Mass Mortality of Short-tailed Shearwaters along the Japanese Coast

Abstract

Mass-mortalities of short-tailed shearwaters (Puffinus tenuirostris) occurred in 1983-1985, along the Pacific coast of central and northern Honshu, Japan, from late May to mid June. The carcass numbers were annually counted along three 20 km courses at three localities on the Pacific coasts; Atsumi Peninsula in Aichi Prefecture, Kujukuri Beach in Chiba Prefecture and Ogawara Coast in Aomori Prefecture. At Kujukuri Beach, annual carcasses were 32.5, 44.0 and 26.8/km from 1983 to 1985; these were two to four times as many as in the previous years, 12.3±5.7/km (1977-1982). Similarly, high values of 16.4 and 47.6/km were recorded at Atumi in the first two years, with lower number in 1985. At Ogawara Coast few carcasses were found in the first two years, but increased in 1985. This northward shift of mortality was likewise indicated by answers to our questionnaire issued to wildlife divisions of Pacific coast prefectures from Okinawa to Hokkaido. Of 2, 258 carcasses collected, more than 99% were considered to be young of the year with a mean weight of 286.4±22.3 (SD) gr. (n=59), about 110 g lighter than that of the live birds, 399.4±32.7 (SD) gr. (n=22), captured in fishing nets. The main cause of mass-mortality of young birds was due to emaciation. Since the mass-mortality of this species has been recorded in 1964 and 1973-1975 in Japan and in 1934, 1942 and 1954 in Australia, a rough ten-year periodicity could be expected, and the recent one of 1983-1985, reported here, supports this theory.