624 



Fishery Bulletin 97(3), 1999 



Tanner crab 



Mixed sexes - full model 



Mixed sexes - reduced model 



Mature females 



Snow crab 



Mixed sexes • full model 



50 100 150 



Mixed sexes - reduced model 



150 

 Carapace width (mm) 



Figure 4 



Fitted model and 95'3 bootstrap confidence intervals about the predicted value of 

 net efficiency. For the mixed-sexes categories of both crab species, values of net 

 efficiency are predicted in two distinct ways after fitting the full model ( Equation 1 1 to 

 the data. First, net efficiency was predicted by evaluating both P and P^ terms of the 

 model (top row), based on the assumption that the entry of small crabs into the trawl 

 net through the belly mesh occurs during normal trawl operations. Second, net effi- 

 ciency was predicted by evaluating only the P. term (i.e. setting P^=0), based on the 

 assumption that the entry of small crab through the belly mesh was an expermental 

 artifact caused by adding the auxiliary trawl (second row). 



Acknowledgments 



We thank J. lanelli, S. Syrjala, and D. Pengilly for 

 reviewing the manuscript and offering helpful com- 

 ments, P. Munro for designing the auxiliary trawl, 

 and D. Nichol and J. Hoff for supervising the field 

 experiment. 



Literature cited 



Alverson, D. L., and W. T. Pereyra. 



1969. Demersal fish explorations in the Northeastern 

 Pacific Ocean — an evaluation of exploratory fishing meth- 

 ods and analytical approaches to stock size and 

 yield forecasts. J. Fish. Res. Board Canada 26:1985- 

 2001. 



