FISHERY BULLETIN: VOL. 84, NO. 4 



shifted 150 m deeper when the females are ovig- 

 erous. Although the data are not corrected for what 

 may have been differences in fishing effort by depth, 

 it is true that fishing was targeted to depths of max- 

 imum shrimp abundance. Based on these findings, 

 and the results presented in Table 5, our data are 

 consistent with a hypothesis of gradual movement 

 of small females from deep to shallow water, with 

 mature shrimp moving between depths of 550 and 

 700 m in synchrony with the ovigerous cycle of 

 females. 



Growth and Mortality 



Clarke (1972) and King (1983) have suggested that 

 Heterocarpus spp. may breed once and die. Indeed 



the results already presented in Table 4 may be con- 

 sidered consistent with the hypothesis that at least 

 female H. laevigatus are semelparous. To further 

 address this question we examined the size struc- 

 ture of male and female shrimp classified as follows: 

 1) during the latter half of the reproductive season 

 (January-February) and 2) immediately following 

 the reproductive season (March-July). If postrepro- 

 ductive mortality of shrimp was severe, a decrease 

 in the relative abundance of large, breeding adults 

 would be expected as the reproductive season 

 waned. 



The results presented in Figure 6 conflict with this 

 expectation, where it is apparent that the propor- 

 tional representation of large reproductive in- 

 dividuals (>40 mm CL) is actually greater imme- 



20 



15 



10 - 



& 



15- 



10- 



5- 



FEMALES 



MALES 



I 

 10 



20 30 40 



Carapace Length -mm 



60 



Figure 6.— Relative size-frequency distributions of male and female Heterocarpus 

 laevigatus during the peak and postreproductive seasons. The solid line represents 

 the peak season (January-February), males N = 78, females N = 207; the dashed 

 line is based on data collected immediately after the peak season (March-July) males 

 AT = 1,717, females N = 1,675. 



922 



