Abundance decline in the narrow‐ridged finless porpoise population off the Pacific coast of eastern Japan

The narrow‐ridged finless porpoise Neophocaena asiaeorientalis is a small‐toothed whale with a coastal habitat and is sensitive to human activity. Aerial sighting surveys were conducted in 2012 to evaluate the abundance and distribution of the Sendai Bay‐Tokyo Bay population off the Pacific coast of eastern Japan. We flew along 35 east–west transects at intervals of 11.6 km over the study area between 34°57′ and 38°21’ N. In total, 25 groups were detected by two observers. The mean group size was 1.44 individuals. Porpoise abundance was estimated to be 1,491 individuals (coefficient of variation = 32.4%), which was lower than the abundance estimated in 2000 (z test, p