Aerial surveys of beluga whales in Cook Inlet, Alaska, between June 2001 and June 2002

Abstract

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.


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