Mass mortality of Slender-billed Shearwater, Pnffinus tenuirostris, in Suruga Bay

Abstract

The authors found a great number of dead or dying Slender-billed Shearwaters, Puffinus tenuirostris, in Suruga Bay from May 23 to 26, 1964, when the plankton survey was made on the Tansei Maru of Ocean Research Institute, University of Tokyo.This phenomenon was observed almost in all parts of the bay, especially in the inner part. Fourteen dead or dying birds were observed in area, 150m in width and 10km in length, in the inner part. From this observation the total number of birds in this inner part was estimated at more than 4, 000.Four specimens were used for dissection. One of these was alive and three were dead when they were collected. Blood was vomitted in two specimens. Stomach contents were absent in three specimens and stomach bleeding was found in two and cloaca was filled with feces in one.The southern wind blew ashore frequently in this period, especially strongly on May 23 and the Kuroshio current was shifted to the south and water temperature was lower than usual.The cause of this mass martality could not perfectly be clarified, but judging from the results of dissection and meteorological and oceanographical data, the unusual sea current of this year caused the scarcity of food in the normal distribution sea area of this shearwater and would have forced them to prostraction, while the strong southern winds that followed drifted exhausted birds to the shore. The authors have no definite evidence to conclude whether this mass mortality was caused by some diseases.