Changes in the numbers of spotted seals (Phoca largha) in Bakkai port and on Yagishiri Island in Hokkaido, Japan from 2003 to 2009

Abstract

In this study, we analyzed annual and seasonal changes in the numbers of spotted seals (Phoca largha) hauled out in the area around Bakkai and Yagishiri in the Japan Sea from 2003 to 2009, for the first time. The number of animals observed tended to increase over the years at both sites, but the increment was bigger in Bakkai than Yagishiri. This is thought to be due to spatial differences among the haul-out sites, with the former location having a larger area. In addition, seasonal changes in the numbers of seals were different; there was a single peak in Bakkai observed in winter, while Yagishiri had two peaks, one during winter and the other in spring. These seasonal changes are thought to be related to changes in the distribution of sea-ice in the Okhotsk Sea. Because adult seals are known to migrate to sea-ice areas to breed after winter, the seals counted in Yagishiri during spring reflect the number of sub-adults staying in this region.