3.1 Sea otter diets across Prince of Wales
Foraging records consisted of 362 foraging bouts. In total, 3,523 dives were recorded between May 6, 2018, and August 13, 2018. The overall success rate was 89.9%, and diet diversity (H’) was 0.81. Mean dive time was 88.4 seconds (± 44.5), and mean surface time was 56.4 seconds (± 42.3). The mean energy intake rate was 7.3 ± 0.22 Kcal/min. Sea otters were observed to consume a total of 44 prey items. When prey selection was examined irrespective of habitat type or site, the dominant prey categories (making up 97.5% of the total diet by biomass) calculated by SOFA were clams (80.9 ± 2.21%), sea cucumbers (8.5 ± 1.13%), crabs (3.8 ± 0.44%), snails (2.7 ± 0.39%), and sea urchins (1.6% ± 0.28%). Within the clam category, butter clams (Saxidomus gigantea ) were the predominant species, comprising 36.9 ± 1.61% of the overall diet.
We observed differences in sea otter diets across recolonization zones and reproductive status. Species diversity and intake rate (kcal/min) varied by recolonization zone (Table 1). The newest recolonization zone (> 7 years) had the lowest species diversity (H’ = 0.39) and highest intake rate (11.06 ± 0.8 Kcal/min). The zone where sea otters have been present for the longest period of time (> 30 years) had the highest species diversity (H’ = 1.19) and lowest intake rate (5.7 ± 0.8 Kcal/min). Clams were the main prey consumed across all recolonization zones (Fig. 2A). Species diversity and intake rate varied by reproductive status (Table 1). Although clams were the dominant prey, sea otter diets varied by reproductive status; females with pups had a more varied diet and higher species diversity than females without pups and males (Table 1, Fig. 2B). Females with pups had the highest species diversity (H’ = 1.23) and highest success rate (90%) whereas males had the lowest species diversity (H’ = 0.34).