Abstract

Two density indices of Dall’s porpoise abundance were estimated for the western North Pacific from 1979 to 1989. One index is the density of animals (number of animals per square n.mile) estimated using line transect methods and the other is the encounter rate (number of Dall’s porpoise sighted per n.mile). The encounter rate increased significantly between 1979 and 1984 (p<0.05), then fell between 1984 and 1986 (p<0.01). The estimated density of animals showed no significant trend between 1979 and 1984. There was evidence of a fall in density between 1984 and 1986 (p<0.05).