Neophocaena asiaeorientalis (Pilleri & Gihr, 1972)

Russell A. Mittermeier & Don E. Wilson, 2014, Phocoenidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 528-545 : 541-542

2.

Narrow-ridged Finless Porpoise

Neophocaena asiaeorientalis

French: Marsouin du Yangzi / German: Ostlicher Glattschweinswal / Spanish: Marsopa sin aleta asiaticoriental

Other common names: Finless Porpoise; Yangtze Finless Porpoise (asiaeorientalis); East Asian Finless Porpoise (sunameri)

Taxonomy. Neomeris asiaeorientalis Pilleri & Gihr, 1972 ,

“Yangtze, Prov. Kiangsu, Shanghai, China.”

Two subspecies are recognized.

Subspecies and Distribution.

N.a.asiaeorientalisPilleri&Gihr,1972—middleandlowerreachesoftheYangtze River,CChina.

N. a. sunameri Pilleri & Gihr, 1975 — shallow marine waters of E Asia; records are known from Japan, South Korea, China, and Taiwan. Occurrence in North Korea is not documented butis strongly suspected, and a stranding record from the island of Okinawa, S Japan, is considered to be extralimital.

Descriptive notes. Total length 130-227 cm; weight 40-72 kg. Of the two species of finless porpoise, the Narrow-ridged Finless Porpoise is the larger species, with a total body length up to 227 cm, although this may be an outlier because most specimens are much smaller. There is no dorsal fin, but the tubercled patch is narrow, 0.2-1.2 cm, occasionally up to 2-4 cm, in width at its widest point. Dorsal ridge is high (up to 5:5 cm), is covered with 1-10 rows of tubercles, and originates at or anterior to the mid-length of the back. There is no beak, and head is blunt, with a steep forehead. Especially in the Yangtze River, body of the Narrow-ridged Finless Porpoise has a very soft and “mushy” texture, different from most cetaceans. Coloration tends to be much paler than in the Indo-Pacific Finless Porpoise ( N. phocaenoides ). Adults range from pale cream to dark gray, but they are a moderate shade of gray in most populations. Newborns are dark gray and get paler as they age. Compared with their congeners, skull of the Narrow-ridged Finless Porpoise has a relatively long and narrow rostrum (length 77-97 mm, with a mean of 86-8 mm). Adult condylobasal skull lengths are 210-295 mm. Teeth are small, and tooth counts in each half of each jaw are 16-21 in the upper row and 15-20 in the lower row.

Habitat. Shallow, temperate waters of eastern Asia. Both marine and fresh waters are inhabited, and there is a population of Narrow-ridged Finless Porpoises found exclusively in the freshwaters of China’s largestriver, the Yangtze. Althoughit tends to occur mostly very near shore, it has a greater tendency than the Indo-Pacific Finless Porpoise to be found in offshore waters. Shallow, offshore (more than 240 km from shore, but less than 200 m deep) regions of the Yellow and Bohai seas are inhabited by the Narrow-ridged Finless Porpoise.

Food and Feeding. Narrow-ridged Finless Porpoises feed on a wide variety of small marine organisms, some of which are pelagic; others are benthic or demersal. Its prey includes fish (families such as Apogonidae , Carangiade , Clupeidae , Sparidae , Engraulidae , Sciaenidae , Gobiidae , and Atherinidae ), cephalopods ( Octopodidae , Sepiidae , Sepiolidae , and Loliginidae ), and crustaceans (mostly shrimps). Available data also indicate that Narrow-ridged Finless Porpoises in the Yangtze River feed on fish and shrimps.

Breeding. Life history of the Narrow-ridged Finless Porpoise has been relatively well studied, largely due to the abundance of specimens available from large bycatches in various fisheries. Newborns are ¢.73-79 cm long and are born mostly in spring and summer, although births in some populations can occur in autumn and winter. Sexual maturity of males occurs at 3-6 years of age and lengths of 132-145 cm, and at c.4-6 years and 132-140 cm for females, with some variation among populations. Gestation lasts ¢.10-11 months. Most individuals appear to reach a maximum age of ¢.20-25 years, but they can live as long as 33 years.

