574 



Fishery Bulletin 89(4), 1991 



1988). Additionally, halibut eggs and larvae may be 

 transported parallel to the shore, since a narrow near- 

 shore current with a generally southward surface flow 

 often occurs within 10-20 km of the coast (Tsuchiya 

 1980, Winant and Bratkovich 1981). 



The passive transport of pelagic halibut larvae off 

 southern California is thus influenced by a variety of 

 currents and oceanographic conditions. Our results in- 

 dicate that halibut larvae that encounter warmer 

 waters during transport may settle much sooner than 

 those remaining in colder waters (Fig. 3). Therefore, 

 larvae carried by alongshore currents might eventual- 

 ly settle near the entrances of bays or estuaries due 

 to warmer waters in these areas. Larvae transported 

 offshore during upwelling events would experience 

 lower temperatures (Dorman and Palmer 1981), result- 

 ing in delayed settlement and the possibility of even- 

 tual shoreward transport into shallow coastal or in- 

 shore nursery areas where warm temperatures could 

 stimulate settlement. 



The ability of pelagic larvae of many marine in- 

 vertebrates to delay settlement until an appropriate 

 habitat is available has been well documented (Schel- 

 tema 1974, Doyle 1975). Fish larvae have not common- 

 ly been demonstrated to have this ability, although 

 Victor (1986) reported that bluehead wrasse Thalas- 

 soma bifasciatum can extend the duration of the 

 planktonic larval period after attaining settlement size 

 by reducing growth rate. We found that halibut larvae 

 at 16°C took about a week longer to 50% settlement 

 than larvae reared initially at 16°C and then exposed 

 to 20°C when 1 month old; one individual at 16°C was 

 pelagic 12 days after all larvae had settled at 20 °C 

 (Fig. 3). Although the observed longer period to settle- 

 ment at 16°C vs. 20°C was to some degree a direct 

 growth response to temperature, halibut larvae in 

 colder waters may additionally be capable of delaying 

 settlement for a limited period until encountering the 

 appropriate cue, higher temperatures. This trait would 

 enhance larval halibut survival by increasing the likeli- 

 hood of settlement in warmer inshore areas. 



Acknowledgments 



Valuable laboratory assistance was provided by G. Cad- 

 dell, T. Caro, K. Fujimoto, L. Abbott, M. Larson, and 

 P. Donahue. Thanks to R. Lavenberg and J. Stephens 

 Jr. for their support. Special thanks to J. Petersen for 

 his many helpful comments, and to two anonymous 

 reviewers. This study was funded by the California 

 Department of Fish and Game and the Southern Cali- 

 fornia Edison Company. 



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