rates (Prager et al 1990)

Our estimate for the size at which 50 of female P pelagicus attain maturity in Wallis Lake (i e 46 mm CL)

35

30

~

r

i 25

0 y ~ 20 ~ c 1l 15 E ii

middot~

10

60 70 ec 90

Cosapll(c Jcn~th (mm)

Fig 5 Es1imatcd number o f egg ha1chcs produced during the ob~rved spawning period

was similar to corresponding estimates for females in Shark Bay (45 mm CL Smith et al 2004) and the Peel Harvey and Leschenault estuaries (43 mm CL de Lestang et al 2003b) in Western Australia but much greater than for females in Spencer Gulf South Australia (29 mm CL Xiao and Kumar 2004) This difference may simply reflect inter-regional differences in the biology ofP p elagic-us but may also be attributable to differences in th e selectivitv of the gears used to obtain samples Trap catches are often biased towards large sexually mature crabs resulting in an overestimation of the proportion of mature crabs in each size class and therefore an underestimation of the mean size at maturity (Smith et al 2004) Our estimaJcd mean size at 50 maturity was derived using samples from seine and beam trawls whereas that of Xiau and Kumar (2004) was derived using samples from trap catches Similarly place of capture (eg estuary vs ocean) may bias the estimation of mean size a t maturity of female P pelagicus (de Lestang et al 2003b) For example cmigralion of mature females from estuaries to the ocean might increase the proportion of immature crabs in each size class in the estuary leading to an over estimation of the overall mean size at 50 maturity for estuary-based samples (de Lestang et at 2003b) For this reason crabs used to estimate mean size at 50 maturity during our study were collected in February and March prior to emigration to ocean waters by sexually mature females

Despite the apparent inter-regional differences in feshycundity and size at maturity other aspects of the reproductive biology of P p elagicus in Wallis Lake appear similar to that reported elsewhere For example length of spawning period of P pelagicus appears to be influenced by water temperature with extended spawning observed in waters with higher temperatures (de Lestang et al 2003b) Reproductively mature P pelaRicus of both sexes (includshying ovigerous females) were found in Wallis Lake in all of the 9 months sampled demonstrating their capability for having a lengthy spawning period in south-eastern

Table 3 Index of reproductive potential of P prlagicmiddotus for each 5 mm si ze cla~s from commercial trap catclJCs

~~-~9

Siu cu t CL mm)

~ M-tV 1()14 75-79

of total female catch (A) 2186 329 1 3084 1208 231 ovigerous 1649 1908 2113 855 2 60 Estimated total potenlial

fecundily ( X 100000) 1462 1732 2867 3711 4737 Index of reproductive potential 10000 20637 35454 7273 539 of total egg production B) 1353 2792 4797 984 073 ReprodUlli~ity (BA) 0 62 084 156 081 032

204 JOLIRIgtAL O F CR l STA(FAIgt BIOU)(Y VOl gt11 NO ~ ~0111

Tnhlc 4 Comparative finding~ of the reproduc1 ivc biology of Porrunut pda11icus Location New Soul h Waks NSW) Weslern AusraliH (WA) Queensland (QLD) St)llh Aus1ralia (SA)

Scit utlll pCtdio ic Siu oil mUuri~v Si7c ot Jmuuri1~middot

Lola1ion CM in CL nmmiddot ( M u Cl nun) fcn1ollity IF_ggt- X Hf) 0 -0U)middot cooditiun ~- omiddoti~crous Soorcc

NSW 3H 56 046-178 Nov-Delt Nov -J an Pn~cn l ~ udy WA 38 43 de Lcsang cl al (2003b) WA 42 47 Smith ct al (2004 ) WA 28 37 027-085 Jan-Fch Pnllcr cl al ( 1983) QLD 34 49 024-188 Jun-Mar Aug-Mar Shields and Wood ( 1993) SA 28 49 048- 160 Oci-Apr Smith (19amp2) India 38 47 Sep-Mar Prnsad and T01mpi ( 1953) India 025-075 Jan-Apr Aug-Feh Sukum aran and Ncelakontan

(1997) Egyp1 31 44 075-081 Apr-Sep Mar-Aug RlZek (198)

Australia This concurs with observations indicating that P pelugicus can spawn over several months (up to 10) in other sub-tropical and temperate regions (Potter et al 1983 de Lestang et al 2003b) Further during our study ovigerous female s were most prevalent (36) in late springearly summer (November and December) which coincides with observations from estuaries and embayments in temperate south-western Australia (de Lestang et al 2003b)

