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SC/69A/ASI/03/Rev2
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Resource ID
19950
Access
Open
Document Number
SC/69A/ASI/03/Rev2
Full Title
Abundance of bowhead whales (Balaena mysticetus)in West Greenland, 2022
Author
Rikke Guldborg Hansen
Authors Summary
A proportion of the East Canada-West Greenland population of bowhead whales (Balaena mysticetus) spends January-June off West Greenland and several aerial surveys (between 1998-2012) have estimated the abundance of bowhead whales on this wintering ground, with the last estimated abundance of 744 whales (CV=0.34) based on an aerial survey conducted in 2012. Between 26 March and 4 April 2022, visual aerial line-transect surveys of bowhead whales were conducted as a double-platform experiment with independent observation platforms covering the main distribution of the local winter aggregation of bowhead whales in West Greenland. The target region included an area of 34,742 km2 and was divided into 6 strata with a total of 3667 km of effort on systematically equally placed transect lines. Abundance of bowhead whales were estimated by using a Mark-Recapture Distance Sampling approach and due to the low number of sightings also by a strip census analysis. Both approaches corrected the final estimate of abundance for both perception- and availability bias. The MRDS estimated individual abundance to 915 whales (CV= 0.46, 95% CI: 385-2175). The strip census analysis estimated individual abundance to 993 whales (CV= 0.52, 95% CI: 380-2597). The median time a bowhead whale was visible for observers was 4.5 sec but this was not accounted for in the final estimate. The confidence limits of the abundance of bowhead whales in the survey area in 2022 are within similar estimates obtained between 2006 and 2012 indicating that there is a somewhat constant proportion of the East Canada-West Greenland population of bowhead whales that spend winter in the survey area off West Greenland.
Publisher
IWC
Publication Year
2023
Abstract
A proportion of the East Canada-West Greenland population of bowhead whales (Balaena mysticetus) spends January-June off West Greenland and several aerial surveys (between 1998-2012) have estimated the abundance of bowhead whales on this wintering ground, with the last estimated abundance of 744 whales (CV=0.34) based on an aerial survey conducted in 2012. Between 26 March and 4 April 2022, visual aerial line-transect surveys of bowhead whales were conducted as a double-platform experiment with independent observation platforms covering the main distribution of the local winter aggregation of bowhead whales in West Greenland. The target region included an area of 34,742 km2 and was divided into 6 strata with a total of 3667 km of effort on systematically equally placed transect lines. Abundance of bowhead whales were estimated by using a Mark-Recapture Distance Sampling approach and due to the low number of sightings also by a strip census analysis. Both approaches corrected the final estimate of abundance for both perception- and availability bias. The MRDS estimated individual abundance to 915 whales (CV= 0.46, 95% CI: 385-2175). The strip census analysis estimated individual abundance to 993 whales (CV= 0.52, 95% CI: 380-2597). The median time a bowhead whale was visible for observers was 4.5 sec but this was not accounted for in the final estimate. The confidence limits of the abundance of bowhead whales in the survey area in 2022 are within similar estimates obtained between 2006 and 2012 indicating that there is a somewhat constant proportion of the East Canada-West Greenland population of bowhead whales that spend winter in the survey area off West Greenland.