Ecological aspects of fin whale and humpback whale distribution during summer in the Norwegian Sea

The Norwegian Sea is a migration and feeding ground for fin whales (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) in summer. During the last decade, significant structural changes in the prey community, including northerly expansion and movement in the distribution of pelagic fish species, have been reported from this ecosystem. However, little information on whale feeding ecology exists in the Norwegian Sea and surrounding waters. A total of 59 fin whales and 48 humpback whales were sighted during 864 h of observation over an observation distance of about 8200 nmi (15,200 km) in the Norwegian Sea from 15 July to 6 August 2006 and 2007. The fin whale group size, as mean (±SD), varied between one and five individuals (2.1 ± 1.2 ind.) and humpback whale group size varied between one and six individuals (2.5 ± 1.7 ind.). Fin- and humpback whales were observed mainly in the northern part of the study area, and were only found correlated with the presence of macro-zooplankton in cold Arctic water. Humpback whales were not correlated with the occurrence of adult Norwegian spring-spawning herring (Clupea harengus) except for the northernmost areas. Despite changes in the whale prey communities in the Norwegian Sea, no apparent changes in fin- or humpback whale distribution pattern could be found in our study compared to their observed summer distribution 10–15 years ago.