Central California gillnet effort and bycatch of sensitive species, 1990-1998

Central California gillnet effort and bycatch of sensitive species, 1990-1998

K.A. Forney, S.R. Benson, and G.A. Cameron

Central California gillnet effort and bycatch of sensitive species, 1990-1998This is part of Seabird Bycatch: Trends, Roadblocks, and Solutions
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During the 1980s, extensive bycatch of seabirds and marine mammals in central California’s set gillnet fisheries prompted a series of area and depth closures, which ultimately appeared successful at reducing mortality of the species of primary concern, Common Murre (Uria aalge), sea otter (Enhydra lutris), and harbor porpoise (Phocoena phocoena). The effects of the restrictions, however, were confounded with changes in the distribution and intensity of fishing effort during the early 1990s. This study documents 1990-1998 patterns of fishing effort in the central California halibut (Paralichthys californicus) gillnet fishery and presents information on bycatch of the above three species. A National Marine Fisheries Service observer program obtained bycatch data from 1990 to 1994, but was discontinued after 1994. Since then, gillnet effort has increased and shifted into the southern areas of Monterey Bay, where bycatch was high during the 1980s. The recent increase in gillnet effort coincides with higher beach deposition rates for all three species. In this study, historical entanglement rate data are combined with estimates of fishing effort for 1995-1998 to produce several sets of mortality estimates based on a variety of assumptions. Without further data, it is not possible to validate most of the assumptions. The range of total mortality estimates for the 4 year period 1995-1998 is 5,918-13,060 Common Murres (S.E. 477-1,252), 144-662 harbor porpoises (S.E. 18-53), and 17-125 sea otters (S.E. 4-25), raising concern for all three species. The recent changes in fishing effort and distribution underscore the importance of monitoring variability in both fishing practices and the distribution of vulnerable species when evaluating long-term fishery impacts.

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