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Fishery Bulletin 101(4) 



in part, differences in such features as genetic 

 composition and density, there is a strong overall 

 tendency for the size at maturity of this crustacean 

 to be inversely related to water temperature (Pillai 

 and Nair, 1971; Jones and Simons, 1983; Polovina, 

 1989; Dugan et al., 1991; Miliou, 1996; Somerton 

 and Donaldson, 1996; Fisher, 1999). 



Estimates of the fecundity of crabs have typically 

 been based on the number of eggs in a single batch 

 of eggs (e.g. Potter et al., 1983; Melville-Smith, 

 1987; Ingles and Braum, 1989). However, such an 

 approach does not take into account the fact that 

 female crabs often produce more than one batch of 

 eggs during a spawning season (Van Engel, 1958; 

 Pillai and Nair, 1971; Campbell, 1984). 



The aims of this study were as follows. 1) 

 Compare the results of three methods directed 

 at determining whether male P. pelagicus have 

 attained maturity and elucidate whether each 

 method produces reliable results. 2) Compare 

 aspects of the reproductive biology oi P. pelagicus 

 in two estuaries and two marine embayments in 

 temperate Australia with those of this species in 

 a large marine embayment in a much warmer 

 and more northern subtropical environment. 

 Particular emphasis will be placed on comparing 

 the size at maturity of both sexes and the periods 

 during which ovigerous females are present, and 

 on proposing reasons for the significance of any 

 differences between the assemblages in these five 

 bodies of water 3) Use the data collected for one of 

 the marine embayments to determine the age and 

 time of year at which P. pelagicus becomes mature 

 and develop a method for deriving the annual fe- 

 cundity that takes into account the fact that the 

 larger individuals of this species are believed to 

 produce more than one batch of eggs in a spawn- 

 ing season. 



 25 S 



Indian Ocean 



30 S 



Cockburn Sound 



Peel-Harvey Estuary , 



Leschenault Estuary 1 . >- 

 Koombana Bay 



110E 



120 E 



Figure 1 



Map showing locations of the five bodies of water in which Portunus pelagi- 

 cus was sampled on the west coast of Australia. The map of Australia (insert 

 top right) shows the location (box) of the five bodies of water, and the map 

 of the lower west of Australia (insert bottom left) shows the location of the 

 four bodies of water sampled in this region. 



Materials and methods 



Sampling regimes 



Up to 100 Portunus pelagicus were collected monthly for 

 two years from the Leschenault Estuary (May 1997-April 

 1999), Koombana Bay, and Cockburn Sound (June 1998- 

 May 2000), for three years from the Peel-Harvey Estuary 

 (May 1995-April 1998), and bimonthly for two years from 

 Shark Bay (July 1998-May 2000). The first four bodies of 

 water are located on the lower west coast of Australia, 

 approximately 800 km to the south of Shark Bay (Fig. 1). 

 The nearshore, shallow waters in each of these bodies of 

 water (water depth <1.5 m) were sampled for P. pelagicus 

 by using a 21.5-m seine net with a bunt of 3-mm mesh; 

 whereas offshore deeper waters were sampled by employ- 

 ing a small otter trawl net with a codend of 25-mm mesh 

 and crab traps consisting of either 12- or 76-mm mesh (see 

 Potter and de Lestang, 2000 for further details of the nets 

 and traps). The mean water depths at the deeper offshore 



sites of the above five bodies of water were 3, 9, 19, 3, and 

 10 m, respectively. The water temperature at the bottom 

 of the water column at each site was recorded on each 

 sampling occasion. 



Measurements and changes at puberty 



The carapace width (CW) of each crab, i.e. the distance 

 between the tips of the two lateral spines of the carapace, 

 was measured to the nearest 1 mm. The length and height 

 of the propodus of the largest cheliped, the length of the 

 merus of the second walking leg, and the length of the pri- 

 mary pleopod of each male crab in Cockburn Sound and 

 Shark Bay were measured to the nearest 0.1 mm. Because 

 the relationship between the length of the dorsal propo- 

 dus of the largest cheliped and the width of the carapace 

 showed the greatest change over the size range of male 

 crabs, that structure was chosen for allometric analysis to 

 determine the size at which males become morphometri- 

 cally mature. 



