Distribution and habitat use of deep-diving cetaceans 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 in the last 30 years. This study aimed to improve understanding of the underlying ecological drivers of any changes in deep-diving cetacean distribution. We used data from two series of summer surveys (in Iceland-Faroes and Norway) to model density of sperm (Physeter macrocephalus), long-finned pilot (Globicephala melas) and northern bottlenose (Hyperoodon ampullatus) whales as a function of static (relief), physical, and biological oceanographic covariates using GAMs. The best models, based on a robust model selection framework, were used to predict distribution. The study period 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 three species’ distributions (in both periods) were bathymetric variables and SST. The selected dynamic temperature-related covariates for sperm and pilot whales were for spring, but for bottlenose whales were for summer. Summer relationships were also found for the three species for the other dynamic variables, except spring chlorophyll-a for bottlenose whales. The difference in seasonal relationships for bottlenose whales may be related to a previously suggested north-south summer migration. As expected, the predicted high-use areas for all three species were deep waters, with some overlap among them in the central Norwegian Sea, and the Central North Atlantic, including the Irminger Sea. Differences in distribution likely reflect differences in prey. Changes in distribution between the two periods appear more as a range expansion than a shift, which could result from an increase in suitable habitat due to warming waters. 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.

Keywords

• Deep-diving cetaceans
• habitat use
• North Atlantic
• summer distribution