Potential Role of the Magnetic Field on Homing in Chum Salmon (Oncorhynchus keta) Tracked from the Open Sea to Coastal Japan

In order to examine the Earth’s magnetic intensity and inclination during homing migration of chum salmon (Oncorhynchus keta) and to present tracking data consistent with the geomagnetic imprinting hypothesis that salmon migrate homeward using the Earth’s magnetic intensity or inclination, archival tagging operations were carried out in the Bering Sea in 2012 and 2013. DST magnetic tags were attached to the bodies of chum salmon on board a research ship. The tags recorded temperature, depth, magnetic intensity and inclination, compass heading, and tilt of the fi sh. Two tagged chum salmon were subsequently recovered near the coast of Hokkaido, Japan, in 2012 and 2013, respectively. The estimated homing route of the 2012 fi sh was linear from the release site to the coast of Hokkaido, Japan. The 2013 fi sh reached the coast of Hokkaido by way of the east coast of Kamchatka, Russia. These estimated homing routes were not consistent with the great circle route. The estimated homing migration routes were consistent with the isoline of magnetic intensity rather than magnetic inclination. For the tag recovered in 2012, the homing migration route was approximately along the isoline of magnetic intensity at the recovery site. Therefore, we conclude that this study supports the geomagnetic imprinting hypothesis that magnetic intensity plays an important role in the homing migration of chum salmon in