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Overview

Brief Summary

Biology

Finless porpoises are rather shy and elusive animals (4), which do not form large schools and are most often seen in pairs consisting of a mother and calf or an adult pair (2). They generally swim quietly, rarely leaping, splashing, or riding the bow waves of boats like other small cetaceans (2). They are opportunistic feeders, consuming a variety of schooling fishes, squids, octopuses, shrimps and prawns. The finless porpoise itself is known to be preyed on by the great white shark (2). Knowledge of reproduction in the finless porpoise currently comes only from individuals in Japanese and Chinese waters. Females are thought to calve every two years, with the peak calving season varying with location. For example, on the Pacific coast of Japan calving takes place in May and June, while it occurs in April and May in the Yangtze River (2). It is estimated that the gestation period in this species is around eleven months and that the mother feeds her calve for approximately seven months. Finless porpoises are known to reach sexual maturity at four to nine years of age and live for up to 25 years (2).
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Description

As its name suggests, this small marine mammal is the only porpoise that lacks a dorsal fin (4), and instead has a ridge that runs down the middle of the back (2). The finless porpoise can also be distinguished by its rounded head, lacking an apparent beak (2), and relatively slender body (4), which is dark to pale grey and lighter on the underside (2). A scattering of horny tubercles (small, raised bumps) are found on the ridge; this is thought to create an anti-slip surface when mothers carry their calves on their back or, more likely, used as sensory organs, as numerous nerve endings are found in the tubercles (2). Three subspecies of the finless porpoise are recognised. Neophocaena phocaenoides asiaorientalis (Yangtze finless porpoise) and Neophocaena phocaenoides sunameri both have narrow and prominent ridges, while the ridge of Neophocaena phocaenoides phocaenoides is wider, and almost flat towards the head. N. p. phocaenoides is also a lighter colour when born, and darkens with age, resulting in almost black adults (2).
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Distribution

Range Description

The type specimen is supposed to have come from the Cape of Good Hope, but this location is believed to be erroneous; it is now generally accepted that the type locality is the Malabar coast of India (Rice 1998, Jefferson and Hung 2004).

In general, Indo-Pacific Finless Porpoises occur in a narrow strip of shallow (usually <50 m deep) coastal marine waters (as well as some river mouths and estuaries) around the northern rim of the Indian and western Pacific Oceans from the Arabian (Persian) Gulf (Preen 2004, Collins et al. 2005) eastwards around the rim of the Indian Ocean to the Indo-Malay region and to Java, Indonesia (but apparently not the Philippines) and northwards to the Taiwan Strait and central Chinese waters (Gao 1991, Gao and Zhou 1995). This is the more tropical and wide-ranging of the two currently recognized species of finless porpoises. A record of the species from northern Chinese waters (Wang 1992) probably represents a rare or extralimital event. Finless porpoises are seen regularly (when sea conditions are favourable) in Sarawak, East Malaysia (Minton et al. 2011), in at least parts of Peninsular Malaysia (e.g. they are the most frequently seen cetaceans in Langkawi according to Louisa Ponnampalam, Reeves pers. comm. 2011), at least seasonally in Hong Kong (Jefferson et al. 2002a), and in parts of the western Taiwan Strait (Wang unpublished data). They are also present along the East Kalimantan coastline of Borneo (D. Kreb pers. comm. 2011).

The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.

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Range Description

The type specimen was from the Yangtze River, Kiangsu [=Jiangsu] Province, China, ~129 km (=80 miles) northwest of Shanghai (Pilleri and Gihr 1972).

In general, the species occurs in a narrow strip of shallow (usually <50 m deep) coastal water around the western Pacific Ocean from the Taiwan Strait to the waters of northern China, Korea and northern Honshu, Japan. (Note that a Narrow-ridged Finless Porpoise was discovered recently in the waters of Okinawa Island, Japan (Yoshida et al. 2010), but it probably represents an extralimital stray rather than an extension of the species’ range.) The distribution also includes a few estuaries and rivers (e.g., the N. a. asiaeorientalis subspecies appears to be found exclusively in the Yangtze River system; Gao 1991, Gao and Zhou 1995). Human coastal development and other activities already may have substantially reduced and fragmented the distribution of Finless Porpoises (Reeves et al. 1997).

N. a. sunameri – Coastal waters from the Taiwan Strait, including the western coast of Taiwan (mainly the Matsu and Chinmen Islands), through the East China Sea north to the Bohai/Yellow Sea in China and the waters of Korea and Japan (Gao 1991, Gao and Zhou 1995). Korean and Japanese populations are geographically separate (Shirakihara et al. 1992, Yoshida et al. 2001, Yoshida 2002).

N. a. asiaeorientalis – Middle and lower reaches of the Yangtze River (= Chang Jiang), where it ranges (or did until recently) to 1,600 km upstream, i.e., to the gorges above Yichang (200 m above sea level). The range includes Poyang and Dongting lakes and their tributaries, the Gan Jiang and the Xiang Jiang (Gao 1991, Gao and Zhou 1995). The subspecies is thought to be restricted to fresh water.

