LENARZ and ADAMS: SOME STATISTICAL CONSIDERATIONS OF TRAWL SURVEYS 



a 



LO 

 1-4 



l_) 



LlI 



a 



Q. 

 Ll. 



a 



o 



2: 



B.O 



7 .0 



6.0 



5 .0 



4 .0 



° St>nPLlNG sreoTEGv 1 



' SOnPLlNO STROTEOV 2 



SOriPLlNG STBOTEOV 3 



^ SOnPLING STROTEGV 4 



Figure 3. — Comparison of precision-density 

 curves of four different sampling strategies 

 for Sebastes aleutianus: ll Three trawls/d 

 with gear at depth for 2.1 h, 2) four trawls/d 

 with gear at depth for 1.2 h, 3) five trawls/d 

 with gear at depth for 0.5 h, and 4) six trawls/d 

 with gear at depth for 0.3 h. 



20 .0 



40.0 60 .0 BO .0 iOO .0 



DENSITY ( NUnBEPS ^Kh . I 



120.0 



which to focus sampling strategies. For rockfish, 

 these are likely to be high density, highly aggre- 

 gated species. Generally, in sampling strategies 

 for these species, the effects of sample element size 

 would be unimportant. Increases in sample size 

 would be much more important in terms of in- 

 creased precision; however, increases in sample 

 size would have to be fairly large to make a 

 significant difference. 



ACKNOWLEDGMENTS 



We owe considerable thanks to Candis Cooper- 

 rider of the Tiburon Laboratory for writing com- 

 puter programs for the study. Reviews by N. 

 Abramson (Southwest Fisheries Center Tiburon 

 Laboratory), T. Foin (University of California at 

 Davis), D. Gunderson (University of Washington), 

 D. Kimura (Washington Department of Fisheries, 

 Seattle), J. Zweifel (Southwest Fisheries Center 

 La Jolla Laboratory), and two anonymous referees 

 resulted in a number of useful suggestions. 



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