Bottlenose dolphins are well known for their extensive sound repertoire (clicks, whistles and many more), yet we can learn valuable information from dolphins without even dropping a hydrophone (underwater microphone) in the water.
The Outer Banks is notable for its pristine beaches, abundant wildlife and beautiful coastline. The health of our marine environment is closely tied to its inhabitants, especially bottlenose dolphins. Dolphins are important environmental indicators, teaching us about the health of the marine environment without even saying a word. Monitoring the numbers, habitat use, and health of dolphins can give us valuable insight into pollution, fisheries, and a changing environment.
Since 2008, the Outer Banks Center for Dolphin Research has conducted a long-term research study of bottlenose dolphins in Roanoke Sound. Here are some clues dolphins can give us about the health of our local marine environment:
Bottlenose dolphins have long life spans, a trait that makes them good indicators of environmental health. Male dolphins are known to live beyond their 40s; some females may live into their 60s. Our oldest known dolphin on the Outer Banks is a male named Onion. As many bottlenose dolphins are identified by markings on their dorsal fins, Onion is distinctive due to the three cuts in his fin that cause it to resemble an onion bulb. Based upon his long-term sighting history, we estimate that he is approximately 40 years old.
Another way to age a dolphin is through its teeth. During strandings or health assessments, scientists may pull a tooth from a dolphin for an aging study. A cross-section of the tooth reveals growth rings, which are used to determine a dolphin’s age.
Many dolphins sighted through our research program have been observed in Roanoke Sound since the late 1990s, indicating that the sound is an important habitat for dolphins. Changes in dolphin numbers and habitat use would alert us to potential changes in the environment, such as changes in prey fish distributions, which may affect fishermen as well.
Bottlenose dolphins are also considered top predators within the marine environment, focusing their diet on soniferous, or sound-producing, fish. As top predators, dolphins serve as an endpoint for contaminants that move up the food chain through bioaccumulation. Unfortunately, dolphins will store chemicals and pollutants from the environment in their blubber. In some areas, scientists sample the blubber from dolphins to learn about chemical pollutants in the water. This insight can teach us about natural and man-made contaminants that are harmful to the environment, as well as to people.
Studying the skin diseases of bottlenose dolphins is another way for scientists to learn about marine environmental health. On the Outer Banks, our research is focused on photographing the distinctive markings on dolphin dorsal fins in order to identify and track individual dolphins over time. While taking these photographs, we also happen to capture evidence of different types of diseases and lesions on the dolphins’ skin. These lesions may be evidence of anything from bacterial or viral disease to reactions towards cold water or fresh water.
However, in other areas, diseases have been linked to water contamination. Certain types of diseases, known as zoonotic, may be transmitted between animals and humans, thus posing a danger to swimmers. In order to learn more about the lesions that we see on the Outer Banks dolphins, we classify them and compare them to other research sites.
Thanks to our long-term study, we are beginning to see trends in dolphin numbers and movements in Roanoke Sound. In fact, last summer was notable for the largest group sizes, dolphin sightings and newborn calves. As spring approaches and dolphins return to Roanoke Sound, we will continue our efforts to watch and learn from the dolphins. If you are out on the water this spring and see a group of dolphins, be sure to remember that there is so much more that they can tell us than just the fleeting sight of their dorsal fins.
Biologist Jessica Taylor is president of the Outer Banks Center for Dolphin Research. She has a Bachelor of Science in marine science from Rutgers University and master’s degree in environmental management from Duke University. She has participated in field research studies of bottlenose dolphins, humpback whales, Steller sea lions and predatory fish in Florida, South Carolina, New Jersey, Alaska and Australia. In 2008, she incorporated the nonprofit Outer Banks Center for Dolphin Research, which is dedicated to conservation of bottlenose dolphins on the Outer Banks. For more information, visit obxdolphins.org.