The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.
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Geographic Range

Neophocaena phocaenoides is found in the coastal waters and rivers of Southeast Asia. It is concentrated in the eastern IndoPacific region. Neophocaena phocaenoides can be found from Pakistan to Korea, Japan, Borneo and Java. (Gaskin 1982, Nowak 1991)

Biogeographic Regions: oriental (Native ); indian ocean (Native ); pacific ocean (Native )

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Range

The finless porpoise occurs along the coasts of southern and eastern Asia, from the Persian Gulf, east to Japan and south to Java, Indonesia (5). N. p. phocaenoides occurs in the Indian Ocean and the South China Sea, N. p. sunameri occurs in the East China Sea, Yellow Sea and off the coast of Korea and Japan, and N. p. asiaorientalis is found only in the middle and lower reaches of the Yangtze River and adjoining lake systems (2) (5).
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Physical Description

Morphology

Physical Description

Neophocaena phocaenoides is sometimes called the Black Finless Porpoise because of the common misconception that its skin is black. In reality, the upper portions of N. phocaenoides are gray with touches of blue on the back and sides. The ventral parts are paler. Pale spots do however decrease with age, and the skin turns black immediately after death. Further, the skin coloring differs from pale in oceanic and brackish waters, to almost black in rivers. Neophocaena phocaenoides has no dorsal fin but has instead has a midline dorsal ridge. This ridge contains horny papillae. Neophocaena phocaenoides is the smallest cetacean and grows to only 150-190cm. It has a distinct eel-like shape due to its lack of dorsal fin and round, beakless head. The jaw of N. phocaenoides contains 15-21 spade shaped teeth on each side of the upper and lower jaw. (Ganslosser 1988, Herman 1980, Nowak 1991)

Range mass: 30 to 45 kg.

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Ecology

Habitat

coastal marine, also in rivers
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Habitat and Ecology

Habitat and Ecology

Indo-Pacific Finless Porpoises are found mainly in coastal waters, including shallow bays, mangrove swamps, and estuaries. They can also occur quite far from shore (up to 240 km) in waters < 200 m deep. It is uncertain which of the two currently recognized species of Finless Porpoises (possibly both) occurs farther offshore, especially in areas of sympatry.

Indo-Pacific Finless Porpoises appear to have a strong preference for waters with a sandy or soft bottom (Jefferson and Hung 2004).

Small fishes, cephalopods, and crustaceans (mainly demersal species) form the diet of Finless Porpoises (see Jefferson and Hung 2004).

Systems
  • Marine
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Habitat and Ecology

Habitat and Ecology

Narrow-ridged Finless Porpoises are found mainly in coastal waters, including shallow bays, possibly mangrove swamps, estuaries, and some large rivers. However, they can also occur in shallow waters (<200 m deep) quite far from shore (up to 240 km). They appear to have a strong preference for waters with a sandy or soft bottom (Jefferson and Hung 2004).

In Japanese waters, finless porpoises prefer shallow depths (<50 m) and close proximity to the shore (<5 km). In the shallow East China Sea, proximity to the shore does not appear to be as important (Amano 2002).

Small fishes, cephalopods, and crustaceans (mainly demersal species) form the diet of finless porpoises (see Jefferson and Hung 2004).


Systems
  • Freshwater
  • Marine
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Neophocaena phocaenoides lives in both fresh and salt water habitats. It is found in shallow coastal waters such as the Sea of Japan as well as fresh water rivers like the Yangtze river in China. Neophocaena phocaenoides is occasionaly found in inland lakes which have been cut off from the ocean but are still salt water. Neophocaena phocaenoides seems to prefer rocky promonotories and strong currents (Ganslosser 1988).

Aquatic Biomes: rivers and streams; coastal

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Depth range based on 639 specimens in 2 taxa.

Environmental ranges
  Depth range (m): 0 - 0
 
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The finless porpoise inhabits tropical and warm temperate coastal waters (4), preferring areas over sandy or soft bottoms, including shallow bays, mangroves and estuaries, but it can also be found in some large rivers (2). The Yangtze finless porpoise is the only subspecies that occurs wholly in freshwater (4), and can be found up to 1,600 kilometres from the sea (2).
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Trophic Strategy

Food Habits

Neophocaena phocaenoides feeds mainly in the euphotic zone. It eats benthic invertebrates, cephalopods such as squid, and small demersal fish. Neophocaena phocaenoides is a very aggresive hunter, and fish have been observed jumping out of the water when chased by it (Bryden & Harrison 1986). (Gaskin 1982)

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore )

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Life History and Behavior

Life Expectancy

Lifespan/Longevity

Average lifespan

Status: wild:
23.0 years.

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Lifespan, longevity, and ageing

Maximum longevity: 33 years (captivity) Observations: Normally, these animals do not live more than 20 years. In Chinese waters, however, they reach sexual maturity at later ages (4-10 years) and also live longer (Ronald Nowak 2003). One captive specimen lived for 28.8 years (Richard Weigl 2005).
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Reproduction

Neophocaena phocaenoides reaches sexual maturity by the age of 2. Reproductive cycles differ among geographic groups such as those located near Japan and those near China. The breeding cycle is 1-2 years and gestation lasts between 10 and 11 months. Births occur between February and August and there is usually 1 young per birth. Newborns are around 25kg and are weaned between September and June. Neophocaena phocaenoides has been found to live up to 23 years. (Bryden & Harrison 1986, Nowak 1991).

Breeding interval: The breeding cycle is 1-2 years

Average number of offspring: 1.

Range gestation period: 10 to 11 months.

Range weaning age: 7 to 10 months.

Range age at sexual or reproductive maturity (female): 2 (high) years.

Range age at sexual or reproductive maturity (male): 2 (high) years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average birth mass: 7000 g.

Average number of offspring: 1.

Mothers carry their offspring on a patch of skin on the dorsal surface which is covered with horny papillae. This acts like a saddle on which the young can attach and be carried. Although obviously for carrying young, the horny papillae contain nerve endings and may be a means of auxillary orientation. This "extra" means of orientation could be very beneficial to N. phocaenoides since it often lives in murky waters.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A2cde

Version
3.1

Year Assessed
2012

Assessor/s
Wang, J.Y. & Reeves, R.

Reviewer/s
Hammond, P.S. & Taylor, B.L.

