Photo identification (Photo ID) is a method used within marine mammal research to identify individuals based on photographs. The identification of dolphins is done via the characteristics of their dorsal fins because these are as unique to each dolphin as fingerprints are to humans. The characteristics found on dorsal fins include scars, notches and variable pigmentation. The study of photo ID enables researchers to obtain longitudinal information regarding the distribution of the species, whilst estimates about the age and population size can be made.
One of the main methods to identify dolphins is by looking at the scars, notches and variable pigmentation found on their dorsal fins
Archipelagos’ Marine Mammal team conducts photo ID research on a range of cetaceans, such as the short-beaked common dolphin (Delphinus delphis), the bottlenose dolphin (Tursiops truncatus), the Risso’s dolphin (Grampus griseus) and the striped dolphin (Stenella coeruleoalba).
Our research team collecting photo identification data during a sighting
To collect the relevant data, our team takes high-quality pictures of each individual (dolphins or whales) observed during boat surveys. Once the team is back at the base, the photo ID process can start. To begin with, only the pictures with a clear view of the dorsal fin are selected (the best pictures are the ones taken from a 90 degree angle with a good focus and contrast). These pictures are then matched with each other to establish how many individual dolphins were seen during each sighting on that day – a process called “internal matching”. The second part of photo ID processing, “external matching”, involves matching the newly encountered dolphins with photos from our catalogue. A photo ID catalogue consists of dolphin individuals that have previously been observed and identified, and is regularly updated when new individuals are encountered (i.e. dorsal fins that do not match any photo in the catalogue). Recently identified individuals are given a unique ID code representing how well marked their fin is and in what year it was observed. Archipelagos’ catalogue contains photos of dolphins for almost 2 decades, allowing us to track long-term dolphin movements, habitat distribution and population dynamics.
Archipelagos’ photo-ID catalog allows us to match dolphin individuals seen from 2015 until present. For example, this individual has been re-sighted on three separate occasions
By
Rob Hyman, MSc. Biology at the University of York, U.K;.
Gaël Gognies, MSc. Agronomy and Environmental Sciences at the University of Lorraie, France;
Patrizia Baldi, BSc. Hons Wildlife Conservartion at Nottingham Trent University, U.K.
