論文ID: 2022F001
The relationships between oceanographic conditions and the distribution of common minke whales off southeastern Hokkaido was investigated in this study. Sighting surveys of common minke whales in this region were conducted in September, in 2002 and from 2004 to 2006. The density index (DI, the number of schools per 100 n.miles) of the whales decreased from 5.6 schools in 2002 to 1.2 schools in 2006. During the 4 years in which surveys were conducted, the monthly mean sea surface temperature (SST) in the survey area increased from 16.6°C in 2002 to 19.5°C in 2006, while the mean SST recorded at sighting locations was 15.5°C. The proportions of surveyed areas with a monthly mean SST ≤16°C in 2002 and 2004 were 46.5% and 17.0% respectively, whereas in 2005 and 2006, none of these areas had a monthly mean SST of less than 16°C. Pacific saury are among the major prey items of the minke whales in this region, and the number of the fishing boats was used as an indicator of the presence of the species in the surveyed area. The 4 year mean SST at the locations of the boats was 15.1°C. A reduction in the local abundance of the saury from 2002 to 2006 was inferred from the number of the boats operating in the region. These findings suggested that the apparent decline in the abundance of whales in the study area was associated with changes in SST and the availability of Pacific saury.
