Coastal use patterns of Japanese harbor seals (Phoca vitulina stejnegeri) in Akkeshi Bay in Hokkaido during the spring season

Abstract

Recently, the number of harbor seals on Daikoku island in the Akkeshi region have tended to increase. Consequently, fishery damage caused by the seals has also increased in the bay, which is located near Daikoku island. However, because the seals leave no trace after they feed, it is unclear how much seals actually feed on the fish and what is the real impact on the fisheries. In this study, we aimed to clarify when and how often seals use the Akkeshi Bay as a feeding ground, and what kind of individuals are utilizing the area. The behavioral patterns of harbor seals that use the Akkeshi Bay were studied based on information from transmitters and land-based observation on Daikoku island. As a result, two individuals—an adult female and a female pup—were captured in Akkeshi Bay. The location used by both individuals in the bay overlapped with small fixed nets, and they generally conducted short, shallow dives. The seals moved to another location from the inside of the Akkeshi Bay after early spring, and the timing of the move overlapped with the end of fishing season. These results showed that fishing and the seals are closely related.