Overview

Brief Summary

Biology

Believed to be reincarnated humans by some of the people of Laos (2), Irrawaddy dolphins are less active than many other dolphins with only the uppermost dorsal surface of the animal becomes visible during a slow rolling dive; they make only occasional low leaps and never bow-ride. Feeding together in groups of usually less than six, but as many as 15 (5), the Irrawaddy dolphin can dive for up to 12 minutes to feed on bony fish, crustaceans, cephalopods and fish eggs. Irrawaddy dolphins are known to spit water to herd fish, and have even been reported to stun large fish with a blow from the lower jaw, only to play with them before casting them aside (2). In some areas of Asia, fishermen consider the Irrawaddy dolphin to be a competitor for fish, but in other areas the fishermen attract them to the boat and encourage them to drive fish into the nets where the dolphins also benefit by preying on fish whose movements are confused by the nets and those that are momentarily trapped around the edges or in the mud (6). Irrawaddy dolphins communicate with clicks, creaks and buzzes (7) at a dominant frequency of about 60 kilohertz which is thought to be used for echolocation (8). Little is known about the reproductive biology of the Irrawaddy dolphin, but it is thought to breed between April and June in the Mahakam River, and gestation is estimated at 14 months and weaning after two years (2). This dolphin species is known to carry out daily migrations from the Semayang Lake in eastern Borneo to the Mahakam River, returning to the lake in the evening. In Indonesia, Irrawaddy dolphins move into tributaries at high water and into the main river during low water (4).
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Description

A particularly distinctive dolphin, the Irrawaddy has a rounded head with no beak and a flexible neck, causing visible creases behind the head (2). Although most closely related to the orca (4), the Irrawaddy dolphin is similar in body form to the beluga whale, but darker in colour, with a pale to dark grey back and a light underside. The dorsal fin is small, triangular and rounded, and the flippers are long and broad (2).
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Deskripsi Umum Orcaella Brevirostris

Pesut atau lumba-lumba air tawar adalah spesies mamalia air yang menghuni wilayah perairan tawar di India, Indocina, Filipina dan Kalimantan. Spesies ini pertama kali dideskripsikan oleh Sir Richard Owen tahun 1866 berdasarkan satu spesiemen yang ditemukan tahun 1852, di pelabuhan Vishakhapatnum di pantai timur India. Kadang-kadang pesut terdaftar dalam beragam famili yang terdiri dari pesut itu sendiri pada Monodontidae dan dalam Delphinapteridae. Sekarang ada persetujuan bahwa pesut termasuk famili Delphinidae.

Spesies ini secara genetis terhubung dengan paus pembunuh. Nama spesies brevirostris berasal dari bahasa Latin yang berarti berparuh pendek. Tahun 2005, analisis genetik menunjukkan bahwa lumba-lumba sirip pendek Australia merupakan spesies kedua dari genus Orcaella. Orcaella brevirostris disebut juga Irrawaddy dolphin dalam bahasa Inggris, dan di Spanyol Delfín del Irrawaddy. Pesut jenis ini dulu populasinya sangat banyak di daerah sungai Mahakam Kalimantan. Tapi sekarang telah diklaim sebagai satwa langka karena populasinya yang berkurang drastis.

Pesut memiliki tubuh yang berwarna kelabu hingga biru tua, bagian bawahnya berwarna lebih pucat dan tidak memiliki pola khas. Sirip punggungnya kecil dan membulat di tengah punggung. Penampilan pesut mirip dengan beluga, meski lebih berkerabat dengan orka.

Spesies ini mempunyai melon (jaringan berlemak dan berminyak di kepala) fungsinya untuk ekolokasi. Sirip punggung yang terletak dua pertiga posterior di punggung, pendek, tumpul, dan segitiga. Sirip tangan panjang dan lebar. Secara keseluruhan ia berwarna cerah, namun lebih putih di bawah tubuh daripada di punggung. Pesut dewasa beratnya lebih dari 130 kg dan panjangnya 2,3 m psaat dewasa. Panjang maksimum yang tercatat adalah jantan 2,75 m dari Thailand.

Pesut mencapai kedewasaan seksual pada 7 sampai 9 tahun. Di belahan bumi utara, perkawinan dilaporkan berlangsung pada bulan Desember sampai Juni. Masa hamilnya 14 bulan, melahirkan seekor anak setiap 2 hingga 3 tahun. Saat lahir panjangnya 1 m dan beratnya 10 kg dan umur pesut dapat mencapai 30 tahun.

