Comparative analyses of cetacean main species and fish distribution in the Barents Sea were conducted based on data from the joint Russian-Norwegian ecosystem surveys (BESS) during August-October 2005-2014.
Spatial overlap between cetaceans (Cetacea) and potential preys
The Barents Sea area was divided into a 50x50 km grid and acoustic fish recordings (SA) and number of observed cetaceans were summed for the period 2005-2014 for each cell. Figure 4.6.1 presented distribution of minke whale (Balaenoptera acutorostrata), humpback whale (Megaptera novaeangliae), fin whale (Balaenoptera physalus), white-beaked dolphin (Lagenorhynchus albirostris) and harbor porpoise (Phocoena phocoena), as well as capelin (Mallotus villosus), polar cod (Boreogadus saida), herring (Clupea sp.), cod (Gadus morhua), haddock (Melanogrammus aeglefinus), saithe (Pollachius virens), o-group fishes, blue whiting (Micromesistius poutassoumes), redfish (Sebastes sp.) and Norway pout (Trisopterus esmarkii).
Figure 4.6.1. Fish and cetacean distributions in the Barents Sea on base of BESS for 2005-2014.
Minke whale and white-beaked dolphins were widely distributed in the entire Barents Sea, which indicates the possible interaction with all fish species used in this analysis. Fin whale and humpback whale were mainly distributed in the western regions and north and east of Svalbard (Spitsbergen archipelago). Harbor porpoise were distributed in the southern Barents Sea and overlapped in lesser degree with studied fish.
In addition, degree of overlap between cetacean and fish distribution was estimated based on grid data as the ratio of total species distribution extent and their overlap and showed in percentage (Fig. 4.6.2).
Figure 4.6.2. Degree of overlap (%) for cetacean distribution with fish areas in the Barents Sea based on data from BESS for 2005-2014.Minke whale, due to its wide distribution, had a high overlap with many fish species areas, mainly with herring, capelin, redfish, haddock, cod and 0-group fish. Humpback whale with limited distribution overlapped in lesser degree, and mainly with polar cod, capelin, redfish, cod and haddock. Fin whale overlapped mainly with Norway pout, haddock, redfish, blue whiting, cod and 0-group of fish. White-beaked dolphin, like minke whale, was widely distributed overlapped with both herring, capelin, redfish, haddock, cod and 0-group fish. The harbor porpoise, unlike other cetaceans, overlapped mainly with herring, saithe, haddock and Norway pout over a limited distribution area.
Principal components and correlation analyses were based on log-transformed grid data and indicated associations between cetaceans and their potential prey (Fig. 4.6.3, Table 4.6.1). Analyses showed that minke whales, humpback whales were highly correlated with polar cod, capelin, indicating a potential predation pressure on these forage fishes from baleen whales in the overlapping area. Minke whales, humpback whales, fin whales and white-beaked dolphins were also significantly correlated with cod, however this most likely indicated that both whales/dolphins and cod overlap with their preferred prey. In contrast to minke whale and humpback whale, the fin whales were positively correlated with the saithe and Norway pout. The white-beaked dolphins were positively correlated with redfish, haddock, cod, and blue whiting and 0-group fish. However, it us most likely that white-beaked dolphins did not preyed on 0-group of fish due to their biological characteristics. The harbor porpoise distributions were correlated with cod and haddock, while not significantly, most likely because of small sample size.
Figure 4.6.3 - The results of principal component analysis of log-transformed data of number cetaceans and SA values fish in the Barents Sea during the period 2005-2014 of BESS.
Table 4.6.1 - Results of the correlation analysis of log-transformed data of number cetaceans and SA values fish in the Barents Sea during the period of BESS in 2005-2014.The widely distributed species (minke whale, white-beaked dolphin) were largely overlapping with the many of studied fish species and therefore their possible influence (predation pressure) could be significant on several prey species and generally on the ecosystem. Contrastingly, locally distributed species, such as harbor porpoise, have a lesser impact on the ecosystem, but could be high on locally distributed preys.
