| Aerial surveys of beluga whales in Cook Inlet, Alaska, June 1991 - :8690 | National Marine Fisheries Service (NMFS)
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Aerial surveys of beluga whales in Cook Inlet, Alaska, June 1991
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    During 18-21 June 1991, aerial surveys were flown to document the distribution and group sizes of beluga whales, Delphinapterus leucas, in Cook Inlet, Alaska. The original data from these surveys were thought to be lost. The only description of these surveys, a short summary and single map (NMFS 1992:7-9), exists within an unpublished document (titled: 'Status Report on Cook Inlet Belugas (Delphinapterus leucas)') prepared by the National Marine Fisheries Service, Alaska Region. In February 2013, a floppy disk containing the original survey flight file data was discovered. Once extracted and analyzed, the recovered data were compared to the information presented in the NMFS (1992) status report (Shelden and Mahoney 2013). These results and additional information from survey participants are presented here. Overall, the beluga sighting locations and tracklines in the recovered data mirrored those in Figure 2 in NMFS (1992:8). The number of nautical miles (nmi) surveyed, reported as 1,600 in NMFS (1992:7) was slightly less than the 1,640 nmi in the recovered data. However, errors were found in the computation of the highest daily count, the correction factor applied to the count, and the resulting abundance estimate. NMFS (1992) reported the highest daily count as 242 belugas, which was also recorded in the recovered data. However, this represented a high count for whale groups observed between the Beluga and Susitna rivers, where two counting passes were conducted. Combining this count with the other areas surveyed that day (Little Susitna to Point MacKenzie and Chickaloon Bay/Turnagain Arm) resulted in a count of 370 whales for 20 June 1991. NMFS (1992:9) also applied a correction factor of 2.72 (attributed to Frost (1987)) to produce an abundance estimate of 653 whales (sic. 658 whales). We could not find the source for this correction factor but note that Frost et al. (1983, 1984, 1985) report a correction factor of 2.75 (for whales missed during aerial surveys because they are submerged below turbid waters). Applying the 2.75 correction to the highest daily count of 370 whales results in an abundance estimate of almost 1,018 beluga whales in Cook Inlet for June 1991. [doi:10.7289/V5/AFSC-PR-2016-02 (http://dx.doi.org/10.7289/V5/AFSC-PR-2016-02)]

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