Narrow-ridged finless porpoise

The narrow-ridged finless porpoise (Neophocaena asiaeorientalis) is a newly accepted species, by the International Union for Conservation of Nature (IUCN), of porpoise endemic to the western Yangtze river in China and the East China Sea, Yellow Sea, and around Japan. There are two subspecies: the Yangtze finless porpoise (N. a. asiaeorientalis) and the East Asian finless porpoise (N. a. sunameri). After the functional extinction of the Yangtze river dolphin and the rapid decreasing of population, the Chinese government has given this species the utmost conservation status of National First Grade Key Protected Wild Animal to ensure its survival. Global conservation agencies and charities, such as the World Wildlife Fund and IUCN, have been collaborating with the Chinese government to ensure the survival of the species. There are two subspecies of narrow-ridged finless porpoise, the Yangtze and the East Asian finless porpoises, the former inhabiting the Yangtze River, and the latter the coastal areas off mainland China (e.g. Chongming Island), the Penghu Islands, and coastal Vietnam, including Halong Bay. The Matsu Islands are thought to be their northern limit, and the local population in this area is physically smaller than the Indo-pacific finless porpoise. These two species overlap in the Matsu region. As the name suggests, the finless porpoise is the only porpoise to lack a true dorsal fin. Instead there is a low, narrow ridge covered in thick skin bearing several lines of tiny tubercles. In addition, the forehead is unusually steep compared with those of other porpoises. They have fifteen to twenty-one teeth in each jaw, and, on average, fewer teeth than other porpoises, although there is some overlap, and this is a not a reliable means of distinguishing them. Finless porpoises can grow to as much as 2.27 m (7 ft 5 in) in length, and can weigh up to 72 kg (159 lb), although most are smaller. Adults grow more than 1.55 m (5 ft) in length and up to 30–45 kg (65–100 lb) in weight. The flippers are moderately large, reaching up to 20% of the total body length. Adults are typically a uniform, light grey colour, although some may have lighter patches of skin around the mouth, or darker patches in front of the flippers. Newborn calves of the central and eastern subspecies are mostly black with grey around the dorsal ridge area, becoming fully grey after four to six months. However, newborn calves of the western subspecies are a light creamy grey, and become darker as they age. The anatomy of finless porpoises has been relatively well studied, compared with that of some other cetacean species. The tubercles along the dorsal ridge are known to contain numerous nerve endings is used as a sensory function. The auditory system also appears well-developed, with numerous nerve fibres specialised for rapid communication between the ears and the brain. Sight is relatively poor, however, due to the overall cloudiness of the Yangtze River; they have a reduced lens and a limited number of fibres in the optic nerve and to the muscles moving the eyes compared to the Indo-pacific finless porpoise. It is speculated that their vision is somewhat better than that of the Yangtze river dolphin. The skeleton is light, accounting for only 5% of the total weight of the animal. There are between 58 and 65 vertebrae, about half of them in the tail, and with the first three cervical vertebrae fused into a single structure. This reduces flexibility of the neck while increasing stability in the water. There are ten to fourteen pairs of ribs in the chest, and an additional set of vestigial ribs has sometimes been reported in the neck, in association with the seventh cervical vertebra. There are 44 sets of spinal nerves. Like all porpoises, they have spade-shaped teethed designed for catching small fish and shrimp. Their skeletal design allows them to leap from the water and perform 'tail stands'. The nasal passage contains nine or ten air sacs, which are capable of sealing off all air within the passage. Behind these are an additional set of vomeronasal sacs. The trachea, however, is short, with only four cartilaginous rings. The stomach has three chambers, with no caecum, and no distinct difference between the small and large intestines. Sexual maturity is thought to occur around six years, with only one calf born at a time. Gestation is approximately one year, and lactation lasts for over six months.