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An 11-digit identification system for individual Nile crocodiles using natural markings

Hindrik Bouwman, Enrico Cronje
Koedoe | Vol 58, No 1 | a1351 | DOI: https://doi.org/10.4102/koedoe.v58i1.1351 | © 2016 Hindrik Bouwman, Enrico Cronje | This work is licensed under CC Attribution 4.0
Submitted: 25 August 2015 | Published: 20 May 2016

About the author(s)

Hindrik Bouwman, Unit for Environmental Sciences and Management, North-West University, Potchefstroom Campus, South Africa
Enrico Cronje, Unit for Environmental Sciences and Management, North-West University, Potchefstroom Campus, South Africa


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Abstract

Research and conservation of wild crocodiles and husbandry of captive crocodiles requires the reliable identification of individuals. We present a method using the individual colour markings on the first 10 single-crest scutes on the tails of Nile crocodiles (Crocodylus niloticus). The scutes are scored by number for colour, with a prefix for left or right providing a binary 11-digit identification number (identification numbers [IDs]; e.g. 12232232242 and 22333233232) per crocodile. A survey of 359 captive Nile crocodiles showed no duplication. However, 42% had asymmetrical scute markings requiring a binary approach. There does not seem to be a change in patterns with age, except that the number of missing scutes increased. A small trial showed that this method can be applied in the field, although more work is needed to determine observer bias and establish parameters for observability in the field. It is unlikely that both left and right IDs would be obtainable for each individual, but other distinctive markings such as scute shape and damage can be used to register the two IDs to one individual. Having two independent IDs for each crocodile provides the possibility of two independent population estimates for equal effort without having to link left and right IDs to individuals. Our proposed method would be useful in conservation, individual tracking and husbandry.

Conservation implications: A non-invasive marking and recapture method for Nile crocodile is presented whereby the first 10 single-crest scutes are scored for colour, allowing conservation practitioners to count and monitor crocodile populations and individuals. This method provides two equal-effort estimations of population size, as left and right hand sides are scored independently.

Keywords: Crocodylus niloticus; identification; mark - recapture; mark - resight


Keywords

Crocodylus niloticus; identification; mark - recapture; mark - resight

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Crossref Citations

1. Challenges and opportunities for monitoring wild Nile crocodiles with scute mark-recapture photography
Bernard W.T. Coetzee, Sam M. Ferreira, Kristine Maciejewski
Koedoe  vol: 60  issue: 1  year: 2018  
doi: 10.4102/koedoe.v60i1.1505