How Genetics and Pollution Are Threatening Wild Dolphins

Dolphins are beautiful, highly intelligent and uncannily human in their interactions. Yet, they also have a language we humans cannot fully hear, and a culture that is in some ways similar to our own, and in others, a complete mystery.

Like us, they have circles of friends and acquaintances, with different greetings for different individuals, as if by name. They travel swiftly within a home range of about 100-square kilometers but can go further when they want to. They have the sleek design of a jet plane fuselage and the intelligence that comes with a 1,600-gram complexly structured brain. (The human brain is 1,300 grams.)

Found in almost all the world’s oceans, they communicate with friends and family through clicks and whistles, and echolocation allows them to view the world around them. They pass on knowledge of culture and tools through the generations from mother to daughter, a matrilineal line that preserves and protects their heritage.

Approximately 40 species of dolphins exist. Many belong to the Delphinidae (ocean dolphin) family, including the orca; others live in rivers. Collectively, there are approximately 90 species of cetaceans, the order comprising whales, dolphins and porpoises.

Scientists analyzing the dolphin brain have determined that, like us, they possess a very complex neocortex — a region of the brain linked to awareness, emotions, problem-solving and other human-like abilities. Further, the limbic (emotional) system in some species is even more complex than humans.

These sensitive creatures have made the headlines in the past few months. An endangered orca known as Tahlequah mourned the tragic loss of her baby, carrying her dead calf for a record 17 days and 1,000 miles on what some have deemed a “tour of grief.”

Shortly following Tahlequah’s tragedy, the Center for Biological Diversity filed a lawsuit against the National Marine Fisheries Service regarding the species of orca on the West coast of the US that has become critically endangered. The suit alleged that the agency has neglected to establish habitat protection for the orcas. With only 75 of these orcas left, the population is the lowest it has been in 30 years.

Meanwhile, a combination of factors is threatening the very survival of these animals.

Genetics and Pollution

A recent study published in the journal Science delivers a serious warning as to the likelihood that dolphins and other marine mammals could be extirpated by pollutants. The discovery concerns an evolutionary change to DNA approximately 53 million years ago, which makes cetaceans particularly sensitive and therefore vulnerable.

Their bodies underwent various gradual changes during this evolutionary period. One of these changes was the alteration of DNA that codes for a particular enzyme known as PON1. Scientists believe the enzyme’s metabolic processes were no longer needed for a life underwater. Terrestrial mammals, by contrast, maintained the intact DNA and its enzyme, which humans have to this day.

But 53 million years later, the genetic change has become marine mammals’ Achilles’ heel, thanks to human invention. The enzyme has a second function — an ability to defend against neurotoxins found in pesticides. Without PON1, these animals are unable to break down the neurotoxin and can be poisoned.

Dolphins and other sea creatures with the PON1 problem are thus defenseless against agricultural runoff containing pesticides. Part of the reason the endangered infant orcas off the coast of California are having trouble is this kind of pollution. Marine mammals by the Florida coast are at risk as well, as scientists sampling waterways have found significant levels of chlorpyrifos pesticide contamination.

Dolphins have also been disappearing from areas around the globe they once inhabited, such as off the coast of Argentina. There, where dolphins were once common, only “a single resident population” is believed to be left. Heavy metal contamination and overfishing are likely contributors the decline. Elevated levels of lead, zinc, copper and cadmium have been found in mollusks, crustaceans and sea lions, as well as elevated levels of mercury, cadmium, zinc and copper in bottlenose dolphins. Metals pass from mother’s milk to the baby, resulting in the newborn dolphin having a weakened immune system and a lower probability of survival. The bottlenose dolphin is believed to be a common species globally, and consequently, people are less concerned about the threat to the species, yet in certain localities these dolphins are quietly disappearing, as along the Argentinian coast. Scientists warn that the Argentina study “provides an example of how the failure to recognize local population declines can threaten the national (and eventually the international) status of a once common marine species.”

To be sure, dolphins are facing similar toxic threats around the world. While metal pollution off the coast of Argentina is assumed to have resulted from decades-old mine waste, it is by no means unique to South America. Scientists examining the waters of Lake Geneva, Switzerland, discovered high levels of toxic metals including bromine, lead, mercury and cadmium. The toxins came from plastics, some of which had been banned or restricted decades ago, indicating the toxins remain in the environment for years. Plastic pollution is especially pervasive in oceans that dolphins inhabit – estimated at 150 million metric tons, with 8 million more tons added annually. Tellingly, a Malaysian dolphin was found dead after digesting nine pounds of plastic bags.

