ESR 13:219-229 (2011)  -  doi:10.3354/esr00327

Sea otter mortality in fish and shellfish traps: estimating potential impacts and exploring possible solutions

Brian B. Hatfield1,*, Jack A. Ames2, James A. Estes3, M. Tim Tinker4, Andrew B. Johnson5, Michelle M. Staedler5, Michael D. Harris6

1US Geological Survey, Western Ecological Research Center, Piedras Blancas Office, PO Box 70, San Simeon, California 93452, USA
2Marine Wildlife Veterinary Care and Research Center, California Department of Fish and Game, 1451 Shaffer Road, Santa Cruz, California 95060, USA
3Department of Ecology and Evolutionary Biology, University of California, Center for Ocean Health, 100 Shaffer Road, Santa Cruz, California 95060, USA
4US Geological Survey, Western Ecological Research Center, Long Marine Laboratory, 100 Shaffer Road, Santa Cruz, California 95060, USA
5Sea Otter Research and Conservation, Monterey Bay Aquarium, 886 Cannery Row, Monterey, California 93940, USA
6California Department of Fish and Game, OSPR–Veterinary Services, 1385 Main Street, Morro Bay, California 93442, USA

ABSTRACT: Sea otters Enhydra lutris can be bycaught and drowned in fishing pots and traps, which may pose a threat to the welfare of otter populations. We explored this potential problem and its solutions using a wide variety of analyses. We exposed live California (USA) sea otters to finfish traps, lobster traps, and mock Dungeness crab traps in captive trials and found that the animals attempted to enter the circular and rectangular fyke openings, with some becoming entrapped. Using both live and dead sea otters, we found that a 3 × 9 inch (7.6 × 22.9 cm) fyke opening (1 inch narrower than the 4 × 9 inch [10.2 × 22.9 cm] openings currently used in California’s commercial Dungeness crab fishery) would exclude most free-living (i.e. weaned from their mothers) otters while permitting the undiminished capture of crabs. Observer programs do not currently exist in California for these fisheries, so we calculated the effort required by an observer program to document sea otter bycatch over a range of hypothetical levels and evaluated the impact of those mortality rates on population growth. These analyses demonstrate that significant mortality from bycatch might easily go undetected, even with seemingly high levels of observer effort. As sea otters reoccupy portions of their former habitat in California, co-occurrence with finfish and shellfish traps with relatively large fyke openings will increase.


KEY WORDS: Sea otter · Enhydra lutris · Bycatch mortality · Shellfish traps · Fish traps


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Cite this article as: Hatfield BB, Ames JA, Estes JA, Tinker MT, Johnson AB, Staedler MM, Harris MD (2011) Sea otter mortality in fish and shellfish traps: estimating potential impacts and exploring possible solutions. Endang Species Res 13:219-229

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