Finless porpoise

Neophocaena phocaenoides (G. Cuvier, 1829)

English: Finless porpoise
German: Indischer Schweinswal
Spanish: Marsopa lisa
French: Marsouin aptère

Photo © Institute of Hydrobiology, Chinese Academy of Sciences

1. Description
The finless porpoise is small and lacks a dorsal fin. The fin is replaced by a ridge which runs down the middle of the back. The head is rounded and there is no apparent beak. The colour is uniformly dark- to pale grey and somewhat lighter on the ventral side. Body size reaches 170 cm and mass 70 kg, with maxima of 200 cm and 100 kg (Amano, 2002).

2. Distribution
The warm, coastal lndo-Pacific waters, both fresh and marine, are home to the finless porpoise (Jefferson et al 1993). There are three well-marked regional populations which warrant subspecific rank. Even within these, significant differences in skull morphology have been found among local populations (Rice, 1998 and refs. therein, Amano, 2002):

N. p. phocaenoides inhabits coastal waters along the mainland of southern Asia from the Persian Gulf east to the South China Sea and southern part of the East China Sea; also the coasts of south-eastern Sumatra, Bangka, Belitung, Sarawak, Palawan, the Turtle Islands in the Sulu Sea, and northern Java. The species has not been found in South African waters, or anywhere else in Africa (Rice, 1998 and refs. therein). It penetrates into the Indus River for 60 km, and into the Brahmaputra River for 40 km from the mouth. (Kasuya 1999).

N. p. sunameri Pilleri and Gihr, 1975, ranges in coastal waters from the southern East China Sea north to the Liaodong Wan in China, Korea, and Kyushu in Japan, thence along the Pacific coast of Japan from the Seto-naikai north to Sendai-wan in northern Honshu (Rice, 1998). Five local populations are identified in Japanese waters based on skull morphology and mt DNA variability (Amano, 2002).

N. p. asiaeorientalis (Pilleri and Gihr, 1972) is found in the lower and middle reaches of the Chang Jiang (Yangtse River), where it ranges 1,600 km upstream as far as the gorges above Yichang (200 m above sea level), and including Poyang Hu and Dongting Hu and their tributaries, the Gan Jiang and the Xiang Jiang (Rice, 1998).

Distribution of the three subspecies of Neophocaena phocaenoides: coastal waters and all major rivers of the Indian ocean and the Western Pacific (mod. from Amano, 2002; copyright CMS / GROMS).

Finless porpoises have been seen off Bahrain but are not found along the coasts of Oman or in the Gulf of Adan off Djibouti. They seem to be absent from the African coast, Sulaweshi, Halmahera and Timor, the Philippines, and the northern coast of Australia (Kasuya, 1999).

3. Population size
Estimates of abundance have been made only for specific areas in China and Japan (IWC, 2000).

Although Zhang et al. (1993) estimated the Yangtze population at about 2,700 individuals, it is unclear if this represents abundance in winter, the highest density, or the low density season of summer.

In the Inland Sea of Japan the number of porpoises observed during the breeding season (April) was 4,900. By early winter the number in the area dropped to 1,600 (Reyes, 1991, and refs. therein). Off western Kyushu, about 3,100 are estimated in the Ariake/Tachibana Bay and 200 in the Omura Bay (Kasuya, 1999 and refs. therein). Recent sightings and questionnaire surveys in the Seto Inland Sea, which is a major habitat of the finless porpoise in Japan, indicated a decrease in abundance of the species (Amano, 2002).

4. Biology and Behaviour
Habitat: The finless porpoise is mainly an inshore species, but occurs in salt and fresh water. N. phocaenoides appears to prefer murky or turbid conditions and can be found in warm rivers, lakes (if connected to rivers), mangroves, estuaries, deltas, and saltmarshes. It prefers areas where river and ocean waters meet (Carwardine, 1995). In the Yangtze River, finless porpoises are found up to 1600 km from the sea and in Japanese waters, they prefer shallow depths (<50 m) and close proximity to the shore (< 5km). In the shallow East China Sea, however, proximity to the shore is not so important (Amano, 2002).

