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Preliminary estimates of marine mammal bycatch, mortality, and biological sampling of cetaceans in California gillnet fisheries for 2004
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    Preliminary estimates of marine mammal bycatch in the California/Oregon large-mesh (e 14-inch) drift gillnet fishery for thresher shark and swordfish and the small-mesh (6.5-inch) drift gillnet fishery for white seabass, yellowtail, barracuda, and tuna are summarized for calendar year 2004. A third fishery, the set gillnet fishery for halibut and angel shark (8.5-inch mesh), has not been observed since 2000 in Monterey Bay and since 1994 in southern California. Although marine mammal mortality is known to have occurred in this fishery in the past, current mortality cannot be estimated because of this lack of recent observer data. In the large-mesh drift gillnet fishery, seven short-beaked common dolphins (Delphinus delphis), one northern right whale dolphin (Lissodelphis borealis), and six California sea lions (Zalophus californianus) were observed killed in 2004. There was also one humpback whale (Megaptera novaeangliae) and one California sea lion entangled and released alive in this fishery in 2004. Estimated annual mortality by species (CVs in parentheses) is: 34 (0.49) shortbeaked common dolphins, five (0.99) northern right whale dolphins, and 29 (0.44) California sea lions. Observer coverage in the thresher shark and swordfish drift gillnet fishery was 21% in 2004 (223 sets observed/1,084 sets estimated fished). Biological samples were collected from all cetaceans observed incidentally killed and life history data from these samples are summarized in the Appendix. In the small-mesh drift gillnet fishery for white seabass, yellowtail, barracuda, and tuna, there was one long-beaked common dolphin (Delphinus capensis) and one California sea lion observed killed in 22 sets. In 2002, the most recent calendar year for which logbook data are available, approximately 200 small-mesh drift gillnet sets were fished in southern California. Based on this level of fishing effort and the observed 2004 kill rates, the annual estimate of mortality in this fishery for 2004 is 9 (0.94) long-beaked common dolphins and 9 (0.94) California sea lions.
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