For the purposes of their study, researchers studied and compared four groups of bottlenose dolphins that lived in aquariums and beyond the American coastline. Multiple wet and dry samples were collected from each of the dolphins. These samples were then subjected to testing that included hormone analyses, serum protein electrophoresis (SPEP) tests, and clinical chemistry tests.
Based on the results, the researchers discovered that the healthiest bottlenose dolphins were from the Georgia Aquarium. The reason for this lies in the water quality of their environment, which subjects the dolphins' immune systems to less stress and fewer diseases. “Dolphins in human care are exposed to fewer pathogens because of environmental controls of water and food quality and preventative medical programmes. Thus, their immune responses tend to be more focused and short acting,” explained Dr. Gregory Bossart, study co-author and chief veterinary officer at the Georgia Aquarium.
On the other hand, the groups of wild dolphins didn't fare as well as the captive ones. Specifically, wild dolphins who lived in the oceans surrounding Florida and South Carolina were found to be struggling with industrial ocean pollution and high levels of mercury. According to the study, published on PLOS.org, the sheer amount of pollutants strained the dolphins' immune systems and made it increasingly difficult for the animals to fight off parasites, bacteria, and viruses. This is because wild dolphins possess immune systems that are “chronically activated and challenged”.
“The immune system is incredibly complex and so very important for health. Microbes are part of the natural world and help to develop the immune system. The key to a healthy immune system is a balance between being able to recognize harmful organisms and overstimulation, and this study demonstrates the importance of the environment in these responses,” Bossart stated.
Lead study author Patricia Fair, also a research professor at the Medical University of South Carolina, further elaborated by stating: “This is likely a result of encountering pathogens, parasites and anthropogenic pollutants in the ocean that do not exist in closely managed zoological habitats.”
However severe the industrial pollution was in Florida, the researchers found it to be at its strongest near Charleston, S.C., where compounds released into the water affected all forms of marine wildlife. The pollutants were absorbed by microorganisms, which in turn were eaten by fish, which were then eaten by dolphins. Toxins become more concentrated with each step up the food chain, reported the Independent.co.uk. (Related: World's oceans now contain 5 trillion pieces of plastic waste created by humans)
Because of this, the researchers have stated that their findings could have greater implications. For instance, the high amount of toxins found in wild dolphins due to their consumption of contaminated fish could very well happen to humans living in the same area. If these people ate the same fish as the sick dolphins, then they would eventually feel the effects themselves.
“These wild dolphins are trying to tell us something and we are not listening. As a sentinel species, dolphins are an important way to gauge the overall health of our oceans. If wild dolphins aren’t doing well, it could also indicate future impacts to ocean health and even our own health,” said Bossart.
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