The Indo-Pacific finless porpoise (Neophocaena phocaenoides) is one of eight porpoise species. This species lives in most of the Indian Ocean and the warmer parts of the Pacific Ocean, from Indonesia north to the Taiwan Strait. In the Taiwan Strait, this porpoise lives alongside the East Asian finless porpoise (N. sunameri). The East Asian finless porpoise takes its place farther north.

Distribution

The Indo-Pacific finless porpoise lives in the coastal waters of Asia, especially around Indonesia, Malaysia, India, and Bangladesh. Their range includes the western coast of India and extends into the Persian Gulf. On the eastern side, they are found throughout the Indonesian archipelago and extend north to the Taiwan Strait. These porpoises are also protected in Sundarbans National Park.

Description

Finless porpoises can grow up to 2.27 meters (7 feet 5 inches) long and weigh as much as 72 kilograms (159 pounds), though most are smaller. Their flippers are medium in size, reaching up to 20% of their total body length. Adult finless porpoises are usually a uniform light grey color, though some may have lighter areas near the mouth or darker patches near the flippers. Newborn calves of the central and eastern subspecies are mostly black with grey coloring along the back, and they turn fully grey after four to six months. Newborns of the western subspecies are light creamy grey and become darker as they grow older.

Adult finless porpoises are more than 1.55 meters (5 feet) long and weigh between 30 and 45 kilograms (65 and 100 pounds).

The anatomy of finless porpoises is better understood than that of some other whale and dolphin species. For example, the bumps along their back contain many nerve endings that may help them sense their environment. Their hearing system is well-developed, with many large nerve fibers that help send sounds quickly from the ears to the brain. However, their eyesight is not very strong, with a small lens and few fibers in the optic nerve and eye muscles.

Their skeleton is unusually light, making up only 5% of their total body weight. They have between 58 and 65 vertebrae, with about half in the tail. The first three neck vertebrae are fused into one structure. They have 10 to 14 pairs of ribs in the chest, and sometimes small, underdeveloped ribs are found near the neck, close to the seventh cervical vertebra. They have 44 sets of spinal nerves.

Their nasal passage has nine or ten air sacs with complex structures that can seal all air inside. Behind these are additional sacs called vomeronasal sacs. Their trachea is short, with only four cartilage rings. Their stomach has three sections, no caecum, and no clear difference between the small and large intestines.

Diet

Finless porpoises eat different types of food found in their environment, such as fish, crustaceans, and animals like squid and octopus. They are known to eat fish, shrimp, and squid near Pakistan. Scientists have not studied how their food choices change with the seasons. They also eat some plant material when living in areas like estuaries, mangroves, and rivers. This includes leaves, rice, and eggs that are found on plants in these habitats.

Behaviour

Recent studies show that the basic group of a finless porpoise pod is a mother and calf or two adults. Groups of three or more individuals are made up of these smaller groups or single porpoises. The social structure of this species is not very complex, and the mother and calf pair is likely the only stable group.

Like other porpoises, their behavior is less active and showy compared to dolphins. They do not ride the waves created by moving boats, and in some areas, they appear to avoid boats.

Finless porpoises produce high-frequency clicking sounds and longer, low-frequency tones. These low-frequency sounds may be used for communication, not for finding food or navigating. The clicks have very high pitch, reaching over 100 kHz.

A study by the Woods Hole Oceanographic Institution (WHOI), published in The Journal of Experimental Biology, shows that dolphins have different hearing abilities depending on their species. This challenges the old idea that all cetaceans hear in the same way.

Although finless porpoises do not perform acrobatic moves in the water, they are strong swimmers. They usually swim just below the water's surface and roll to one side when they come up to breathe. This rolling movement causes little disturbance on the water’s surface, making them hard to notice when they surface. When they breathe, they take three to four quick breaths over about one minute before diving again. They often surface far from where they first dived. Dives lasting more than four minutes have been recorded, and a common pattern is one long dive followed by two shorter ones.

Breeding happens in late spring or early summer. Young porpoises are born in spring, summer, or winter, depending on their location, after a pregnancy period of ten to eleven months. Newborns are about 72 to 84 cm (28 to 33 inches) long. Males become sexually mature at four to six years old, and females at six to nine years. Finless porpoises can live up to 33 years.

Some people say young calves cling to the rough, tooth-like skin on their mother’s back and are carried as she swims, but there is no clear proof of this. Calves stop nursing and begin eating solid food at 6 to 15 months.

Conservation

The finless porpoise is listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). This listing means the species is not doing well or could benefit from help from other countries through special agreements.

These porpoises live near coasts, where they often interact with humans. This interaction puts them at risk. Like other porpoises, many are killed by getting caught in fishing nets called gill nets. The main threat to the species is harm to the environment. Unlike other porpoises in its family, finless porpoises have lived in captivity for more than 15 years.

There are no clear numbers about how many finless porpoises exist. However, comparing surveys from the late 1970s and from 1999–2000 shows fewer porpoises and a smaller area where they live. Scientists believe this decline has happened for many years, and the current population is much smaller than it was in the past. Along the southern coast of Pakistan in the Arabian Sea, the species is declared as endangered.

The WWF website says the finless porpoise is Critically endangered. However, this is not the official status given by the International Union for Conservation of Nature (IUCN).