Table 9. — Catch by mesh size and catch ratio of adjacent 

 mesh sizes, sockeye salmon, 1957 



1 Original catches of the 4H-inch mesh were 3 times as large as shown; 

 they were divided by 3 to equalize fishing effort between mesh sizes. 



Note. — Catch ratios in parentheses were not used. See text. 



tangled rather than gilled. At 56 cm. and 59 cm. 

 the fish in the 3%-inch mesh were mainly snagged 

 rather than gilled. Some fish within the 38-cm. 

 to 53-cm. length range also were snagged or 

 tangled, but the numbers were so small that 

 the linear relation between fish length and log of 

 catch ratio was unaffected. 



The procedure for developing mesh selection 

 curves and a catch efficiency curve for sockeye 



1959 



- UNCORRECTED CATCH 

 CORRECTED CATCH 



26 



32 



38 44 50 56 



FORK LENGTH (CM) 



62 



68 



Figure 6. — Length frequency distributions of sockeye 

 salmon adjusted for effect of gill net selectivity, 1957 

 and 1959. 



salmon followed that for pink salmon. Table 10 

 shows the summation of the ordinate heights of 

 the mesh selection curves for the four mesh sizes. 

 The composite curve was used to adjust for 

 selectivity effect (table 11). 



A comparison of the uncorrected and corrected 

 length frequency distributions of sockeye salmon 

 in 1957 and 1959 shows that the 44-cm. and 47-cm. 

 fish are under-represented, the 53-cm. to 59-cm. 

 over-represented in the uncorrected catches (fig. 6). 

 Over most of the length range, adjustments were 

 quite minor. 



Adjustments for the effect of gill net selectivity 

 changed slightly the shape of the length-frequency 

 distribution curve of sockeye salmon. The 

 length-frequency distributions in 1957 and 1959 

 were bimodal. Mode 1 consisted of small fish 

 (highly abundant in 1959) that had spent one 

 winter at sea. Mode 2 consisted of large fish that 



Table 10. — Summation of ordinate heights of four mesh 

 selection curves, sockeye salmon, 1959 



Table 11. — Adjustment of the 1959 catches of sockeye salmon 

 for effect of gill net selectivity 



Note.— Length class 74 cm. was omitted. 



:;s t) 



U.S. FISH AND WILDLIFE SERVICE 



