Age is essential for studying population dynamics yet is challenging to estimate for individuals in wild populations. While methods exist for aging dead animals, it is difficult to obtain reasonably accurate age estimates of free-ranging animals, especially for cetaceans. We developed a protocol for deriving age estimates using information commonly curated in marine mammal photo-identification catalogs and applied the approach to biopsy-sampled false killer whales (Pseudorca crassidens) from the endangered main Hawaiian Islands insular population. The protocol integrates qualitative lines of evidence into a quantitative framework for deriving age point estimates and plausible ranges. Confidence ratings reflecting the strength of supporting evidence were developed to account for uncertainty in age estimates. These estimates were then translated to a statistical distribution that can be used in further analyses. Age point estimates of biopsy-sampled false killer whales ranged from three to 40 years (minimum range: 2-33; maximum range: 5-65) and were strongly influenced by the estimated age when first seen and span of years since first seen. Overall, this method provides a useful approach for aging individuals with common metrics from photo-identification catalogs and for which other aging methods of biological samples are not yet feasible or available.
Citation:
Kratofil, M.A., S.D. Mahaffy, K.K. Martien, F.I. Archer, and R.W. Baird. 2023. A Protocol for Photo-Identification Catalog-Based Age Estimation: An Application to Endangered Hawaiian False Killer Whales (Pseudorca crassidens). Document PSRG_2023_B23 submitted to the Pacific Scientific Review Group, NOAA Fisheries.
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