Female P pelaricus can produce several batches of eggs from a single mating (Meagher 1971) and our estimates of the relationship between CL and number of batches of eggs produced were similar to that reported by de Lestang et at (2003b) Crabs lt 55 mm CL tended to produce only one batch whereas crabs gt 75 mm CL produced up to three batches The greater number of egg batches produced by larger crabs can be explained by their longer interrnolt period between copulation and egg extrusion (de Lestang et al 2003b)

Female P pelagicus in Wallis Lake attain sexual maturity below the current minimum legal CL for retention by commercial and rec1eational fishers of 60 mm The lower fecundity of newly matured females (55-59 mm CL) combined with the small proportion of ovigerous females observed in this size class (Johnson and Gray submitted) means that these sized crabs probably make only a small contribution to the total egg production of the entire population Similarly because of their low abundances the largest sized crabs (75-79 mm CL) probably do not contribute greatly to the estimated total egg production of the population despite their potentially greater overall total fecundity compared with other size classes Egg production in the Wallis Lake population appears to be heavily dependent on crabs between 60-69 mm CL which are subject to the highest level of fishing pressure (Johnson and Gray submitted) Increased fishing effort for or catchshyability of crabs in this size class could potentially result in large reductions in egg production and depending on environmental conditions could lead to reuced levels of recruitment

A possible mechanism to increase the total reproductive output of P pelagicus populations in Wallis Lake might be to increase the minimum legal CL Increasing the current minimum legal CL from 60 mm to 65-70 mm could potentially protect 55-86 of the estimated egg producing females from harvesting and increase total egg production

by 14-34 respectively A legal CL of 70 mm would potentially enable female crabs in the 65-70 mm size class to produce a greater number of egg batches prior to harvesting Such a change would however probably also result in a large reduction in total retained catches in the commercial trap fishery and would impact on the burgeoning recreational fishery in NSW Before any change in the legally retainable size of crabs is implemenshyted further information on growth and mortality and spawner-recruitment relationships would also be required to properly assess the statu s of the P pelagicus stocks of southeastern Australia and their susceptibility with respect to harvesting under s uch a regime

ACKNOWLEDGEMENTS

Professor Don Gartside (Sombern Cros s Univcrsily) provided assistance and guidance throughou the duration of his researc h Thi s study would noc huvc been po~sihle withou1 the ~upport of the commercial fishers in Wallis Llke Cluis Walsh provided cri1icnl comments on 1he d mft manuscript

REFERENCES

Addison J T and D B Bennett 1992 Assessm ent of minimum landing sizes ofthe edible crab Cancer pagurtts L on the east coast of England Fisheries Research 13 67-88

Campbell A aud MD Eagles 1982 Size at maturity and fec undity of rock crabs CalCmiddotebullmiddot irroratus from he Bay of Fundy ~nd souhwestern Nova Scotia Fishery Bullftin 81 357-362

Chande A 1 andY D Mgaya 003 The Fishery of Portunus ptiagitus and ~~cies diversity of portunid cmbs along he coasl of Dar es Salaam Tanzania Western lndiln Ocean Journal of Marine Sci~nce 2 75-84

de-Lestang S bull N Hall and I C Poner 2003a Changes in d ensity age composition lind growth rn1e of Pormnus pelagicus in a large embayment in which fis hing pressunS and environmental conditions hnvc been nltcred Journal of Crustacean Biology 23 908-919

-- --- - - middot middot - 2003b Reproductive biology of the blu~ swimmer crab (Ponunus pelagilttS Decapodt Portunidac) in live bodies of water on the west coas1 of Auslralia Fishery Bulletin 101 745-757

DeMartini E E G T D iNardo and H A Williams 2003 Tempornl changes in population density fecundity und egg size o f th~ Hawaiian spiny lobster (Pamtlirumiddot mr1rJ1itwtus) nt Necker Bank north-western Hawa iian Islands Fishery Bulletin 101 22-3 1

Hcruy G W and J M Lyle 2003 The national recreational and Indigenous Fishing Survey Final R eport to the Fisheries research and development Corpornlion and the Fisheries aclion Program Projecc No 1999158 188 pp

204 JOLIRIgtAL O F CR l STA(FAIgt BIOU)(Y VOl gt11 NO ~ ~0111

Tnhlc 4 Comparative finding~ of the reproduc1 ivc biology of Porrunut pda11icus Location New Soul h Waks NSW) Weslern AusraliH (WA) Queensland (QLD) St)llh Aus1ralia (SA)

Scit utlll pCtdio ic Siu oil mUuri~v Si7c ot Jmuuri1~middot

Lola1ion CM in CL nmmiddot ( M u Cl nun) fcn1ollity IF_ggt- X Hf) 0 -0U)middot cooditiun ~- omiddoti~crous Soorcc

