Table 14. — Summation of ordinate heights of four tnesh 

 selection curves, chum salmon, 1959 



salmon. In 1957 and 1959 the corrected catches 

 increased at 44 cm. and 47 cm. and decreased at 

 53 cm. to 59 cm. As with sockeye, the mode of 

 the large chum salmon shifted to smaller fish when 

 adjusted for selectivity. 



SELECTIVITY COMPARED FOR THE 

 THREE SPECIES 



The catch efficiency of the combined mesh sizes 

 was compared for pink, sockeye, and chum salmon 

 (fig. 10). Curves were given for sockeye and chum 

 salmon ranging in length from 29 cm. to 62 cm. 

 and for pink salmon from 38 cm. to 56 cm.; these 

 covered 98 percent of the samples. Chum and 

 sockeye curves are similar and show a dip in catch 

 efficiencv at 44 cm. and 47 cm., resulting from the 



38 44 50 56 



FORK LENGTH (CM.) 



62 



68 



32 



38 44 50 56 



FORK LENGTH (CM) 



62 



Figure 10. — Comparison of catch efficiency of combined 

 mesh sizes on pink, sockeye, and chum salmon, 1957 and 

 1959. 



Table 15. — Adjustment of the 1959 catches of chum salmon 

 for effect of gill net selectivity 



Figure 9. — Length frequency distribution of chum salmon 

 adjusted for effect of Rill net selectivity, 1957 and 1959. 



Note.— Length class 71 cm. was omitted. 



lK-inch gap between the Zy 4 - and 4^-inch mesh 

 sizes. Both curves show peak catch efficiency at 

 56 cm. and 59 cm. The mode for sockeye is about 

 56 cm., for chum about 57 cm. The pink salmon 

 curve shows peak catch efficiency at 53 cm. and 

 lowest catch efficiency at 41 cm. 



388 



U.S. FISH AND WILDLIFE SERVICE 



