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Studying the health of dolphins after pollution

Assessments provide important data about the effects of chemical pollution on marine mammals.

National Marine Mammal Foundation veterinarian performs a dental exam

National Marine Mammal Foundation veterinarian performs a dental exam. All activities are performed under NOAA permits and strict guidelines to protect the health of marine mammals. Credit: NOAA.

You can't bring a wild dolphin to the veterinarian for a checkup. So when chemical pollution impacts dolphins, NOAA sometimes brings veterinarians to the dolphins.

After an oil spill or release of industrial chemicals, it is important to determine if the health of wild dolphins has been impacted. In some cases, a team of scientists and veterinarians may temporarily capture wild dolphins to assess their health. These capture-release health assessments are an important tool for collecting in-depth data about the potential harmful impacts of pollution.

Dolphins are protected under the Marine Mammal Protection Act and are wild animals that can weigh several hundred pounds. We need a team of highly trained and experienced marine scientists and veterinarians to ensure the safety of the dolphins and the scientists. The team will track a group of dolphins to verify there are no young calves present and will wait until the target dolphins are in an area that is optimal for setting a net (e.g., shallow water with slow/no currents, with a relatively soft bottom like sand). Throughout the entire process of catching and holding the dolphins, veterinarians carefully monitor their health and behavior to ensure they are doing well and remain stable. This work is always conducted by trained professionals under a research permit issued by NOAA Fisheries.

The video below highlights some of the methods experts use to study the health of wild dolphins and what we can learn from them. Many of these methods are similar to what is used to examine the health of people and their pets.

This video offers an in-depth look at a dolphin capture-release health assessment, from start to finish. After a large net is deployed to capture it, the dolphin is photographed and tagged with a satellite telemetry transmitter. The team measures the animal's length and weight and collects blood, blowhole, skin, and blubber samples. Additional assessments include an ultrasound, a dental exam, and a pectoral fin X-ray.

  • Net deployment: A net is carefully and quickly released off the back of a special boat in a circle around the target dolphin to capture it.
  • Photo identification: Dolphins can be identified by the unique shape and markings on their dorsal fins. Taking quality photos to identify individual dolphins allows researchers to track them over time and determine how long they live and whether they reproduce.
  • Satellite telemetry: Satellite-linked tags attached to the dolphin's dorsal fin enable researchers to follow their movements for up to several months after the health assessment, providing information about habitat use and movements.
  • Blood draw: Blood can be analyzed for hormone levels, infectious diseases, chemistry (such as iron or glucose), red and white blood cell counts, immune system function, and other measures.
  • Blowhole sample: Evaluation of exhaled mucus can provide information about disease and microorganisms in the lungs.
  • Skin and blubber sample: After a veterinarian numbs the area with an anesthetic, they take a sample of a dolphin's skin and blubber. These samples provide a wealth of information including genetic information, hormone levels, diet, and the amount of chemical compounds.
  • Ultrasound: Used to examine the health of a dolphin's internal organs. It is also used to determine if a female dolphin is pregnant, the stage (trimester) of the pregnancy, and general health of the mother and fetus.
  • Physical measurements: Body size (length, girth, and weight) is an important indicator of health.
  • Dental Exam: Dental health can be an indicator of overall poor health.
  • Pectoral Fin X-ray: Just like human hands change as we age, dolphin flippers change as they grow older. Using portable X-rays, scientists can examine dolphin pectoral flippers and estimate their age.

Dolphin health assessments require a large team of experienced marine scientists, veterinarians, and other highly trained professionals and provide significant information on the health status and impacts of stressors.

Understanding rates of survival and reproduction for a wild population is key for effective management and conservation. However, these rates are challenging to estimate for dolphins, which, except for surfacing to breathe, spend their lives underwater and out of human view. A study just released in the journal Conservation Biology demonstrates how data collected from health assessments such as NOAA conducts can be used to predict survival rates for dolphin populations.

For this study, NOAA is grateful for the support we receive from collaborators such as the National Marine Mammal Foundation, Georgia Department of Natural Resources, Chicago Zoological Society's Sarasota Dolphin Research Program, SeaWorld Rescue Program, Force Blue, North Carolina State University, and University of St. Andrews.

To learn more about how NOAA studies dolphins after exposure to pollution, view "Dolphin Discoveries in the Decade Since Deepwater Horizon."