Fine-scale prey aggregations and foraging ecology of humpback whales Megaptera novaeangliae

Analyses of the foraging behavior of large cetaceans have generally focused on either correlations with environmental conditions at regional scales or observations of surface behavior. We employed a novel approach combining multi-scale analyses of simultaneous environmental conditions, surface and subsurface humpback whale Megaptera novaeangliae movements, and sand lance Ammodytes spp. prey aggregations in the Gulf of Maine, USA. At the fine scale (<1 km), digital tags recorded whale movement and behavior in 3 dimensions. Concurrent synoptic prey data were collected using EK60 echosounders with simultaneous surface measurements of temperature and relative fluorescence within 1 km of the tagged whale. A geospatial analysis of environmental features and foraging patterns was conducted at the regional, seascape scale (similar to 10 km). At the seascape scale, we found: (1) a negative relationship between relative fluorescence and sand lance density; (2) a positive relationship between predator surface feeding, presumed sand lance density, and sand bottom types near high-slope edges; (3) a cyclical relationship for predator surface-feeding likelihood and prey density with tidal height; and (4) an observed temporal lag between peak prey density and predator surface-feeding likelihood. At the fine scale, we found that: (1) time of day was the most important factor in predicting whether a whale was feeding when it surfaced; and (2) surface feeding occurred more often around more dense, vertically distributed schools of prey. Multiscale and multi-trophic level studies are an important component in understanding the foraging ecology of top predators in marine systems.