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The California Current Ecosystem Program conducted population assessment studies of harbor porpoise, gray whales, harbor seals, California sea lions, Steller sea lions, and northern fur seals in Washington, Oregon and California between July and September 2003.

Harbor Porpoise Surveys

Aerial surveys of harbor porpoise were conducted by Cascadia Research Collective under contract to the National Marine Mammal Laboratory (NMML) during 1-31 August 2003. The surveys covered the coastal and inland waters from lat. 47°30’ N to 50°00’ N. The survey data will be combined with data collected in 2002 to update the stock assessment reports for harbor porpoise in Oregon and Washington. Concurrent small boat surveys were conducted during 12-29 August 2003 of U.S. inland waters from Freshwater Bay to Whidbey Island, Washington, and north to 49° 00’ N. The concurrent surveys conducted in 2003 were the second of three survey years that will be used to calibrate aerial and vessel surveys in the inland waters.

Eight harbor porpoises were captured and instrumented with VHF radio transmitters in September in the Strait of Juan de Fuca, Washington. The animals will be followed from shore-based observation points throughout the winter and spring to study seasonal movements of harbor porpoise in the area. This study is a cooperative study with the Northwest Fisheries Science Center.

Gray Whale Surveys

Photo identification surveys of gray whales in Washington waters were conducted in the Strait of Juan de Fuca from Tatoosh Island to Sekiu Point and along the northern Washington coast from Tatoosh Island to Carroll Island. Surveys for gray whales in the Strait of Juan de Fuca were conducted for 18 hours and covered 250 nautical miles (nmi). Sixteen gray whales were sighted and 15 were photographed. Biopsy samples were collected from three of these whales. During the same period, surveys for gray whales along the northern Washington coast were conducted for 16 hours and covered 207 nmi. Twenty-four gray whales were sighted along the Washington coast and 19 of these whales were photographed for later identification.

Surveys for gray whales were also conducted off the east coast of Kodiak Island, Alaska, for 3 days in August 2003. During this period, 11 gray whales were photographed for later identification.

Steller Sea Lion Branding

In July 2003, Steller sea lion pups were branded at Rogue Reef, Oregon, as part of a long-term study to estimate the survival of juveniles born in Oregon and northern California. Resights of animals branded in previous years were obtained from monthly resight trips to haul-out sites along the northern California, Oregon, and Washington coasts between July and September. Resights were also obtained from remote cameras located at Rogue Reef and Cape St. George, California.

Harbor Seal Branding

Observations of tagged and branded harbor seals at Gertrude Island, south Puget Sound began in early July and are scheduled to continued until the end of October. The peak number of seals was 623 in mid-August. About 110 pups were observed. These counts are similar to previous years. Resights of tagged and branded seals are used to determine survival and natality rates and age of first reproduction. Analysis of the Puget Sound branding data indicates that harbor seals are unusual in that the survival of yearlings is equal to survival of adults. In other pinnipeds, yearling survival is intermediate between pup and adult survival. In late September, 51 harbor seals were caught and tagged; 44 of those were branded, increasing the number of seals branded since 1993 to 512.

California Sea Lion Population Assessment

Survival and natality rates for California sea lions in 2003 will be estimated from a total of 4,600 observations recorded between June and September 2003 at San Miguel Island, California, of 1,373 branded individual California sea lions. The number of adult females sighted with pups decreased 13% from 2002. The total pup production (19,963) declined 15% from 2002. The declines in natality and pup production rates are likely due to the residual effects of the 2001-2002 El Niño conditions during winter 2003, a large scale domoic acid event in April and May which resulted in females aborting pregnancies, and the continuation of a hookworm epidemic in the population which resulted in high mortality of pups.

Northern Fur Seal Population Assessment

Total production for northern fur seals was 2,373 in 2003, an 84% increase from 2002. After an 80% decrease in pup production in 1998, the northern fur seal pup production has slowly increased, but was still 3% below 1997 production in 2003. The slow recovery of the population from the 1997-98 El Niño event indicates that adult mortality, in addition to pup and juvenile mortality, occurred during the 1997-98 El Niño event. We anticipate that a full recovery should occur in the next year or two.

In September, we branded 500 California sea lion pups and tagged 200 northern fur seal pups to continue the long-term monitoring studies of survival and natality of the two species.

By Sharon Melin.


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