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

Christina McCosker^1,*, Kelly Flanders¹, Kathryn Ono¹, Michelle Dufault¹, Dominique Mellone¹, and Zachary Olson²

¹School of Marine Programs, University of New England, 11 Hills Beach Road, Biddeford, ME 04005. ²Department of Psychology, Animal Behavior Program, University of New England, 11 Hills Beach Road, Biddeford, ME 04005. *Corresponding author.

Northeastern Naturalist, Volume 27, Issue 4 (2020): 681–700

Abstract
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.

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