Sea otter diet nutrient composition with respect to recolonization, life
history, and season in southern Southeast Alaska
Abstract
The sea otter (Enhydra lutris) population of Southeast Alaska has been
growing at a higher rate than other regions along the Pacific coast.
While good for the recovery of this endangered species, rapid population
growth of this apex predator can create a human-wildlife conflict,
negatively impacting commercial and subsistence fishing. Previous
foraging studies throughout the sea otter range have shown they will
reduce invertebrate prey biomass when recolonizing an area. The goal of
this study was to examine and quantify the energetic content of sea
otter diets through direct foraging observations and prey collection.
Our study area, Prince of Wales Island in southern Southeast Alaska,
exhibits a gradient of sea otter recolonization, thus providing a
natural experiment to test diet change in regions with different
recolonization histories. Sea otter prey items were collected in three
seasons (spring, summer, winter) to measure caloric value and lipid and
protein content. We observed 3,523 sea otter dives during the spring and
summer. A majority of the sea otter diet consisted of clams. Sea otters
in newly recolonized areas had lower diet diversity, higher kcal/gram
intake rates, and higher energetic intake rates. Females with pups had
the highest diet diversity and the lowest energetic intake rates
(calories per gram consumed). Sea otter energetic intake rates were
higher in the fall and winter vs. spring and summer. Sea cucumber energy
and lipid content appeared to correspond with times when sea otters
consumed the highest proportion of sea cucumbers. These caloric
variations are an important component of understanding ecosystem level
effects sea otters have in the nearshore environment.