Photo identification is a scientific method of identifying individual animals using their unique markings. It is a non-invasive mark-recapture survey technique. By using the animals’ natural markings it avoids the need to physically capture and mark or tag the animal, greatly reducing the stress on the individual and having a much lower impact in general. Each animal will have markings as unique to them as a finger print is on humans.
The method was first developed in the 1970s and has become progressively more accessible and practical as technology has improved. The use of photo identification methods changed drastically in the 1990s once digital cameras became more wide spread and affordable. This allowed researchers to take hundreds of pictures if necessary without the practical limitations of changing the film in the camera or getting the photos developed. Digital photography also allows the photographer to check the photos immediately and assess the quality of the shot. Additionally, with the development of photo editing software, photos can be manipulated to enhance and improve the ID features. Photo ID can be used to look at site fidelity, habitat use, population dynamics and to calculate abundance using various statistical models.
Though Photo ID does have limitations in its use, it is becoming an increasingly valuable research method in regard to the marine environment, where the subject species are often elusive and challenging to ‘capture’. The exact area of the animal used for identification purposes varies with species, with new and improved methodologies constantly being tested.
Dolphins
With dolphin species the dorsal fin is often the primary focus of photo identification. Individuals may be born with particular markings, colouration patterns or deformities which remain largely unchanged as they age, making them ideal markers for identification. Additionally, throughout their lives dolphins will obtain different cuts and markings through interactions with others, either from intraspecific interactions for example resource competition, socialising or conflict, or from interspecific interactions, for example predation. Using these different fin shapes, individuals can be identified and tracked. As yet there is no internationally used database for dolphin ID. Local research organisations will have their own ID catalogues and only through collaboration with other groups would they be able to track an individual’s movements further afield.
Dolphin ID: Both pictures are of Bottlenose Dolphins (Tursiops truncatus), taken in Cardigan Bay, Wales. The pictures highlight the extreme differences that can be found in fin shape and appearance within the same species. The process does have its limitations when it comes to identifying individuals with unmarked fins as pictured above, however high quality photos can be enhanced to help identify smaller, less obvious markings. Photo Credit ©Anna Lucey/Sea Watch Foundation
Humpback Whales
As the Humpback Whale (Megaptera novaengliae) dives they often raise their tails in the air, the underside of which is distinctly marked, providing a feasible method of identification. Between individuals the shape of the tail, or fluke, can vary and the trailing edge will have a differing silhouette. Humpbacks also have distinct natural pigmentation markings that will stay the same their entire lives. In addition to these morphological features humpbacks will acquire scaring, through either interactions with other individuals or from barnacles which accumulate when the whale is young.
For a migratory species such as the humpback, photo ID can prove an invaluable tool in tracking migration routes without the need, or expense, of tagging the animal with a tracking tag. Using photo ID it has been established that humpbacks can migrate over 10,000 miles!
Humpback Whale ID: These pictures demonstrate the different pigmentation patterns that can be found on the underside of individual whale flukes. Photo Credit © Alan Airey/ Sea Watch Foundation (Left) and Peter Evans/Sea Watch Foundation (Right).
Whale Sharks
For Whale Shark (Rhincodon typus) photo identification there is an internationally established methodology used to compare the spot pattern on the side of the body, between the end of the gills and the dorsal fin. Using software designed by NASA to map stars it is possible to ‘plot the spots’ of a Whale Shark, the software then analyses the pattern, calculating the angles between each marking. As the shark grows the distance between the marks will increase but the angle will not. This provides a high level of accuracy when matching individuals. As with all photo ID the quality and angle of the photo used can impact the accuracy of the match. There is also an international database, the ECOCEAN Whale Shark Photo-Identification Library, to which the public and researchers can upload their photos and the images are analysed. Each individual is given an ID code. The site will also send out updates for where and when that shark has been seen. This has proved very useful in tracking Whale Shark movement between countries.
Whale Shark ID: Above are four examples of individual sharks seen in the Philippines. Spot patterns are clearly distinguishable between sharks just by using the naked eye but can be confirmed by uploading the image to the ECOCEAN ID library, which software to analyse the spot pattern and calculate and compare the internal angle between spots. Photo Credit © Anna Lucey/Large Marine Vertebrates Project
Turtles
Turtle photo ID is a relatively new form of photographic identification, where by researchers use the scales on the turtles face to distinguish individuals. The validity of this method is still being tested over long periods, however a study by Reisser et al., 2008 has demonstrated that there are notable differences in scute patterns on the turtles in their study and the arrangement of the facial scutes did not change over the 3 year study period. This would imply that the use of photo ID for turtle populations could be a viable alternative to capture and tag methods historically used. An international database is currently being developed to help standardise the ID protocols.
Turtle ID: Above is an image taken from Reisser et al., 2008 demonstrating the difference in scute facial patterns of two Green Turtles (Chelonia mydas).
References
Reisser J, Proietti M, Kinas P, Sazima I (2008) Photographic identification of sea turtles: method description and validation, with an estimation of tag loss. Endang Species Res 5:73-82
Written by Research Intern, Anna Lucey
