Observation on the Emaciated and Dead Short-tailed Shearwaters, Puffinus tenuirostris, in the North-Western Sea Area of the North Pacific in 1983

Abstract

A study on migratory activities of the short-tailed shearwaters, Puffinus tenuirostris, was conducted during a voyage of trans-North Pacific from Japan to the United States. Its mass mortality was found occurring off Kashima-nada, Honshu, early June 1983. No weakened nor dead birds were observed on the navigation routes from Toyohashi to Portland, via the Hawaii, and from Portland to the Kuril Islands, via the Unimak Pass and Attu Island. A first floating emaciated bird occurred on June 5, when we came to off Hokkaido; in the waters south of it, along Tohoku to Kashima-nada, most of the 294 birds we encountered on June 6 were apparently emaciated, with 3 floating birds already dead. This sea area well coincided with the northern limit of the mass mortality recorded in that year, and was within the Kuroshio warm current. This suggests that birds which were strong enough to pass into the northern cold current, richer in marine productivity, would survive and that those exhausted not reaching there would die within the Kuroshio Current, owing to the food shortage.