Activity patterns. Both species of finless porpoises are very cryptic, and they generally have a low surfacing profile. Although they do not appear to leap from the water very frequently, individuals have been observed performing “tail stands” in the Yangtze River. They can be very active at times and will often chase fish at very high speeds, making sharp turns and fast accelerations. There are reports of mother porpoises carrying young on their backs (supposedly with the offspring lying on the roughened dorsal ridge), but these reports are somewhat questionable. They do not ride bow waves of vessels, and they may move away with rooster-tail-type splashes when they are startled by a motor boat.

Movements, Home range and Social organization. Not much is known about individual movements or home range patterns of the Narrow-ridged Finless Porpoise because few studies have been able to track individual movements through tagging or individual identification work. Nonetheless, moderately extensive movements in the Yangtze River are known or suspected. Seasonal shifts in abundance are known from some waters of China and Japan, although these do not appear to qualify as well-defined migrations. Group sizes tend to be small. Narrow-ridged Finless Porpoises generally occuras singles or in small groups of up to ten individuals or so. Larger aggregations of up to several dozen sometimes form in areas of good feeding opportunities, but these groups do not have a cohesive structure.

Status and Conservation. CITES Appendix I (under N. phocaenoides ). Classified as Vulnerable on The IUCN Red List. The nominate subspecies asiaeorientalis is classified as Critically Endangered, and the subspecies sunameri has not been evaluated separately on The IUCN Red List. Vulnerable status is due to observed population declines and inferred reductions of at least 30% in the past three generations. In particular, populations in the Yangtze River and the Inland Sea ofJapan have suffered dramatic declines in recent decades, and the future of both populationsis in serious doubt. Although the Narrow-ridged Finless Porpoise has an extensive distribution, no global assessment of abundance has been attempted. There are, however, thought to be somewhat more than 1800 individuals in the Yangtze River and 5000-10,000 individuals in 5-6 different populations in Japanese waters. In the Yellow Sea of Korea, c.21,500 individuals were estimated to occur in offshore waters and ¢.5500 in coastal waters, but these estimates are thought to be low. They are faced with a number of threats, including destruction of habitat from coastal development, disturbance from vessel traffic and other coastal activities, vessel strikes, and various forms of pollution and noise disturbance. As for the Indo-Pacific Finless Porpoise, the major threat to the Narrow-ridged Finless Porpoise may come from entanglement in equipment of various fisheries, especially those using gillnets and related trammel nets.

Bibliography. Akamatsu et al. (2010), Amano (2009), Amano et al. (1992), Gao Anli & Zhou Kaiya (1995a, 1995b, 1995c), Jefferson & Hung (2004), Kasuya (1999b), Kasuya et al. (2002), Li Songhai et al. (2010), Mei Zhigang et al. (2012), Park Kyum-Joon et al. (2007), Reeves et al. (1997), Shirakihara, K. et al. (2007), Shirakihara, M., Shirakihara & Takemura (1994), Shirakihara, M., Takemura & Shirakihara (1993), Tanabe et al. (1998), Wang Ding (2009), Wang, J.Y., Frasier et al. (2008), Wang, J.Y., Yang Shihchu et al. (2010), Wang Peilie (1992), Wei Zhuo, Wang Ding et al. (2002), Wei Zhuo, Zhang Xianfeng et al. (2003), Yamada & Okamoto (2000), Yoshida (2002), Yoshida et al. (1998), Zhang Chang-lk et al. (2004), Zhao Xiujiang et al. (2008), Zheng Jinsong et al. (2005), Zhou Kaiya, Yang Guang et al. (1998).

Figures

1. Indo-Pacific Finless Porpoise (Neophocaena phocaenoides), 2. Narrow-ridged Finless Porpoise (Neophocaena asiaeorientalis), 3. Spectacled Porpoise (Phocoena dioptrica), 4. Burmeister’s Porpoise (Phocoena spinipinnis), 5. Vaquita (Phocoena sinus), 6. Harbor Porpoise (Phocoena phocoena), 7. Dall’s 9 Porpoise. Phocoenoides. (null)

Subspecies and Distribution. N.a.asiaeorientalisPilleri&Gihr,1972—middleandlowerreachesoftheYangtze River,CChina. N. a. sunameri Pilleri & Gihr, 1975 — shallow marine waters of E Asia; records are known from Japan, South Korea, China, and Taiwan. Occurrence in North Korea is not documented butis strongly suspected, and a stranding record from the island of Okinawa, S Japan, is considered to be extralimital.