Contributor/s

Justification
There is no population estimate for Indo-Pacific Finless Porpoises throughout their wide range, which appears to be discontinuous (Pilleri and Gihr 1975, Reeves et al. 1997). They are regularly sighted in some areas.

Partly because of their small size, phocoenids are exceptionally vulnerable to incidental mortality in gillnets (e.g., Jefferson and Curry 1994). Neophocaena phocaenoides is smaller than N. asiaeorientalis (thus, if anything, probably even less able to break free once entangled in a net) and incidental mortality in fishing gear has been documented throughout its range. Fishing effort with gear documented to catch Finless Porpoises (including gillnets, trawls, stow nets and seines) is intense in many areas where the species occurs or occurred. With some of the largest concentrations of humans in the world living along the shores of and harvesting the resources from the warm coastal waters inhabited by Indo-Pacific Finless Porpoises, the impacts of human activities on this species must be considerable. Although not quantified rigorously as for some N. asiaeorientalis populations, regional declines (and possible local extirpations) of N. phocaenoides have been reported, presumably due to fishing pressure, coastal development and industrialization, pollution and heavy vessel traffic (see Reeves et al. 1997, Collins et al. 2005, Braulik et al. 2010).

Although the data are far from sufficient to make a rigorous quantitative assessment of population trend for this species throughout its range, the scale of threats is large enough over enough of the range to suspect and infer a decline of at least 30% over the last three generations (about 50 years, see Taylor et al. 2007). The factor most responsible for such a decline would be incidental mortality in fisheries, but the loss and degradation of habitat are likely contributing factors as well. None of the threats has been seriously addressed in any part of the species’ range, even though threat levels are likely increasing.

Therefore, as is true of the other species of Finless Porpoise (N. asiaeorientalis), the Indo-Pacific species qualifies for Vulnerable A2cde, considering that the causes of the suspected/inferred decline in population size—bycatch (interpreted here as “exploitation”), decline in habitat quality, and possibly pollution—have not ceased and are not well understood.

History
  • 2011
    Vulnerable
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IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A2cde

Version
3.1

Year Assessed
2012

Assessor/s
Wang, J.Y. & Reeves, R.

Reviewer/s
Taylor, B.L. & Hammond, P.S.

Contributor/s

Justification

Although the data are far from sufficient to make a rigorous quantitative assessment of population trend for N. asiaeorientalis throughout its range, the scale of threats is large enough over enough of the range to suspect and infer a decline of at least 30% over the last three generations (about 50 years, see Taylor et al. 2007). The factor most responsible for such a decline would be incidental mortality in fisheries, but the loss and degradation of habitat (including chemical pollution) and vessel strikes (at least in the Yangtze River system; Turvey et al. submitted) are likely contributing factors as well. As the Scientific Committee of the International Whaling Commission concluded after a review of the species (both N. phocaenoides and N. asiaeorientalis) in 2005 (IWC 2006), “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.” None of the threats has been seriously addressed in any part of the species’ range, even though threat levels are likely increasing.

Partly because of their small size, phocoenids are exceptionally vulnerable to incidental mortality in gillnets (e.g. Jefferson and Curry 1994). Incidental mortality in fishing gear is either known or presumed to occur throughout the range of Narrow-ridged Finless Porpoises (Reeves et al. 1997, IWC 2006).

There is clear evidence of a declining trend in two major parts of this species’ range. In the Inland Sea of Japan, a decline of nearly 70% was estimated over a period of 22 years, from 1976-1978 to 1999-2000 (Kasuya et al. 2002). There is also evidence of a rapid decline in recent decades in the Yangtze River and adjoining lake systems of China (Zhao et al. 2008, Wang 2009); the subspecies there (N. a. asiaeorientalis), which was classified as Endangered in 1996 under the IUCN 1994 Red List Categories and Criteria, is currently being reassessed to determine whether it should be uplisted to Critically Endangered.

Therefore, as is true of the other species of finless porpoise (N. phocaenoides), the Narrow-ridged species qualifies for Vulnerable A2cde, considering that the causes of the suspected/inferred decline in population size--bycatch and mortality from vessel strikes (both interpreted here as “exploitation”), decline in habitat quality, and possibly pollution--have not ceased and are not well understood.

There should be sufficient information for separate assessment of at least two threatened subpopulations or subspecies – the subpopulation in the Inland Sea of Japan, which likely qualifies for Endangered (Shirakihara et al. 2007), and the Yangtze River subspecies for which a new assessment is underway.

History
  • 2011
    Vulnerable
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Although N. phocaenoides is not endangered, there are many threats to its survival as individuals if not as a species. Neophocaena phocaenoides is effected by pollution as well as bottom dredging. It is also killed by motor boat collisions, hunters, fish and shrimp nets, and its natural predator, the shark. (Bryden & Harrison 1986, Nowak 1991)

IUCN Red List of Threatened Species: vulnerable

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Status

Classified as Data Deficient (DD) on the IUCN Red List (1) and listed on Appendix I of CITES (3). Subspecies: Neophocaena phocaenoides asiaeorientalis (Yangtze finless porpoise) is classified as Endangered (EN) on the IUCN Red List 2007 (1).
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Population

Population

Finless porpoises are small and cryptic and therefore difficult to survey. Estimates of abundance have been made for only a few areas (Jefferson and Hung 2004, IWC 2006) but mostly in regions where the Narrow-ridged species (N. asiaeorientalis) dominates, if not exists solely.

Numbers of Indo-Pacific Finless Porpoises in Hong Kong and adjacent waters were estimated to be at least 217 (CV= 21-150%) (Jefferson et al. 2002a). An estimate for the coastal waters of Bangladesh was 1,382 (CV=55%) but the density was very low compared to reported densities of Narrow-ridged Finless Porpoises in Japanese waters (Smith et al. 2008).