Behaviour: Like other porpoises, their behaviour tends to be not as energetic and showy as that of dolphins. They do not ride bow waves, and in some areas appear to be shy of boats. Mothers have been seen carrying calves on the denticulated area on their backs. In the Yangtze River, finless porpoises are known to leap from the water and perform “tail stands” (Jefferson et al. 1993).

Schooling: Finless porpoises are generally found as singles, pairs, or in groups of up to 12, although aggregations of up to about 50 have been reported (Jefferson et al. 1993). Recent data suggest, that the basic unit of a finless porpoise school is a mother/calf pair or two adults, and that schools of three or more individuals are aggregations of these units or of solitary individuals. Social structure seems to be underdeveloped in the species, and the mother/calf pair is probably the only stable social unit (Kasuya, 1999).

Reproduction: Reproduction in most areas has not been well studied. Reports indicate that calving in the Yangtze River occurs between April to May whereas on the Pacific coast of Japan it occurs between May and June and November - December in western Kyushu. Animals form Kyushu live 25 years and attain sexual maturity at 4 - 9 years of age. Gestation lasts 11 months (Amano, 2002).

Food: Finless porpoises are reported to eat fish and shrimp in the Yangtze River, and fish, shrimp and squid in the Yellow Sea/Bohai area and off Pakistan. In Japanese waters they are known to eat fish, shrimp, squid, cuttle fish and octopus. Finless porpoises are opportunistic feeders utilising various kinds of available food items available in their habitat. Seasonal changes in the diet have not been studied (Kasuya, 1999). They also apparently ingest some plant material, including leaves and rice (Jefferson et al. 1993).

5. Migration
Available information suggests that finless porpoises are probably found year-round throughout their range, and show various degrees of seasonal movement and density change which are not well documented in most areas (Kasuya, 1999).

An annual migration is reported in the Inland Sea of Japan, where porpoises are faced with drastic seasonal changes in surface water temperature between 6 °C (March) and 28 °C (September). Their density is lowest (40% of the peak season) in early winter, and starts to increase in January, reaching its peak in April. Finless porpoises migrate to and from the Pacific coast mainly through two passes at the eastern Inland Sea of Japan. From observations in the fluctuation of the proportion of mother-calf pairs, it is suggested that porpoises use the Inland Sea of Japan as a breeding ground. In summer, the animals move out to the Pacific coast (Reyes, 1991 and refs. therein; Kasuya, 1999).

Finless porpoises are known to occur year-round in Ise and Mikawa Bays with a peak abundance in April-June. They also occur year-round off western Kyushu where density is high in coastal waters less than 50 m deep in winter and spring. Along the Chinese coast, finless porpoises are present all year, but reported to have some seasonal density changes in Bohai and on the Yellow Sea coast (low in winter and high in summer/autumn). There, they apparently move from shallow to deeper water in winter. Movement of finless porpoises between the Yangtze and the ocean has yet to be confirmed (Kasuya, 1999). Akamatsu et al. (2002) recently documented daily horizontal travel distances of two finless porpoises in the Yangtze River as 94.4 km and 90.3 km.

In the Indus delta, finless porpoises move to the sea in April and return to the creeks and delta in October; here the movements of porpoises are said to follow movements of prawns (Reyes, 1991 and refs. therein).

Parsons (1998a) reports on 154 small cetacean strandings in Hong Kong territorial waters. Finless porpoises and Indo-Pacific hump-backed dolphins accounted for 77% of these strandings. N. phocaenoides was more frequent in the winter. Almost a third of all finless porpoises stranded were calves. At sea finless porpoises were only sighted south of Lantau Island and were more frequently observed during the winter. Their abundance was correlated with water temperature (negatively) and salinity (positively) and also with the number of reported neonatal porpoise strandings. Seasonal distribution appears to be linked with reproductive cycles and hydrography. Diurnal patterns and tidal state seem to affect abundance (Parsons, 1998b).

