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Cruise Report of the New Scientific Whale Research Program in the western North Pacific (NEWREP-NP) in 2017 -Coastal component off Abashiri in the southern Okhotsk Sea-
Yoshida, H., Ito, N., Maeda, H., Nakamura, G., Inoue, S., Hirose, A., Nishimura, F., Asano, Y., Yamamoto, R., Watanabe H., Agari T., Sonobe N., Kumagai S., Sazawa R., Takahashi, T., Hatsuse A., Sato, S., Higa, H., Hiruda, H., Miyashita. T., Kato, H.
International Whaling Commission
The NEWREP-NP coastal component off Abashiri, northern Japan (southwestern part of the sub-area 11), was conducted in the southern Okhotsk Sea, from 11 June to 6 July 2017. The survey was carried out using five small-type whaling catcher boats as sampling vessels, in coastal waters mainly within about 40 nautical miles from Abashiri port. Common minke whales collected were landed at the NEWREP-NP research station for biological examination. During the survey, a total of 2,449.9 nautical miles (243.4 hours) was searched and the 128 schools (132 individuals) of common minke whales were encountered. Sightings of 39 schools (55 animals) of fin whales, of 4 schools (10 individuals) of humpback whales, of two blue whales, and of a sperm whale were also made. Of 132 common minke whales encountered, 47 animals were collected. Ear plugs and eye lenses for age determination and gonad for reproductive study were collected from all the whales. Sex of animals caught was biased towards the female (9 males and 38 females). Average body length of males was 6.92m (SD=0.55, Range=5.62-7.55m) and 7.35m (SD=0.85, Range=4.96-8.18m) for females. Of 9 males, 8 were sexually mature (88.9%) and 30 of 38 females attained to sexual maturity (78.9%). The 25 mature females were pregnant. Stock assignment was conducted from nuclear microsatellite data. Of 47 animals collected, 28 were assigned to J stock and 17 were identified as O stock. The remaining two animals could not be assigned. Proportion of J stock animals increased from June (53.6%) to July (76.5%). Sex ratio of males was higher in J stock animals (28.6%) than in O stock animals (5.9%). In females, proportion of mature animals was higher in O stock (93.8%) than in J stock (65.0%). From foetus body length, conception date was estimated using the growth formula. Results indicate that animals migrating to the Okhotsk Sea possess separate two breeding seasons, i.e., autumn breeding season and winter breeding season prolonged to spring. Females pregnant with foetus estimated to be conception in autumn were assigned to J stock. All females assigned to O stock conceived in a period from winter to spring. Dominant prey species detected from whale forestomach was Krill (89.4%), followed by Copepoda (4.3%) and only one animal feed on walleye pollock (2.1%). Animals feeding on copepods were assigned to O stock. An individual taking walleye pollock was identified as J stock.