Brodziak and Hendrickson: Environmental effects on survey catches of Loligo pealei and lllex illecebrosus 



23 



the other hand, squid population size and its vari- 

 ance could be calculated on the basis of only day- 

 light tows in the standard manner. In this case, 

 roughly 1/3 of the available survey data would be 

 used owing to the exclusion of time zone I and II tows. 

 As a result, some survey strata would be under- 

 sampled and precision would be lower. In general, 

 the trade-off between bias due to diel correction and 

 loss of precision due to use of only daylight tows 

 warrants further study. 



Differences between L. pealei and /. illecebrosus 

 catches by depth suggest that the stratification of 

 the NEFSC bottom trawl survey, which was designed 

 to sample groundfish populations, is appropriate for 

 both species. Differences in L. pealei and /. 

 illecebrosus catches by temperature imply that pre- 

 ferred temperature ranges likely exist for both spe- 

 cies within the survey region. However, temperature 

 would not be a useful stratification variable for analy- 

 sis of squid catches because temperature strata are 

 dynamic and would fluctuate each year and because 

 such a variable would lead to overstratification given 

 the current depth and geographic stratification of the 

 NEFSC survey. Regardless of how temperature af- 

 fects survey catches of squids, the growth, recruit- 

 ment, and abundance of L. pealei and /. illecebrosus 

 can be expected to vary with ocean temperature re- 

 gime (e.g. Dawe and Warren, 1993; Brodziak and 

 Macy, 1996) because both are ecological opportun- 

 ists with high, intrinsic population growth rates. 

 Understanding how environmental factors, such as 

 temperature, influence the productivity and distri- 

 bution of squid stocks remains an important topic 

 for fisheries research and management. 



Acknowledgments 



We thank the Captains, crew, and scientific staff of 

 the RV Albatross TV and RV Delaware II for their 

 dedicated efforts to survey fishery resources which 

 provided the data for this study. We also thank F. 

 Serchuk, L. Jacobson, and three anonymous reviewers 

 for their helpful comments on the draft manuscript. 



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