Large scale molecular barcoding of prey DNA reveals environmental predictors of intrapopulation feeding diversity in a marine predator

Predator-prey interactions are critical to understand how communities function. However, we need to describe intraspecific variation in diet to accurately depict those interactions. Harbor seals (Phoca vitulina, Linnaeus 1758) are an abundant marine predator that prey on species of conservation concern. We estimated intrapopulation feeding diversity of harbor seals in the Salish Sea relative to sex, time, and location with a novel approach that combined molecular techniques, repeated cross-sectional sampling of scat, and a specialization metric (within-individual consistency in diet). Based on 1,083 scat samples collected from five haul-out sites during four non-sequential years, we quantified diet using metabarcoding techniques, and determined the sex of the scat depositor using a molecular assay. Results suggest that intrapopulation feeding diversity was pervasive. Specialization was high over short periods (24 - 48 hours,〖PS〗_i = 0.392, 95% CI = 0.013, R = 100,000) and variable in time and space. Females showed more specialization than males, particularly during summer and fall, and demersal and benthic prey species were correlated with more specialized diets. The latter finding suggests that this type of prey likely require specific foraging strategies and that there are trade-offs between pelagic and benthic foraging styles for harbor seals. This differential feeding on prey species, as well as between sexes of harbor seals, indicate that predator-prey interactions in harbor seals are complex and that each sex may have a different impact on species of conservation concern. As such, describing intraspecific variation in diet may unravel hitherto unknown complex predator-prey interactions in the community.