Harbor Porpoise, Phocoena phocoena (L.), in the coastal waters of northern Japan

Little is known of the distribution, life cycle, and status of the harbor porpoise Phocoena phocoena in the northwestern Pacific Ocean and adjacent seas. In the present study we assess information in the literature and re-examine 15 specimens in the National Science Museum, Tokyo, in conjunction with data from 45 new animals collected from a variety of sources between 1983 and 1989. Maximum recorded lengths of harbor porpoises from Japanese waters are 158 cm for males, and 185 cm for females, and maximum age was 11 years. All females exceeded the average length of North Sea females at given ages. Size at birth is probably about 80 cm, and parturition likely occurs in May-June in northern Japanese waters, as in the North Atlantic. Known and historical geographical limits are given and compared with the equivalent habitat conditions extant in the western North Atlantic. The most southerly winter record is from Taiji, Wakayama, at latitude 34 degree 15'N and the most northerly confirmed sighting from Shelikhova Bay in the northeastern Sea of Okhotsk at 57 degree -58 degree N, in August 1989. The latter is unlikely to represent the northern limit of the summer-fall distribution. Seasonal migrations, especially in and out of the Sea of Okhotsk, must occur because of extensive ice coverage in winter, but in Japanese waters there are confirmed records of porpoises as far north as the northern tip of Hokkaido Island in January.