Population Trend
Decreasing
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Population

Population
These porpoises are small and cryptic and therefore difficult to survey. Estimates of abundance have been made for only a few areas (IWC 2006). Estimates from the early 2000s are available for five subpopulations in Japanese waters, distinguished on the basis of skull morphology and mtDNA variability (Yoshida et al. 1995, Yoshida 2002), as follows: 3,807 (CV=16%) in Ariake Sound/Tachibana Bay (Shirakihara and Shirakihara 2002); 289 (CV=19%) in Omura Bay (Shirakihara and Shirakihara 2002); 3,743 (CV=24%) in Ise/Mikawa Bay (Yoshida 2002); 3,387 (CV=33%) in Chiba/Sendai Bay (Amano et al. 2003); and 7,572 (CV=17%) in the Inland Sea (Shirakihara et al. 2007). Most of the estimates were summarized in IWC (2006). For the Inland Sea subpopulation, Kasuya et al. (2002) recorded a decline in sighting rate of 18–100% for 18 tracklines surveyed in 1976–78 and again in 1999–2000. The declines for 11 of these tracklines were statistically significant. Using abundance indices calculated by multiplying the density indices (no. individuals/cruise distance) and area size of each stratum, an overall decline of 69% is inferred over the 22 years between the two sets of surveys (T. Kasuya pers. comm. 2007, data from Kasuya et al. 2002).

Surveys in western Korean waters (Yellow Sea) in the early 2000s estimated 21,532 (CV=39%) finless porpoises in offshore waters and 5,464 (CV=20%) in inshore waters (Zhang et al. 2005). The Scientific Committee of the International Whaling Commission (IWC) considered these estimates to be negatively biased (IWC 2006, p. 223).

Based on surveys from 1984 to 1991, Zhang et al. (1993) estimated that there were about 2,700 porpoises in the Yangtze River, while Zhou et al. (2000) estimated that only 700 remained in the lower reaches between Nanjing and Hukou between 1989 and 1992. Wang et al. (2000) concluded that finless porpoise abundance in the Yangtze River had declined considerably and that there could be fewer than 2,000 animals (although this was not based on a rigorous assessment). A two-vessel survey of the Yangtze mainstem in 2006 yielded an estimate of 1,225 (CV 0.13) which, when combined with earlier estimates for Poyang and Dongting Lakes, was interpreted as implying an overall number of about 1,800 in the Yangtze system (Zhao et al. 2008). In some portions of the river where porpoises had been reported to be present in the past, none were seen during the 2006 survey. Estimates of the annual rate of decline of Yangtze finless porpoises have varied from 5 to 7.3% (see Wang 2009 for a review).

There are no abundance estimates for finless porpoises in Chinese marine waters other than Hong Kong (IWC 2006), which would be for N. phocaenoides and not N. asiaeorientalis.

Population Trend
Decreasing
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Threats

Major Threats

Finless Porpoises, like other phocoenids (Jefferson and Curry 1994), are extremely susceptible to entanglement in gillnets, and large numbers have been, and continue to be, killed in many parts of their range (Jefferson et al. 2002b). Finless Porpoises are caught in nets in Iranian, Indian, Pakistani and Malaysian coastal waters, although there are no good estimates of the magnitude of such catches (e.g., see Collins et al. 2005, Jaaman et al. 2009, Braulik et al. 2010). In East Malaysia, Finless Porpoises are caught as bycatch in ‘fish stakes’ in Sabah (Jaaman et al. 2009) and one individual was found entangled in the line of a crab trap in Sarawak (G. Minton pers. comm. 2011). Yang et al. (1999) reported that Finless Porpoises were the most frequently captured cetaceans in fishing gear along the Chinese coast and estimated that more than 2,000 were taken in 1994, mainly in trawl, gill, and stow nets. In the waters of western Taiwan (where the two species of Finless Porpoises are sympatric), a considerable number of both species are taken in trammel nets, trawl nets, stow nets, and other gear (Wang unpublished data). In Hong Kong waters, porpoises are caught regularly by trawl nets and gillnets, but there are no estimates of bycatch levels (Parsons and Jefferson 2000, Jefferson et al. 2002b). Given the numbers and types of net fisheries in Chinese coastal waters, the apparently high bycatch of Finless Porpoises (e.g. Zhou and Wang 1994, Yang et al. 1999) is a serious concern. No large-scale direct hunting of this species is known to occur. In some parts of their range, people apparently are averse to eating finless porpoises (Kasuya 1999, Wang unpublished data) but in other areas they are consumed.

As a coastal species, the Indo-Pacific Finless Porpoise is also affected by habitat loss and degradation, boat traffic, and pollution. The extensive modification of coastlines for shrimp farming, causeways and harbour (and other) development throughout Asia (including the Arabian Gulf) means that there is less habitat for Finless Porpoises (Reeves et al. 2003, Braulik et al. 2010). Although pathology related to contaminant exposure has not been reported in Finless Porpoises, pollution is considered a potentially serious threat (Kasuya 1999, Iwata et al. 1994, Parsons and Chan 1998, Minh et al. 1999, Parsons 1999, Jefferson et al. 2002b, Ramu et al. 2005). The number of reported small cetacean strandings in Hong Kong has increased in recent years, partly due to increasing public awareness of local cetaceans, but also possibly due to escalating levels of human disturbance and pollution (T.A. Jefferson pers. comm. 2007). In the Arabian Gulf and Gulf of Oman/Sea of Oman, chemicals from recent wars exacerbate total pollution loads in coastal waters from the usual sources such as industry, agriculture and households (Braulik et al. 2010). Vessel collisions, especially involving high-speed ferries, may be a particular problem for porpoises in Hong Kong (Parsons and Jefferson 2000).

