The effect of recent warming on polar cod and beaked redfish juveniles in the Barents Sea

During 1980-2008, climatic conditions in the Barents Sea changed from cold to warm. This recent warming has led to a greater area of Atlantic water and a smaller area of Arctic water within the Barents Sea, which influences suitable habitats for arctic and boreal fish. Using extensive survey observations of temperature and the presence of juvenile polar cod (arctic) and beaked redfish (boreal), we defined a core thermal habitat for these species and studied how climate variability has influenced abundance indices, fish density and length, and geographical distribution. The distribution of polar cod has often been split into western (Svalbard) and eastern (Novaya Zemlya) components, which correspond to spawning sites. Most polar cod were found in a temperature band of 2-5.5 °C (core thermal habitat, CTH). Higher temperatures will lead to worse conditions (less CTH) for polar cod, which will result in decreased fish density and distribution for this species in the Barents Sea. Decreased ice cover provides less suitable spawning sites for polar cod, which may result in reduced abundance (0-group index). Redfish were primarily distributed in the western and central parts of the Barents Sea and were seldom observed east of 30°E. The majority of beaked redfish were found in a temperature band of a 5.5-8.5 °C. For redfish, higher temperatures resulted in better conditions (larger CTH), but redfish did not seem to utilise the increased habitat. The abundance of redfish (0-group index) seemed to depend more on exploitation than on CTH. Thus, recent warming negatively influenced polar cod recruitment due to a shrinking habitat, but it positively affected redfish recruitment.