Life History Transmitters (LHX) in Steller sea lions: assessing the effects of health status, foraging ability, and environmental variability on juvenile survival and population trends.

The Objectives of the LHX Project

This study will address these primary questions:

• Does reduced juvenile survival contribute to the population decline of the western Steller sea lion stock?
• Is juvenile survival related to early body condition, and health?
• Is a hypothetically reduced juvenile survival related to foraging efficiency and possibly to nutritional stress?
• Can we obtain any indication that death by predation contributes to juvenile mortality?
• Can we predict future juvenile survival in Steller sea lions, based on parameters that can be sampled early in life?

The specific objectives of the LHX Project are to:

1. Verify the validity of using implanted, satellite-linked life-history transmitters to assess survival in juvenile Steller sea lions.
2. Provide accurate correction factors for instrument / transmission failure rates for use of LHXs on Steller sea lions, through redundant deployments (two implants per animal).
3. Provide an initial estimate of juvenile mortality. If continued funding is obtained, this will be expanded into a more accurate juvenile survival figure.
4. Provide an estimate for time of year of greatest mortality (i.e. summer- / reproductive season; winter / fishing season) for juvenile Steller sea lions.
5. Obtain summary dive effort data (weekly values for % dive time, number & mean depth of dives, as well as Vertical Travel Distance per week) for the period from implantation to death for deceased juvenile sea lions.
6. Estimate seasonal and developmental changes in dive effort of deceased animals (dependent on actual sample size).
7. Obtain detailed dive behavior data from animals that have died, for the period immediately preceeding death (2-4 weeks prior to death).
8. Provide a preliminary assessment of the relationship between pre-weaning body condition & health, and survival of individual juvenile Stellers.
9. Develop and refine methods to detect cause of death.

The specific objectives listed above are based on our initial funding of $300,000 for two years from the North Pacific Marine Resarch Program. With this funding, we completed the development and bench testing of LHX devices, and are continuing the carcass testing of LHX tags. With newly obtained funding from the National Marine Fisheries Service, we will continue the LHX project to work on up to 72 juvenile Steller sea lions. Based on power tests, and estimates of age-specific mortality, we expect to fully test decreased juvenile Steller survival as the leading hypothesis for the decline of this species.

© M. Horning 1999.

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