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NOAA Technical Memorandum NMFS-AFSC-263

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Aerial surveys of beluga whales, Delphinapterus leucas, in Cook Inlet, Alaska, June 2005 to 2012


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 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 year 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 NMFS' 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.

During the 8 years of surveys from 2005 to 2012, belugas were not seen in lower Cook Inlet (south of East and West Foreland) nor in the upper inlet south of North Foreland and Point Possession until 2012 when a group of at least seven belugas was observed headed toward West Foreland on 31 May. Before 1996, it was common to see beluga groups south of North Foreland in Trading Bay. Since the mid-1990s to early 2000s, only one or two beluga groups have been found in lower Cook Inlet south of East and West Foreland and none in the region between the Forelands and North Foreland. Groups of more than one or two whales have not been seen in the lower inlet since 1995. During the 2012 survey, this beluga group moved into the upper inlet and was observed in Trading Bay for the remainder of the survey (highest median count = 21 whales). 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 from 2005 to 2012 (192, 153, 224, 126, 303, 291, 208, and 319, respectively) included the lowest (2008) and highest (2012) counts recorded since surveys began in 1993 (1993-2004 counts: 302, 276, 322, 287, 261, 192, 217, 184, 210, 181, 174, and 187).

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