3.3 Energetic content of sea otter prey
Overall, sea otter prey had a similar makeup of protein and
lipid content; sea urchins were the only prey group significantly
different from other prey groups for lipid-to-protein ratio (Fig. 4, p
< 0.01). Functional prey groups varied in their energy, lipid,
and protein content across seasons (Table 2). Across all seasons, sea
cucumbers exhibited lower energy than all other prey types (Fig. 5), and
their energy and lipid varied significantly by season (Table 2). Sea
urchins had significant variability in lipid content across seasons
(Table 2). Clams exhibited a significant change in energy and lipid over
seasons as well, but R values were low, which means the overall seasonal
effect was low (Table 2). Crabs did not vary significantly across
seasons or sex. Snails did not vary significantly across seasons.
Pairwise comparisons for all prey groups and seasons revealed
significant differences in energy for clams and sea cucumbers (Table 3).
Lipid varied for clams, sea cucumbers, and sea urchins, whereas protein
only varied between seasons for clams. Snails were not compared across
seasons due to the small sample size.
When we compared year-round energetic changes in sea otter prey
with diet proportion estimates, we found consumption rates of most
functional prey groups did not correlate with energy density. Clam
consumption, the major diet item for sea otters in this study, did not
correspond with changes in energy (Fig. 6A) or lipid (Fig. 6C). Based on
LaRoche et al. (2021), sea otters consumed more clams in the fall and
winter months, when the energetic and lipid contents of clams were lower
than the spring season. Sea cucumber consumption, the second most
abundant diet contribution, did appear to correspond with changes in
energy (Fig. 6B) and lipid (Fig. 6D). Sea otters decreased their
consumption of sea cucumber in the fall and winter months, which
corresponded with declining energetic value.