The following summary of examples illustrates the problems faced by this species:

In Chinese waters (excluding the considerable fisheries operating in Taiwanese waters), more than 3.5 million gillnets were estimated to be in use in the early 1990s (Zhou and Wang 1994). In India, the use of gillnets reportedly had increased from about 18,000 in 1950 to more than 216,000 by 1980 and gillnets were also being used extensively in Sri Lanka, Bangladesh and Myanmar (Mohan 1994). Since the time of those reports, gillnetting effort certainly would have increased considerably in these and other regions because there are few (if any) restrictions on this kind of fishing gear anywhere in the range of the species. Porpoise habitat in Myanmar is heavily fished with gillnets and other types of gear capable of taking small cetaceans incidentally (Smith and Than Tun 2008). A drift gillnet fishery for elasmobranchs is of concern in the Bangladesh Sundarbans (Smith et al. 2008). In East Malaysia, Finless Porpoise numbers are thought to have ‘greatly declined’ due to bycatch in fisheries (Jaaman et al. 2009), and commercial fishing (gillnetting, trawling, purse-seining) is intensive off Langkawi, Peninsular Malaysia, where bycatch of Finless Porpoises is known to occur even though it is not monitored regularly (L. Ponnampalam pers. comm. 2011). Surveys in the coastal waters of Vietnam resulted in very few sightings of cetaceans; none of the sightings were of Finless Porpoises yet local whale temples contained numerous cetacean skulls, including many from Finless Porpoises (Smith et al. 1997). The impacts of war several decades ago, compounded by intense fishing (especially the use of gillnets) in recent years and ongoing, are likely at least partly responsible for the near absence of cetaceans from these waters. In Iran (Arabian Gulf and Gulf of Oman/Sea of Oman), bycatch in fisheries appears to be the greatest threat to marine mammals and takes from apparently small, localized populations of Finless Porpoises may be unsustainable (Braulik et al. 2010). Two major marine mammal die-offs occurred in the Arabian Gulf in the 1980s and 1990s, possibly related to major oil spills (Collins et al. 2005). Even in the 1970s, Finless Porpoise sightings in Pakistani coastal waters around the Indus Delta region were apparently decreasing (Pilleri and Gihr 1972, Pilleri and Pilleri 1979) and by the 1990s the species may have virtually disappeared from this badly degraded area (see Reeves et al. 1997). The Finless Porpoise was one of several cetacean species thought to have disappeared from large parts of their previous ranges in Thailand, largely as a result of coastal habitat degradation and fisheries (IWC 1994).

Direct killing or capture of Finless Porpoises appears to be relatively rare (Reeves et al. 1997) but development of intentional fisheries for marine mammals from incidental captures (and economic benefits from subsequent consumption and marketing) may have increased in parts of Southeast Asia as preferred marine resources have been over-fished (see Perrin 2002).

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Major Threats

Finless porpoises, like other phocoenids (Jefferson and Curry 1994), are extremely susceptible to entanglement in gillnets, and large numbers have been, and continue to be, killed in many parts of their range. In Japan Narrow-ridged Finless Porpoises become entangled in a variety of types of fishing gear. Changes in fishing methods may have reduced the incidental catch in some areas such as western Kyushu (Kasuya 1999), but substantial numbers are still being taken in gill nets and other fishing gear. A total of 114 specimens were collected in Japan during 1985–1992 from western and north-eastern Kyushu including parts of the western Inland Sea (Shirakihara et al. 1993): 84 of them had been killed incidentally in fisheries, 25 had been found dead on the beach or in the sea, and there was no information on the other five. Fishing gears that killed the 84 porpoises were bottom-set gill nets (58), surface gill nets (17), trap nets (7), trawl nets (1) and drifting (ghost) nets (1). Such fishing gears aree common in Japan and probably kill finless porpoises off other coasts, although usually such catches go unreported. Yang et al. (1999) reported that finless porpoises were the most frequently captured cetaceans in fishing gear along the Chinese coast and estimated that more than 2,000 were taken in 1994, mainly in trawl, gill, and stow nets. In the waters of western Taiwan, including the Matsu and Chinmen Islands (western Taiwan Strait), a considerable number of finless porpoises are taken in trammel nets, trawl nets, stow nets, and other gear (J.Y. Wang unpublished). Given the numbers and types of net fisheries in Chinese coastal waters (e.g. Zhou and Wang 1994, Yang et al. 1999), there are serious concerns about the level of bycatch of both finless porpoise species. Although illegal, electric fishing became widespread in the Yangtze River during the 1990s, and it probably kills porpoises outright and contributes to the depletion of their prey (Reeves et al. 2000).

In some parts of their range, there is an aversion to eating finless porpoises (Kasuya 1999, J.Y. Wang unpublished). However, there is a long history of porpoises taken incidentally being sold for human consumption in at least parts of Japan (e.g., Mizue et al. 1965) and on the Korean peninsula (IWC 2000). From an analysis of the species composition of odontocete products in Korean markets during 2003–2004, it was estimated that the true catch of finless porpoises in Korean waters during this period was probably about four times the officially reported catch of 142 animals (Baker et al. 2006).

As coastal and riverine animals, Narrow-ridged Finless Porpoises are also affected by habitat loss and degradation, boat traffic, and pollution. The extensive modification of coastlines for shrimp farming and rampant harbor (and other) development throughout East Asia means that there is less habitat for finless porpoises (Reeves et al. 2003). Porpoise habitat in the Yangtze River system has been degraded by water development, including the Gezhouba and Three Gorges dams and about 1300 smaller dams in tributaries (Liu et al. 2000, Smith et al. 2000). Sand mining is intensive in Poyang Lake, until recently a stronghold for Yangtze finless porpoises (Zhao et al. 2008). Although pathology related to contaminant exposure has not been reported in Narrow-ridged Finless Porpoises, pollution is considered a potentially serious threat (Kasuya 1999; see Kannan et al. 1989; Iwata et al. 1994, 1995; Le et al. 1999; Zhao et al. 2008).

