Abstract
In order to elucidate the occurrence of narrow-ridged finless porpoises (Neophocaena asiaeorientalis sunameri) in the northern part of Harima Nada, line-transect sighting surveys were conducted on the car ferry route between Himeji and Fukuda of Shodoshima Island in 2010–2012. A single observer detected a total of 167 individuals in 93 groups, while on ferries that ran a total of 5482.5 km under the conditions of the Beaufort wind force scale < 3 and without glare. There were more finless porpoise sightings in the survey area from March to June. The sighting rate in the coastal waters of Shodoshima Island was higher than in other waters in April–June. Sightings in the survey area also tended to increase in August. In this season, a high sighting rate was recorded off the coast of Himeji. The density in the survey area was estimated at 0.304 individuals/km2 (CV = 0.287) in April–June, 2011 and at 0.276 individuals/km2 (CV = 0.372) in March–May, 2012. The mean number of porpoises per one way ferry trip under the conditions of the Beaufort wind force scale < 3 in March-June was 1.88 individuals in 2011 and 1.78 individuals in 2012. These sighting rates were higher than values evaluated from similar surveys in the 1970s and 1999–2000 (Kasuya et al. 2002).
