Development of Ultrasonic Telemetry Technique for Investigating the Magnetic Sense of Salmonids

Abstract

We developed an ultrasonic telemetry technique for investigating the magnetic sense of the ocean migrating adult salmonids and applied it to maturing chum salmon Oncorhynchus keta off the Kuril Islands in the western North Pacific in September 1994. We made artificial magnetic field generators, consisting of an electromagnetic coil and a drive circuit, which periodically disturb the geomagnetic field around their heads. Tracking was carried out under the following three conditions. Condition 1: the coil and drive circuit were attached to the head and back of three salmon, respectively and an ultrasonic transmitter was also inserted into the stomach for tracking. Condition 2: the dummy coil and drive circuit were attached to the head and back of other three salmon, respectively and an ultrasonic transmitter was also inserted into the stomach. Condition 3: only either a transmitter or a transmitter and the dummy drive circuit were attached to the remaining two salmon. We collected information on the horizontal and vertical movements of the fish. Most salmon moved in southerly directions and swam upper 40 m. The average ground speeds ranged from 1.11-1.84 fork length/s for magnetically disturbed salmon (condition 1) and 0.96-1.65 fork length/s for the others (conditions 2 and 3). No significant differences with respect to horizontal movement, vertical movement, and/or swimming speed were found between the magnetically disturbed salmon and the others. The attached devices might give no serious damage to the swimming activity of salmon.