The Biggest Threats to Endangered Dolphin Species

The Society of Marine Mammalogy recognizes 41 distinct dolphin species, nine of which are considered endangered by either the IUCN, the Endangered Species Act (ESA), or both, and one that may already be extinct. The IUCN considers the Yangtze river dolphin, the Atlantic humpback dolphin, the South Asian river dolphin, the Amazon river dolphin, the Irrawaddy dolphin, the Indian Ocean humpback dolphin, and Hector’s dolphin to be endangered, while the ESA also includes the killer whale and the false killer whale. In addition, all endangered dolphin populations are either unknown or believed to be decreasing.

A vast majority of these species are oceanic, while just four are considered river dolphins. As is the case with all marine mammals, dolphins are also protected by the Marine Mammal Protection Act, which keeps them safe from being hunted, captured, or killed in U.S. waters.

Critically Endangered Species

Two species, the Yangtze river dolphin and the Atlantic humpback dolphin, are critically endangered, with the latter making a dramatic jump from “vulnerable” to “critically endangered” on the IUCN Red List of Endangered Species in 2017. IUCN attributed this rapid decline to low reproductive capability and threats from fishing industry bycatch, predicting an 80% population reduction over the next three generations. Today, there are an estimated 1,500 Atlantic humpback dolphins left in the wild.

Though universally believed to be one of the most endangered cetaceans on the planet, many scientists maintain that the Yangtze river dolphin, also known as the baiji, became extinct in 2007. Until 2006, this elusive freshwater dolphin’s status hadn’t been investigated since the population numbered 13 individuals in the 1990s. In 2006, an intensive six-week survey found zero evidence of the species’ survival, which researchers linked to a combination of dam construction and bycatch entanglement. If truly extinct, the baiji would represent the first global extinction of a large vertebrate in 50 years, the fourth extinction of an entire mammal family since 1500 A.D., and the first cetacean to be driven to extinction by humans.

Threats

Since different types of dolphins are found throughout the world in various habitats and ocean depths, they all face several threats no matter where they call home. Most of these challenges stem from humans, whether it be indirect conflict from fishing net bycatch or vessel strikes. Other factors, like the climate crisis and pollution, affect dolphins as well.

Habitat Loss

As the human population continues to grow, man-made structures such as dams and waterfront developments are pushing dolphins out of their natural habitats. Dolphins that prefer to live close to shore, like the common bottlenose dolphin, can often be affected by contaminants like oil spills.

A long-term study of the vulnerable subspecies Indo-Pacific humpback dolphin, found that the construction of an international airport runway in Hong Kong could be responsible for the changing rates of breeding females. The project threatened the viability of the region’s dolphin population by degrading sections of the current habitat and blocking access to alternative habitats. Similarly, the endangered Indus river dolphin subspecies, which once roamed throughout 2,000 miles of water within the Indus River system in Asia, lost 80% of its range due to large scale irrigation projects.

Bycatch

Seeing as the fishing industry and dolphins share the same goal — catching fish — it is common for dolphins to become entangled on transparent fishing wire or nets. And since dolphins breathe through lungs rather than gills, this can cut off their access to oxygen on the surface and drown them if they remain tangled in the water. According to a 2019 review by the NOAA, 11 out of the 13 critically endangered small cetaceans are threatened by bycatch. 

The use of gill nets, vertical panels of synthetic nets that suspend in the water to ensnare fish, was promoted as an inexpensive and durable fishing method after World War II. By the end of the 20th century, bycatch in gillnets became the primary driver of population decrease among marine animals.

Pollution

Pollution threats to dolphins come both in the form of chemical pollution and noise pollution. Like whales, dolphins depend on pulsed and tonal sounds for communication, navigating, and finding food, making them especially susceptible to underwater noise caused by boat traffic, sonar, and underwater construction. Studies conducted on an endangered river dolphin species found that dolphins suppress their acoustic activity in areas where vessel traffic exceeds five vessels per hour. As several river dolphins are essentially blind and therefore rely heavily on sound, losing their ability to communicate through sound could cause irreparable opportunity costs for food foraging and important social behaviors.

