Fin whales Balaenoptera physalus and minke whales Balaenoptera acutorostrata exploit a tidally driven island wake ecosystem in the Bay of Fundy

摘要

Marine predators forage in tidally induced oceanographic features, where they exploit predictable aggregations of prey. Very little, however, is known about how the physical forcing within these features affects their behaviour at a fine scale. During the summers of 2000 and 2002, we combined a series of cliff-top observations and boat-based surveys to describe the movements of fin whales Balaenoptera physalus and minke whales Balaenoptera acutorostrata within a predictable island wake occurring near Grand Manan Island in the Bay of Fundy, Canada. We recorded the location of fin and minke whales as they surfaced in or near the wake. We also examined the movements of individual fin whales using focal follow techniques to assess their habitat use within 3 distinct oceanographic regions (non-wake habitat, eddy habitat and free stream habitat) of the study area. Fin and minke whale occurrence was highest during flood tides and lowest during the mid-ebb phases. Fin (33) and minke whale (64) sightings were concentrated in areas characterised by slower current velocities — the region influenced by the eddy system formed within the wake. Nine individual fin whales, identified through photographs, spent a disproportionate amount of time within the eddy habitat portion of the study area, with occasional forays into free stream habitat. Foraging in the high-vorticity regions of the wake likely allows whales to exploit higher prey concentrations than in the free stream habitat or non-wake habitat.