Stranding, entangling, and sighting records of marine mammals along the beach and offshore of Niigata Prefecture, Sea of Japan, were compiled from June 2001 to May 2005, in order to understand the relationship between the species characteristics and oceanographic conditions. As a result, 64 instances, comprising 31 stranding, 16 entangling, and 18 sighting records, were estimated. These records were widely distributed throughout the coast of Niigata Prefecture. The species composition was 9 species of cetaceans (minke whale, sperm whale, Baird’s beaked whale, Stejneger’s beaked whale, Risso’s dolphin, Pacific white sided dolphin, bottlenose dolphin, spinner dolphin, and Dall’s porpoise) and 2 species of pinnipeds (northern fur seal and harbor seal). The Pacific white sided dolphins occupied the greatest number among the stranding animals, while most of the entangling animals were the minke whales. It seems likely that an occasional observation of a sperm whale and a stranding record of a spinner dolphin were the first discovery from the central zone of Sea of Japan.
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