Sara Andreotti, An Automated Categorization System For Large Photo ID Databases Of White Sharks
Channel: African Campus
Date: 13/06/2013

Oral Presentation

Sara Andreotti1, Michael Rutzen3, Michael Meÿer2, Herman Oosthuizen2, Stéfan van der Walt4, Conrad A. Matthee1
1Evolutionary Genomics Group, Department of Botany and Zoology, Private Bag X1, Stellenbosch University, Stellenbosch 7600, South Africa
2Department of Environmental Affairs, Branch Oceans and Coasts, Private Bag X2, Roggebaai 8012, South Africa
3Shark Diving Unlimited, Kleinbaai, Gansbaai, 7220, South Africa
4Applied Mathematics, Stellenbosch University, Matieland 7602, South Africa

Non-invasive methods such as photo identification offer unique opportunities to study the population ecology of species, particularly those under serious threat. The white shark (Carcharodon carcharias) is one of the first elasmobranch species for which photo identification was used, but, despite its advantages, photo identification still presents significant challenges in terms of data organization and time consuming matching processes when used for population dynamics studies. As in other biometric photo identification systems such as fingerprint or iris analysis, images should be comparable in terms of quality, size and observation angle to allow for subsequent matches to be accurate. Also, processing large catalogues is labour-intensive and increases human errors in subsequent individual matching.
We propose (1) acquisition guidelines for improving the accuracy of white shark photo identification, (2) a novel categorization system (the Rutzen Method), used in the manual processing and organization of 4398 dorsal fin photo identifications of 426 specimens within the Dyer Island Nature Reserve (South Africa) (3) storage and processing guidelines for a large database of photo identification data. The strict criteria adopted in terms of photographic collection and data processing form the basis of a web application, Sharkbook, for storing photographic identification collections of shark fins. It also automates the processing of both images and meta-data, and allows queries, such as the re-capture matrix, to be made.
Despite the challenges mentioned, photo identification of white sharks is a cheap and non-invasive technique that, if applied consistently, will allow the global adoption of Sharkbook for population dynamic studies and thereby facilitate cross-referencing of studies from various congregation sites.