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Distribution

Range Description

Irrawaddy dolphins have a discontinuous distribution in the tropical and subtropical Indo-Pacific, almost exclusively in estuarine and fresh waters (Stacey and Arnold 1999; Arnold 2002). They occur from Borneo and the central islands of the Indonesian Archipelago north to Palawan, Philippines, and west to the Bay of Bengal, including the Gulf of Thailand. There are freshwater subpopulations in three large rivers: Ayeyarwady (up to 1,400 km upstream) in Myanmar, Mahakam (up to 560 km upstream) in Indonesia, and Mekong (up to 690 km upstream) in Viet Nam, Cambodia and Lao PDR, and two marine-appended brackish water bodies or lakes: Chilika in India and Songkhla in Thailand. The fine-scale range of the species is poorly documented throughout much of its range in estuarine waters.
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Geographic Range

Irrawaddy dolphins (Orcaella brevirostris) are found throughout much of the tropical and subtropical Indo-Pacific region; along the coasts of India, Bangladesh, Myanmar (Burma), Thailand, Cambodia (Kampuchea), Lao Peoples' Democratic Republic (Laos), Socialist Republic of Vietnam, Malaysia, Singapore, Brunei Darrusalam, Indonesia, Papua New Guinea, and Australia.

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

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Range

The Irrawaddy dolphin has a patchy distribution in the shallow, coastal waters of the Indo-Pacific from the Philippines to northeastern India. Freshwater subpopulations occur in three river systems: the Mahakam of Indonesia, the Ayeyarwady (previously Irrawaddy) of Burma, and the Mekong of Laos, Cambodia and Viet Nam. It is also found in completely or partially isolated brackish water bodies such as Chika Lake in India and Songkhla Lake in Thailand (1).
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Physical Description

Morphology

Physical Description

Unlike other dolphins, Irrawaddy dolphins lack a beak and have flexible necks. The flexibility in the neck causes visible creases behind the head. Additionally, Irrawaddy dolphins have bulging heads, with the forehead extending past the mouth, broad triangular, paddle-like, pectoral fins, and small, triangular dorsal fins set approximately two-thirds of the body length along the back. Skin coloration varies from slate-blue to slate-gray with a lighter underside. The face and head are similar in appearance to beluga whales (Delphinapterus leucas). Irrawaddy dolphins have narrow, pointed, peg-like teeth about 1 cm in length in both the upper and lower jaws. Body mass varies from 114 kg to 143 kg and the length ranges from 146 cm to 275 cm. Males tend to be larger in mass and length, with a larger dorsal fin. Irrawaddy dolphins lack a cardiac sphincter and the stomach is subdivided into compartments.

Range mass: 114 to 133 kg.

Average mass: 124 kg.

Range length: 146 to 275 cm.

Average length: 210 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

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Ecology

Habitat

in coastal, brackish and fresh waters, tropical and subtropical
  • UNESCO-IOC Register of Marine Organisms
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Habitat and Ecology

Habitat and Ecology
Irrawaddy dolphins prefer coastal areas associated with the muddy, brackish waters at river mouths, ranging offshore as far as the extent of the freshwater plume – often only a few km but more than 60 km at the Meghna River mouth in Bangladesh (Smith et al. 2005). In rivers and mangrove channels, the species is most often observed at channel confluences and divergences and downstream of sharp meanders. They have been seen in the same area as finless porpoises in coastal waters of Bangladesh and Myanmar (Smith et al. 2005), and Ganges River dolphins in the waterways of the Sundarbans mangrove forest (Smith et al. 2006).

Systems
  • Freshwater
  • Marine
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Irrawaddy dolphins prefer coastal areas, particularly muddy, brackish waters at river mouths and deltas, and do not appear to venture far offshore. Most sightings have been made within 1.6 km of the coastline, but some have been reported in waters greater than 5 km from shore. Some populations are apparently restricted to fresh water, e.g. Chilka Lake, India, and Songhkla, Thailand.

Range depth: 2.5 to 18.0 m.

Habitat Regions: tropical ; saltwater or marine ; freshwater

Aquatic Biomes: rivers and streams; coastal ; brackish water

Other Habitat Features: riparian ; estuarine

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Inhabits coastal, brackish and freshwaters of the tropical and sub-tropical Indo-Pacific (2).
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Trophic Strategy

Food Habits

Irrawaddy dolphins feed on fish, cephalopods, and crustaceans. Irrawaddy dolphins sometimes spit water while feeding, which may be used to herd fish.

Researchers have documented that in the Irrawaddy (or Ayerarwady) River, Myanmar, these dolphins engage in cooperative fishing with cast-net fishermen. Fishermen search for dolphins and call them by tapping a lahai kway, wooden key, on the sides of their boats. One or two lead dolphins then swim in smaller and smaller semi-circles herding the fish towards the shore. During cooperative fishing, the dolphins often dive deeply with their flukes aloft just after the net is cast and create turbulence under the surface around the outside of the net. The dolphins seem to benefit from the fishing by preying on fish that are confused by the sinking net, and those trapped around the edges of the lead line or stuck in the mud bottom just after the net is pulled up.