A recent survey of levels and drivers of human-caused mortality carried out in 27 fishing settlements along the middle-lower Yangtze channel identified three main categories of observed porpoise deaths: (1) interaction with fishing gear, (2) vessel strikes, and (3) unknown cause (S.T. Turvey pers. comm. 2011). A total of 344 dated porpoise mortality events directly observed by informants between 1950 and 2008 were reported, including 75 porpoise deaths from 1989–1998 and 147 from 1999–2008. This change was driven by the greater number of deaths attributed to vessel strikes (19 to 35) and unknown causes (31 to 94) in the more recent decade. Comparison of the reported mortality with the estimated abundance suggests that the fraction of individuals removed from the declining porpoise population in the Yangtze has quadrupled over the course of two decades. Turvey concluded that entanglement in rolling hook long-lines is probably responsible for the greatest number of porpoise deaths in fishing gear and that vessel strikes and other anthropogenic factors, such as electrofishing, are likely now the dominant and increasing causes of mortality in the Yangtze.

The causes of an apparent decline in porpoise numbers in the Inland Sea of Japan are not fully understood but include incidental mortality in fisheries as well as various forms of habitat degradation (IWC 2000, 2006). Parts of the coastal regions of the Inland Sea are highly developed and industrialized so the associated threats of habitat loss and pollution are suspected to have had some (undetermined) level of impact

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The finless porpoise's preference for coastal and riverine habitats makes it highly vulnerable to the impacts of human activities that take place in these regions (2). Although the finless porpoise is not directly targeted by fishermen, large numbers die when they become entangled in fishing nets, particularly gillnets (2) (5). Electric fishing also threatens the finless porpoise in the Yangtze River; despite being illegal, this destructive fishing method has become widespread in the river system during the last decade, not only killing some porpoises outright but also depleting their prey (5). Furthermore, high levels of toxic pollutants have been reported from Japanese finless porpoises, and while finless porpoises tend to avoid boats (2), mortalities caused by collisions with vessels may be a problem in busy shipping areas, such as Hong Kong (5). The deforestation of mangrove areas, rampant harbour expansion and the development of shrimp farms is taking place throughout Asia, degrading the porpoises' coastal habitat (2) (5). The Yangtze River finless porpoise is particularly vulnerable to habitat degradation, with the river not only being impacted by fishing and pollution, but also by the numerous dams that dot the Yangtze River basin (5). The impact that these threats may have on the Yangtze finless porpoise is illustrated only too well by the recent tragic demise of the baiji (Lipotes vexillifer), which was believed to have gone extinct from the Yangtze River in 2006 (6).
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Management

Conservation Actions

Conservation Actions

The species (which presently also includes N. asiaeorientalis) is listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), and in Appendix II of the Convention on Migratory Species (CMS). Management measures are needed to address the threats, especially bycatch in fisheries.

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Conservation Actions

Conservation Actions
Neophocaena phocaenoides (meant at the time of listing to include N. asiaeorientalis) is listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), and in Appendix II of the Convention on Migratory Species (CMS). Management measures are needed to reduce the threats, particularly incidental mortality in fisheries and vessel strikes, but also to protect (or if possible restore) the environmental conditions needed for these animals to survive and reproduce.
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Conservation

Currently, conservation measures appear to only exist for the Yangtze finless porpoise. Since the 1980s, conservation measures have been proposed and implemented for this Endangered subspecies (7). Preserving its natural habitat within the river has been the principal concern and so by 2008, six natural reserves had been created in areas of the river that contain high numbers of the porpoise (7) (8). In these reserves, the use of harmful fishing gear has been banned and these parts of the river are patrolled. However, these reserves are unable to eliminate all threats to the finless porpoise and thus ex-situ conservation has also been undertaken (7). The Baiji Dolphinarium was established in China in 1992, creating the opportunity to study endangered river animals in captivity. Yangtze finless porpoise have been reared here for several years, with one giving birth in 2005; the first freshwater cetacean to have ever been born in captivity (7). Another calf was born in 2008 (9). Another small group inhabit a 'semi-natural reserve', which was initially created for the baiji (10), comprising an oxbow lake and an 89 kilometre long section of river section (8). While such efforts should be commended, not all have had particularly promising outcomes and the future of the Yangtze finless porpoise remains uncertain (10). Hopefully the fate of the baiji will act as a poignant warning and lesson for the Yangtze finless porpoise (10), and that research is promptly undertaken on the other finless porpoise subspecies (2), to determine whether they may also be in need of rapid and intensive conservation efforts.
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Positive

Neophocaena phocaenoides is hunted by humans for its meat, skin and oil (Nowak 1991).

