Mechanism of body cavity temperature regulation of chum salmon (Oncorhynchus keta) during homing migration in the North Pacific Ocean

Abstract

AbstractVertical movement patterns of five chum salmon (Oncorhynchus keta) during homing migration were examined using archival tags. The standard deviation of the depth and ambient and body cavity temperatures during daytime were larger than those during night‐time. Vertical movements through the thermocline with a periodicity of less than 1 h were observed during daytime in addition to the diel vertical movement patterns in the open ocean. During these periods of frequent short‐term vertical movements, the difference between the body cavity temperature and ambient temperature was large while the variance of the body cavity temperature was less than that of the ambient temperature. From the results of a random simulation, the variation of the body cavity temperature was shown to decrease due to these periodic high frequency movements in comparison with random vertical movements. The whole‐body heat‐transfer coefficient k (s−1), which was estimated by a heat budget model, was 1.48 × 10−3. The k of chum salmon was larger than that of bigeye tuna (Thunnus obesus) by about one order of magnitude for the cooling of the body. The k of chum salmon did not change like tuna, which are physiologically adapted to conserve body cavity temperature. This indicates that the regulation of body cavity temperature by chum salmon is dependent on the vertical movements only. The maintenance of the body cavity temperature is concluded to be advantageous for their maturation and growth from the relationship between energy input and output during their homing migration.