FISHERY BULLETIN: VOL. 84, NO. 4 



1972; Wilder 1977). King and Moffitt (1984) also 

 argue for dioecy in this species based upon relative 

 changes in the morphology of the appendix 

 masculina. 



Evidence now exists to suggest that the sex ratio 

 of if. laevigatus undergoes a seasonal change (Table 

 4), although the reasons for this are at present 

 unknown. A biological alteration in population struc- 

 ture of this order seems unlikely. Rather, the rela- 

 tively high catch of females during the December- 

 January period may be due to seasonal changes in 

 catchability or vulnerability of one or both sexes to 

 the traps. Alternatively, the spatial dispersion of H. 

 laevigatus may depend on sex. If males and females 

 are spatially segregated, the high proportion of 

 females in the December-January sample may have 

 been due to small sample size (N = 207). 



We have also shown that sex ratio depends strong- 

 ly on the depth sampled (Table 5), with diminishing 

 representation of females as depth increases. This 

 spatial heterogeneity between the sexes may be due 

 to directed movements. Based on size trends of 

 females we conclude that they recruit to deeper 

 water and subsequently migrate to shallower water. 

 We have no evidence for similar movement of males. 



Studies by King (1983) on Pacific Heterocarpus 

 spp. showed cyclic migrations in these shrimps, sug- 

 gesting that depth distribution may change season- 

 ally, with an annual migration up and down the slope 

 of the sea floor. The data presented in Figure 5 in- 

 dicate that mature H. laevigatus in Hawaii do 

 migrate seasonally, demonstrating distinct shifts in 

 the depth distributions of both sexes during the 

 reproductive season. Because this result is con- 

 founded by what may be a location effect, however, 

 we view them as preliminary and in need of further 

 confirmation. King (1983) also reported that Hetero- 

 carpus spp. were found in stomachs of tuna in Fiji, 

 indicating perhaps some type of vertical migration 

 in the water column. 



King (1985), based on work completed in Fiji, ex- 

 amined the question of iteroparity and semelparity 

 in several genera of pandalid shrimp (Plesionika, 

 Saron, Parapandalus, and Heterocarpus). Based on 

 the difference between length at sexual maturity 

 and maximum length, he concluded that shallow- 

 water species (e.g., H. ensifer) are semelparous. He 

 states that deepwater Heterocarpus spp. "have an 

 extended reproductive lifespan, the length of which 

 may be taken to indicate the number of spawnings." 

 We conclude, based on the relative size-frequency 

 distributions of males and females during peak and 

 postreproductive seasons, that both sexes survive 

 well after reproducing— evidence in favor of itero- 



parity. Although a high mortality of shrimp follow- 

 ing the breeding season would be evidence consis- 

 tent with a semelparous life history, it is not a 

 sufficient result to prove it. This is because each 

 female, before dying, could have sequential multi- 

 ple clutches during the October-February ovigerous 

 period. Nonetheless, good survival oiH. laevigatus 

 females after carrying eggs (Fig. 6) is indicative of 

 iteroparous reproduction. 



The regression technique of Wetherall et al. (in 

 press) produced estimates of the ratio of mortality 

 to growth coefficient of 2.9 and 4.3 for females and 

 males respectively. Moffitt and Polovina (fn. 5), 

 using similar methods, estimated L m = 55.2 mm 

 CL and ZIK = 2.5 for combined male and female 

 samples of H. laevigatus from essentially unfished 

 stocks in Guam and the Marianas. Ralston (1986) 

 also reported that the ZIK ratio of an unexploited 

 population of H. laevigatus at Alamagan in the 

 Marianas was about 2.0. The differences between 

 estimates may therefore relate to differences in 

 levels of exploitation. Moreover, the higher mortal- 

 ity rate of male shrimp when compared with females 

 (1.51 versus 0.73 yr _1 ) may explain the somewhat 

 biased sex ratio in favor of females. 



ACKNOWLEDGMENTS 



We acknowledge the help of the fishing vessels 

 Easy Rider, Easy Rider Too, and Mokihana. Special 

 thanks go to Jack Klein of the Mokihana crew for 

 his collection of material. Also, we thank Robert 

 Richlynski and Patricia M. Van Nuis for their 

 technical help during the collection of data. 



LITERATURE CITED 



Clarke, T. A. 



1972. Exploration for deep benthic fish and crustacean 

 resources in Hawaii. Univ. Hawaii, Hawaii Inst. Mar. Biol. 

 Tech. Rep. 29:1-18. 

 BMDP. 



1977. BMDP Biomedical Computer Programs, P-Series. 

 Univ. Calif. Press, Los Ang., 880 p. 

 Department of Land and Natural Resources. 



1979. Hawaii fisheries development plan. Department of 

 Land and Natural Resources, State of Hawaii, 297 p. 

 Gallucci, V. F., and T. J. Quinn II. 



1979. Reparameterizing, fitting, and testing a simple growth 

 model. Trans. Am. Fish. Soc. 108:14-25. 



Gooding, R. M. 



1984. Trapping surveys for the deepwater caridean shrimps, 

 Heterocarpus laevigatus and H. ensifer, in the Northwestern 

 Hawaiian Islands. Mar. Fish. Rev. 46(2): 18-26. 

 Gunderson, D. R., P. Callahan, and B. Goiney. 



1980. Maturation and fecundity of four species of Sebastes. 

 Mar. Fish. Rev. 42(3-4):74-79. 



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