NSW 3H 56 046-178 Nov-Delt Nov -J an Pn~cn l ~ udy WA 38 43 de Lcsang cl al (2003b) WA 42 47 Smith ct al (2004 ) WA 28 37 027-085 Jan-Fch Pnllcr cl al ( 1983) QLD 34 49 024-188 Jun-Mar Aug-Mar Shields and Wood ( 1993) SA 28 49 048- 160 Oci-Apr Smith (19amp2) India 38 47 Sep-Mar Prnsad and T01mpi ( 1953) India 025-075 Jan-Apr Aug-Feh Sukum aran and Ncelakontan

(1997) Egyp1 31 44 075-081 Apr-Sep Mar-Aug RlZek (198)

Australia This concurs with observations indicating that P pelugicus can spawn over several months (up to 10) in other sub-tropical and temperate regions (Potter et al 1983 de Lestang et al 2003b) Further during our study ovigerous female s were most prevalent (36) in late springearly summer (November and December) which coincides with observations from estuaries and embayments in temperate south-western Australia (de Lestang et al 2003b)

Female P pelaricus can produce several batches of eggs from a single mating (Meagher 1971) and our estimates of the relationship between CL and number of batches of eggs produced were similar to that reported by de Lestang et at (2003b) Crabs lt 55 mm CL tended to produce only one batch whereas crabs gt 75 mm CL produced up to three batches The greater number of egg batches produced by larger crabs can be explained by their longer interrnolt period between copulation and egg extrusion (de Lestang et al 2003b)

Female P pelagicus in Wallis Lake attain sexual maturity below the current minimum legal CL for retention by commercial and rec1eational fishers of 60 mm The lower fecundity of newly matured females (55-59 mm CL) combined with the small proportion of ovigerous females observed in this size class (Johnson and Gray submitted) means that these sized crabs probably make only a small contribution to the total egg production of the entire population Similarly because of their low abundances the largest sized crabs (75-79 mm CL) probably do not contribute greatly to the estimated total egg production of the population despite their potentially greater overall total fecundity compared with other size classes Egg production in the Wallis Lake population appears to be heavily dependent on crabs between 60-69 mm CL which are subject to the highest level of fishing pressure (Johnson and Gray submitted) Increased fishing effort for or catchshyability of crabs in this size class could potentially result in large reductions in egg production and depending on environmental conditions could lead to reuced levels of recruitment

A possible mechanism to increase the total reproductive output of P pelagicus populations in Wallis Lake might be to increase the minimum legal CL Increasing the current minimum legal CL from 60 mm to 65-70 mm could potentially protect 55-86 of the estimated egg producing females from harvesting and increase total egg production

by 14-34 respectively A legal CL of 70 mm would potentially enable female crabs in the 65-70 mm size class to produce a greater number of egg batches prior to harvesting Such a change would however probably also result in a large reduction in total retained catches in the commercial trap fishery and would impact on the burgeoning recreational fishery in NSW Before any change in the legally retainable size of crabs is implemenshyted further information on growth and mortality and spawner-recruitment relationships would also be required to properly assess the statu s of the P pelagicus stocks of southeastern Australia and their susceptibility with respect to harvesting under s uch a regime

ACKNOWLEDGEMENTS

Professor Don Gartside (Sombern Cros s Univcrsily) provided assistance and guidance throughou the duration of his researc h Thi s study would noc huvc been po~sihle withou1 the ~upport of the commercial fishers in Wallis Llke Cluis Walsh provided cri1icnl comments on 1he d mft manuscript

REFERENCES

Addison J T and D B Bennett 1992 Assessm ent of minimum landing sizes ofthe edible crab Cancer pagurtts L on the east coast of England Fisheries Research 13 67-88

Campbell A aud MD Eagles 1982 Size at maturity and fec undity of rock crabs CalCmiddotebullmiddot irroratus from he Bay of Fundy ~nd souhwestern Nova Scotia Fishery Bullftin 81 357-362

Chande A 1 andY D Mgaya 003 The Fishery of Portunus ptiagitus and ~~cies diversity of portunid cmbs along he coasl of Dar es Salaam Tanzania Western lndiln Ocean Journal of Marine Sci~nce 2 75-84

de-Lestang S bull N Hall and I C Poner 2003a Changes in d ensity age composition lind growth rn1e of Pormnus pelagicus in a large embayment in which fis hing pressunS and environmental conditions hnvc been nltcred Journal of Crustacean Biology 23 908-919

-- --- - - middot middot - 2003b Reproductive biology of the blu~ swimmer crab (Ponunus pelagilttS Decapodt Portunidac) in live bodies of water on the west coas1 of Auslralia Fishery Bulletin 101 745-757

