Cetacean distribution and habitat use in the central and north-eastern North Atlantic

Abstract

Major changes in the distribution of some cetaceans have been observed coincident with changing oceanography of the North Atlantic over the last 30 years. This study aimed to improve understanding of the underlying ecological drivers and their mechanisms on the changes in cetacean distribution. Data from two series of summer surveys were used to model density of sperm, long-finned pilot, northern bottlenose (deep diver guild), fin, humpback, minke (baleen whale guild) and killer whales, and white-beaked dolphins (delphinid guild) as a function of static (relief), physical and biological oceanographic covariates using GAMs. The best models were used to predict distribution. The study was divided into two periods, 1987-1989 and 1998-2015, based on environmental changes in the area and data availability. The common covariates that best explained these species’ distributions in both periods were depth and sea surface temperature, indicating these are useful indirect proxies for prey. Relationships between cetacean density and depth were generally maintained over time, except for the year-round species pilot whale, killer whale, and white-beaked dolphin. The relationships between cetacean density and dynamic oceanographic variables were found in summer for baleen whales (lower trophic feeders), in spring for sperm and pilot whales (higher trophic feeders) and unclear for northern bottlenose whale and the two delphinid species. Changes in distribution between the two periods varied among species and guilds. Overall, there was an expansion to a broader distribution, especially in new areas close to the limits with Arctic waters, and increased usage of some areas, for example the Barents Sea for baleen whales. This new knowledge will help improve understanding of how these species may respond over this wide area to a changing environment and inform their conservation and management to reduce the negative effects of climate change and the increasing anthropogenic impacts.