Ocean pollution from oil or chemical spills can result in disease among large populations of dolphins, which typically leads to adverse effects, death, or reproductive failure. In 2010, the Deepwater Horizon oil spill caused 4.9 million barrels of oil to leak into the Gulf of Mexico, the largest recorded marine oil spill in world history. Subsequent research concluded that stranded dolphins in the area were 20% more likely to have died from bacterial pneumonia and 26% more likely to have died from adrenal crisis than dolphins from unaffected regions.

Climate Change

It’s no secret that ocean life is suffering due to the climate crisis, especially when it comes to rising sea temperatures. Ocean acidification, rising water levels, declines in prey species, and other negatives pose threats to dolphins. Massive marine mammal die offs have also been linked to poisonous algae bloom, such as red tide, resulting from warming oceans. Dolphins can become exposed to these biotoxins through the air or by eating contaminated prey, leading to acute or chronic health conditions.

Hunting

Although the flesh of dolphins and other small cetaceans has been found to have dangerously high mercury levels, they are still hunted in some parts of the world. In certain regions of Japan, dolphins are hunted for their meat, blubber, and organs, which has raised controversy in the past. This is despite the fact that the average maximum amount of mercury found in Japan’s dolphins exceeds the provisional permitted level by about 5,000 times, suggesting that humans could develop mercury poisoning after a single consumption.

Dolphin hunting doesn’t just happen in Japan. In the Mediterranean, dolphins were seen as a pest species by certain fishing organizations, which led to several national laws permitting the hunting of the animals. It is estimated that over 6,700 dolphins were killed in a ten-year period from 1927 to 1937, which Italian zoologists believe may have had a significant effect on the local dolphin populations.

What We Can Do

Considering that oceans make up more than half of the planet’s surface, a large part of dolphin conservation stems from finding ways for humans and dolphins to coexist. Long-term solutions to problems like bycatch include developing more sustainable fishing methods, such as line fishing or using biodegradable fishing nets, that will neither harm dolphins nor jeopardize the livelihoods of fishing communities.

For some areas, especially those where threatened dolphin species live, establishing adequately sized marine protection zones and fair fishery management is key. This is especially true for species like the pink Amazon river dolphin, a large endangered freshwater species that fishermen often hunt to use as bait. Scientific research can help identify oceanic and river segments where dolphins thrive in large, viable population sizes in order to find the best places to enforce restrictive laws and conservation efforts. Long-term studies on dolphin stranding events are important as well, so that we can better understand the reasons why they occur.

The IUCN has highlighted marine conservation through establishing protected areas for cetaceans, citing the need for large-scale integrated approaches for dolphins as a whole instead of limiting studies to single areas or species at a time. Marine Protected Areas are found offshore or along the coast, and are specifically designated for their conservation values, ecosystem services, or cultural values.

There are also plenty of ways in which individuals — even those who aren’t professional scientists or conservationists — can affect positive change when it comes to these incredibly intelligent mammals.

Be a Responsible Consumer

Choose line-caught fish and only buy fish from sustainable fisheries to ensure that no accidental dolphin bycatch occurred. Also, opt only for sustainable tourism practices during ocean activities. Pick a company that actively (and transparently) contributes to marine conservation, so you can not only ensure that your activity is responsibly managed, but also that your money goes towards keeping dolphins safe. Look for accreditation organizations (like Dolphin SMART) that identify sustainable companies and train ocean tourism workers on responsible practices, ways to minimize stress to wild dolphins, and how to approach them. And if you haven’t already, ditch single use plastics. 

Participate in a Beach Cleanup

Curb the spread of ocean pollution at the source by volunteering at a local beach cleanup. Organized by the Ocean Conservancy, the International Coastal Cleanup occurs every year and includes cleanups all over the world. Anyone is welcomed to participate, and the project even helps provide valuable insights as to which types of trash pollutes the ocean the most.

Support Marine Protection Organizations and Marine Environmental Legislation

Find an ocean conservation program that speaks to you, like the Ocean Conservancy, which focuses on long-term solutions for marine wildlife, or Oceana, which focuses on winning legislation victories in the countries where marine life is most affected.