NOAA Technical Memorandum NMFS-AFSC-385 (2019)


Little is known about Dall’s porpoise (Phocoenoides dalli) population biology in Southeast Alaska. Here we present the first abundance estimates for Dall’s porpoise in the waters of Southeast Alaska. We studied the density and abundance of Dall’s porpoise during 19 line-transect vessel surveys covering the major inland waters of Southeast Alaska between the months of April and September, from 1991 to 2012. Dall’s porpoise was the most frequently encountered odontocete (toothed cetacean) within the study area and abundance was estimated with multiple-covariate distance sampling methods. Highest abundance was recorded in spring months (N = 5,381, CV = 25.4%), with lower numbers in summer (N = 2,680, CV = 19.6%), and lowest in fall (N = 1,637, CV = 23.3%). Peak density in spring months (31.6 porpoises/100 km2) was the highest ever reliably recorded for inshore areas of the species’ range. Estimates of abundance for comparable areas (i.e., those surveyed consistently in each study year) showed strong yearly fluctuations, and demonstrate that this species is a common inhabitant of these waters from at least spring to early fall.