THE BEHAVIOR AND AMBIENT TEMPERATURE OF HOMING CHUM SALMON MONITORED BY A DATA LOGGER (19th Symposium on Polar Biology)

We studied the behavior of homing chum salmon in coastal waters using a data logger tagging method that will increase the duration of study and sample size without tracking effort We used data loggers, which can record the depth data and the temperature data simultaneously for 19.3 days at 5 and 10 s intervals, respectively. In late November 1994 off the coast of Sannku, northern Honshu, we released eight homing adults with data loggers, three loggers were retrieved near the release site after 0.8-1 3 days. A possible reason for missing loggers is the accidental detachment of instruments General feature of vertical behavior of salmon was similar to previous results obtained by a transmitter-tracking system; salmon made a series of ascents and descents, whose vertical speed was about 0 1-0.3m/s, and returned frequently to the surface water. As a result, salmon made large amplitude zigzag motions starting from the surface water The median thickness of the water column where salmon traveled through in two minutes was 3 2-6 5 m The vertical thermal structure was well mixed. There was no consistent tendency of behavior in relation to the ambient water temperature The observed large amplitude of vertical zigzag motion could be typical behavior of homing chum salmon in our study area in the isothermal water column. We conclude that use of a data logger holds promise for behavior studies of homing adult salmon, which facilitate recovery of the instruments by returning to natal rivers