2015 Volume 25 Pages 7-16
In March and April 2015, a gray whale Eschrichtius robustus was sighted in two areas off central Niigata Prefecture, Sea of Japan. First, off Teradomari, Nagaoka City, adjacent to the estuary of the Ohkouzu Diversion Channel of the Shinano River in the same location where a gray whale was observed in the spring of 2014. The other sighting was in the coastal area off Tainai City, adjacent to the estuary of the Tainai River. It was identified that the Teradomari whale was the same as the Tainai whale based on the body markings. Also, the 2015 gray whale appeared was identified as the same individual as the one appeared off Teradomari in 2014. The whale was observed between 31 March and 10 April 2015 in Teradomari area, and was sighted along about 1,000m length of coast and 100m to 500m offshore from the mouth of the Ohkouzu Channel. The whale frequently appeared on the northern side of the river mouth and whale stayed for a shorter period and the area the whale was observed was smaller in 2015 than in 2014. The whale was observed in Tainai between 11 and 21 April 2015, and was sighted along a 1,200m length of the coast 100m offshore from the mouth of the Tainai River. The whale frequently appeared around outside of the breakwater structure on the southern side of the river mouth. The whale remained in areas where the bottom was sandy mud, at a depth of 3 to 7m in Teradomari and about 3m in Tainai. In both areas, the whale repeated diving and surfacing suggesting feeding behavior. The whale traveled about 70km from Teradomari to Tainai in one day. The whale stayed at central Niigata prefecture at least 22 days. This behavior of the whale suggests it was migrating to the north while feeding opportunistically. It seems the area off central Niigata was used not only for the migration route but also for feeding.
