Sea Otter Time Budgets and Prey Relationships in Alaska

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Abstract
Sea otters (Enhydra lutris) in Prince William Sound, Alaska [USA] obtained more calories/time foraging in areas occupied by otters for < 3 years (> 500 kcal/hour) than in an area occupied for .gtoreq. 30 years (300 kcal/hour). Diminished abundance of dungeness crabs (Cancer magister) in the newly occupied area followed the arrival and heavy predation on crabs by otters. In the area of prolonged otter occupation, large crabs were virtually absent and otters spent significantly more (P < 0.001) time feeding/day (.hivin.x = 11.5 hours) than where food was more abundant (.hivin.x = 8.8 hours). This relationship between time budgets and food availability suggests that time budgets may be used to assess whether otter populations are limited by food. However, the reliability of such assessments depends greatly on the methods used to obtain the time budget data. Time budget data in this study were obtained telemetrically over 24-hour periods, whereas most previous investigators derived time budgets from diurnal, visual observations. Diurnal sampling of time budgets may be biased because assumptions regarding nocturnal feeding may be incorrect. Population assessments based on comparisons of time budget data from widely differing areas may be inappropriate because factors other than food availability may affect the amount of time otters spend feeding. In this study pup rearing, as well as rainy, windy, or cold weather conditions, prompted otters to feed more.