Abstract
Fish behaviour varies considerably in response to changes in environmental and biological conditions. Cod ( Gadus morhua ) is not a homeothermic species and recent research has suggested that the recruitment and distribution of cod stocks may be influenced by temperature. Concerns have therefore been raised about the potential effect of climate change on stocks that are already at the southern limits of their range. We used data storage tags (DSTs) to observe the behaviour of cod in relation to temperature between 1999 and 2002. Over 3500 days of data were collected from 17 individuals tagged in the North and Irish Seas. We describe how the patterns in the temperature experience of cod are related to behavioural mechanisms, such as horizontal and vertical migration, that match habitat choice to physiological preferences. The results are discussed in the context of this behavioural response to short‐ and long‐term shifts in thermal regime and the potential consequences on the overall behaviour and distribution of cod stocks.