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Risks

IUCN Red List Category

Vulnerable (VU)
  • IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
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Wikipedia

Finless porpoise

The finless porpoise (Neophocaena phocaenoides) is one of six porpoise species. A freshwater population found in the Yangtze River in China is known locally as the jiāngtún (Chinese: 江豚, "river porpoise" or "river pig"). In the waters around Japan, at the northern end of its range, it is known as the sunameri (Japanese: 砂滑, "slick sand"). There is a degree of taxonomic uncertainty surrounding the species, with the N. p. phocaenoides subspecies perhaps representing a different species from N. p. sunameri and N. p. asiaeorientalis. Genetic studies indicate that the finless porpoise is the most basal living member of the porpoise family.[2]

Distribution[edit]

The finless porpoise lives in the coastal waters of Asia, especially around Korea, India, China, Indonesia, Bangladesh and Japan. Throughout their range, the porpoises stay in shallow waters, up to 50 m (160 ft) deep, close to the shore, in waters with soft or sandy seabeds, or in estuaries and mangrove swamps. In exceptional cases, they have been encountered as far as 135 km (84 mi) off-shore in the East China and Yellow Seas, albeit still in shallow water.[3]

There are three recognised subspecies:[3]

A genetically unique freshwater population (N. p. asiaeorientalis) is found in the Yangtze River.[4] At the western end, their range includes the length of the western coast of India and continues up into the Persian Gulf. N. p. phocaenoides has a wide ridge on its back and ranges from Pakistan to the Taiwan straits. N. p. sunameri has a narrower ridge, and is found from Taiwan, north to the Sea of Japan. The population in coastal waters around Japan is geographically isolated by the deep waters between Japan and continental Asia.[1] Vagrant animals can reach the Ryukyu Islands.[citation needed] Finless porpoises are also one of the species protected at Sundarbans National Park.

Physical description[edit]

Size compared to an average human

The finless porpoise is the only porpoise to lack a true dorsal fin. Instead there is a low ridge covered in thick skin bearing several lines of tiny tubercles. In addition, the forehead is unusually steep compared with those of other porpoises. With fifteen to twenty-one teeth in each jaw, they also have, on average, fewer teeth than other porpoises, although there is some overlap, and this is a not a reliable means of distinguishing them.[3]

Finless porpoises can grow to as much as 2.27 m (7 ft 5 in) in length, and can weight up to 72 kg (159 lb), although most are rather smaller.[3] 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.[3]

Adults grow more than 1.55 m (5 ft) in length and up to 30–45 kg (65–100 lb) in weight.[citation needed]

Internal anatomy[edit]

The anatomy of finless porpoises has been relatively well studied, compared with that of some other cetacean species. For example, the tubercles along the dorsal ridge are known to contain numerous nerve endings that may possess a sensory function. The auditory system also appears well-developed, with numerous large nerve fibres specialised for rapid communication between the ears and the brain. On the other hand, sight is relatively poor, especially in finless porpoises living in the Yangtze River, with a reduced lens and a limited number of fibres in the optic nerve and to the muscles moving the eyes. However, even the vision of these riverine finless porpoises is probably superior to that of the baiji, which once lived in the same river system.[3]

The skeleton is unusually 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. 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.[3] There are 44 sets of spinal nerves.[5]

The nasal passage contains nine or ten air sacs, which have a complicated structure, and are capable of sealing off all air within the passage. Behind these are an additional set of vomeronasal sacs.[6] The trachea, however, is short, with only four cartilaginous rings.[3] The stomach has three chambers, there is no caecum, and no distinct difference between the small and large intestines.[7][8]

Diet[edit]

Finless porpoises are opportunistic feeders using various kinds of available food items available in their habitat, including fish, crustaceans, and cephalopods.[9] They are reported[by whom?] 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 octopuses.[citation needed] Seasonal changes in their diets have not been studied. They also apparently ingest some plant material when living in estuaries, mangroves, and rivers, including leaves, rice, and eggs deposited on vegetation.[citation needed]

Behaviour[edit]

In Chinese coastal waters and the Yangtze River, finless porpoises are generally found in groups of three to six,[10] although aggregations of up to about fifty have been reported.[3] In Japanese waters, groups appear to be smaller, with pairs being typical, and even rare aggregations being no larger than thirteen individuals.[3] Recent data[clarification needed] suggest the basic unit of a finless porpoise pod is a mother/calf pair or two adults, and 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.[citation needed]

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. In the Yangtze River, finless porpoises are known to leap from the water and perform "tail stands".[3]

Finless porpoises make both high frequency clicking sounds, and longer, low frequency tones, the latter perhaps being for communication, rather than echolocation.[11] The clicks are narrow-band, with peaks of over 100 kHz.[12]

A new study from Woods Hole Oceanographic Institution (WHOI) study that was published in The Journal of Experimental Biology, "highlights the differences in dolphins' ability to hear across species, reshaping the previous 'one-size-fits-all' approach taken on the hearing ability of the cetaceans".[13]

Swimming style[edit]

Although they show no acrobatics in the water,[citation needed] finless porpoises are believed to be very active swimmers. They typically swim just beneath the surface of the water and roll to one side when surfacing to breathe. This rolling movement disturbs very little water on the surface, so they are often overlooked when rising to breathe. Surfacing generally lasts for one minute, as they take three to four quick successive breaths, then quickly submerge into the water. They often surface a great distance from the point where they dive beneath the water's surface.[citation needed] Dives lasting over four minutes have been recorded, and a common pattern of behaviour is to take one long dive, followed by two shorter ones.[3]

Reproduction[edit]

Breeding occurs in late spring and early summer.[citation needed]. The young are born in in spring, summer, or winter, depending on the geographic locality, after a gestation period of ten to eleven months. Newborn finless porpoises are reported to 72 to 84 cm (28 to 33 in) in length.[3][14] Males reach sexual maturity at four to six years of age, and females at six to nine years.[14] Finless porpoises have lived up to 33 years.[3]

It has been claimed that young calves cling to the denticulated area of skin on their mother's back and are carried by her as she swims, but there is no clear evidence of this happening.[3] Calves are weaned at 6–15 months.[citation needed]

Conservation[edit]

The finless porpoise is listed on Appendix II[15] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II[15] as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.

