Use of fish-borne camera to study chum salmon homing behavior in response to coastal features

Abstract

We used a fish-borne digital still-camera logger (DSL) to obtain visual information on surrounding environments encountered by homing chum salmon Oncorhynchus keta in the final period of migration at their southernmost distribution in Japan. Two salmon, a female and a male, were released with a DSL and were recovered 7 h and 8 d after release, respectively; we provide image data of their views. Of the underwater photos taken from the female and male, 99 and 88% (of a total 842 and 831 images), respectively, were taken in good light conditions. Both chum salmon vis- ited the sea surface and sea floor but stayed in shallow water most of time. The salmon sometimes encountered floats of fishing gear, other chum salmon, Nomura's jelly fish, and other organisms, but very few scallop culturing rafts. The results suggest that the salmon swam in a group during this phase of the homing migration. The salmon were not attracted to farming gear (for shade or refuge), and in fact seemed to avoid it. The present study demonstrated that a fish-borne DSL is a useful and reliable tool for monitoring fish behavior and the relationship between their behavior and the sur- rounding environment.