Aerial Surveys of Belugas in Cook Inlet 2001-2002

July 10, 2004

The National Marine Fisheries Service (NMFS) conducted aerial surveys of the beluga whale (Delphinapterus leucas) population in Cook Inlet, Alaska, almost monthly between June 2001 and June 2002. The surveys were flown in a twin-engine, high-wing aircraft at an altitude of 244 m (800 ft) and speed of 185 km/hour (100 kt). Tracklines were approximately 1.4 km offshore, and systematic transects were made across the inlet, covering much of upper Cook Inlet. These methods were consistent with NMFS= abundance surveys conducted each June or July since 1993, except that only in June were there multiple surveys (repeat samplings) within a block of days. During the 2001­ 02 monthly surveys, aerial counts of belugas (median counts when more than one observer was counting) generally stayed high from June through October (n = 211 in June, 39 and 152 in July, 205 in August, 185 in September, 162 in October, respectively), but counts dropped from November to April (n = 24 in November, 15 in January, 0 in February, 18 in April, respectively) before rising again the following June (n = 192). Low counts in winter were probably due to ice in the inlet, making it hard to see the white whales. This study provides evidence of the presence of belugas in upper Cook Inlet in nearly every month of the year, but it is not clear what proportion of the population remains in the upper inlet year-round.

Each June or July since 1993, the National Marine Fisheries Service (NMFS) has conducted annual aerial surveys to document the distribution and abundance of belugas (Delphinapterus leucas) in Cook Inlet (Withrow et al. 1994; Rugh et al. 1995, 1996, 1997a, 1997b, 1999, 2000a, 2001, 2002, 2003).  The small size of this beluga stock (approximately 350 whales; Hobbs et al. 2000a) and their isolation from other stocks (O=Corry-Crowe et al. 1997; Laidre et al. 2000;  Rugh et al. 2000b) has raised concerns about the management of this population.  On 31 May 2000, this stock was designated as depleted under the Marine Mammal Protection Act (65 FR 34590).  A small, regulated harvest by Alaska Native has continued.

As a part of the research to help reach management goals, it has proved important to establish where the Cook Inlet stock of belugas are throughout the year, not just in June or July when all of the abundance surveys have been conducted.  The winter distribution has been an issue raised by local Natives (Huntington 2000), and establishing whether the whales use upper Cook Inlet year-round may play an important role in identifying and protecting appropriate habitat.  Accordingly, the current study was designed to survey beluga distribution in upper Cook Inlet (north of East and West Forelands) every 1-2 months between the annual abundance surveys conducted in June 2001 (Rugh 2002a) and June 2002 (Rugh 2002b).  The intent was to keep the search effort as consistent as possible with the previous surveys, except the emphasis would be on beluga distribution, not abundance, reducing the need for multiple counts across several days.

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

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