Zoology: Marine mammals meet, greet and feed

Mapping of the spatial distributions of over eight marine mammal species converging towards their fish prey reveals the existence of species-specific foraging zones in the Atlantic Ocean.These findings,reported in Nature this week, add to our record of the distribution of these mammals and helps understand their behaviour and interaction with prey species.

Using a technique known as passive ocean acoustic waveguide remote sensing, Purnima Ratilal and colleagues mapped the vocalizations and spatial distributions of various whale species - including blue, fin, humpback, sei, minke, sperm, pilot and killer whales - and dolphin species over an area of 100,000 km2 in the Gulf of Maine, a herring feeding ground in the Atlantic Ocean. The authorswereable to instantaneously detect, localize and classify marine mammal vocalizations from diverse species and they find that predators divide the shoal into overlapping foraging sectors, which are species-specific and have varying degrees of spatial overlap. The sectors are maintained for at least two weeks of the herring spawning period, they find.

The vocalization rates of all thestudied marine mammals are found to follow a 24-hour cycle, with some being more vocal at night and others during the day. These results add to our knowledge of the temporospatial dynamics of combined foraging activities of multiple marine mammal species in the vicinity of an extensive fish prey field that forms a massive ecological hotspot. It is hoped that these results will aid management of marine ecosystems and improve understanding of the anthropogenic impacts on these marine protected species.