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Recommendations for photo-identification methods used in capture-recapture models with cetaceans

Lookup NU author(s): Professor Per Berggren


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Capture-recapture methods are frequently employed to estimate abundance of cetaceans using photographic techniques and a variety of statistical models. However, there are many unresolved issues regarding the selection and manipulation of images that can potentially impose bias on resulting estimates. To examine the potential impact of these issues we circulated a test data set of dorsal fin images from bottlenose dolphins to several independent research groups. Photo-identification methods were generally similar, but the selection, scoring, and matching of images varied greatly amongst groups. Based on these results we make the following recommendations. Researchers should: (1) determine the degree of marking, or level of distinctiveness, and use images of sufficient quality to recognize animals of that level of distinctiveness; (2) ensure that markings are sufficiently distinct to eliminate the potential for “twins” to occur; (3) stratify data sets by distinctiveness and generate a series of abundance estimates to investigate the influence of including animals of varying degrees of markings; and (4) strive to examine and incorporate variability among analysts into capture-recapture estimation. In this paper we summarize these potential sources of bias and provide recommendations for best practices for using natural markings in a capture-recapture framework.

Publication metadata

Author(s): Urian K, Gorgone A, Read A, Balmer B, Wells RS, Berggren P, Durban J, Egushi T, Rayment W, Hammond PS

Publication type: Article

Publication status: Published

Journal: Marine Mammal Science

Year: 2015

Volume: 31

Issue: 1

Pages: 298–321

Print publication date: 02/01/2015

Online publication date: 14/05/2014

Acceptance date: 25/03/2014

ISSN (print): 0824-0469

ISSN (electronic): 1748-7692

Publisher: Wiley-Blackwell Publishing, Inc.


DOI: 10.1111/mms.12141


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