Since 1997, my marine biologist wife, Katie Iverson, and I have been conducting a photo-identification study of populations of bottlenose dolphins in the upper Gulf of California. From our 14-foot inflatable boat, "The Collapso," we have identified over 100 dolphins we believe to be residents of the area around Puerto Peņasco and Cholla Bay.
For our research, we use 35 mm SLR and digital high speed cameras and lenses. We approach the animals slowly and from an angle (not heading straight for the pod), allowing them the choice of an encounter.
Fortunately, the dorsal fins of bottlenose dolphins are as distinct as fingerprints, so we do not have to "tag" the animals. We "shoot" the photographs perpendicular to the fins, most often with black and white film. Each dolphin is assigned a permanent number. If a particular dolphin has a distinct appearance, we will provide a name in order to simplify data-taking into the tape recorder.
In order to identify the dolphins, we examine the photographs of their dorsal fins and backs (the parts exposed when they come up for air). We look at height and base width, size, and curvature of edges of the fins. Nicks found in the profile of the fins are permanent and distinct. Surface scars and rake marks (parallel marks made by other dolphins' teeth during play, aggression, or courtship) are also valuable identifiers. Below the fin on the backs of each dolphin is a light stripe that sweeps up toward the dorsal fin. These "speed stripes" also differ between animals.
Below is an illustration showing identification markings and an example of dolphin number 19 (first sighted on 4/20/98).