Sighting records of whales by the Sado Line (Sado Kisen) jetfoils and car ferry boats operated on Niigata-Ryotsu route, Sado Strait, Sea of Japan, were compiled from March to November, 2005. This work was carried out successibly since 1994, in order to avoid the ship collision with cetaceans. Twenty two instances, comprising 16 jetfoil and 6 car ferry observations, were enumerated. These numbers were less than those of hitherto known records. More than two sighting records in a day were seen only in twice a year. The greatest number was enumerated in May, with the next months of April and March. The time zone of higher frequencies was concentrated in 8 a.m. and 2 p.m. On 19 November, 2005, a jetfoil collision occurred without human injury. In relation to an increase in high-speed ship collisions with cetaceans in several seas of the world, the better counterplan was considered and discussed to prevent collisions.
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.
Pacific white-sided dolphins (PWS) are the most frequently observed cetacean in the Tsugaru Strait. In this study, the data of sighting survey conducted from ferry vessels between Hakodate and Aomori from May 2003 to February 2006 was analyzed. Seasonal and geographical distributions of PWS in the strait were discussed. Four areas in the strait were defined according to the latitude, and the number of observations and encounter rate of PWS in each area was calculated monthly for the investigation of the difference of the distribution. The results indicated that PWS were frequently appeared only from April to June. The encounter rates in the southern 3 areas were peaked in May, and then declined in June. It suggests that they appeared frequently in spring in the strait, and appeared occasionally in the other seasons, and most of the PWS stayed once around the mouth or inside of the Mutsu bay, and then moved to Pacific Ocean following the Tsugaru warm current.
The tongues of two Pacific white-sided dolphins were examined by light and scanning electron microscopy.Each tongue was triangular shaped with about 15 cm in length and 6.5 cm in width. The surface of the tongue appeared relatively smooth and no lingual papillae were observed. Parakeratinization was observed in the stratum corneum epidermidis. The tongue was formed of V shape with 6 to 8 grooves on the dorsal surface posterior of the tongue. The taste buds were observed on the papillae in the grooves. By removing the epithelium, it was revealed that the conical connective tissue cores were densely distributed. The morphological characters of the tongue of the Pacific white-sided dolphin were similar to those of the Striped dolphin and Bottlenose dolphin.