CALIFORNIA CURRENT PROGRAM:
California Sea Lion Research
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 NiƱo or increased mortality related to demoic acid toxicity.
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.
ALASKA ECOSYSTEM PROGRAM:
Research Cruises Help Estimate Steller Sea Lion Survival
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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.)
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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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