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SC/69B/IA/05
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Resource ID
22122
Access
Open
Document Number
SC/69B/IA/05
Full Title
Preliminary results from an updated population assessment of Antarctic blue whales
Author
Zoe Rand, Trevor Branch
Authors Summary
This paper provides preliminary results from first comprehensive assessment of Antarcitc blue whales in 16 years. Using a Bayesian theta-logistic population model, the authors estimate the intrinsic rate of increase of 0.067 and a carrying capacity of 216,000. While they estimate that the population was at less than 0.1% of pre-whaling abundance at the end of whaling, they project a total population size of 5,543 in 2024, 2.6% of pre-whaling levels. This suggests that Antarctic blue whales are continuing to increase but still have many decades left before returning to pre-whaling levels.
Publisher
IWC
Publication Year
2024
Abstract
Antarctic blue whales were a primary target for 20th century commercial whaling, decimating their abundance. Here we provide the first new population assessment in 16 years, incorporating new information about Antarctic blue whale catches as well as more recent abundance estimates. Our preliminary results use a Bayesian theta-logistic population model fit to abundance estimates from SOWER and JARPA line-transect surveys, sightings from Japanese scouting vessels, and a mark-recapture abundance estimate from photo-identification data. We estimated the intrinsic rate of increase as 0.067 (0.036?0.107), and a carrying capacity (and assumed pre-whaling abundance) of 215,741 (177,646?261,105). Abundance was just 213 (39?665) at the end of whaling in 1973 and, at its lowest, the population was at less than 0.1% of pre-whaling levels. The population is projected to have increased in 2024 to 5,543 (3,239?9,534) which is 2.6% (1.3?5.1%) of pre-whaling levels. Models that excluded one data source at a time displayed a wider variety of outcomes, with median intrinsic rates of increase from 0.052?0.101 and median abundance in 2024 from 5,445?9,237. These models suggest that Antarctic blue whales are continuing to increase, but still have many decades left before returning to pre-whaling levels.