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SC/68C/ASW/03Rev1
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Resource ID
19192
Access
Open
Document Number
SC/68C/ASW/03Rev1
Full Title
FIELD REPORT OF THE 2019 ICE-BASED BOWHEAD SURVEY OFF POINT BARROW, ALASKA
Author
J. Craig George, Andy Von Duyke, Robert Suydam, Kate Stafford, Ethan Roth, Barbara Tudor, Ross Burgener, Todd Sformo, Billy Adams, Brian Person, Leandra Sousa, Geof Givens, and Rob DeLong
Publisher
IWC
Publication Year
2021
Abstract
The 2019 bowhead whale ice-based abundance survey was conducted near Point Barrow, Alaska, from 16 March to 23 May. A total of 2,409 “New” (primary sighting), which includes34 calves, and 353 “Conditional” whales (50% chance of being “New” sighting) were counted in 657 hours of watch.While every effort was made to conduct the survey in a manner consistent with past surveys, severalfactors compromised visual detection in 2019. Leads were closed during the beginning of the migration; however once they opened, the leadswere much wider than in most past surveys. An unusual shorefast ice event in which a large portion of ice broke off close to shore between Point Franklin and Utqiaġvik likely caused whales to migrate farther from the lead edge than usual. The Point Barrow area was designated as a power-boat hunting area; however, due to the ice conditions, it was also the best location for the observation perch. The motorized skiffs appeared to have a substantial effect on whale behavior, distribution, and the number of whales observed in 2019. Other locations farther south were not suitable for counting bowheads because an ice attachment(iiguaq)blocked the view of the lead and made these locations unusable. The primaryperch was in relatively shallow water which is typicallyassociated with a lower proportion of whales with 4 km of the ice edge (termed P4) than perches in deeper water, such as in the 1993, 2001, and 2011seasons. Five ice floes became grounded inthe lead partially obstructing the viewing area at the primary perch in the north. The 2019 survey was visual-only and, unlike previoussurveys, did not include an acoustic array to locate whale call positions. Two acoustic recording units, however,were deployed on 24 and 31 March to acoustically document the season (i.e., call rates, call types, whale song, etc). Unfortunately, neither could be retrieved post-season. Since an acoustic array was not deployed, a P4 estimate for the 2019 was not computed. Instead, a weighted average of past P4 statistics wasused to correct the estimated number of whales with 4 km of the lead edge (N4). Despite these limitations, sufficient visual effort occurred during periods with open leads, and sufficient numbers of whales were seen to allow calculation of an abundance estimate. Givens et al. (2020) calculated an abundance estimate of 12,505 whales (CV 0.228) for the 2019 season.In a subsequent paper, Givens et al. (2021) estimated a correction factor for boat disturbance that increased the initial abundance estimate by about 12%, yielding a corrected abundance of 14,025 (CV=0.228).