Results of the Japanese dedicated cetacean sighting survey in the North Pacific in 2021 summer season
Taika Katsumata, Megumi Takahashi, Seiichiro Teruya, Ryu Watanabe, Aoi Irie and Koji Matsuoka
A systematic largescale vessel-based sighting survey was conducted in summer 2021 by Japan to examine the distribution and abundance of large whales in the North Pacific. The research area was set between 30oN-53oN and 150oE-155oW. The survey was conducted between 4 August and 30 September. The research vessels Yushin-Maru and Kaiyo-Maru No.7 were engaged in the surveys. A total of 3,713.8 n.miles was searched by the passing mode in the research area. Coverage of the searching effort on the planned cruise track line was 70.4%. In total, seven large whale species were sighted: blue (17 schools/20 individuals), fin (78/124), sei (102/156), Bryde's (57/72), common minke (1/1), humpback (13/16), and sperm (94/193) whales. Photo-ID images were collected from blue (12 individuals), humpback (5 individuals), and sperm (1 individual) whales. Biopsy skin samples using a Larsen system were collected from blue (n=1), fin (n=5), sei (n=15), and humpback (n=3) whales. Also satellite tracking experiments were conducted on fin and sei whales. The density index of blue and fin whales has increased notably since the last survey in 2010 and 2011 in this area, and Bryde's and humpback whales, which were not detected in the previous survey, were also sighted. The sighting data will contribute to the work on the management and conservation of large whales in the North Pacific.