6. Threats
Direct catch: According to Reyes (1991 and refs. therein), the species has been hunted in Japan, in particular in the East China Sea, although direct catches were not large and have not been reported since the mid-1980’s. No direct catches of small cetaceans existed in China in 1994-95. Incidentally captured small cetaceans did not occupy an important place in the daily life of people in coastal China, and they were discarded in the sea or sold at a very low price in fish markets (Yang et al. 1999). According to Kasuya (1999) there is some controversy about the usefulness of this species for human consumption. People in Ayukawa on the Oshika Peninsula at the northern limit of this species, for instance, do not eat them, believing that they have a strong purgative effect, which was confirmed by a small experiment. However, the species is known to be sold for human consumption in Korea (IWC, 2000), although the source of these animals is unknown.

Incidental catch: Finless porpoises are accidentally caught in nets along the Indian and Pakistani coast, and off the Malay Peninsula although there is no estimate of the magnitude of these catches. Incidental catches are also reported from Japan, where porpoises get entangled in a variety of nets. Changes in fishing methods may have reduced the incidental catch in areas such as western Kyushu (Reyes, 1991 and refs. therein; Kasuya, 1999 and refs. therein). A total of 114 specimens were collected during 1985-1992 off the coasts of western and north-eastern Kyushu including part of the western Inland Sea of Japan: 84 of them were killed incidentally by fisheries, 25 were found dead on the beach or in the sea, and five were of unknown origin. Fisheries that killed the 84 porpoises were bottom gill net (58), surface gill net (17), trap net (7), trawl net (1) and drifting (ghost) net (1). The operation of such fishing gear is common in other parts of Japan and probably is killing finless porpoises off other coasts, although usually such catches remain unreported. Live captures have been reported from Ise Bay (Kasuya 1999 and refs. therein). Yang et al. (1999) surveyed incidental cetacean catches in coastal waters of China in 1994 - 1995. Finless porpoises were captured most frequently, totalling about 2132 + 1484 individuals. Fishing gear employed were predominantly trawl-, gill-, and stow nets.

Habitat degradation: Finless porpoises are vulnerable to habitat encroachment, which is particularly true for the population in the Yangtze River, that may face the same threats as the baiji. Increasing development requires construction of dams for hydroelectric power and diversion of water for agriculture. Dams may prevent movements of dolphins or reduce food availability (Reyes, 1991).

Pollution: Damage to the riverine ecosystem comes from the high level of pollution produced by several industries located along the Yangtze River. In coastal areas, increasing boat traffic and pollution may also affect this species. Finless porpoises disappeared from Ise Bay in Japan during a time of high pollution and returned when pollution was reduced. There has been some concern about the levels of pollution in the Inland Sea of Japan, where the largest population may be present, at least seasonally (Reyes, 1991 and refs. therein). Blubber samples of finless porpoises from the Inland Sea of Japan and Pacific area contained DDT isomers and metabolites at levels up to 10 times the concentration found in striped dolphins off the Pacific coast of Japan, and similar to those found in Baltic ringed seals with stenosis and uterus occlusion. Although such pathology has not been reported in the finless porpoise, pollution is very possibly a threat to the species (Kasuya, 1999 and refs. therein). Recently Le et al. (1999) reported concentrations of butyltin and Minh et a. (1999) of persistent organochlorines in finless porpoises. Parsons (1999) reports that mercury levels were high enough in some individuals as to pose a health risk and Parsons (1998a) noted that the number of reported small cetacean strandings in Hong Kong has increased dramatically in recent years: partially due to an increasing public awareness of local cetaceans and possibly due to escalating levels of human disturbance and anthropogenic pollution.

7. Remarks
The finless porpoise is protected directly or indirectly through national legislation in only a few countries in the range; these include Pakistan, Bangladesh, India, and Iran. In Japan it has been protected since 1930 in a 1.5 km radius around Awashima Island, where finless porpoises were used by fishermen as indicators of the presence of fish (Reyes, 1991 and refs. therein). The exact impact of incidental catches on small cetaceans in Chinese waters was not clear at present, but it has probably caused the decline of their populations (Yang et al. 1999).

