Laboratory studies on the effects of thermal change on the behaviour and distribution of juvenile chum salmon in sea water

Schooling chum salmon Oncorhynchus keta were biased towards the water surface (median position 83·5% of the fish occupied a ‘preferred’ temperature range of 13·7–17·9° C. The mean temperature at which 50% of chum salmon avoided rising temperature by shifting deeper in the water column and using the cooler thermocline was 20·2° C, and 90% avoidance occurred at 22·9° C. Behavioural responses to thermal stratification were consistent amongst underyearling fish of differing size and age.