Ambient temperature and distribution of north-east Arctic cod

Many studies on the effects of temperature on fish distribution and population parameters have considered the temperature and its variability at fixed stations or sections rather than the ambient temperature actually surrounding the fish. In the present paper ambient winter temperature was estimated for 1-7 year-old north-east Arctic cod in the period 1988-1995 from spatial distributions of fish density and temperature. Four different estimates were calculated for each age and year based on fish density observations from acoustic and bottom-trawl surveys and temperature recordings at the bottom, as well as averaged from 100 m depth to bottom. The estimates of ambient temperature were compared with each other and with temperature series in fixed areas and a standard section, the Kola meridian. The inter-annual variability in ambient winter temperature was found to be larger than in the Kola section series. Older fish were found at higher temperatures. For the younger age groups the range extended eastwards when numbers were high. This could explain the observed decrease of mean ambient temperatures in which cod were found during a relatively warm period in the Barents Sea. The mean ambient temperatures are also compared with the temperatures used for calculations of consumption rate by cod in the ICES Working groups.