Effects of fine-scale oceanographic features on the distribution and movements of harbour porpoises Phocoena phocoena in the Bay of Fundy

Abstract

We describe an integrative approach to studying the fine-scale distribution of harbour porpoises Phocoena phocoena in the Bay of Fundy, using satellite telemetry, line transect surveys and remote sensing techniques. Analysis of satellite telemetry data from 6 porpoises (5 male, 1 female) revealed that over the course of a month individuals ranged across large areas (7738 to 11 289 km 2 ) but concentrated their movements in small focal regions (August mean = 294 km 2 , September mean = 252 km 2 ), often proximate to islands, headlands, or restricted channels. Line transect surveys (n = 25 flood tide, n = 20 ebb tide) in the focal region of 2 tagged animals revealed that relative porpoise density (animals km -2 ) was significantly greater during flood (9.59) than ebb tide phases (1.79). Hydro-acoustic prey surveys revealed aggregations of prey along localized fronts in this region. Remote sensing images indicated the presence of an island wake in the focal region during flood tides, providing an ecological context for our observations of high densities of porpoises. Remote sensing revealed the existence of a headland wake in the focal region of another porpoise near Campobello Island. These results support the hypothesis that regions of enhanced relative vorticity, like island and headland wakes, aggregate prey and represent important foraging habitat for harbour porpoises in the Bay of Fundy.KEY WORDS: Harbour porpoise · Foraging · Fine-scale oceanography · Island wake · Satellite telemetry · Line transects · Remote sensing Resale or republication not permitted without written consent of the publisher

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