Pollock Conservation Cooperative Research Center
2000 Awarded Research Projects
Do Steller sea lions at the Pribilofs have enough to eat? Evidence from diet and stress hormones
Award: $87,051
Estimated Completion: February 28, 2003
Abstract
Steller sea lions at the Pribilof Islands consume principally walleye pollock in winter-spring and flatfishes in fall-winter. Other common prey species include Pacific cod, octopus, sculpins, and skates. These all tend to be low-fat forage species and are considered to be less nutritious than species such as herring, capelin, sand lance, and salmon, which occur rarely in sea lion diets at the Pribilofs. We propose to evaluate the "junk-food hypothesis," namely that diets high in prey of low nutritional quality impose physiological costs to wild sea lions that may be detrimental to the health of individuals. The measure of physiological cost will be levels of cortisol, a sensitive indicator of stress. Cortisol will be determined in scats collected from haulouts and rookeries at the Pribilofs in summer, fall, winter, and spring. Hormone levels will be compared to data on sea lion diets and the energy density of prey, and evaluated in relation to hormone levels in other wild populations and in captive animals in controlled feeding trials. Diets, in terms of energy consumption, will be further evaluated using bioenergetic models of Steller sea lions. The results will provide information on the adequacy of the forage base at the Pribilofs in maintaining healthy individuals and populations of sea lions in the current meteorological/oceanographic regime. The study also will help to answer the contentious questions of whether there are too many or too few pollock, and whether large protected areas, such as the Pribilof Islands Habitat Conservation Area, are sufficient to ensure adequate prey resources for sea lions.
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