Aerial Surveys of Belugas in Cook Inlet

September 10, 2005

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).

Belugas (Delphinapterus leucas) are distributed around most of Alaska from Yakutat Bay to the Alaska/Yukon border (Hazard 1988).  Five stocks are recognized in this region: Cook Inlet, Bristol Bay, Eastern Bering Sea, Eastern Chukchi Sea, and the Beaufort Sea (Angliss and Lodge 2004, O’Corry-Crowe et al. 1997).  The most isolated of these is the Cook Inlet stock, separated from the others by the Alaska Peninsula (Laidre et al. 2000). Belugas in Cook Inlet are very concentrated in a few river mouths and bays during parts of the year (Rugh et al. 2000a).  The small size (approximately 400 whales; Hobbs et al. 2000a) and geographic and genetic isolation of the whales in Cook Inlet (O’Corry-Crowe et al. 1997, Laidre et al. 2000, Rugh et al. 2000a), in combination with their strong site fidelity, has made this stock vulnerable to anthropogenic impacts. Until 1999, these whales were subjected to an unregulated harvest (Mahoney and Shelden 2000), but on 31 May 2000, the stock of belugas in Cook Inlet was designated as depleted under the Marine Mammal Protection Act (65 FR 34590) and is now managed with a small, regulated, subsistence harvest by Alaska Natives.

Each June/July since 1993, the National Marine Fisheries Service (NMFS) has conducted annual aerial surveys to study the distribution and abundance of belugas in Cook Inlet (Withrow et al. 1994, Rugh et al. 1995, 1996, 1997a, 1997b, 1999, 2000b, 2001, 2002, 2003, 2004).  This project has been in cooperation with the Cook Inlet Marine Mammal Council (CIMMC) and the Alaska Beluga Whale Commission (ABWC).  Aerial surveys are proven to be the most efficient method for collecting distribution and abundance data for belugas in Cook Inlet and have been used for many years prior to the NMFS surveys (e.g., Klinkhart 1966, Calkins et al. 1975, Murray and Fay 1979, Calkins 1984).  The NMFS studies have been the most thorough and intensive (Rugh et al. 2000a).  The primary objectives for the current study are to document sighting locations and count belugas in Cook Inlet while maintaining a continuity with preceding studies to allow for inter-year trend analyses.  Results from 1993 to 2000 were published in Rugh et al. (2000a).  The current document is a collation of field reports for subsequent years from 2001 to 2004.

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Last updated by Alaska Fisheries Science Center on 09/11/2018

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