Weise and Harvey: Impact of Zalophus caltfornianus on salmon fisheries 



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1969 commercial and sport salmon season. Miller et al. 6 

 reported that in 1981 sea lions took 3.0% of the legal 

 catch during commercial salmon activities, and Beeson 

 and Hanan 1 found that sea lions took 159r of the legal 

 catch in commercial fisheries in 1995. In Monterey Bay 

 in 1997, 12.5% of the legal catch was taken by sea lions, 

 71.1% in 1998. and 11.1 % in 1999. 



Predation levels in the CPFV fishery have increased 

 by at least 8% since 1983, and approximately 3% since 

 1995. Miller et al. 6 reported predation rates of 5.2 % 

 for the CPFV legal catch in Monterey Bay, and Beeson 

 and Hanan 1 reported predation rates of 10.5 % of the 

 legal catch for the recreational fishery in 1995 (CPFV 

 and private skiff combined). In Monterey Bay, 13.7 % 

 of the legal catch was taken by sea lions in 1997, 26.3 

 % in 1998, and 2.5 % in 1999. 



In the skiff portion of the recreational salmon fish- 

 ery, predation of the legal catch has increased by at 

 least 26% since 1983, and 17% since 1995. Miller et al. 6 

 reported predation levels of 1.4% on the legal catch for 

 skiff fisheries in Monterey Bay, and Beeson and Hanan 1 

 reported predation levels of 10.5% on the legal catch for 

 the 1995 recreational fishery season (CPFV and private 

 skiff combined). In Monterey Bay, predation on the le- 

 gal catch was 27.7% in 1997, 31.0% in 1998, and 5.1% 

 in 1999. Skiff fishermen typically fish in large groups 

 called "the fleet." Sea lions had a greater probability 

 of getting a hooked salmon when there were greater 

 numbers of hooks in the water; therefore, sea lions 

 most likely target a fleet of fishing boats. Skiff fisher- 

 men caught fewer fish than did commercial or CPFV 

 fishermen, but lost a proportionally greater number of 

 fish to sea lions. 



The greatest levels of sea lion predation in commer- 

 cial and recreational fisheries occurred in spring when 

 the greatest numbers of adult male sea lions were mi- 

 grating south to breeding rookeries in southern Cali- 

 fornia and Baja California, Mexico. In 1997 and 1999, 

 predation levels dropped significantly in June and July 

 following a high level in May, corresponding to de- 

 clines in numbers of sea lions in Monterey Bay as males 

 headed southward to breeding colonies (Weise, 2000). 

 In 1998, loss of catch to sea lions was greatest in May; 

 slight decreases occurred in percentages of fish taken 

 during June and July because the decline in numbers 

 of adult male sea lions during the breeding season was 

 far less and shorter in duration than in June and July 

 of 1997 and 1999. 



We concluded that adult male sea lions took the ma- 

 jority of hooked fish because animals identified taking 

 fish during boat surveys were almost exclusively adult 

 male sea lions and percentages of fish taken by sea 

 lions were less during the sea lion breeding season. 

 Briggs and Davis (1972), Miller et al. 6 , and Beeson 

 and Hanan 1 also reported greater numbers of salmon 

 taken in spring (the nonbreeding season) in the com- 

 mercial and recreational salmon fisheries. Loss of catch 

 to sea lions would most likely be greater during the 

 northward migration of male sea lions because greater 

 numbers of animals would be in the Monterey Bay re- 



gion; however, fishing effort declined sharply and the 

 commercial season was closed during a portion of that 

 period in 1997. 



Sea lions took most salmon below the water's surface 

 in the commercial fishery and both at and below the 

 surface in recreational fisheries. Commercial fisher- 

 men lost fish below the surface as a result of the large 

 amount of trolling gear used, and the time required 

 for pulling gear when fish were hooked. Commercial 

 fishermen typically need five to 10 minutes, and as 

 long as 20 minutes to pull hooked fish from the water, 

 allowing ample time for sea lions to take fish. Before 

 the 1994 amendments to the MMPA, sea lions were 

 legally killed for endangering commercial catches, gear, 

 and fishermen, and are still at risk for harassment for 

 taking fish off hooks today. Consequently, most fish in 

 the commercial fishery are taken below the surface and 

 consumed at the surface some distance from the boat 

 because of a combination of the time required to bring 

 a fish to the surface and the threat of harassment. Less 

 gear and perhaps different types of gear that can bring 

 a fish to the surface faster may reduce the number of 

 takes below the surface and overall predation levels. In 

 recreational fisheries, fishermen typically used rod and 

 reel, which allowed fish to be reeled in within minutes. 

 It has been illegal for recreational fishermen to harass 

 or kill sea lions since the passage of the MMPA in 1972; 

 therefore it is not uncommon to see sea lions swimming 

 next to recreational boats in close pursuit of fish that 

 are pulled from the water or that are taken just before 

 they are netted. 



Increased depredation levels in the commercial and 

 recreational salmon fisheries in 1998 were most likely 

 the result of the large El Nino Southern Oscillation 

 (ENSO) event that occurred during 1997-98. The 1997- 

 98 ENSO event created large anomalies in physical and 

 biological conditions in the coastal waters off Califor- 

 nia resulting in above average seasonal norms in sea 

 surface temperatures and large displacements in the 

 distribution of many fish species (Lynn et al., 1998). 

 A combination of factors during the large ENSO event 

 contributed to increased predation on salmon catches. 

 These factors included shifts in sea lion prey composi- 

 tion, decreases in sea lion prey populations, increases in 

 number of sea lions in the region, decreases in fishing 

 effort by commercial and recreational salmon fishermen, 

 and decreases in number of salmon landed. Intensified 

 depredation of catch has been reported during past 

 ENSO events by commercial gillnet fishermen (Beeson 

 and Hanan 1 ). 



Increased intensity in depredation of hooked fish by 

 pinnipeds during ENSO events may be indicative of 

 decreased foraging success resulting from shifts in prey 

 availability and abundance. A significant shift in sea 

 lion diet occurred between 1997 and 1998 from market 

 squid, northern anchovy, and Pacific sardine to Pacific 

 sardine and anchovy (Weise, 2000). Concurrently, com- 

 mercial catches of squid, hake, and herring, common 

 prey of sea lions, were low or virtually nonexistent from 

 the fall of 1997 through the summer of 1998 (CalCOFI, 