DeMartini E E G T D iNardo and H A Williams 2003 Tempornl changes in population density fecundity und egg size o f th~ Hawaiian spiny lobster (Pamtlirumiddot mr1rJ1itwtus) nt Necker Bank north-western Hawa iian Islands Fishery Bulletin 101 22-3 1

Hcruy G W and J M Lyle 2003 The national recreational and Indigenous Fishing Survey Final R eport to the Fisheries research and development Corpornlion and the Fisheries aclion Program Projecc No 1999158 188 pp

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Kancimk P and W f llerrnkind J976 Autumnal reproduction in Punulirultar~u at llirnini Ehama~ Bulletin of Marine Science 26 417-42

Kin~ M 1995 Fisheries Hiology Mscss one nt and Managemenl Fishing News Books lllackwell Science Oxford 34 1 pp

Kumar MS Y S Xiao S Venema and G Hooper 2003 Reproductive cycle of the blutgt swillllller crab PortuWl ptlugicus off soulhem Australia Joumal of the Marine Biolog ical Association of tbe United Kingdom 83 983-994

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Oh C W and L J J~J- 2003 Reproduction and population dynamics of Atmiddot~tr chinrmis (Decapodn Sergestidae) on the western coast or Koren Yellow Sea Journal of Crus tacean Biology 23 827-835

Potter I C P J Chrystal and N R Loneragan 1983 The Biology of the Blue Manna Crab f()171tniS peloRicw in an Australian E~tuary Marine Biology 78 75-85

Prager M H J R McConaugha C M J oncs und P J Geer 1990 Fecundity of Bluc -CTIIb Calineclel sapidus in Chesapeake Bay -Riologicol Statistical and Management Considero~tions Bulletin of Marine Science 46 170-179

Prasad R R nnd PR S Tempi 1953 A contribution to the hiology of the blue swimmer crab Ncplmlus pt1a8icumiddot (Linnaeus) with a note on the Z()(a of Tlwlamita crmato Latreille Joumal or Bombay Natural History Society 51 674-689

Rathbun M J_ 1986 The geous Collinecus Proceedings of thlt United States National Museum XVlll 349-375

Raze~ F A A 1988 Some biological studies on lhe Egyptian crab Portunult pelogicus (Linnaeus 1766) Acta Adriatica 29 133-144

Rothemam D C A Gray D D Johnson and P Lokys 2008 Effects of diet period and tow duration on estuarine fauna sampled with a beam trawl over bare sediment Consequences for designing more reliable and efliciem surveys Estuarine Coastal and Shelf Science 78 179-189

Roy P S R Williams A R Joocl Y~sini P J Gihhs B Coates R J WlSt P R Sluncs J P Hudson and S Nichol 2001 Structure und Funltion of Soutb-e~st Australian F~tuarie~ Es tua rine Coutal and Shelf Science 53 35 1-384

Shields J D und F E 1 Wood 1993 Im pact of para~itcs on th ~ reproduction nnd fecundity lf the blue sand c rdb Portunur p~lofintr from Moreton Bay AuMrnlin Marin Etolog~ Pwglt Serielt 9 2 159shy170

Smith H J112 Blue crobs in South Australia - their statu s potent ial nnd hiollgy South Australiu Fishing Council Adelaide Australia (gt

6-9 Smith K D N G Hall S d~ Lcstang und I C Potter 2004 Potential

bias in e~timatcs of the size of maturity of crahil derivecl from trap samples lees Journal ofMnrine Science 61 906-91 2

Smith G S and W D Sumpton 1989 Behavior of the commercial sand crab Porwtws peagicu~ (LI at trap entrances Asian Fisheries Science Metro Manila 3 101-113

Sukumaran K K and B Ncclakantan 1997 Sex ratio fecundity and reproductive potential in two marine portunid crabs Portwws (Portwws) ltOIIIuinoltgtntus (Hcrhst) and Ponum1s (Porwws) p~loJiicus (Linnaeus) along thr Karnatako Coast Indian Journal of Marine Sciences 26 43 -48

- -- --- 1998 Maturation process and reproductive cyelt in two marine crabgt Portum1r (Porwnus ) smoguinol~11rus (Herbst) and Porlunus (lorrunus) pela~icus (Linna~us) olon lht Karnatnka eoa5L Indian Journal of Fisheries 45 257 -264

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growth of the commerc ial sand crab Portunult ptlogicu (L) in MoretOn Bny Qu~ocnsland Asian Fisheries Science 7 103-113

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RECEIVED 8 August 2008 AccEPnlo 29 June 2009