Humpback Dolphins: Facts About Unusual and Beautiful Animals
What Are Humpback Dolphins?
Many people have heard of humpback whales, but fewer people realize that humpback dolphins also exist. The dorsal fin on the back of these dolphins often sits on top of a fatty, hump-like structure, which gives the animals their name.
Humpback dolphins are found in the oceans around West and East Africa, India, Southeast Asia, and Australia. Most are grey in color. The dolphins that live near Hong Kong have a range of colors, however. They are black or dark grey as youngsters and then gradually become light grey, a mixture of grey and a lighter color, white, or pink as they grow up.
Four species of humpback dolphins exist. There is still much to learn about them. There may not be much time left for this process, since some populations are in trouble.
Humpback dolphins are small to medium-sized dolphins. Like their relatives, they are mammals and must come to the surface of the water to breathe. Also like other dolphins, they are intelligent animals that generally live in groups.
A humpback dolphin has a streamlined body, a rounded melon, or forehead, and a long beak, as the projection containing the teeth is called. It also has a flipper on each side of its body, a dorsal fin on its back, and a tail with two lobes, which are called flukes. Not all humpback dolphins have a noticeable hump on their back, but many do. Adults reach a length of up to 8.8 feet (2.7 meters) and weigh up to 573 pounds (260 kg). Most are a little smaller than this, however.
Life of a Humpback Dolphin
Other dolphins that have been studied are very social animals with complex communication systems. Humpback dolphins almost certainly share these characteristics. There isn't much known about their lives at the moment, however, especially in relation to the two species that live around Africa. Researchers do know that the animals live in shallow water and frequently travel in small groups. Like other dolphins, they perform acrobatic displays above the water surface and swim beside boats. They aren't known to ride on bow waves, though.
Humpback dolphins hunt for fish, which they catch on reefs and in estuaries. Although fish seems to be their main food source, the animals also eat invertebrates, such as squid, octopuses, and crabs.
The gestation period of the dolphins is believed to be between ten and twelve months. The animals may not breed every year. They are thought to live for over forty years.
Like many other cetaceans (whales, dolphins, and porpoises), humpback dolphins use echolocation to help them find food. This process enables a cetacean to learn about objects in its environment in amazing detail.
In echolocation, a dolphin first produces high frequency sound waves, most likely in its nasal passages. The structures that are believed to produce the sounds are known as phonic lips. The sound waves are sent through the fatty melon into the water. The melon acts as a focusing device for the sound. The sound waves bounce off an object in the water and return to the dolphin. They are received by the dolphin's jawbone and sent to its middle and inner ear. A message is then sent to the animal's brain, which is able to sense the object's location, size, shape, and other features from the sound information.
Until quite recently, the most popular classification method for humpback dolphins was to divide the animals into two species—the Atlantic humpback dolphin, or Sousa teuszii, and the Indo-Pacific humpback dolphin, or Sousa chinensis.
A 2013 analysis by a group of wildlife organizations, including the American Museum of Natural History, proposed that the dolphins should be divided into four species. The proposal was based on an analysis of 180 skulls from dead dolphins and museum specimens as well as on genetic material obtained from 235 tissue samples.
Today the four species classification system is generally used. In this system, the Atlantic humpback dolphin retains its scientific name. The Indo-Pacific humpback dolphin has been split into three different species: Sousa plumbea (the Indian Ocean humpback dolphin), Sousa chinensis (the Indo-Pacific humpback dolphin, Chinese white dolphin, or Taiwanese white dolphin), and Sousa sahulensis (the Australian humpback dolphin).
The Four Species of Humpback Dolphins
Indo-Pacific Humpback Dolphin or Chinese White Dolphin
Eastern Indian and Western Pacific Oceans
Vulnerable (The Taiwanese White Dolphin is critically endangered.)
Atlantic Humpback Dolphin
Eastern Atlantic off the coast of West Africa
Indian Ocean Humpback Dolphin
Western and Central Indian Ocean
Australian Humpback Dolphin
Northern Australia and Southern New Guinea
Indo-Pacific Humpback Dolphin
Based on observations that have been made so far, researchers say that the Indo-Pacific humpback dolphin performs the following behaviors. The observations may apply to the other species, too.
The dolphins travel in small groups of about three to seven animals. The animals swim quite slowly. Like other dolphins, though, they perform energetic and impressive aerial displays at the water surface. These displays include:
- Porpoising: leaping out of the water, traveling over the water surface in an arc, re-entering the water, and then swimming rapidly just under the surface
- Breaching: leaping completely out of the water and then falling back into it with the side of the body hitting the water
- Spyhopping: slowly raising the head out of the water from a vertical position to view the surroundings and then slowly lowering the head again
- Lob tailing: hitting the water surface with the tail
- Somersaulting: occasionally leaping out of the water and turning "head over heels"
The animals have also been observed slapping the water with their flippers in what are believed to be mating displays.
Chinese White Dolphins in Hong Kong
Chinese white dolphins are sometimes grey in color, like other humpback dolphins, but many are multicolored, white, or even a beautiful pink color. Despite being classified as a humpback dolphin, Chinese white dolphins don't have a noticeable hump on their back.
The animals can be observed in Hong Kong Bay and the Pearl River Delta, which enters the bay. They are black or dark grey when they're born. As they grow up they turn a lighter grey and then develop white or pink spots. When they reach adulthood they may become entirely white or pink. The pink color is due to expanded blood vessels close to the surface of the skin and not to the development of a pink pigment.
The Chinese white dolphin was chosen as the official mascot for the 1997 ceremony in which Hong Kong was returned to China. The pink dolphins of Hong Kong Bay are a major tourist attraction today.
