Aerial Surveys of Beluga Whales, Delphinapterus leucas, in Cook Inlet, Alaska, June 2005 to 2012
Aerial surveys of the beluga population in Cook Inlet, Alaska, 2005 to 2012
NOAA Fisheries has conducted aerial surveys of the beluga population in Cook Inlet, Alaska, each June and/or July since 1993. Results from 1993 to 2000 and 2001 to 2004 were published previously. The current document is a compilation of data from field reports for the subsequent years, from 2005 to 2012.
Surveys during these years occurred 31 May-9 June 2005 (54.5 flight hours), 6-15 June 2006 (58.4 flight hours), 7-15 June 2007 (47.2 flight hours), 3-12 June 2008 (47.7 flight hours), 2-9 June 2009 (39.4 flight hours), 1-10 June 2010 (48.4 flight hours), 31 May-9 June 2011 (47.0 flight hours), and 29 May-7 June 2012 (53.0 flight hours). All surveys were flown in twin-engine, high-wing aircraft (i.e., an Aero Commander or Twin Otter) at a target altitude of 244 m (800 ft) and speed of 185 km/hour (100 knots), consistent with NOAA Fisheries’ surveys of Cook Inlet conducted in previous years. Tracklines were flown 1.4 km from the shoreline along the entire Cook Inlet coast, including islands. Offshore transects were designed to run the length of Cook Inlet or in a sawtooth pattern across the inlet, minimizing overlap within each season, as well as between years. These aerial surveys effectively covered 25% to 34 % of the total surface area of Cook Inlet in each of the 8 years and nearly 100% of the coastline (with the exception of 2007: 71%). In particular, most of the upper inlet, north of the Forelands where beluga whales are consistently found, was surveyed five to six times each year.
Paired, independent observers searched on the coastal side of the plane, where virtually all beluga sightings occur, while a single observer searched on the offshore side. A computer operator/data recorder periodically monitored distance from the shoreline (1.4 km) with a clinometer (angle 10 °). After finding beluga groups, a series of aerial passes allowed all four observers to each make four or more independent counts of every group, (i.e., typically 16 counts of each group conducted during 8 passes). In addition, whale groups were video recorded for later analysis and more precise counts in the laboratory.