In the article, published this week and available online, Masters student Anna Taylor, from the University of Georgia (USA), and colleagues studied the common bottlenose dolphin, which migrates seasonally along the southeastern United States Atlantic coast. While this species of dolphin is widely studied, surprisingly little is known about what influences the timing of these migrations.
The scientists needed to track the comings and goings of dolphins at their study sites on the Georgia and South Carolina coasts, and they did so using photographic identification of individual dolphin fins. This technique is used with many studies of Cetaceans (whales, dolphins and porpoises), which all have dorsal fins. As the animals age, their dorsal (back) fins become worn and chipped, which allows individuals to be uniquely identified, much like fingerprints.
By teaming up with the National Oceanic and Atmospheric Administration (NOAA) and the Georgia Dolphin Ecology Program (GDEP), the researchers conducted boat-based surveys, where they photographed all dolphins (or their fins) they came across. They then used photo analysis software to analyze each dolphin's fin shape and pattern, which told them when and where each dolphin (nearly 1000 uniquely-identified individuals) went over the course of their study. Then, by combining the dolphin movement data with information on various aspects of water quality, the authors discovered that seasonal movements, or migrations, were best explained by water temperature; while seasonal abundance was best explained by water salinity.
The authors pointed out that this information can inform conservation strategies for common bottlenose dolphins, and help managers predict when a migration event is likely to occur. According to the Georgia Aquarium in Atlanta, Georgia, one of the main threats facing this species is from "entanglement in recreational and commercial fishing gear"; therefore, understanding when dolphins are in the area might mitigate the chances that these dolphins are injured.