Since this species remains in coastal waters, it has a high degree of interaction with humans, which often puts the finless porpoise at risk. Like other porpoises, large numbers of this species are killed by entanglement in gill nets. Except for being briefly hunted after World War II due to the lack of seaworthy fishing boats, finless porpoises have never been widely hunted in Japan. It is a species protected since 1930 at the area around Awajima Island, Takehara and this coverage had since been extended to all Japanese coastal waters. The primary danger to the species is environmental degradation. Unlike other members of this family, finless porpoises have lived in captivity for over 15 years.[citation needed]

There are no well-established estimates of the animals' abundance. However, a comparison of two surveys, one from the late 1970s and the other from 1999–2000, shows a decline in population and distribution. Scientists believe this decline has been ongoing for decades, and the current population is just a fraction of its historical levels. Along the southern coast of Pakistan in the Arabian Sea it is declared as an endangered species.[citation needed]

Freshwater population[edit]

The Yangtze finless porpoise is genetically distinct from seawater populations,[4] with estimated divergence over a million years ago.[16] Due to a rapidly falling population, the International Union for Conservation of Nature (IUCN) Red List of Threatened Species adjusted its conservation status to critically endangered in 2013.[16]

Current conservation efforts were undertaken alongside those for the baiji. In 1990, five Yangtze porpoises were relocated to the Tian-e-Zhou Oxbow Nature Reserve, and now a population of 28 inhabits the lake.[17] In 2006, after the baiji was declared functionally extinct, hydrobiologist Wang Ding stated, "The situation of the finless porpoise is just like that of the baiji 20 years ago. Their numbers are declining at an alarming rate."[18] In 2007, the population was less than half the 1997 level, and was dropping at a rate of 7.3% per year. A 2012 survey indicated the rate of decline had accelerated to 13.7% per year.[19][20]

The Poyang Lake population is threatened by sand dredging, particularly high-density dredging projects, which increase the muddiness of the water, reducing visibility. Frequent ship traffic also hinders hunting and movement from one bank to the other.[21]

See also[edit]

References[edit]

  1. ^ a b Wang, J. Y. & Reeves, R. (2011). "Neophocaena phocaenoides". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 18 January 2012. 
  2. ^ Rosel, P.E., et al. (1995). "Phylogenetic relationships among the true porpoises (Cetacea: Phocoenidae)". Molecular Phylogenetics and Evolution 4 (4): 463–474. doi:10.1006/mpev.1995.1043. 
  3. ^ a b c d e f g h i j k l m n o Jefferson, T.A. & Hung, S.K. (2004). "Neophocaena phocaenoides". Mammalian Species 746: 1–12. doi:10.1644/746. 
  4. ^ a b Walker, Matt (29 June 2010). "Finless porpoises in China on brink of extinction". BBC News. 
  5. ^ Wu, B. (1989). "The spinal cord of finless porpoise, Neophocaena phocaenoides". Acta Theriological Sinica 9 (1): 16–23. 
  6. ^ Gao, G. & Zhou, K. (1989). "Anatomy of the nasal passage and associated structures of Neophocaena phocaenoides". Acta Theriologica Sinica 9 (4): 275–280. 
  7. ^ Li, Y., et al. (1984). "The digestive organs of the finless porpoise (Neophocaena asiaeorientalis). I. Tongue, oesophagus and stomach". Acta Theriologica Sinica 4 (4): 257–264. 
  8. ^ Qian, W., et al. (1985). "The digestive organs of the finless porpoise Neophocaena asiaeorientalis. II. Intestines, liver and pancreas". Acta Theriologica Sinica 5 (1): 3–9. 
  9. ^ Shirakihara, M., et al. (1992). "Records of the finless porpoise (Neophocaena phoceanoides) in the waters adjacent to Kanmon Pass, Japan". Marine Mammal Science 8 (1): 82–85. doi:10.1111/j.1748-7692.1992.tb00128.x. 
  10. ^ Parsons, E.C.M. (1998). "The behaviour of Hong Kong's resident cetaceans: the Indo-Pacific hump-backed dolphin and the finless porpoise". Aquatic Mammals 24 (3): 91–110. 
  11. ^ Wang, D. (1996). "A preliminary study on sound and acoustic behavior of the Yangtze River finless porpoise, Neophocaena phocaenoides". Acta Hydrobiologica Sinica 20 (2): 127–133. 
  12. ^ Kamminga, C., et al. (1996). "Investigations on cetacean sonar XI: Intrinsic comparison of the wave shapes of some members of the Phocoenidae family". Aquatic Mammals 22 (1): 45–56. 
  13. ^ Foley, James A. (21 October 2013). "Study of Yangtze Finless Porpoise Reveals Not All Cetaceans Hear Alike". Nature World News. Retrieved 22 October 2013. 
  14. ^ a b Shirakihara, M., et al. (1993). "Age, growth, and reproduction of the finless porpoise, Neophocaena phocaenoides, in the coastal waters of western Kyushu, Japan". Marine Mammal Science 9 (4): 392–406. doi:10.1111/j.1748-7692.1993.tb00472.x. 
  15. ^ a b "Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS)". Convention on Migratory Species. 5 March 2009. 
  16. ^ a b Hooper, Rowan (2 July 2013). "World's only freshwater porpoise on brink of extinction". New Scientist. 
  17. ^ "Scientists Join Hands to Seek the Last Yangtze River Dolphin". WWF China. Archived from the original on 12 November 2007. 
  18. ^ "China's white dolphin called extinct after 20 million years". CNN. Associated Press. 13 December 2006. Archived from the original on 10 January 2007. 
  19. ^ "Rare porpoise halved in six years, endangered". China Daily. 29 March 2013. 
  20. ^ "Yangtze River expedition points to decline of endangered finless porpoise". World Wildlife Fund. 20 November 2012. 
  21. ^ Zhang, Kejia (9 March 2007). "Poyang Lake: saving the finless porpoise". China Dialogue. Archived from the original on 18 July 2011. 
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