Research Document - 2010/124

Winter foraging by a top predator, the grey seal, in relation to the distribution of prey

By V. Harvey, M.O. Hammill, D.P. Swain, G.A. Breed, C. Lydersen, and K.M. Kovacs

Abstract

Identifying areas of restricted search (ARS) of an individual and correlating them with resource abundance may allow a better understanding of predator-prey relationships. Using satellite telemetry data from a large marine predator, the grey seal, collected between 1993 and 2005 and trawl survey data on the winter distribution of ground-fish prey species in 1994-1997, we examined whether seal movements were associated with overwintering concentrations of several commercially important fish species in the Cabot Strait area of Atlantic Canada. The distribution of ARS sites differed between males and females. Male foraging zones were distinguished from female foraging zones by higher densities of herring and medium and large cod. The distribution of searching effort of males varied throughout the winter. In early winter, males were more likely to use habitats around St. Paul’s Island where their ARSs were positively related to the abundances of medium and large cod. In late winter, they were found to the southeast of this area and their ARS were negatively associated with large turbot, medium cod and small witch flounder. Females ARSs were also more likely to occur in this southern region. They were negatively related to high abundance of small witch flounder while the probability of having an ARS along their path increased with the abundance of medium sized redfish and decreased with large redfish and white hake. Spatiotemporal differences in distribution and fish communities targeted by male and female ARS may reflect sexual differences in energetic requirements for reproduction. By concentrating their activity in areas of high abundance of large fishes targeted by the fishery in early winter, male grey seals may have an impact on fishes of commercial concern.

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