Description of the diving and foraging behaviour of fin whales (Balaenoptera physalus) in the Azores using Time-Depth Recorders

Catarina Fonseca

Conservation of all baleen whales relies on the understanding of their distribution and behaviour. Baleen whales are greatly dependent on the availability of abundant and dense prey aggregations, because they must eat vast amounts of food to maintain their high metabolic costs. Although there are now a handful of studies that have documented the diving behaviour of baleen whales, most were carried out in productive feeding areas. In this study, Time-depth recorders deployed on 18 fin whales were used to describe the 2D diving and foraging behaviour of fin whales in a mid-latitude foraging habitat to investigate the strategies of these migratory whales in a low productive ecosystem. Whales dove deeper during daytime and shallower at night, suggesting that they track the vertical migration of prey. Foraging dives were longer and deeper than non-foraging dives, and included longer periods at the bottom phase. Whales performed less lunges per dive than reported in previous literature and foraged mostly within the first 100m of the water column, suggesting that they employ a different strategy in this area that minimizes energy expenditure. A follow up study including concurrent data on prey distribution is required to advance the understanding of the foraging strategies and efficiency of baleen whales during their migration.