Population trends of the Kuril harbour seal Phoca vitulina stejnegeri from 1974 to 2010 in southeastern Hokkaido, Japan

Abstract

The Kuril harbour seal Phoca vitulina stejnegeri is an endangered species which inhabits southeastern Hokkaido, Japan. Its population declined precipitously from between 1500 and 4800 individuals in the 1940s to a few hundred individuals in the early 1970s. The causes of this decline are thought to be commercial harvesting, bycatch in autumn set-net salmon fishing, and other human activities, including coastal fisheries. To quantify Kuril seal population trends, counts were performed each year at haul-out sites during the pupping season from 1974 to 2010 and during the moulting season from 1983 to 2010. The average population growth rate was ~4% per annum over the past 37 yr. Two haul-out sites (Kenbokki Island and Hattaushi) from which the species had disappeared in the early 1980s showed no evidence of being recolonized. Commercial harvesting ended in the late 1980s and probably had an effect on population trends until the 1990s. The bycatch of seals during autumn set-net salmon fishing in the 2000s remained similar to, or slightly greater than, that during the 1980s. Recently, seals have been observed at 9 haul-out sites during the pupping/moulting season along the coast of southeastern Hokkaido. Approximately 70% of the seals found were at Cape Erimo (~500 seals) and at Daikoku Island and Akkeshi (~250 seals).