We investigated the spatial associations between minke Balaenoptera acutorostrata, fin B. physalus and humpback Megaptera novaeangliae whales and their prey in the Barents Sea in late summer of 2003 to 2007. During these years the abundance of their assumed primary prey, capelin Mallotus villotus, was low due to a stock collapse. The whales were therefore expected to associate with abundant herring Clupea harengus in the southern Barents Sea and krill (Euphausiacea) in the central and northern Barents Sea. The baleen whales predominantly occupied a narrow, northern area that had high densities of krill, amphipods Themisto spp., and polar cod Boreogadus saida along the northern range of the capelin distribution. A small proportion of the Barents Sea minke and fin whales occurred in the southern areas. Herring was therefore not an important prey species in the Barents Sea in this season. Ecosystem-scale associations, which were determined by spatial associations between species distributions averaged across years, indicated that krill was the predominant prey species. However, contrasting mesoscale associations with their prey in 50 km grid cells and a preference for shallow northern banks suggests that these whales have a diverse diet within a preferred habitat. Finally, positive density dependence and facilitation can be significant processes that influence whale distributions, as the 3 baleen whale species were positively associated at both ecosystem-and mesoscales.
KEY WORDS: Ecosystem survey · Pelagic communities · Trophic interactions · Marine mammals
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 426: [289][290][291][292][293][294][295][296][297][298][299][300][301] 2011 while herring and krill (Euphausiacea) were abundant (Gjøsaeter et al. 2009, Zhukova et al. 2009). The diet and prey selection of minke whales has been thoroughly studied in early summer (May to June) when the northern Barents Sea is ice-covered (e.g. , Smout & Lindstrøm 2007. During this season, minke whales in the Barents Sea preferentially forage on capelin, but the dietary importance of herring and krill increases when capelin abundance decreases , Smout & Lindstrøm 2007. However, little knowledge exists on minke whale-prey interactions in late summer or on interactions between fin and humpback whales and their prey in this ecosystem.Minke, fin and humpback whales often congregate in the same feeding areas, likely targeting similar prey (Piatt & Methven 1992, Murase et al. 2002). In general, they seem to prefer pelagic fish to zooplankton in northern ecosystems (Murase et al. 2007, Smout & Lindstrøm 2007, Witteveen et al. 2008. However, in comparison with that in early summer, the prey assemblage in late summer (e.g. August to September) may include additional species. Northern areas with high amphipod Themisto spp. (Dalpadado et al. 2001) and polar cod Boreogadus saida (Stiansen & Filin 2008) densities are exposed so these prey species become available for pelagic predators ...