Chemicals can have a lasting and sometimes irreversible impact on the environment. Without containment, poisons that were banned years ago seep out of landfills, into streams and oceans, permanently contaminating water. For some species, a death sentence has already been assured. Change has come too late for the orca variety of dolphin, also known as the killer whale. This is the sad revelation recently published in the journal Science regarding polychlorinated biphenyls (PCBs) and orcas. PCBs banned more than 30 years ago have leached into the oceans, and killer whales as apex predators are “the most PCB contaminated mammals in the world,” say the researchers, who found some of the killer whales had 1,300 milligrams per kilo of PCBs in their blubber – 50 milligrams per kilo has been shown in previous research to be sufficient to cause infertility and serious immune system problems. As with metals, mothers pass the PCBs on to their babies through milk. The researchers predict that “PCB-mediated effects on reproduction and immune function threaten the long-term viability of [more than] 50% of the world’s killer whale populations.” They forecast a population collapse of orcas near industrialized regions, as well as in regions where orcas feed on larger prey. In short, half of the world’s orcas will be gone in just a few decades.

Some dolphin species are already very close to extinction. The Yangtze River dolphin, also known as “baiji,” has lived in the river for 20 million years. There were thousands in the 1950s, but in the year 2000, there were a mere 13. By 2006, scientists pronounced the species extinct after an unsuccessful six-week hunt by conservationists. Its current status is either extinct or near extinction — in 2016, some amateurs believe they may have seen a baiji, although they are not certain. The baiji would be the first dolphin made extinct by humans, in this case through pollution, dam-building, overfishing and boat traffic.

Dolphins face threats from climate change as well. Twelve dolphins were washed ashore in one week this summer in Florida, as a result of a red tide disaster, due in part to rising temperatures, with six killed in 24 hours. Such numbers have usually been an annual loss in the past.

Dolphins face a particular and cruel peril in Japan. The town of Taiji holds an annual dolphin “drive hunt” in which more than 1,000 dolphins are massacred each year. Hunters find a pod of dolphins and first create a clamor to disrupt the dolphins’ sonar, upsetting the dolphins and driving them into a cove, where they are then killed one by one, as the water in the cove turns red.

Even when dolphins are captured and kept in captivity, they react to their surroundings.

Dolphin Intelligence and the Future of the Animal Population

That dolphins are highly emotional is well-known. Peter — a dolphin kept in captivity after being moved to a smaller facility and permanently separated from the regular keeper he loved — fell into depression. Dolphins do not breathe air automatically the way humans do; each breath must be made consciously. A dolphin who has lost the will to live does not swim to the surface for his next breath. This was the fate of Peter; imprisoned and friendless at the new facility, he did not swim up for air and was found lifeless on the tank floor.

The emotional intelligence of dolphins reveals that trauma and separation will hurt dolphin families for years to come. The bloody waters of Taiji might hold the carcasses but not all the casualties. The many Peters of the world, having lost loved ones forever, can also lose the will to live.

At the 2010 annual meeting of the American Association for the Advancement of Science, scientists pondered the ethical and policy implications of dolphin intelligence. Neurobiologist Lori Marino argued that they may be Earth’s second-smartest creature. One can only agree.

A philosopher at the meeting proposed that dolphins perhaps ought to be considered “nonhuman persons.” He marvels at how, in addition to emotions and self-awareness, dolphins have personalities, exhibit self-control and even treat others ethically.

If a dolphin species becomes extinct, we lose not only a beautiful animal but a society and its culture. Dolphin habitat often spans the seas of many countries. Preserving them at home only to have them slaughtered on another shore is heart-wrenching. Preserving them abroad only to see them poisoned by pollution here is equally tragic. Countries must work together to ensure the survival of dolphins who swim beyond our borders, particularly as risks are compounded by climate change and pollution. The killing of whales for commercial purposes has been banned for many years. At the very least, this can be extended to their cousins now that we know they are under threat.

Pesticide use has to be regulated, particularly along the coasts to minimize PON1-related neurotoxic poisoning. Allowing a 53-million-year-old Achilles’ heel to be shot with the dart of human invention would be a tragedy. Minimizing plastic pollution is essential to dolphins as well. Preventing further PCB leakage into the oceans must also be a priority to save the orca populations, half of which are already facing collapse due to PCB-poisoning.

We have already witnessed the long-lasting effects of chemical runoff, from the decades-old plastic-derived toxins in Lake Geneva, to the 30-year-old PCBs seeping into oceans around the world. Once waters are contaminated, no one can go back. It is already too late for some orcas. Consequently, while we still can, we must prevent further contamination.

If nations can work together to minimize ocean pollution and affect laws to prevent chemical runoff, perhaps then Tahlequah and her fellow orcas will have greater success with the next generation of calves, and hopefully, our own children and grandchildren will continue to know the pleasure of seeing an orca or a bottlenose dolphin leap magnificently from the ocean.