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SC/69A/ASI/01 Rev
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Resource ID
19945
Access
Open
Document Number
SC/69A/ASI/01 Rev
Full Title
Capture-recapture estimates of abundance of Antarctic blue whales
Author
Paula A. Olson, Douglas Kinzey, Michael C. Double, Koji Matsuoka, Ken Findlay
Authors Summary
Photo-identification data of Antarctic blue whales from 2003/2004 to 2018/2019 were used in a capture-recapture analysis to produce estimates of population abundance and growth rate for the circumpolar Antarctic. Two capture-recapture models, POPAN and Pradel, were applied to these data to estimate superpopulation abundance (N), recruitment-immigration (pent), and probability of capture (p) from the POPAN model and probability of capture and population growth rate (lambda) from the Pradel model. Separate capture-recapture estimates were made using photos taken of the right and left sides of the whales. Assigning a survival rate of 0.92 to the combined and right and left side models produced an abundance estimate for the last year, 2018/2019 (2,089 whales ; CI = 1,316 to 6,697). This estimate was lower than the projected abundance assuming exponential growth since 1997/1998 from Branch (2007) (12,758 whales; CI = 6,436 to 25,289 whales). Assigning a higher survival rate of 0.99 for the POPAN models produced higher annual estimates of abundance although still less than the projections from Branch (2007).
Publisher
IWC
Publication Year
2023
Abstract
Photo-identification data of Antarctic blue whales from 2003/2004 to 2018/2019 were used in a capture-recapture analysis to produce estimates of population abundance and growth rate for the circumpolar Antarctic. Photographs were collected during IWC-SOWER, IWC-SORP, ICR, and SAABWS cruises and also made available by opportunistic contributors. Separate capture-recapture estimates were made using photos taken of the right and left sides of the whales. Two capture-recapture models, POPAN and Pradel, were applied to these data to estimate superpopulation abundance (N), recruitment-immigration (pent), and probability of capture (p) from the POPAN model and probability of capture and population growth rate (lambda) from the Pradel model. The fits of a series of pre-specified apparent survival rates from 0.75 to 1 were compared using ?AICc. Derived parameters of annual abundances and population growth rate were calculated from the POPAN models. A wide range of annual survival rates were consistent with the capture-recapture data based on ?AICc scores. Four different best-fitting configurations of left side data, right side data, POPAN, and PradLambda had survival rates of 0.94, 0.87, 0.97 and 0.9 (mean 0.92). The best superpopulation estimates from POPAN for the left and right sides were 3,488 (95% CI = 1754, 7178) and 3,659 (95% CI = 1906, 7241) whales, respectively. Assigning a survival rate of 0.92 to the combined and right and left side models produced an abundance estimate for the last year, 2018/2019 (2,050 whales ; CI = 1,135 to 3,704) that was lower than the projected abundance for 2019 from Branch (2004) (9,608 whales (CI = 1257 to 26,060 whales)). Assigning a higher survival rate of 0.99 for the POPAN models produced higher annual estimates of abundance although still less than the projections from Branch (2004). Population growth rates from Pradel, POPAN and Branch (2007) were also compared. Estimated population growth rates from the Pradel and POPAN models during 2003/2004 – 2018/2019 were at the upper end of the Branch (2007) growth estimates for 1997/1998. The Pradel and POPAN models suggested annual population growth was slowing by the end of the time series instead of increasing exponentially.