The species is categorised as “Data Deficient” by the IUCN, but the population from the Yangtze and Chinese coastal waters is considered “Endangered (En C2b)” based on the fact that C) the population is estimated to number less than 250 mature individuals 2) a continuing decline, observed, projected, or inferred, in numbers of mature individuals and population structure in the form of b) all individuals are in a single subpopulation. N. phocaenoides is listed in Appendices I&II of CITES (see “links”).

Range States so far identified include Bangladesh, Burma, India, Indonesia, Iran, Iraq, Japan, Kampuchea, Kuwait, North Korea, Oman, Pakistan, People’s Republic of China (including Taiwan), Qatar, Saudi Arabia, Singapore, South Korea, Sri Lanka, United Arab Emirates, and Vietnam. Movements of the species across international boundaries are likely to occur, in particular in coastal areas at the mouth of major rivers such as the Ganges and Indus. The species is therefore listed in CMS Appendix II.

The species as a whole is in no immediate danger of extinction, but several populations (possibly representing separate taxa) are apparently declining. The IWC sub-committee discussed, in particular, the Inland Sea of Japan, where this species has declined in abundance in recent years (IWC, 2000). The causes of this decline are not fully understood. Incidental mortality in various kinds of fisheries is the only documented anthropogenic factor affecting the survival of finless porpoises. However, a number of anthropogenic influences such as chemical pollution, depletion of prey species, loss of habitat due to construction or extraction of sand, may all have contributed to the decline. Here, as elsewhere in the species’ range, human populations adjacent to the finless porpoise’s habitat are increasing in size and becoming more industrialised, so the expectation should be that anthropogenic pressures will continue and intensify:

The IWC sub-committee (2000) recommended: - that molecular genetic and morphometric studies of finless porpoises be conducted to assist in clarifying taxonomy and stock structure in the genus Neophocaena. These studies should include analysis of existing specimens and new samples from areas that are currently underrepresented in collections, - that a detailed assessment be conducted of variation in the density of finless porpoises in the Yangtze River system, to identify areas of high porpoise abundance, such as the Poyang Lake, that may deserve special protection, - that the magnitude and effects of by-catches be investigated as a matter of priority, - that further research be conducted to determine the causes of the population decline of this species in the Inland Sea of Japan and how to best stop or reverse this decline, - that surveys be conducted throughout its known and suspected range, particularly in areas where little current information exists, for example along the coasts of the Indian Ocean.

In a recent workshop, Reeves et al. (2000) summarise that threats to finless porpoises in the Yangtze river include incidental mortality from entanglement in passive fishing gear, electric fishing, collisions with powered vessels, and exposure to explosives used for harbor construction. Much of their habitat has been severely degraded, due to the damming of Yangtze tributaries and the intensive use of the river as a transportation corridor. The effects of pollution and reduced availability of prey species are not well documented, but they represent serious additional concerns. The finless porpoise population in the Yangtze river is likely to continue declining unless serious efforts are made to protect the animals and their habitat. The ultimate goal of conservation efforts must be to maintain a viable wild population of porpoises in the river, and any ex-situ conservation strategy can only be justified if it contributes to that goal. Any proposal in this direction, in relation with the Shishou semi-natural reserve, should evaluate carefully the existing population on the site, that harmful fishing can be eliminated. A critical review of available information is needed on water and sediment quality. A programme of studying the animals presently in the reserve should be initiated. The need to educate people about and to strictly enforce regulations concerning the use of destructive fishing gear or methods is recognised.

For further recommendations, please see Perrin et al. (1996).

8. Sources
- Akamatsu T, Ding W, Kexiong W, Zhuo W, Zhao Q, Naito Y (2002) Diving behaviour of freshwater finless porpoises (Neophocaena phocaenoides) in an oxbow of the Yangtze River, China. ICES J Mar Sci 59: 438-443

- Amano M (2002) Finless porpoise - Neophocaena phocaenoides. In: Encyclopedia of marine mammals (Perrin WF, Würsig B, Thewissen JGM, eds.) Academic Press, San Diego, 432 - 435.

