756 



Fishery Bulletin 101(4) 



in the sampling sites in Shark Bay, 0.6 crabs/100 m'-, than 

 those in Cockburn Sound and Koombana Bay, 2.80 and 2.94 

 crabs/100 m-, respectively. The mean density in Shark Bay 

 was also far lower than those recorded in the Leschenault 

 and Peel-Harvey estuaries between the middle of spring 

 and middle of autumn, when P. pelagicus colonizes estu- 

 aries (Potter et al., 1983; Potter and de Lestang, 2000). 

 Furthermore, commercial or recreational fishing pressure 

 (or both), which leads to a reduction in CWgy's at maturity 

 in the spiny lobster (Polovina, 1989), is far greater for 

 P. pelagicus in the southern bodies of water than in Shark 

 Bay (Bellchambers''). Recent work with microsatellite 

 DNA has also shown that the assemblages of P. pelagicus 

 in Shark Bay are genetically distinct from those in more 

 southern bodies of water, such as Cockburn Sound and the 

 Peel-Harvey Estuary (Chaplin et al.^). 



The marked differences between the CWjq's at maturity 

 for P. pelagicus in Shark Bay and bodies of water farther 

 south emphasize the need for managers to take into ac- 

 count this type of variation when determining a minimum 

 legal carapace width (MLCW) for capture. However, the 

 current MLCW for P. pelagicus in Western Australia, 

 127 mm, is well above even the CW^^ for this species at 

 maturity in Shark Bay. 



The prevalence of ovigerous females did not peak sharply 

 at any time of the year in Shark Bay, whereas ovigerous 

 females were found predominantly during spring and 

 summer in Cockburn Sound and Koombana Bay. Moreover, 

 the mean monthly gonad weights of a female P. pelagicus 

 of standard carapace width lay within a relatively narrow 

 range of 0.9 to 1.8 g in Shark Bay, whereas they rose to a 

 sharp peak of about 5 g in spring and fell below 1 g in some 

 months in Cockburn Sound and Koombana Bay. The trends 

 exhibited by the reproductive variables of female P. pelagi- 

 cus thus provided strong evidence that reproductive activity 

 extends over much or all of the year in Shark Bay, whereas 

 it occurs predominantly in spring and summer in the two 

 southern embayments. The more protracted spawning 

 period in Shark Bay presumably reflects the presence of 

 higher water temperatures throughout the year and in par- 

 ticular during winter and early spring. Such a conclusion 

 is consistent with the results of other studies, which have 

 shown that water temperature influences ovulation and egg 

 development in P. pelagicus and other decapods (Rahaman, 

 1980; Campbell, 1984; Pollock, 1995; Kumar et al.^). 



Fecundity 



The vast majority of previous estimates of the fecundity 

 of crustaceans have been based on the number of eggs 

 borne by females at a particular time which, in the case of 

 multiple spawners, does not take into account the fact that 



■' Bellchambers, L. 2002. Personal conimun. Fisheries West- 

 ern Australia, WA Marine Research Laboratories, West Coast 

 Drive, Waterman, 6020, Perth, Australia. 



5 Chaplin, J., E.S.Yap.E.Sezmis.andl. C.Potter. 2001. Genetic 

 (microsatellite) determination of the stock structure of the blue 

 swimmer crab in Australia. FRDC project 98/1 18. 84 p. Mur- 

 doch University, South Street, Murdoch, 6150, Perth, Australia. 



larger crabs can produce two or more batches of eggs within 

 a spawning period. The few previous attempts to obtain the 

 total fecundity of crustaceans have involved tracking the 

 number of batches of eggs borne by particular individuals 

 at different times (e.g. Chubb et al.^). The advantage of 

 the approach developed during the current study is that 

 it uses a combination of batch fecundity and an estimate 

 of the number of batches produced during the spawning 

 period by female P. pelagicus of different carapace widths 

 to determine the relationship between the total fecundity 

 and body size of this species in a given population. Because 

 the older crabs have a far longer intermolt period between 

 copulation and egg extrusion than younger crabs, i.e. eight 

 versus four months, they have a far greater amount of time 

 to accumulate the energy reserves required to produce 

 eggs. This difference accounts for the greater number of 

 egg batches produced by larger than small crabs. 



Acknowledgments 



Thanks are expressed to many colleagues and friends, 

 and particularly R. Melville-Smith, D. Fairclough, M. 

 Pember, T Linke, M. Travers, and W. White, who assisted 

 with sampling. Our thanks are also expressed to the three 

 anonymous referees for their constructive criticisms. Fund- 

 ing was provided by the Australian Fisheries Research and 

 Development Corporation and Murdoch University. 



Literature cited 



Anonymous. 



2000. FAO yearbook. Fisheries statistics. Capture produc- 

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 Campbell, G. R. 



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 Campbell, A., and D. G. Robinson. 



1983. Reproductive potential of three American lobster 

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1990. Interpretable statistical tests for growth comparisons 

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