Weise and Harvey: Impact of Zolophus califormanus on salmon fisheries 



691 



breeding season of 1997 (P<0.000), whereas in 1998 

 (P=0.158) and 1999 (P=0.358) there was no significant 

 difference. During all three years, surveys were con- 

 ducted on commercial, CPFV, and skiff fisheries during 

 August and September; however, there was little to no 

 salmon fishing effort because of the perceived sea lion 

 problem and because the remaining fishermen targeted 

 albacore tuna or rockfishes (or both). 



Because of the different styles of hook-and-line fishing 

 in the commercial troll and recreational salmon fisheries, 

 sea lions were more likely to take fish below the surface 

 from commercial trollers but to take fish at and below 

 the surface from recreational vessels. In the commercial 

 fishery, according to dockside interviews and onboard 



Commercial 



CPFV 



Skiff 



Figure 5 



Mean catch per unit of effort (mean number offish caught 

 per day! in commercial, commercial passenger fishing 

 vessel (CPFV). and skiff fisheries in Monterey Bay, Cali- 

 fornia, from 1997 to 1999. Error bars indicate one stan- 

 dard error. 



surveys combined, percentages of takes by sea lions 

 below the surface of the water varied throughout the 

 season and were significantly greater than surface takes 

 in 1997 (P=0.001), 1998 (P<0.000), and 1999 (P<0.000; 

 Table 2). In contrast, in the recreational fishery the per- 

 centages of takes by sea lions below the water's surface 

 and at the surface varied by year. During 1997, greater 

 percentages of takes by sea lions occurred at the surface 

 than below the surface on CPFVs (P=0.082) and skiffs 

 (P=0.001; Table 2). Whereas in 1998, significantly great- 

 er percentages of takes occurred below the surface in the 

 CPFV <P<0.000) and skiff fisheries <P<0.000; Table 2). 

 And in 1999, no differences between surface and below 

 surface takes were detected for CPFV (P<0.972) or skiff 

 fisheries (P<0.310); however this lack of significance was 

 likely due to small sample sizes. 



The catch per unit of effort (CPUE: number of fish 

 landed per boat per day) was significantly less in 1998 

 than in 1997 for the commercial (P<0.000), CPFV 

 (P=0.011), and skiff fisheries (P<0.000) in Monterey 

 Bay (Fig. 5). In 1999, significantly fewer fish were caught 

 than in 1998 and 1997 in the commercial (P<0.000) and 

 CPFV (P<0.000) fisheries; however, there was no signifi- 

 cant difference in the skiff fishery. The percentage of the 

 CVI abundance for chinook salmon taken by sea lions 

 from 1997 to 1999 ranged from 1.4% to 6.2% (Table 3). 



From 1997 to 1999, commercial fishermen lost an 

 estimated $22,333-$60,077 of gear, and $224,011- 

 $504,548 worth offish as a result of interactions with 

 sea lions (Table 4). The recreational fisheries lost be- 

 tween $172 and $18,533 worth of gear as a result of sea 

 lion interactions from 1997 to 1999. Estimates of gear 

 and fish loss were extrapolated from observed losses to 

 total losses based on percentages of the fisheries that 

 were sampled. Gear types varied among commercial 



