FISHERY BULLETIN: VOL. 71. NO. 3 



Table 12. — Decoy loss rates in relation to distance from shore, spring and summer 



1968-70. 



Total 



89 1,724 



> 145 km from shore 



744 



56.9 



91 



'Potential predators or carrion eaters include: fur seal, sea lion, albatross, shark, porpoise. 



Table 13. — Numbers of salmon marked and observed for 

 varying periods of time for sets far offshore (> 145 km). 



' Number of possible observations for time period indicated in 

 parentheses. 



is evidence that sea lions rob salmon from gill 

 nets and trolling gear (Pike, 1958; Thorstein- 

 son, Nelson and Lall, 1961) and cause damage 

 to gear. Furthermore, some authors (Mathisen, 

 1959; Tikhomirov, 1964) feel that sea lions 

 may be attracted to areas where fishing boats 

 are operating. 



During our experimental gillnetting in the 

 central Aleutians over a number of years, sea 

 lions have been observed around gill nets 

 much more frequently at inshore (within 145 

 km) than at offshore stations (Table 12). Dur- 

 ing studies of predation (French et al., 1970, 

 1971, 1972) in which frozen "decoy" salmon 

 were tied to the nets when they were set and 

 the numbers remaining counted at haul, the 



percentage loss of decoys was smaller at dis- 

 tances greater than 145 km than at stations 

 closer to shore (26% vs. 57% , see Table 12). 



These studies, though, were not conclusive 

 when applied to the dropout data. For example, 

 the mean decoy loss rate for all stations (44% ) 

 was similar to the average loss (40.5%) of 

 salmon marked in gill nets (Tables 10, 12). In 

 addition, the decoy loss rate beyond 145 km 

 (26% ) was similar to the dropout loss (30% ) for 

 the same area (Tables 12, 13). 



As French et al. (1970, 1971, 1972) pointed 

 out, the results of the decoy studies are dif- 

 ficult to relate to actual gill net catches. For 

 example, the decoy fish normally were exposed 

 to predators and carrion eaters from the time 

 the gear was set (at about 2000 h) until com- 

 pletion of haul at about 1000 h, whereas sal- 

 mon are not normally caught in gill nets on the 

 high seas until dark and would, therefore, be 

 subjected to predation for fewer hours than the 

 decoy fish. The food preference of some ani- 

 mals may also vary between the dead decoy fish 

 and the live gill net-caught salmon. Percent- 

 ages of decoy fish removed by these animals 

 therefore, may not be directly comparable to 

 predation upon fish captured by gill nets. The 



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