Population Status of White and Pink Dolphins
The Chinese white dolphin population is discontinuous. In addition to the Hong Kong population, there is a separate population off the west coast of Taiwan. The Taiwanese animals are reproductively isolated from other Chinese white dolphins and have some distinct features. They are given the common name of "Taiwanese white dolphin" to distinguish them from their Chinese relatives. They are classified in a separate subspecies from the Chinese animals (Sousa chinensis ssp. taiwanensis).
The population of the Taiwanese white dolphin is critically endangered. As the video below describes, the intense industrialization of Taiwan's coast is very detrimental for the dolphins, who live close to shore. The second video below is narrated by a researcher who is studying the dolphins. He says that in 2014 only 74 animals existed.
In addition to the pollution that's being created, other problems for the Taiwanese dolphins are harmful fishing methods, land reclamation for industry, and the presence of a military practice firing range. The noise created by the firing range interferes with the dolphin's sonar, or echolocation.
The Chinese white dolphin in Hong Kong is also facing problems. Industrial pollution, land reclamation, boat noise, and construction noise from a nearby airport are all affecting the animals. Their population is decreasing on a yearly basis. The calves seem to be especially susceptible to the changing conditions.
Small cetaceans around the world are disappearing — baiji in China went extinct, and the vaquita in Mexico and Taiwan’s humpback dolphin are nearing extinction — and we need bold action to save them— Miyoko Sakashita, Center for Biological Diversity
The Atlantic Humpback Dolphin
The Atlantic humpback dolphin is found off the west coast of Africa and is one of the least known of all dolphins. Its external appearance is very similar to that of its relatives. It's a slightly smaller animal, however, and exhibits less color variation. The dolphin often has a hump, which becomes more noticeable as the animal ages.
The dolphins live in shallow water that is less than 20 meters deep. They are thought to stay close to shore to reduce the chance of being caught by killer whales. The animals have been observed in the ocean, in estuaries, and as far as 50 km up rivers. They feed on mullet, grunts, bongo fish, and perhaps other fish as well.
Atlantic humpback dolphins are generally shy animals. They seem to perform fewer acrobatic displays at the water surface than other humpback dolphins and they are less attracted to boats. The haven't been widely studied, since they often live next to areas where human fighting is taking place. A survey was carried out in 2017, however. Unfortunately, the researchers discovered that the previous population status of "vulnerable" was inaccurate. The species is now classified as critically endangered.
In at least some areas, human fishing techniques are a threat to Atlantic humpback dolphins. This is thought to be the biggest danger for the animals. Dolphins become entangled in fishing nets and lines, for example, as well as anti-shark nets placed near beaches. Since they need to breathe air, the dolphins will drown if they can't rise to the water surface. Pollution and loss of habitat may also be problems, although the seriousness of these threats isn't known.
Humpback dolphins have one of the most specific habitat preferences and restricted distributions of any marine megafauna, and both of these characteristics are well known to reduce the resilience of species to environmental change and anthropogenic threats and to increase their extinction risk.— International Union for Conservation of Nature
The Indian Ocean Humpback Dolphin
The Indian Ocean humpback dolphin can be found off the east coast of Africa. Like the species on the west coast of the continent, it's a shy and little-known animal, despite the fact that it often swims less than 2 km away from the shore and in water less than 30 m deep. It's seen in small groups and is classified as endangered.
The dolphins are often seen within a few hundred meters of the shore. This brings them into contact with human activities, including fishing. The animals sometimes become entangled in gillnets and drown. The dolphins that are seen often have scars that are assumed to have come from conflicts with fishing gear. According to one scientist studying the animals, shark nets, pollution, and habitat degradation affect the population "enormously".
Based on the current classification system, the video above shows Australian humpback dolphins, not Indo-Pacific ones.
The Australian Humpback Dolphins of Tin Can Bay
Tin Can Bay in Australia is a very special place for people interested in humpback dolphins. Here individual dolphins come very close to people, interact with humans, accept food, and even allow naturalists to touch them. (There is a hefty fine for anyone who approaches, touches, or feeds the dolphins without supervision.)
The unique relationship between humpback dolphins and people is due to the intelligence and confidence of the dolphins and their realization that the humans at the bay are not only harmless but can also be of some benefit to them.
The first record of a visiting humpback dolphin appeared in the 1950s. An injured animal swam onto the beach by the Barnacles Cafe. The local people fed him and cared for him until he recovered and returned to the ocean. He remembered his experience, however, and returned to the bay regularly to receive more free meals.
Since the first arrival, other dolphins have entered the bay and voluntarily approached humans. Some continue to do so. Visitors to the bay are allowed to feed the dolphins under strictly monitored conditions.
Cetaceans in Trouble
The Tin Can Bay dolphins are providing us with an exciting glimpse into the lives of some fascinating mammals. It would be wonderful if interest in the animals raises awareness of the population status of other humpback dolphin species.
Cetaceans are clever animals. It's always worrying to hear that they are in trouble. It's especially sad when human activity is responsible for their disappearance. Some cetaceans—including humpback dolphins—need our help in order to survive.
The Wildlife Conservation Centre website discusses the new system of classification of humpback dolphins.
Researchers say that the Taiwanese white dolphin should be classified as a distinct subspecies in this article from Springer.
Taiwanese white dolphin population status according to the IUCN
Sousa teuszii information from the IUCN
Sousa plumbea facts from The Conversation
Information about the Australian humpback dolphin from the Queensland Government
Naturalists at the Barnacles Dolphin Centre in Tin Can Bay have made some interesting observations of humpback dolphins.
© 2013 Linda Crampton