Polar cod Boreogadus saida occurrence is driven by temperature at the margin of its distribution

With a warming Arctic, suitable habitat for polar cod Boreogadus saida (Lepechin 1774) is predicted to decrease. We investigated the changes in distribution of polar cod on the southern limit of its distribution in the Atlantic Ocean (around Iceland) during both autumn and spring after a recent period of warming in the area. Polar cod was distributed from a depth of 50 to 1249 m, with the highest occurrence at 350-500 m. It was primarily found in areas of colder water to the north and east of the country and in deeper water to the northwest. A decrease in occurrence and a change in distribution were observed over the time period analysed (1985-2024). There was a more pronounced shift in distribution during spring than autumn, with a retreat of the population from the shallower shelf areas to the north of Iceland to deeper colder water. Polar cod were found at a wide range of temperatures during the autumn (-1.8-9.0°C), but in the spring, their occurrence decreased sharply at temperatures >2°C. Predictive modelling demonstrated that changes in temperature have contributed to shifts in distribution of polar cod around Iceland and suggests that future warming could further decrease areas of suitable habitat.