Spatial scale and environmental determinants in minke whale habitat use and foraging

Because pelagic prey concentrations are patchy in both space and time, predators such as marine mammals require high degrees of flexibility in their habitat use. We tested the hypothesis that minke whales Balaenoptera acutorostrata adjust their habitat use during the feeding season at different spatial scales: their overall distribution should be determined by broad-scale oceanographic features, while foraging activity at finer scales should be dictated by short-term changes in habitat conditions. Results from generalized additive models indicate that minke whale distribution off the west coast of Scotland is dependent largely on temporally variable parameters (sea surface temperature in spring, chlorophyll concentration in autumn), in addition to depth and topography. However, fine-scale foraging behaviour was dictated by the strength and direction of tidal currents. Seasonal distribution patterns according to environmental parameters were largely consistent between 2 different spatial scales, and over a time period of 15 yr. Significantly higher sighting rates occurred in areas of predicted sandeel Ammodytes marinus presence in spring, but not during the rest of the summer, while in August and September, prey samples from the core study area consisted almost entirely of sprat Sprattus sprattus. The low energetic cost of swimming in minke whales and their ability to switch between different prey according to their seasonal availability thus appears to allow them to readily respond to temporal changes in pelagic prey concentrations at different scales. This occurs through a distribution influenced by temporally variable parameters (temperature and chlorophyll concentration), combined with adjustments in foraging activity dependent on variable conditions at fine spatial scales (tides).