AFSC/NMML: Bowhead Whale Aerial Abundance Survey off Barrow, Alaska, Spring 2011

Aerial photographic surveys for bowhead whales were conducted near Point Barrow, Alaska, from 19 April to 6 June in 2011. Approximately 4,594 photographs containing 6,801 bowhead whale images were obtained (not accounting for resightings). The 2011 field season was very successful: we flew 36 out of 49 available days and conducted 49 flights in that time; we were grounded due to weather on 13 days. The longest period of time that we were grounded due to weather (low ceilings/fog) was three days. This occurred after the migration had slowed down, during a time when few whales passed the ice perches according to the ice-based visual survey. The 2011 migration was steady with several peaks (30 April, 4-5 May, 12 May), and then the migration rate slowed down considerably after 14 May. The photographs taken in 2011 are a significant contribution to the bowhead whale photographic catalogue. They will be used to calculate a population estimate that may be used for comparison with the 2011 ice-based estimate and will provide better precision in estimates of bowhead whale life-history parameters.

To photograph bowhead whales from the Western Arctic (Bering-Chukchi-Beaufort) stock during the annual spring migration past Barrow, Alaska in order to derive a capture-recapture abundance estimate.

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The 2011 spring aerial abundance survey was conducted jointly by the North Slope Borough Department of Wildlife Management (NSB-DWM) and the National Marine Mammal Laboratory (NMML). Methodology was similar to earlier studies (Koski et al. 1992; Angliss et al. 1995). Surveys were conducted in an Aero Commander 690 with bubble windows in the two forward observer positions. The aircraft flew at an average air speed of ~217km/h (117kts) and altitude of 200m (656ft), and flew directly over bowhead whales during photographic passes. Photographs were taken with a Canon Mark III-1DS digital camera affixed with a Zeiss 85mm fixed f/1.4 Planar T* lens pointed directly downward through the aircraft's ventral camera port that was covered with optical quality glass. Shutter speed was typically 1/2500th second or faster. Aircraft altitude was recorded every 2 seconds with a portable Garmin 76CSx GPS unit and saved on a laptop computer. Robogeo software was used to embed latitude, longitude and altitude into the Exif metadata of each photograph. Calibration targets of known dimensions were photographed twice during the season, at the beginning and end of the survey. These calibration photographs were taken from the same altitudes flown during survey effort. Additionally, each flight began with a photographic pass over a table of known dimensions at a set altitude of 152m (500ft) to act as a daily check of altimeter performance.