60' 



59" - 



58" - 



57* 



56" - 



55" - 



Figure 11. — Distribution of sockeye salmon in eastern Bering Sea and Bristol Bay during spawning migration, showing main 

 migration route. Distribution was determined from results of exploratory fishing. 



«.-(l)'^.) 



where 



R^ = expected number of tag recoveries from the 

 ith fishing district 



R = tag recoveries in total Bristol Bay commer- 

 cial catch 



C = total Bristol Bay commercial catch 



Cj = catch in the ith fishing district. 



For most years, the recoveries from several tagging 

 locations have been grouped for computation of ex- 

 pected recoveries (Table 1). This was done because 

 tagging was often carried out in the same general area 

 or to provide a larger number of recoveries in the 

 analysis. 



Several factors inherent in the commercial fishery 

 could cause the smaller tagged fish to be more 

 vulnerable to capture than untagged fish of the same 

 size. 



Commercial fishing in all districts of Bristol Bay is 

 done entirely with gill nets. Working with Fraser 



River sockeye salmon, Peterson (1954) showed that 

 gill nets of the type and mesh size (13.65-cm stretch 

 measure) used in Bristol Bay were selective for size of 

 fish. Differences in the size composition between the 

 commercial catch and the escapement indicate that 

 the gill nets used by Bristol Bay fishermen are selec- 

 tive for the larger .3 fish' (Mathisen 1971). Apparent- 

 ly, many of the smaller .2 fish are able to pass through 

 the gill nets and escape. 



Ricker (1958) found that fish tagged with plastic 

 disk tags, the type used most frequently in the 

 offshore tagging studies, are more vulnerable to cap- 

 ture by gill nets than untagged fish because the twine 

 of the net catches under the disk. Because of the tag, a 



'The terms .2 and .3 refer to the number of winters a salmon has 

 spent in the ocean. A numeral to the left of the dot indicates the 

 number of winters the fish has spent in fresh water and the numeral 

 to the right of the dot the number of winters in the ocean. Thus a 2.3 

 adult salmon is one which has spent 2 winters in fresh water and 3 

 winters in the ocean and is in its sixth year of life. The use of this 

 method (European method) for designating the age of adult Pacific 

 salmon (marine life only) was proposed by Koo (1962). 