- Carwardine M (1995) Whales, Dolphins and Porpoises. Dorling Kindersley, London, UK, 257 pp.

- Carwardine M, Hoyt E, Fordyce RE, Gill P (2000) Wale Delphine und Tümmler. Könemann-Verlag, Köln, Germany

- IWC (2000) Annex K: Report of the sub-committee on small cetaceans. Rep Int Whal Comm, Cambridge, UK.

- Jefferson TA, Kung SK (2000) Review of knowledge on the global status of the finless porpoise (Neophocaena phocaenoides). Rep Int Whal Comm, Cambridge, UK.

- Jefferson TA, Leatherwood S, Webber MA (1993) FAO Species identification guide. Marine mammals of the world. UNEP / FAO, Rome, 320 pp.

- Kasuya T (1999) Finless porpoise - Neophocaena phocoenoides (G. Cuvier, 1829). In: Handbook of Marine Mammals (Ridgway SH, Harrison SR Eds.) Vol. 6: The second book of dolphins and porpoises. pp. 411 - 442

- Le L-T-H, Takahashi S, Saeki K, Nakatani N, Tanabe S, Miyazaki N, Fujise Y (1999) High percentage of butyltin residues in total tin in the livers of cetaceans from Japanese coastal waters. Environmental Science and Technology 33:1781-1786

- Minh T-B, Watanabe M, Nakata H, Tanabe S, Jefferson TA (1999) Contamination by Persistent Organochlorines in Small Cetaceans from Hong Kong Coastal Waters. Marine Pollution Bulletin 39: 383-392

- Parsons ECM (1998a) The behaviour of Hong Kong’s resident cetaceans: The Indo-Pacific hump-backed dolphin and the finless porpoise. Aquatic Mammals 24:91-110

- Parsons ECM (1998b) Strandings of small cetaceans in Hong Kong territorial waters. J Mar Biol Assoc Uk 78:1039-1042

- Parsons ECM (1999) Trace element concentrations in the tissues of cetaceans from Hong Kong’s territorial waters. Environmental Conservation 26:30-40

- Perrin WF, Dolar MLL, Alava MNR (1996) Report of the workshop on the biology and conservation of small cetaceans and dugongs of Southeast Asia. East Asia Seas Action Plan. UNEP(W)/EAS WG. 1/2, Bangkok, Thailand.101 pp.

- Reeves RR, Jefferson TA, Kasuya T, Smith BD, Wang D, Wang P, Wells RS, Wuersig B, Zhou K (2002) Yangtze river population of finless porpoises (Neophocaena phocaenoides). Report of the workshop to develop a conservation action plan for the Yantze river finless porpoise. In: Reeves, RR (ed); Smith, BD (ed); Kasuya, T (ed), Biology and conservation of freshwater cetaceans in Asia. Vol. 23, IUCN, Gland, Switzerland.

- Reyes JC (1991) The conservation of small cetaceans: a review. Report prepared for the Secretariat of the Convention on the Conservation of Migratory Species of Wild Animals. UNEP / CMS Secretariat, Bonn.

- Rice DW (1998) Marine mammals of the world: systematics and distribution. Society for Marine Mammalogy, Special Publication Number 4 (Wartzok D, Ed.), Lawrence, KS. USA

- Yang G, Zhou K, Xu X, Leatherwood S (1999) A survey on the incidental catches of small cetaceans in coastal waters of China. Yingyong Shengtai Xuebao 10 (6): 713-716

- Zhang X, Liu R, Zhao Q, Zhang G, Wei Z, Wang X, Yang J (1993) The population of finless porpoise in the middle and lower reaches of Yangtze River. Acta Theriologica Sinica 13(4): 260-270

- A Special Thanks to Boris Michael Culik at WCMC http://www.wcmc.org.uk/cms/reports/small_cetaceans/comments.htm