,.^'' 



in the summer compared to spring. Although the effect on 

 catch rates is difficult to measure, the loss of decoys shows 

 that predators could reduce the catch severely in certain 

 areas. 



Fish enmeshed in nets fight to break loose. Their 

 struggles increase the lactic acid in their bodies, and high 

 levels may cause death. Biochemists in 1965-66 examined 

 the possible physiological stress caused in salmon by capture, 

 tagging, and forced exercise. Maturing sockeye salmon, 

 captured principally with longlines and purse seines in 

 Bristol Bay and near the eastern Aleutian Islands, were 

 tagged and held in shipboard tanks. Immature fall chinook 



FIGURE 14.— Floating enclosure at Bowman Bay for gill net 

 experiments under controlled conditions. Marked salmon were 

 exposed to gill nets in the larger area. Those that escaped 

 from nets werd transferred to the smaller area at left end and 

 held with noncxposed control fish. 



Sea lions, seals, sharks, and birds feed on salmon en- 

 meshed in gill nets (fig. 15), but how they affect the catch 

 rates is unknown. During the spring and summer cruises 

 of 1968, freshly frozen salmon were attached to cork and 

 lead lines of gill nets as decoys for predators. In the spring, 

 after albatross were found feeding on salmon fastened at 

 the surface, the decoys were fastened deeper to more nearly 

 simulate fishing conditions. More than twice as many decoys 

 were missing when nets were hauled in the summer (67 per- 

 cent) than in the spring (29 percent). Losses were highest 

 from sets where sea lions were observed along the nets; they 

 were higher within 100 miles of shore (spring 48 percent, 

 summer 82 percent) than beyond 100 miles (spring 17 per- 

 cent, summer 39 percent) . Higher total losses in summer 

 were partly the result of more frequent fishing near shore 







FIGUKE 15.-A fur seal finds a ready-made banquet of a salmon 

 taken from a gill net. Net floats in foreground (and weights 

 under water) hold the net vertical. 



12 — 



