Evaluation of the Potential to Use Capture-recapture Analyses of Photographs to Estimate the Size of the Eastern Canada — West Greenland Bowhead Whale (Balaena mysticetus) Population

Posted on Dec 13, 2012

Author

William R. KOSKI, Cibele Q. DA-SILVA, Judith ZEH, and Randall R. REEVES

Correspondence: William R. Koski, LGL Limited, environmental research associates, 22 Fisher St., P.O. Box 280, King City, Ontario, L7B 1A6, Canada. Email: bkoski@lgl.com

Received 19 September2012 – Accepted 13 December 2012


Abstract

The summering areas of the Eastern Canada-West Greenland (EC-WG) population of Bowhead Whales (Balaena mysticetus) are large and remote, making it difficult to conduct a systematic aerial survey of the entire range in a short period of time. Surveys conducted in different parts of the Bowhead Whales’ summer range at different times or in different years cannot be used to obtain a robust estimate of population size because whales may move among summering areas within and between years. We suggest an alternative approach to estimate the size of the EC-WG population using photographic surveys of spring and summer aggregation areas. With two years of photographic surveys, capture-recapture estimates can be made of the number of marked whales in the population, and the proportion of the population that has recognizable marks can be estimated using data from the BeringChukchi-Beaufort (BCB) population of Bowhead Whales. These two populations appear to be increasing at near their maximum possible rate, based on estimates of age at sexual maturity and calving interval for the BCB population, and this justifies using the proportion that is marked from the BCB population for analyses of the EC-WG population. Confidence intervals for the photograph-based population estimate are likely to be narrower than those from systematic aerial surveys. A major side-benefit of the photographic surveys is that life history information, which is sparse for the EC-WG population, would be obtained.

Key Words: Aerial survey, Atlantic, Arctic, Bowhead Whale, Balaena mysticetus, photo-identification, population estimation.

 

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