Harbor porpoise (Phocoena phocoena) abundance in Alaska: Bristol Bay to Southeast Alaska, 1991-1993

Between 1991 and 1993, Alaska harbor porpoise (Phocoena phacoena) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entranc e in Southeast Alaska. Line-transect methodology was used, and only those o bservations made during optimal conditions were analyzed. Survey data indic ated densities of 4.48 groups/100 km(2), or approximately 3,531 harbor porp oises (95% C.I. 2,206-5,651) in Bristol Bay and 0.54 groups/100 km(2), or 1 36 harbor porpoises (35% C.I. 11-1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km(2), or an abundance esti mate of 740 (95% C.I. 253-2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km2 and an abundance estimate of 551 (95% C.I. 423-713). Surveys of offshore waters from Prince William S ound to Dixon Entrance yielded densities of 4.02 groups/100 km(2) and an ab undance estimate of 3,382 (35% C.I. 2,567-6,177). Combining all years and a reas yielded an uncorrected density estimate of 3.82 porpoises per 100 km(2 ), resulting in an abundance estimate of 8,340 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746-11,848. Using correction factors from ot her studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number.