Photo-Identification

To capture a dorsal fin on film is a challenging task! The size, shape and position of the dorsal fin vary greatly amongst Cetacean species, and can be a helpful tool when identifying species during an encounter. With Photo-Identification, dorsal fin recognition can be taken one step further and this is the technique used by researchers to identify individual whales and dolphins within a population.

When studied closely, dorsal fins can be highly distinctive. Nicks and scratches along the trailing edge of the fin from interactions with other animals (especially young, boisterous males), variations in skin pigmentations, as well as scars from parasites, prey such as squid, and even wounds from Cookie Cutter Sharks, all go towards making up distinctive and recognisable patterns. Once individuals are recognised, catalogues of whales within a population can be developed. This allows researchers to monitor the movements of whales, determine their social structure and in some cases allow the number of animals in a population to be estimated.

When Cetaceans are sighted at sea, HWDT do their best to take photographs of every encounter (using a long camera lens and rapid-fire shutter speed). It is important to regularly update the catalogue of dorsal fin images; to compare and contrast changes to known individuals, and hopefully add new animals to the database. Along with the photo-ID shots, records are kept of the time, date, latitude and longitude of each individual sighting. Any behaviour is noted, as well as interactions with other animals, birds or boat traffic.

HWDT have on-going photo-ID projects for local Orcas (Killer Whales), Basking Sharks, Bottlenose Dolphins and Minke Whales – please click below to find out more:

There can of course be problems with photo-identification, not least with the skill needed to take a good, clear shot. (Minke whales, for example, can swim at speeds of 10kmph, dive for up to 20 minutes and are often unpredictable underwater, tending to vanish without a trace…) The angle of the cetacean to the photographer, and of the sun, can greatly affect the usefulness of the image obtained. The ideal photo-ID shot is taken perpendicular to the dorsal fin, lit by the sun, in close range and without lots of splashes which might be confused for fin markings. Also, right and left sides of the fin should ideally be taken, so that animals can be recognised whichever way they surface in the future. Recognised individuals can be followed within a survey area, using ongoing photographic recording throughout a season, and even over consecutive years.