IMIS

The National Marine Mammal Laboratory (NMML) conducted an aerial survey for small cetaceans from 5 June to 4 July, 1999 in Bristol Bay and along southwestern Alaska Peninsula (out to the 1,829 m [1,000 fm] depth contour). A total of 8,522 km were surveyed in a Dehavilland Twin Otter at 152.5 m (500 ft) altitude and 185 km/hr (100 kts). Two overlapping sawtooth lines were designed along the coastline of Bristol Bay. Both sides of each sawtooth were approximately 37 km with a 46 km base. Large bays were also included in the survey. Primary observers searched through bubble windows on the left and right sides of the aircraft and reported sightings to a computer operator. To estimate a perception bias correction factor for this study, an independent observer was added at a belly window position to determine the number of animals in the immediate vicinity of the trackline that were missed by the primary observers. There were 215 sightings of harbor porpoise (260 individuals), 12 Dall's porpoise (24 individuals), and 16 Pacific white-sided dolphins (170 individuals) while surveying tracklines. Additional cetacean sightings included 12 gray whales (13 individuals), 18 humpback whales (29 individuals), 8 minke whales (13 individuals), and 3 killer whales (11 individuals). Purpose The current study (1997-1999) will provide new abundance estimates for each stock of harbor porpoise and Dall's porpoise. Although the previous harbor porpoise surveys (1991-1993) used a vessel platform for the inside waters of southeast Alaska (Dahlheim et al. 1992, 1993, 1994), the current survey was conducted entirely from aircraft. However, a concurrent vessel survey in a selected portion of southeastern Alaska and a calibration study with the survey vessel. We report here the results from the third year of surveys (1999).