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Cetacean Assessment & Ecology Program

August 2006 Survey of Belugas in Cook Inlet

Cook Inlet map, see caption
Figure 1.  On-effort tracklines and beluga sightings for upper Cook Inlet on 16-17 August 2006.  (click map to enlarge)

NMFS biologists conducted an aerial survey of the beluga whale population in upper Cook Inlet, Alaska, 16-17 August 2006. The survey (10.1 flight hours) provided thorough coverage of all coastal areas north of East and West Forelands in the upper inlet (Fig. 1). Consistent with NMFS surveys conducted since 1993, the August 2006 survey was flown in a high-wing, twin-engine aircraft at an altitude of 244 m (800 ft) and a speed of 185 km/hr (100 kt).

The survey in August 2006 was different from most previous surveys in that it was done in a Twin Otter aircraft, instead of an Aero Commander, and paired, independent searches were not conducted. Tracklines were flown both parallel to the coast (1.4 km offshore) and across the inlet. When beluga groups were encountered, a series of aerial passes was made with two observers each making four or more independent counts. The primary intent of the survey was to document whale groups in video cameras for an analysis of age structure (white adults relative to dark juveniles).

Belugas were found near the mouth of the Susitna River (median counts of 116 whales on one day and 47 on the second day), in Knik Arm (10 belugas on the first day and 95 on the second), and in Turnagain Arm near Bird Point (2 belugas seen on the second day).

These sighting locations were fairly typical of the distribution seen each June except that it was unusual to find no whales in Chickaloon Bay. The density of the whale group seen near the Susitna River on 17 August was one of the highest ever observed; but on the next day, belugas were in small, somewhat dispersed groups in this area. Meanwhile there was nearly a tenfold increase in whales at the far end of Knik Arm indicating that many whales had moved from the Susitna River to Knik Arm.

The daily median estimates (a quick index of relative abundance not corrected for missed whales) were 126 for 16 August and 143 for 17 August. The latter count compares favorably with the index count for June 2006 (153 belugas) but is below the similar count done in August 2005 (236 belugas on 11 August and 277 on 12 August).

By Dave Rugh, Kim Goetz, and Christy Sims

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