Reproduction of Short-Term Vertical Movements Observed Using Archival Tags on Chum Salmon (Oncorhynchus keta) by a Simple Model

Vertical movement patterns of chum salmon (Oncorhynchus keta) during their homing migration were examined using archival tags. Vertical movements through the thermocline with a periodicity of less than 1 h were observed during the day in the North Pacific. To examine the dynamics of these short-term vertical movements, we developed a simple one-dimensional vertical movement model. It is assumed that chum salmon have an optimal body temperature and that they regulate their dive behavior to depths with relatively high prey densities in a manner that conserves their body temperature. The model reproduced the short-term vertical movements such as those observed from archival tagging data. The model provides evidence that the high frequency movements allow conservation of the body temperature at an optimal level during foraging dives for prey. All correspondence should be addressed to T. Azumaya. e-mail: [email protected] Reproduction of Short-Term Vertical Movements Observed Using Archival Tags on Chum Salmon (Oncorhynchus keta) by a Simple Model Tomonori Azumaya and Toru Nagasawa Hokkaido National Fisheries Research Institute, Fisheries Research Agency, 116 Katsurakoi, Kushiro 085-0802, Japan