Metabarcoding Fecal DNA Reveals Extent of Halichoerus grypus (Gray Seal) Foraging on Invertebrates and Incidence of Parasite Exposure

Halichoerus grypus (Gray Seal) is a top predator in New England waters, yet little data exists on seals foraging on invertebrate prey. We combined analysis of hard parts of scat samples (n = 98) from 2 breeding sites in Massachusetts with metabarcoding of fecal DNA. Invertebrates were detected in 4 samples via analysis of hard parts (4.1%) but in 35 samples (35.7%) using a metabarcoding approach. Metabarcoding also detected parasite DNA in 82.7% of scat samples. Nematode DNA (78.6%) was more prevalent than trematode (28.6%) or cestode (22.5%) DNA. Prey species, biomass, and diversity within each sample were not affected by seal sex, parasite exposure, or type of parasitic exposure. Previous diet studies may have underestimated the diversity and abundance of invertebrates in the diet of Gray Seals.