820 



Fishery Bulletin 88(4), 1990 



relative abundance of females at depth, though the na- 

 ture and extent of such spawning migrations is poorly 

 understood. It is unclear, for instance, whether females 

 spawning nearshore reside nearby at depth and make 

 vertical seasonal migrations to spawn, or whether fe- 

 male lingcod migrate seasonally from the deep offshore 

 trawling grounds to spawn nearshore. Such movements 

 have been widely accepted as fact, though tagging ex- 

 periments to date have failed to confirm a seasonal 

 mass spawning migration (Miller and Geibel 1973). 



An appropriate tagging study design to model coastal 

 lingcod movement will require tagging in both near- 

 shore and offshore areas and the estimation of both the 

 probability of survival as well as the probability of cap- 

 ture across the time-area strata. To separate movement 

 from survival, a minimum of three samples is needed. 

 Iwao (1963) and Arnason (1972) gave models under this 

 scenario, but only for the case with multiple recaptures. 

 These approaches are not applicable to most fisheries 

 tagging studies in which individuals are recaptured 

 once by a commercial or recreational fishery and 

 recovered dead. Potentially more applicable to fisheries 

 tagging studies, Schwarz (1988) and Schwarz and Ar- 

 nason (1990) have extended the traditional exploitation- 

 based models of Brownie et al. (1985) to include tag 

 recoveries over both time and space, and Hilborn (1990) 

 recently provided a general framework for analysis of 

 movement and mortality which incorporates a popula- 

 tion dynamics and movement model using a maximum- 

 likelihood minimization approach. 



In conclusion, this study gives evidence that a compo- 

 nent of the lingcod population at Neah Bay is exposed 

 to fishing mortality from the offshore trawling fleet. 

 Research is needed to yield quantitative estimates of 

 lingcod mixing rates, stratified by sex and size, be- 

 tween the nearshore and offshore fishing grounds. 

 These mixing rates will be essential to establish mor- 

 tality rates by sex and age for the population as a 

 whole, to clarify the collective impact of the nearshore 

 and offshore fisheries on the coastal lingcod population. 



Acknowledgments 



This research was supported by the Washington De- 

 partment of Fisheries and the Federal Aid in Sport 

 Fish Restoration (Wallop-Breaux) Program. Special 

 thanks are due to Donald "Bud" Carleson, skipper of 

 the commercial troUer P«m/ Revere, for his knowledge 

 of lingcod habits and help in capturing lingcod for 

 tagging. 



Citations 



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