Project:
Physiological monitoring of Steller sea lions using fecal hormone analyses: Validation and range-wide assessment

Supervisor: Andrew W. Trites

The measurement of triiodothyronine (T3) shed in feces was validated as a non-invasive means of quantifying the metabolic status of Steller sea lions (Eumetopias jubatus). Validation was achieved using captive sea lions and the radioimmunoassay of fecal samples collected pre and post intramuscular injections of thyroid stimulating hormone (TSH) to demonstrate that known physiological changes can be detected via feces. The technique was then applied to fecal samples from free-ranging Steller sea lion populations, measuring glucocorticoid (GC) metabolites as a proxy for stress and T3 for metabolism, in order to investigate diet as a cause of population declines. Ultimately, we operated under the hypothesis that diets of low energy-content would be associated with increased GC metabolite concentrations and decreased T3 concentrations. Examinations at the population scale found that the western haulout population was associated with the highest GC metabolite concentration and the lowest energy-content diet, but T3 concentrations could not confirm our hypothesis due to complications of study design related to the 2006 Humane Society litigation against SSL research permits. Comparisons of the western haulout population and the eastern haulout and rookery populations found that the rookery population exhibited the lowest T3 concentration and highest GC metabolite concentration, but was also associated with the highest energy-content diet. The predicted hormone response found at rookeries did not appear to be related to diet quality, but may have been a product of lactation and a female-biased population composition occurring at rookeries relative to haulouts.