Cruise Report of the New Scientific Whale Research Program in the western North Pacific (NEWREP-NP) in 2018 -Coastal component off Abashiri in the southern Okhotsk Sea
Yoshida, H., Shimetani, K., Maeda, H., Nakamura, G., Ogihara, M., Hirose, A., Yamamoto, R., Watanabe, H., Koda, N., Yagi, G., Uruma, H., Murata, H., Kumagai, S., Sazawa, R., Takahashi, T., Fukuyoshi, M., Ogawa, M., Noda, A. and Kato, H.
The second survey of the NEWREP-NP coastal component off Abashiri, northern Japan (southwestern part of the sub-area 11), was conducted in the southern Okhotsk Sea, from 1 to 30 August 2018. 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 4,013.7 nautical miles (400.6 hours) was searched and the 91 schools (93 individuals) of common minke whales were encountered. Sightings of 114 schools (163 animals) of fin whales, and of a humpback whale were also made. Of 93 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 (16 males and 31 females), as same with the last yearâ€™s survey. But, in the second half of the survey, i.e., on or after 16 August, more males were collected (12 males and 8 females). Average body length of males was 6.62m (SD=1.02, Range=4.40-7.58m) and 7.37m (SD=0.98, Range=4.79-8.55m) for females. Of 16 males, 12 were sexually mature (75.0%) and 26 of 31 females attained to sexual maturity (83.9%). The 21 mature females were pregnant. Stock assignment was conducted from nuclear microsatellite data. Of 47 animals collected, 28 (59.6%) were assigned to J stock and 15 (31.9%) were identified as O stock. The remaining four animals could not be assigned. Proportion of J stock animals increased from the first half of the survey (58.3%) to the second half (73.7%). Eleven of 15 females identified as J stock and 8 of 13 O stock females were pregnant. From foetus body length, conception date was estimated using the growth formula. Results show long tailed distribution of conception date with a peak around March. The distribution shape was almost same with that observed in the previous study on conception date in the southern Okhotsk Sea. Dominant prey species detected from whale forestomach was Krill (59.6%), followed by Japanese sardine (38.3%). An animal feed on Pacific herring (2.1%). In the first half of the survey, krill was major prey species (92.6%) and sardine was little observed (7.4%). But, in the second half, sardine was more frequently taken (80.0%).