Genetic markers validate photo-identification and uniqueness of spot patterns in whale sharks

Abstract

Monitoring the demographics and movement patterns of mobile marine species underpins appropriate management and conservation strategies. Photographic identification of whale sharks Rhincodon typus based on individual variations in spot patterns is a widely used technique for monitoring of populations, but relies on the untested assumptions that these variations in spot patterns are unique to each shark and can be reliably detected using photo-matching software. This study validated the accuracy of photo-identification technique by manually determining the number of photo-identified individuals showing mismatched genetic profiles created for the individuals using 12 microsatellite markers. Results from 154 photographic and genetic identifications of whale sharks were 100% concordant, showing the uniqueness of spot patterns to each shark and high accuracy of the photo-identification technique. Based on these techniques, we observed an annual resighting rate of approximately 10% at Ningaloo Reef, Western Australia, between 2016 and 2018, showing evidence that variations in spot patterns did not change over a time scale of years. Our study shows that the photographic identification technique provides a reliable means to recognise individuals and monitor whale sharks through time.