Have you ever had that feeling where you are talking to someone at a party and you are sure that you have met them before but you just can’t seem to place them? Did you meet them at your cousin’s wedding last summer maybe? Did they go to elementary school with you perhaps? This can be frustrating. Now take that feeling and multiply it by about a million, and you will have a pretty good idea what it feels like as a scientist trying to identify individual dolphins. Dolphins, unlike humans, rarely wear nametags, they never style their hair into a unique coiffure that make them easy to pick out in a crowd, and you won’t ever be able to recognize a dolphin because of the shoes it is wearing.
For scientists studying wild dolphin populations, being able to identify individual dolphins is a vital component of their research. Studies gathering information about individual dolphins are used for research on population size estimations, migration patterns, social structure, group movements, life histories, and behavior. For example; researchers may be interested in learning how often individuals within a group interact with other individuals – patterns of association. Scientists may want to learn what kinds of behaviors are being produced by the adults, the juveniles, the males, the females and so on – all of this requires the scientist to know and recognize which individual dolphins they are observing.
To do this, researchers rely on a variety of identification or “ID” techniques. The most popular technique is photographing the dorsal fin of the dolphin as it breaks the surface to breathe – this is often called photo-ID. Dorsal fins can function a lot like human fingerprints – the notches and nicks along the edge of the fin allow researchers to recognize and categorize individuals. This technique is very handy for species that don’t really like the presence of boats – researchers can use telephoto lenses to capture a picture of a dorsal fin from a greater distance. There is even some pretty fancy computer software that will help researchers search through scanned dorsal fin images to try and match photographs to the fins of previously identified dolphins. Some dolphin species will have natural markings or coloring patters that are visible when they surface, and these can be used for ID as well.
For those scientists able to actually enter the water to film or photograph wild dolphins under water, or for those using an underwater camera from their boat, it is possible to identify dolphins based on a variety of body features. Sometimes deformities like missing fins or a prominent under-bite can be used to ID individuals. Wild dolphins accumulate a huge variety of scars and marks throughout their lifetime: everything from shark bites to cuts and scratches from contact with rocks, and even injuries resulting from fights with other dolphins. If the dolphin is unlucky enough to have a nasty scar, or a chunk missing from its fluke, a scientist will have a relatively easy time re-identifying this individual based on underwater video or still photos. For the Indo-Pacific bottlenose dolphins that the Dolphin Communication Project studies around Mikura Island, scars from shark bites are all too common. One shark in particular, the cookie cutter shark, is known for taking a nasty circular bite out of the dolphin’s flesh – it leaves a prominent scar that makes it very easy to recognize specific individuals. For images of cookie cutter and other shark bite scars from the Mikura dolphins, check out The Dolphin Pod website for links.
Shark bite images
Cookie cutter shark bite images
The trick is of course finding scars that are going to stick around for a few years – many species of dolphins are covered in ‘rake marks’ – these are shallow scars caused by the teeth of other dolphins, and they occur when dolphins are fighting or playing with each other. Since rake marks are often shallow, they will only be visible for a few weeks to a few months, and are not a reliable way to identify individuals over longer periods of time (i.e., between years). Some species of dolphins, like spotted dolphins, develop spots as they age. If researchers remain vigilant and keep clear records of the development of these spots over years, these distinctive spot patterns will allow them to reliably recognize individuals.
The key to being able to identify individual dolphins is keeping good records – well organized photographic and video records are invaluable. Many scientists will keep a book with sketches of individual dolphins that can be easily updated as dolphins accumulate new scars. Individual dolphins are typically assigned names and/or numbers. To learn about some of the research groups working on identifying individual dolphins as part of their research, visit The Dolphin Pod website for links. There is even a link to an online test to see how skilled you are at identifying individual dolphin dorsal fins.
Of course, these kinds of ID techniques could be used to avoid the predicament described at the start of this episode. Imagine how handy it would be if, when you came across that person at the party who you just couldn’t place, you pulled out your photo-ID book and flipped through until you found out who they were. “Ah yes, your name is Todd Johnson – I lasted sighted you on June 15 at the Henderson’s housewarming party. You were seen associating with an adult female and two juvenile males. How have you been, Todd?”