685 



Abstract — To assess the impact of 

 California sea lions (Zalophus cali- 

 fornianus) on salmon fisheries in the 

 Monterey Bay region of California, 

 the percentages of hooked fish taken 

 by sea lions in commercial and rec- 

 reational salmon fisheries were esti- 

 mated from 1997 to 1999. Onboard 

 surveys of sea lion interactions with 

 the commercial and recreational 

 fisheries and dockside interviews 

 with fishermen after their return 

 to port were conducted in the ports 

 of Santa Cruz, Moss Landing, and 

 Monterey. Approximately 1745 hours 

 of onboard and dockside surveys were 

 conducted — 924 hours in the com- 

 mercial fishery and 821 hours in the 

 recreational fishery (commercial pas- 

 senger fishing vessels [CPFVs] and 

 personal skiffs combined I. Adult male 

 California sea lions were responsible 

 for 98. 4*5 of the observed depredations 

 of hooked salmon in the commercial 

 and recreational fisheries in Mon- 

 terey Bay. Mean annual percentages 

 of hooked salmon taken by sea lions 

 ranged from 8.5% to 28.6% in the 

 commercial fishery, 2. 2% to 18.36% 

 in the CPFVs, and 4.0% to 17.5% in 

 the personal skiff fishery. Depreda- 

 tion levels in the commercial and 

 recreational salmon fisheries were 

 greatest in 1998 — likely a result of 

 the large El Nino Southern Oscilla- 

 tion (ENSO) event that occurred from 

 1997 to 1998 that reduced natural 

 prey resources. Commercial fishermen 

 lost an estimated $18,031-$60,570 of 

 gear and $225.833-$498,076 worth of 

 salmon as a result of interactions with 

 sea lions. Approximately 1.4-6.2% of 

 the available salmon population was 

 removed from the system as a result of 

 sea lion interactions with the fishery. 

 Assessing the impact of a growing sea 

 lion population on fisheries stocks is 

 difficult, but may be necessary for 

 effective fisheries management. 



Impact of the California sea lion 



{Zalophus californianus) on salmon fisheries 



in Monterey Bay, California 



Michael J. Weise 



James T. Harvey 



Moss Landing Marine Laboratories 



8272 Moss Landing Road 



Moss Landing, CA 95039-9647 



Present address (lor M. J. Weise): Department of Ecology and Evolutionary Biology 



University of California Santa Cruz 



Center for Ocean Health 



100 Shaffer Rd 



Santa Cruz, California 95060 

 E-mail address (for M J Weise): weiseiu'biology ucsc edu 



Manuscript submitted 13 August 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 10 June 2005 by the Scientific Editor. 



Fish. Bull. 103:685-696(2005). 



California sea lions (Zalophus cali- 

 fornianus) interact with almost all 

 commercial and recreational fisheries 

 along the California coast, causing 

 entanglement and damage to fishing 

 gear and loss of catch (Beeson and 

 Hanan 1 ; NMFS 2 ). The prey of these 

 pinnipeds has been of interest for 

 years because pinnipeds have been 

 viewed as competitors with humans for 

 a variety of fish species. Historically, 

 this competition between pinnipeds 

 and fishermen was of limited impor- 

 tance because fishes and pinnipeds 

 were harvested. However, the increas- 

 ing specialization within the fishing 

 industry during the twentieth century 

 and changing attitudes toward pinni- 

 peds have intensified this competition 

 (Harwood and Croxall, 1988). Since 

 the passage of the Marine Mammal 

 Protection Act (MMPA) in 1972, the 

 population of California sea lions 

 has increased along the West Coast 

 of North America (NMFS 2 ). This 

 increase in pinniped populations has 

 resulted in an increase in the number 

 of reports of pinnipeds interacting 

 with fishing boats and depredating 

 the catch in fisheries along the West 

 Coast (Beeson and Hanan 1 ; NMFS 2 ). 

 The California sea lion popula- 

 tion, found from offshore islands in 

 Mexico north to Vancouver Island, 

 British Columbia, has increased 

 steadily throughout the latter part 

 of the twentieth century (NMFS 2 ). 

 In the early 1900s, the over-riding 

 management philosophy was to limit 



the California sea lion population 

 because of damage to commercial 

 catches and competition for salmonid 

 fishery resources (Everitt and Beach, 

 1982). Numbers of sea lions began to 

 increase in the 1940s with curtail- 

 ment of commercial harvests, but 

 bounties were paid for seals and sea 

 lions in Oregon and Washington until 

 the early 1970s. Following passage 

 of the MMPA in 1972, the California 

 sea lion population increased at an 

 annual average of 5.0-6.2% along the 

 West Coast (Carretta et al. 3 ). There 

 are an estimated 204,000-214,000 

 sea lions in U.S. waters (Carretta et 



1 Beeson, M. J., and D. A. Hanan. 1996. 

 An evaluation of pinniped-fisheries 

 interactions in California. Report to 

 the Pacific States Marine Fisheries Com- 

 mission, 46 p. Pacific States Marine 

 Fisheries Commission, 205 SE Spokane 

 St., Portland, OR 97202. 



2 NMFS (National Marine Fisheries Ser- 

 vice). 1997. Impacts of California sea 

 lions and Pacific harbor seals on salmo- 

 nids and the coastal ecosystems of Wash- 

 ington, Oregon, and California. NOAA 

 Tech. Memo. NMFS-NWFSC-28, 150 p. 

 Northwest Fisheries Science Center, 

 2725 Montlake Blvd. East, Seattle, WA 

 98112-2097. 



3 Carretta, J. V., M. M. Muto, J. Barlow, 

 J. Baker, K. A. Forney, and M. Lowry, 

 editors. 2002. U.S. Pacific Marine 

 Mammal Stock Assessments: 2002. 

 NOAA/NMFS Tech. Memo., NOAA-TM- 

 NMFS-SWFSC-346, 290 p. Southwest 

 Fisheries Science Center, 8604 La Jolla 

 Shores Drive, La Jolla, California 92037- 

 1508. 



