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National Marine Mammal Laboratory (NMML)

California Sea Lion Research

picture of Point Bennet rookery
Adams Cove study area of the Point Bennet Rookery on the west end of
San Miguel, California, during the 2003 breeding season of California sea lions.
(Photo by Sharon Melin.)

The 2003 field season began for the long-term monitoring program of California sea lions (Zalophus californianus) on San Miguel Island. The southern California population experienced a large die-off of adult and juvenile sea lions due to domoic acid toxicity. Domoic acid is a naturally occurring toxin in dinoflagellates which concentrates in top predators such as sea lions. Resighting efforts of branded sea lions started in May for information on survival and reproductive success. Preliminary observations indicate fewer animals and an increase in premature pups. This could be due to residual effects of el Niņo or increased mortality related to demoic acid toxicity.

See a slide show of life in the field as viewed through the eyes of AFSC biologists and crew!

Research continued on the California sea lion cancer project funded by the National Institute of Health in collaboration with the University of California at Davis. The project is investigating the relationships between California sea lion foraging areas, contaminant loads (DDT and PCB), and a predisposition to develop a herpes virus as a precursor to cancer. Work continued in April with samples taken from adult females at San Miguel Island and adult males in Puget Sound, Washington. Ten juvenile sea lions were fitted with instruments at San Miguel Island; eight of them foraged near San Miguel Island, and two moved north to forage in Monterey Bay.

By Harriet Huber.

Research Cruises Help Estimate Steller Sea Lion Survival

  picture of a branded Steller sea lion
Steller sea lion brand X85, branded at Sugarloaf Island, Alaska, on 3 July, 2000 and resighted at Cape Elizabeth on 20 May, 2003. (Photo by Carolyn J. Gudmundson.)

Steller sea lion abundance continues to decline throughout parts of their western range in Alaska, but little is known about how survival is related to age or whether survival varies by region. Other vital rates essential to understanding sea lion population dynamics are also unknown. For example, how old are they when weaned? How old are they when they start breeding? How far do they disperse? And does that range depend on where they were born or reared? The answers to these questions are fundamental to understanding the nature of the sea lion decline and evaluating potential commercial fisheries effects and the efficacy of management measures.

To estimate survival and vital rates, the National Marine Mammal Laboratory (NMML) and Alaska Department of Fish and Game (ADF&G) have been marking pups with brands or flipper tags at six sites in the eastern Aleutian Islands and Gulf of Alaska and at three sites in southeast Alaska each summer since 2000. Juvenile sea lions captured for telemetry studies throughout the year have been similarly marked. Undertaking extensive efforts to observe marked animals each year is crucial for obtaining the best possible survival estimates. This observational effort was the primary objective of two cruises conducted by NMML to the eastern Aleutian Islands and Gulf of Alaska during May 2003.

During 13-27 May 2003, NMML researchers visited haulouts and rookeries from Samalga Pass (Aleutian Islands) to Outer Island (Kenai Peninsula) aboard two chartered crab catcher vessels, the Aleutian Mariner out of Dutch Harbor and the Big Valley out of Kodiak. During these two cruises, 93 branded and 30 flipper-tagged sea lions were identified among approximately 7,630 sea lions at 85 sites. These included 12 sea lions that had been captured as juveniles for telemetry studies, 21 one-year olds from Marmot Island, 25 one-year olds from Sugarloaf Island, 7 two-year olds from Ugamak Island, 2 two-year olds from Seal Rocks, 11 three-year olds from Marmot Island, 12 three-year olds from Sugarloaf Island, and 2 sixteen-year olds from Marmot Island.

Immature sea lions can range far from their natal rookeries. Notable observations were of a juvenile from Hazy Island in Southeast Alaska observed at Shakun Rocks, approximately 650 nmi away, and one Seal Rocks 2-year-old observed at Twoheaded Island, approximately 300 nmi away, and another near the Shumagin Islands. In addition to observing marked sea lions, 333 scats were collected for analysis to determine dietary habits, and 93 scats were sampled for hormonal and DNA analyses by colleagues from the University of California at Davis.

By Brian Fadely.


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