MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14655

ABSTRACT: Predation shapes ecosystems, and quantifying the impacts of predation on the distribution and abundance of prey requires substantial effort at appropriate spatial and temporal scales for diet estimation of predators. Here we present diet estimates of a marine predator (harbour seal Phoca vitulina richardsi) from scat collections (n = 3420) sampled at multiple haul out sites (n = 64) in the Strait of Georgia and other coastal regions around Vancouver Island, British Columbia, Canada, between 2015–2019. DNA metabarcoding and hard part analysis were used to identify the proportion and sizes of prey species consumed respectively. We found that harbour seals consumed 62 primary prey species, that the diversity in the diet was highly affected by the number of samples collected, and varied at small spatial scales (haul out site) as well as among broad bioregions. Three to five species dominated the diet depending on location, season and year, including: Pacific hake Merluccius productus, Pacific herring Clupea pallasii, and walleye pollock Gadus chalcogrammus. Within the Strait of Georgia, both male and female harbour seals consumed more hake and walleye pollock in areas and seasons in which they were more abundant. Harbour seals consumed a wide size range of prey which also varied by species, season, and region. These results indicate that harbour seal foraging is influenced by both the local abundance and composition of prey. Attempts to model the impact of predation on species of concern risk bias in their estimates and under representing uncertainty if spatial and temporal variation in the diet is not accounted for.