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Summer Foraging Tactics in Sea Otters (Enhydra lutris): Maintaining Foraging Efficiencies in a Stable Population in Alaska
Abstract: Foraging specializations in large populations can reduce intraspecific competition for food. When individuals do not specialize on particular prey species, resource partitioning might occur as different search strategies at the sex and age group levels. This study focused on the foraging tactics of sea otters in a stable population in Alaska by testing cost-minimizing, energy-maximizing, and efficiency-maximizing models. Canonical Correspondence Analysis (CCA) was used to analyze the boat-based behavioral observations of 119 foraging bouts for adult males and females, females with pups, and juveniles. Observations were conducted during one summer breeding season. A foraging efficiency ratio was calculated using the gain variable—estimated mean energy values from captured prey—and the cost variables—inter-dive distances traveled and dive depths. Foraging efficiency ratios were not significantly different between all adults, including females with pups. Juveniles had significantly lower foraging efficiency ratios related to low mean energy gains and a higher proportion of unsuccessful dives. A cost-minimizing strategy was identified in females with pups that minimized travel costs and obtained low prey energy per dive. Adult males and females without pups used an energy-maximizing strategy of high travel costs and high prey energy gains per dive. The ability of adult females to change foraging strategies with the demands of raising a pup indicate female adult sea otters can have flexible foraging strategies while maintaining high foraging efficiencies.
Key Words: sea otter, Enhydra lutris, optimal foraging, niche partitioning, foraging tactics
Document Type: Research article
Page Numbers: 351-364