How do researchers recognize individual dolphins?

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?”

Did you know that a killer whale, otherwise known as an orca, is actually a dolphin? Orcas are in fact the largest dolphin species in the world today. So, why are they called whales and not killer dolphins? Which, by the way, sounds downright terrifying? Well, that is a good question, and there is no easy answer. So instead of an easy answer, here is a complicated one: There are around 35 species of oceanic dolphin. All of these species can be correctly referred to as dolphins because they are in the scientific family known as delphinidae. Species in this family all have cone shaped teeth, a single blowhole on the top of the head, among other morphological traits that separate them from the other families. What makes this a little confusing is that the common name for many of these dolphin species as the word whale in the name. The killer whale is a fine example. But there are more, including the melon-headed whale, the pygmy killer whale, the false killer whale, the long-finned pilot whale, and the short-finned pilot whale. To complicate the issue even further, all of the species I just listed are sometimes called blackfish, although they are of course not actually fish, and not really whales, but simply dolphins. You think that us confusing? Try figuring out how the word porpoise fits in. In North America, many people refer to dolphins (the species in the family delphinidae) as porpoises. They may even call a bottlenose dolphin, the most famous dolphin of all, simply a porpoise. This term came about from fisherman who call most dolphin species a porpoise to differentiate between them and the dolphin fish, otherwise known as mahi-mahi. Now the problem is that science recognizes the porpoise as a different kind of animal altogether. There is a scientific family known as phocoenidae that contains 6 species of what are officially known in science as porpoises. So to be scientifically proper, a porpoise is an animal belonging to the phocoenidae family, and the term porpoise should only be used to describe one of those 6 species. Unless of course you are a fisherman and you want to call a melon-headed whale a porpoise, which you might do, even though it is actually a blackfish or officially a dolphin. But let us return to the first question: what us a whale? Well according to official scientific terminology, there is no such thing as a whale at all. Science does not formally use the standalone word whale to refer to any of the animals found in the scientific order cetacea; that is the order containing all animals commonly referred to as whales, dolphins and porpoises. The term whale is usually used in the common name of the largest of the animals in the order cetacea, including the blue whale, the sperm whale and the beluga whale. That is because the word whale in English was in use for many centuries before scientists came on the scene and tried classify all of the cetaceans, and it was probably applied rather indiscriminately to most large animals seen swimming in the oceans. Nowadays, a scientist might refer to animals like the blue whale (the species with baleen instead of teeth and grooves on their throats) as rorquals, or they might call the Sperm whale by the name Physeter. Because common names often vary from place to place and language to language, the only way to be sure of what animal you are talking about is to use its scientific name. In English, a Killer Whale therefore was probably originally referred to as a whale simply because it is large; it otherwise has very little in common with an animal like the Blue whale. As we now know, science recognizes the Killer Whale as a dolphin because it is in the delphinidae family. But here is one more snag: there are 5 species of freshwater river dolphins that are NOT in the dolphin family, but in separate families altogether. These river dolphins are nonetheless correctly referred to as dolphins. As you can see, it us not easy to tell a dolphin from a whale. When in doubt, you can always just shout ‘hey, look – there’s a cetacean! ‘ Maybe that us cheating, but at least you will be correct! Wouldn’t it be easier if we all just spoke Latin?