The Importance of Foraging Pattern on Reproductive Success in the Northern Fur Seal, Callorhinus Ursinus

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9500072 Costa Over the last several decades many populations of pinnipeds and seabirds have undergone significant declines. Many hypotheses to explain the declines have been made and numerous studies have been undertaken to search for the underlying causes. Juvenile survival, however, may be one of the most critical factors influencing the growth and recovery of depleted populations of pinnipeds. Maternal resources imparted to offspring prior to weaning are important for a successful transition from nutritional dependence to independence and subsequent survival. This may be particularly so of species whose life histories are constrained by rearing young at high-latitudes and species which wean their young abruptly. Growth and recovery of depleted populations at high-latitudes are further constrained when life- history fecundity schedules limit individuals to producing one offspring per year. Thus, the quantity and quality of maternal investment to the young are a critical determinant of post- weaning survival. This research will examine the relationship between foraging behavior and maternal investment in northern fur seals. The research will be conducted in the Pribilof Islands; Alaska, where lactating northern fur seals have been shown to have three distinct foraging patterns (shallow, deep, and mixed). The location of the Pribilof Islands, near the edge of an extensive continental shelf, fortuitously gives animals breeding there two distinct foraging environments, one on the continental and one off. Each environment has a distinct assemblage of prey species. Previous studies show the deep diving foraging pattern to be associated with foraging over the continental shelf. We will quantify the foraging costs and total investment in pups associated with the different foraging strategies observed in northern fur seals. This will be done by comparing the maternal investment in terms of both the actual energy and material delivered to the pup and the ene rgetic cost to the mother. These data will be used to determine if one foraging strategy is energetically more efficient or beneficial and if this is so, does it allow the mother to make a greater investment in her young.