Examining Space Use of Foraging Gray Seals (Halichoerus grypus) off the New England Coast

Abstract

The Gray seal (Halichoerus grypus) is a highly migratory large phocid species occurring in the waters of the Northeast Atlantic Ocean. After severe depletion during the 19th and 20th century, this species has recolonized southerly US habitats around the Gulf of Maine (GOM) and Cape Cod, resulting in increasing conflict with commercial fisheries that overlap with seal foraging grounds. With uncertainty surrounding gray seal population dynamics as well as methods for the management of this ecologically important protected predator, there is an incentive to expand knowledge of gray seal feeding ecology, diet and foraging behavior to better understand interactions between this species and economically profitable fishing sectors. This study investigates gray seal foraging behavior off the coast of Cape Cod and throughout the GOM. Examining data from 4 tagged individuals, this analysis implements a potential path volume (PPV) methodology (Demšar and Long, 2019), to estimate space use in order to assess the effect of sex and season on seal foraging volume. Additionally, a generalized additive model (GAM) was used to predict species distribution and habitat suitability for a commercially important gray seal prey item, Atlantic cod, to better understand potential spatial overlap between commercial fisheries and foraging seals. Results from PPV analysis shows highly variable space use by foraging seals, with greater overall volumetric range during the Spring/Summer months. Spatial analysis of overlap between foraging seals and predicted higher quality cod habitat was shown to vary by season. The methodologies used in this study to assess overlap between commercially valuable fish species and foraging gray seals have the potential to act as a valuable tool for managers and fishers moving forward. Additionally, seal PPV is a useful metric to consider when evaluating trends in foraging ecology of this species. Finally, the combination of the two methodologies implemented in this paper might help shed light on recovery of vulnerable cod stocks.