Weise and Harvey. Impact of Zalophus califormanus on salmon fisheries 



695 



Valley chinook salmon population went from a low of 

 approximately 1.4% during a non-ENSO year to an 

 estimated 6.2% during an ENSO season. High harvest 

 levels coupled with high natural depredation of salmon 

 during an ENSO year could be devastating for the Cen- 

 tral Valley Chinook salmon population. Further, when 

 sea lions take fish in the fishery, fishermen continue to 

 fish to replace depredated fish, further impacting the 

 salmon population. Hooked salmon lost to sea lions are 

 losses to the population and need to be considered when 

 determining allotments, quotas, and area closures. To 

 better estimate impacts of sea lion predation on the 

 CVI, concurrent studies of sea lion and salmon fishery 

 interactions and sea lion food habits need to be conduct- 

 ed along the entire Central California coast, including 

 Half Moon Bay, San Francisco Bay, and the Farrallon 

 Islands. Sea lions are only one of many natural preda- 

 tors of commercially important fish species. Identifying 

 other natural predators and assessing their impact on 

 prey populations is difficult but necessary for effective 

 fisheries management. 



It is likely that only a small proportion of the sea lion 

 population, particularly adult males, were responsible 

 for salmon taken off hooks in salmon fisheries. Percent- 

 ages of fish taken off the hook declined in all years 

 when adult males moved south during the breeding sea- 

 son in June and July. However, greater percentages of 

 takes occurred in the fisheries in August and Septem- 

 ber when lesser numbers of adult male sea lions were 

 present in the region. On any given fishing day peak 

 numbers of sea lions were counted at haul-out sites 

 from late-morning to early afternoon, which is also the 

 period when most fishing occurred (Weise, 2000). Miller 

 et al. 6 suggested that the total damage to fisheries by 

 California sea lions was not proportional to the number 

 of sea lions in the area. It is likely that takes on a given 

 day in Monterey Bay were repeat occurrences by the 

 same animals. We agree with DeMaster et al. (1982) 

 that a reduction in the number of animals or culling 

 of the population would probably not reduce sea lion 

 depredation levels unless the few animals responsible 

 were identified and removed. Instead, there is a need 

 for nonlethal deterrents to keep sea lions from taking 

 hooked fish in open-ocean fisheries. A change in types of 

 fishing gear, a limit in the amount of gear in the water, 

 use of various harassment techniques, as well as area 

 closures and a tolerance for sea lion predation most 

 likely encompass other possible management options. 



An increasing sea lion population and increased inter- 

 actions with salmon fisheries resulting in salmon and 

 gear losses will certainly affect individual fishermen 

 negatively and possibly California's economy (Beeson 

 and Hanan 1 ). Comparisons of economic losses between 

 years and among studies must consider average fish 

 weight, exvessel price per year, and definitions of fish- 

 ing regions. For example, if greater numbers of fish 

 were lost in a given year but exvessel prices were low, 

 the overall economic impact would be less than during 

 a year when fewer fish were taken but the exvessel 

 prices were high. 



In past studies, all ports in California were surveyed, 

 and impacts were analyzed by port, but these studies 

 encompassed different fishing areas under the same port 

 names. For example, Miller et al. fi estimated annual 

 losses resulting from sea lion interactions in 1980 at 

 $274,000 for California, and an estimated $21,536 for 

 Monterey Bay. It is unclear, however, if these figures 

 included fishing areas south of Monterey, such as Morro 

 Bay, and fishing areas north, such as Half Moon Bay. 

 Beeson and Hanan 1 estimated 86,900 fish or $1,734,000 

 was lost in 1995 because of sea lion interactions, and 

 48,000 fish were taken in Monterey, representing ap- 

 proximately $960,000. Beeson and Hanan 1 included the 

 Port of Princeton in Half Moon Bay in figures reported 

 for Monterey. Therefore, it was not possible to make 

 direct comparisons among studies, but it appears that 

 economic losses per individual fisherman have increased 

 since the 1980s and will probably continue to increase 

 if the sea lion population and interactions with salmon 

 fisheries increase. Assessment of economic impacts of 

 salmon fisheries in Monterey Bay in the present study 

 was limited to gear and fish loss; however impacts are 

 most likely widespread. For example, during the salmon 

 season when interactions with sea lions are great, CPFV 

 operators report that customers will cancel or postpone 

 trips, which decreases the amount of money infused into 

 the local economy from trip expenditures, including hotel 

 stays, restaurants meals, and gas. Estimating the eco- 

 nomic impact of sea lion interactions on the local economy 

 of Monterey Bay was beyond the scope of our study. 



Discussions about the competition between sea li- 

 ons and fisheries tend to arouse controversy because of 

 the complex mix of biological, economic, social, politi- 

 cal, and moral factors involved (Harwood and Croxall. 

 1988). Fishermen claim regularly that their activities 

 are regulated, whereas predation by marine mammals 

 is unrestricted (Harwood, 1992). Although losses in 

 Monterey Bay in 1998 were most likely anomalously 

 large because of ENSO conditions, this anomaly offered 

 little reassurance to those fishermen whose livelihoods 

 were threatened. Growing sea lion populations have 

 undoubtedly intensified competition with fisheries, but 

 greater fishing effort, more sophisticated fish equipment 

 and fisheries methods, and less than rigorous fisheries 

 management is equally responsible. Segments of the 

 American public find marine mammals appealing and 

 demand that populations be protected; whereas other 

 segments demand protection from economic ruin result- 

 ing from marine mammal-fishery interactions. Clearly, 

 demands from both segments of the public must be ad- 

 dressed (Everitt and Beach. 1982). Continued research 

 to assess and refine our understanding of food habits of 

 marine mammals is essential, and incorporating this 

 information into fisheries management is equally impor- 

 tant. When conflicts between fisheries and marine mam- 

 mals are identified, population management strategies 

 and nonlethal deterrent solutions need to be developed. 

 Any management solutions need to consider not only the 

 specific interactions but also the ecosystem as a whole 

 and the viewpoints of all segments of the public. 



