Changes in Norway pout (Trisopterus esmarkii) abundance and distribution under warming conditions in the Barents Sea

This study uses a 20-year time series of standardized bottom trawl winter survey data (1994 -2013) from the Barents Sea, to investigate the changes in abundance and distributional range of Norway pout (Trisopterus esmarkii) in response to changing sea temperatures. Due to the boreal Norway pout’s rather limited geographical distribution in the Barents Sea, and that Norway pout suffers no targeted fishing mortality in the Barents Sea, the species may be a well suited indicator species of climate and ecosystem change here. Annual Norway pout abundance indices were adjusted for diel changes in catchability, and an evident increase in Norway pout abundance was found during the study period, although a marked decrease the last two years was also evident. The distributional range was also found to increase, especially northwards from the distinct core area in the southwestern part of the Barents Sea. Although a rather weak correlation was found when comparing annual Norway pout abundance indices with annual corresponding sea temperatures (r = 0.32), stronger correlations were found when abundance indices were compared to sea temperatures which were measured two (r = 0.67) and three years (r = 0.72) in advance. Reasons for these rather strong lagged (delayed) correlations are briefly being discussed in this thesis, and may be related to temperature effects on recruitment, maternal conditions (e.g. fecundity), changes in abundance/distribution of other species which affect Norway pout abundance (prey, predators or competitors), and/or a gradual expansion due to increased suitable habitat.MAR399