Gulf of Alaska | Mammals
A tale of two surveys: Cook Inlet beluga whale distribution June 2021 & June 2022 Presenter: Kim Shelden , kim.shelden@noaa.gov, NOAA, NMFS, Alaska Fisheries Science Center Kim Goetz , kim.goetz@noaa.gov, NOAA, NMFS, Alaska Fisheries Science Center Amelia Brower , amelia.brower@noaa.gov, Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington Amy Willoughby , amy.willoughby@noaa.gov, Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington Christy Sims , christy.sims@noaa.gov, Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington Navigating field seasons during a pandemic has not been easy. Add on top of that delays and unusually foul weather, and the result is troubleshooting on the fly (literally) to obtain aerial counts needed to estimate the abundance of the endangered Cook Inlet beluga population. Aerial surveys to obtain abundance estimates began in 1994 and occurred annually until 2012, then biennially until 2018. No survey occurred in 2020 due to the pandemic. Surveys resumed in 2021 and were conducted again in 2022 to continue the biennial cycle. During low tides, whales typically aggregate along the edge of tidal mudflats waiting to access channels and rivers on the incoming tide. Minus tides (-3 ft. or more) that expose the mudflats for extended periods are preferable for standard survey methods (collecting video group size data and counting passes). Unfortunately, high winds, low ceilings, and heavy rain coincided with many of the lowest low tide days during the 2021 survey. With preferable tides missed and whales dispersed, we recognized that modifications to our survey methods were needed. The decision was made to conduct line-transect distance sampling experiments similar to those introduced during the 2018 survey. We dedicated two survey days to flying line transects (spaced 2 km apart running from the 10 m isobath to shore) in passing mode in 2021, surveying strata in the Susitna Delta and Chickaloon Bay similar to 2018, and adding strata in Trading Bay. These days also included coastal surveys of the other portions of the upper inlet (Knik Arm, Turnagain Arm, and from Point Possession to East Foreland), where sighting rates are usually low. The same distance sampling experiment was conducted in 2022, in concert with standard survey methods which occurred during the optimal tides. Evaluation of standard survey and distance sampling methods provide a unique opportunity to compare methods for future abundance and trend analyses. The results of this comparison, which suggest distance sampling methods are equally applicable, could provide greater flexibility for future survey planning and mitigation of unforeseen obstacles.
Alaska Marine Science Symposium 2023 241
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