Activity Budget, Field Metabolic Rate, and Foraging Ecology of Female Sea Otters (Enhydra lutris kenyoni) with Dependent Pups in Alaska



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Sea otter (Enhydra lutris kenyoni) foraging behavior and prey preference (2001- 2004) and the behavior and activity budgets of females with dependent pups (2005- 2010) were studied during the summer (June-August) in Simpson Bay, Prince William Sound, Alaska. Unlike most previous studies of sea otters which were conducted in coastal areas with a rocky benthos and kelp canopy, the benthic habitat in this study was primarily soft sediment (mud or mixed mud and gravel) with no canopy-forming kelps.

Foraging behavior and prey preference. A total of 1,816 foraging dives from 211 bouts were recorded. 87% of foraging dives were successful, and 44% of the prey was identified: 75% clams, 9% Pacific blue mussels, 6% crabs, 2% scallops and a variety of other invertebrates. Significantly more prey items/area were brought up from mixed mud/gravel than mud (p-value <0.0001). Sea otters in Simpson Bay have relied heavily on bivalves for the past 20 years, and the summer population has been constant for at least the past twelve years. It appears that bivalves are the predominant and stable component of the diet, and their productivity is sufficient to sustain a stable population of sea otters with a peak summer density of 4.3 adult otters km^(-2) for the past twelve years and probably longer.

Behavior and activity budgets of females with dependent pups. Females with dependent pups spent the greatest percentage of the day resting (42%), about equal percentages foraging (18%), grooming (15%) and swimming (15%), and the remainder swimming slowly (8%) and interacting (2%). The estimated FMR was 12.69 MJ day^(-1). Sea otters reoccupied the study area in the early 1980s, and the population has been stable for over a decade. However, the time spent foraging is more similar to areas that have been recently occupied. The relatively small amount of time spent foraging may indicate that geographic differences (structure of the near-shore community: substrate, water depth, kelp canopy, prey assemblage, and competitors) may play a greater role in determining the amount of time spent foraging than population status.