Aerial surveys of belugas in Cook Inlet, Alaska, June and July 2001, 2002, 2003, and 2004

Abstract

The National Marine Fisheries Service (NMFS) has conducted aerial surveys of the beluga population in Cook Inlet, Alaska, each June and/or July since 1993. Results from 1993 to 2000 were published in Rugh et al. (2000a). The current document is a collection of field reports for the subsequent years, from 2001 to 2004. Surveys were done 5-12 June 2001 (55 flight hours; 29.3 hours good effort), 4-11 June 2002 (45 flight hours; 24.4 hours good effort), 31 May -12 June 2003 (61 flight hours; 30.5 hours good effort), and 2-9 June 2004 (45 flight hours; 19.0 hours good effort).

All surveys were flown in an Aero Commander (twin-engine, high-wing aircraft) at a target altitude of 244 m (800 ft) and speed of 185 km/hour (100 knots), consistent with previous surveys. Tracklines were flown 1.4 km from shore along coastal areas around the entire Inlet, including islands, and offshore transects were designed to run the length of Cook Inlet or cross it, minimizing overlap within each season as well as between years. These searches effectively covered 25% to 31% of the entire Inlet in each of the 4 years, but nearly 100% of the coastal areas were surveyed each year. In particular, most of the upper Inlet, where belugas have been found consistently, was surveyed five to six times each year. Paired, independent observers searched on the coastal (left) side of the plane, where virtually all beluga sightings occur, while a single observer searched on the right. A computer operator/data recorder was also on the left side. After finding beluga groups, a series of aerial passes allowed four primary observers to each make four or more independent counts of every group, (i.e., typically 16 aerial counts for each group).

In addition, whale groups were videotaped for later analysis and more precise counts in the laboratory. During these surveys, only two belugas were seen in lower Cook Inlet (south of East and West Foreland), none were seen in the upper Inlet south of North Foreland and Point Possession, but many were seen in the Susitna Delta (33%), Knik Arm (31%), and Turnagain Arm/Chickaloon Bay (36%). The annual sums of medians from aerial counts provide a quick index of relative abundance, not corrected for estimates of whales missed and assuming there may be some exchange of whales between areas. Annual index counts have not changed appreciably from 1998 to 2004 (192, 217, 184, 210, 181, 174, and 187, respectively), but these counts are lower than those made from 1993 to 1997 (302, 276, 322, 287, and 261, respectively). These annual medians mirror the abundance estimates that have been corrected for missed whales (653, 491, 594, 440, 347, 367, 435, 386, 313, 357, and 366 for the years 1994-2004, respectively).


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