How is Pollution Affecting Dolphins in the Wild?

Jun 28 2017 Read 931 Times

A new study from the Medical University of South Carolina has suggested that elevated levels of water pollution may be having an adverse effect on the immune systems of wild dolphins. The authors compared the relative immune systems of four different groups of bottlenose dolphins, some of which were living in captivity and some in the wild, and concluded that the latter were far more at risk than the former. This, they believe, can be attributed to manmade pollution in oceanic waters.

Top of the food chain

As larger sea-dwelling mammals, dolphins find themselves fairly high up the food chain. Though this means that they do not have to deal with the threat of many predators, it does mean that they are susceptible to ingesting greater amounts of toxins.

That’s because industrial contaminants generally accumulate in small microorganisms, such as phytoplankton and zooplankton. In turn, these are eaten by a wide variety of fish, which are themselves consumed by dolphins. At every level of the food chain, the concentration of the toxins becomes ever higher.

In this recent study, for example, dolphins living near Florida’s Indian River Lagoon were found to have ingested harmful amounts of mercury. A powerful toxin, there is already a big market for chemicals to capture mercury with regards to air and soil pollution, as well as wastewater treatment.

Dolphins in captivity living a charmed life?

In addition to the polluted waters off the coast of Florida, the researchers found that dolphins living near South Carolina were also exposed to high levels of contaminants. This exposure is believed to be having a chronic effect on the dolphins’ immune systems, thus making them vulnerable to bacteria, fungi, parasites and viruses.

“This is likely a result of encountering and fighting off illness caused by pathogens, parasites and anthropogenic pollutants in the ocean that do not exist in closely managed zoological habitats,” explains Patricia Fair, lead author on the paper. “The key to a healthy immune system is a balance between being able to recognise harmful organisms and over-stimulation and this study demonstrates the importance of the environment in these responses.”

Looking to the future

It shouldn’t come as a surprise to anyone that aquarium dolphins are healthier than those found in the wild. After all, a balanced diet, controlled habitat, top class medical treatment and freedom from predators and parasites would improve the well-being of any species.

However, the state of these dolphins’ health can be seen as something of a barometer for how polluted our oceans are in general. Obviously, the wanton profligacy and improper disposal methods of our waste is a cause for concern with regards to the dolphins’ health, but highlights a wider issue concerning the world’s waters, as well.

“These wild dolphins are trying to tell us something and we are not listening,” says Dr Gregory Bossart, chief vet at Georgia Aquarium and co-author on the study. “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.”


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