At least 44 species of dolphins (6 river dolphins) and 6 species of porpoises populate the ocean waters. Dolphins can be found swimming in all of the worlds major oceans though most species tend to prefer living in warmer climates in and around the equator due to their small size and thin layer of blubber, which makes it difficult to stay warm in extremely cold environments. Porpoises live in all shallow, relatively cold coastal seas.
Not only are dolphins and porpoises highly intelligent marine species, but they also play an important role in ecology. Sick, injured or dead dolphins and porpoises are a big indicator that something is wrong in their environment that also affects the safety and health of other ocean creatures, as well as humans.
When we monitor and study dolphins and porpoises, we can find out if something is wrong with their ocean environment. When these mammals are found with a disease, such as immune system dysfunction, reproductive malformations or cancer, this shows us that something needs to be addressed, such as water pollution from agricultural, residential and industrial runoff.
According to the IUCN (International Union for Conservation of Nature) Red List, 5 species and 6 subspecies of dolphins are endangered and the reasons are all man-made. Many human activities, whether done intentionally or by accident, have adverse environmental impacts and result to the decline of dolphin and porpoise population and increase their risk of becoming extinct.
Dolphins and porpoises belong to the Cetacean family made entirely of aquatic mammals commonly known as whales, dolphins, and porpoises. Cetaceans are warm blooded, breathe air through lungs, give birth to live young that they produce milk to nurse and have traces of hair or fur —all features of mammals.
There are around 89 living species, divided into two parvorders:
Odontoceti (the toothed whales) consisting of around 70 species including the dolphin (includes killer whales), porpoise, beluga whale, narwhal, sperm whale, and beaked whale.
Mysticeti (the baleen whales which have a filter-feeder system) consisting of fifteen species including the blue whale, right whale, bowhead whale, rorqual, and gray whale.
Baiji / Yangtze River Dolphin
Ganges River Dolphin
Indus River Dolphin
Southern Resident Killer Whales (Orcas)
Atlantic Humpbacked Dolphin
La Plata River Dolphin or Franciscana
Black Sea Bottlenose Dolphin
Black Sea Common Dolphin
Eastern Spinner Dolphin
Threats to Dolphins and Porpoises
The oceans were teaming with dolphins and porpoises a century ago, but human intervention has changed this.
Commercial harvest of dolphins for food occurs at an alarmingly high rate globally. Countries like Japan is recognized for its large dolphin harvest which occurs despite illness and disorders documented in humans directly linked to the consumption of dolphin.
Persistent organic pollutantssuch asoil slicks, chemical contaminants (PCBs-polychlorinated biphenyls, dichlorodiphenyl trichloroethane-DDT, polybrominated diphenyl ethers-PBDEs, mercury, dioxins and furans) and other man-made toxins are commonplace in the oceans. These pollutants have many adverse health effects on dolphins and porpoises – affecting their reproduction, development, endocrine and nervous systems – ultimately increasing their susceptibility to cancer, pathogens and diseases.
Loss of food source and impact to habitats resulting from climate change and coastal developments have increased mortality rates and reduced populations. While many animals may not die specifically from ‘starvation’, low prey availability may result in ‘nutritional stress’ – and this can make them prone to illness, infection, and the affects of contaminants. Man-made fixtures like dams, waterfront residential and commercial development, and boat traffic destroy the habit of river dolphins each year.
Noise from shipping, seismic exploration and military sonar contribute to underwater noise and may impact the ability of cetaceans (whales, dolphins, and porpoises) to conduct critical life processes such as communicating, foraging, finding mates, and navigating through their underwater environment.
Fishingis a huge business because people like eating tuna fish, crabs, and other seafood. When dolphins are swimming nearby, they can get tangled in fishing nets and can't come up for air. When dolphins get hurt or die in fishing nets meant for other fish, they are called bycatch. The World Wildlife Foundation says that more than 300,000 dolphins, porpoises, and whales die this way every year. Fishing also affects dolphins when we catch too much of the fish that they eat.
Vessel disturbance by large and small ships may interrupt natural behavior and alter activities that are crucial for survival such as foraging, feeding, socializing and breeding. For example, when vessels are nearby, dolphins and porpoises reduce the time spent foraging in favor of traveling. The interruption of feeding may impact the energy intake of these animals, which if persistent over time, may have individual and population-level impacts. Vessel collisions causing serious injury or death pose a real risk to many species of dolphins and porpoises worldwide.
Marine pollution is anything from a discarded plastic to a lost fishing net. Every ocean in the world is littered with some form of debris which resembles food for marine life. Many animals accidentally eat marine debris causing internal injury, intestinal blockage, and starvation. Plastics may be ingested by dolphins and porpoises mistakenly while feeding on prey, or may enter their digestive system from inside of prey that has previously fed on plastic. Once ingested, the plastic piles up in the whale's stomach and can then obstruct bowels, preventing whales from digesting food and leading them to starve to death. It can also give a whale a false sense of being full, leading the dolphins and porpoises to eat less and get weaker. That leaves it vulnerable to predators and disease.