Animal Foods: fish; eggs; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods, Molluscivore )

  • 2004. "Facultative river dolphins : conservation and social ecology of freshwater and coastal Irrawaddy dolphins in Indonesia" (On-line). University Van Amsterdam Digital Academic Repository. Accessed March 08, 2010 at http://dare.uva.nl/document/115596.
  • Smith, B., T. Mya. 2007. Status and conservation of Irrawaddy Dolphins in Ayeyarwady river of Myanmar. Status and conservation of freshwater populations of irrawaddy dolphins, 31: 21-40.
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Associations

Ecosystem Roles

Irrawaddy dolphins are top ecosystem predators, feeding on fish, cephalopods, and crustaceans. They are hosts for parasites including roundworms (Anisakis simplex), flukes (Braunina cordiformis), and tapeworms (Monorygma delphini). Healthy dolphin populations indicate a healthy marine ecosystem.

Ecosystem Impact: keystone species

Commensal/Parasitic Species:

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Predation

Other than humans, there are no known natural predators of Irrawaddy dolphins. Humans are responsible for a large number of deaths because Irrawaddy dolphins are often caught in nets or harmed through destructive fishing practices (e.g., dynamite fishing). Otherwise, they are typically considered the top predator in their river ecosystems.

Known Predators:

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Life History and Behavior

Behavior

Communication and Perception

Vocalizations of Irrawaddy dolphins in captivity within the Mahakam River, Indonesia included a single-component sonar signal, with the majority of frequencies captured at 60 kHz. Pulse trains were consistent with rates repeated at 40 to 60 kHz. Researchers theorize that Irrawaddy dolphins have a narrow sonar field. Little is known or recorded regarding courtship communication or other social signals.

Communication Channels: visual ; acoustic ; chemical

Perception Channels: visual ; acoustic ; ultrasound

  • Kamminga, C., H. Wiersma, W. Dudok Van Heel. 1983. Sonar sounds from Orcaella brevirostris of the Mahakam River, East Kalimantan Indonesia. Aquatic Mammals, 10: 83-95.
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Life Expectancy

Lifespan/Longevity

The oldest recorded Irrawaddy dolphins, all of which were found dead in fishing nets, were estimated to be 28 years old. Several individuals of this age have been found, all entangled in nets, so it is believed that Irrawaddy dolphins can live longer. Due to the small population size of Irrawady dolphins and subsequent difficulty in tracking the species, no further information is known regarding average lifespan.

Range lifespan

Status: wild:
28 to 30 years.

Average lifespan

Status: wild:
32 years.

Typical lifespan

Status: wild:
5 to 32 years.

Average lifespan

Status: wild:
16 years.

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Lifespan, longevity, and ageing

Maximum longevity: 30 years (wild) Observations: One study in the wild estimated age for 18 individuals with the oldest estimated to be around 30 years (Stacey and Arnold 1999).
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Reproduction

Little is currently known about mating systems in Irrawaddy dolphins. Since the animals live in small groups averaging between three to six individuals, it is presumed that breeding happens outside of those groups. The breeding season is between December and June; however, little is known about mating behavior. As in other dolphin species, it can be presumed that males mate with multiple females and compete over mates.

Mating System: polygynous

There is relatively little information on reproduction in Irrawaddy dolphins. The mating season in the northern hemisphere is reported to be December to June. The calving season seems to be from June to August, with noted exceptions. Data from Chilka Lake, India shows a low rate of breeding and production of only a single calf in three years. Additionally, gestation is approximately nine months, but data from two captive births estimate the gestation period at fourteen months.  Captive born Irrawaddy dolphin calves measured 96 cm in length and weighed 12.3 kg. In the first seven months the calves increased in length by 59% and 266% in weight. Calves begin eating fish around six months and are fully weaned at about two years old. Adult length is achieved between three and five years old. Rate of sexual maturation is thought to be positively correlated with growth rate.

Breeding interval: Females may not reproduce yearly, in one population females give birth every 3 years.

Breeding season: Irrawaddy dolphins breed in December through June.

Average number of offspring: 1.

Range gestation period: 9 to 14 months.

Average birth mass: 12.3 kg.

Average weaning age: 24 months.

Range age at sexual or reproductive maturity (female): 3 to 6 years.

Range age at sexual or reproductive maturity (male): 3 to 6 years.

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

Average birth mass: 12300 g.

Average number of offspring: 1.

Irrawaddy dolphins are not completely weaned until 2 years. From birth to approximately seven months old, the calf survives solely on the nutrition from the mother. For the following seven months the calves stay within the pod and continue to receive nourishment from the mother while also eating fish. It is presumed the calves learn to prey on fish by copying behavior of the mother's and pod mates. There is little information on the rearing of calves. Currently it is not known if both males and females are involved in the upbringing of calves. Like most mammals, females invest heavily in their young.

Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); post-independence association with parents; extended period of juvenile learning

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Orcaella brevirostris

The following is a representative barcode sequence, the centroid of all available sequences for this species.


No available public DNA sequences.

Download FASTA File
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Statistics of barcoding coverage: Orcaella brevirostris

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Specimens with Barcodes: 1
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A4cd

Version
3.1

Year Assessed
2008

Assessor/s
Reeves, R.R., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K.

Reviewer/s
Brownell Jr., R.L. & Cooke, J. (Cetacean Red List Authority)

Contributor/s

Justification
The species was listed as Data Deficient in 1996, but a great deal of new information has become available and five subpopulations have been listed as Critically Endangered since that time. Where the species has been studied: (1) subpopulation sizes are generally low (10s to low 100s) with the single exception of Bangladesh (approximately 5800), (2) there have been significant range declines, and (3) threats, especially bycatch and habitat degradation, have been well documented and remain severe and pervasive. Even within the largest known population of the species in Bangladesh (see above), opportunistic observations of deaths in drifting gillnets and reports from local fishermen suggest that bycatch rates are not sustainable (Smith et al. 2005).

At least a 30% reduction in the range-wide population size is suspected over a period of three generations (45-48 years), including the past and future, based on increasing levels of bycatch and habitat degradation in recent years. Generation length (15-16 years) was assumed to be similar to that of Sotalia fluviatilis – a species that lives in similar habitat and has similar, but better known, life history characteristics (Taylor et al. 2007 estimated generation length for S. fluviatilis as 15.6 years). The species therefore qualifies as Vulnerable A4cd. Given the vast area and complexity of coastline inhabited by this species, it is unlikely that a more quantitative assessment of the global population will be feasible in the near future.

History
  • 1996
    Data Deficient
  • 1994
    Insufficiently Known
    (Groombridge 1994)
  • 1990
    Insufficiently Known
    (IUCN 1990)
  • 1988
    Insufficiently Known
    (IUCN Conservation Monitoring Centre 1988)
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Currently, the most immediate threat facing Irrawaddy dolphins is drowning in gill nets. The threat of gill net entanglement occurs primarily during the dry season (December to May), when dolphins settle in deep water pools. Dynamite and electric fishing occur in some important habitats. These activities are causing depletion of the dolphin's fish supply and noise from the explosions is potentially dangerous to dolphins. Due to the small population size and their narrow distribution, it is quite possible that dam construction anywhere within their habitat might critically endanger populations. Furthermore, uncontrolled tourism can harass dolphins in important habitats during the dry season and interfere with normal activities, such as feeding, resting, and socializing. Overfishing, collisions with boats and injuries from boat propellers are also threats to their survival.

US Federal List: no special status

CITES: appendix i

State of Michigan List: no special status

IUCN Red List of Threatened Species: critically endangered

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Status

The Irrawaddy dolphin is classified as Vulnerable (VU) on the IUCN Red List (1) and is listed on Appendix I of CITES (3). Geographically isolated populations in the Ayeyarwady River (Myanmar), Mahakam River (Indonesia), Malampaya Sound (Philippines), Mekong River (Lao PDR, Cambodia and Vietnam) and Songkhla Lake (India) are classified as Critically Endangered on the IUCN Red List (1).
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Population

Population
No range-wide survey has been conducted for this species; nor is there a synoptic estimate of total numbers from local or regional surveys. Statistically rigorous abundance estimates are available for only a few portions of the range: 77 (CV = 27.4%) in Malampaya Sound, Philippines (Smith et al. 2004); at least 125 (95% CI = 114-152) in the Mekong River (Beasley et al. 2007); 70 (CV = 10%; 95% CL = 58-79) in the Mahakam River, Indonesia (Kreb et al. 2007); 58-72 in the Ayeyarwady River, Myanmar (Smith et al. 2007-a); 5,383 (CV=40%) in coastal waters of Bangladesh (Smith et al. 2005); and 451 (CV=9.6%) in the Sundarbans mangrove forest of Bangladesh (Smith et al,/i>. 2006).

Recent surveys indicate dramatic range declines in the Mekong, Mahakam and Ayeyarwady freshwater subpopulations (IWC 2001, Smith et al. 2007-b). All three of these subpopulations were classified as Critically Endangered in the 2004 Red List because the numbers of reproductively mature individuals were estimated to be
Population Trend
Decreasing

Habitat and Ecology


Habitat and Ecology
Irrawaddy dolphins prefer coastal areas associated with the muddy, brackish waters at river mouths, ranging offshore as far as the extent of the freshwater plume – often only a few km but more than 60 km at the Meghna River mouth in Bangladesh (Smith et al. 2005). In rivers and mangrove channels, the species is most often observed at channel confluences and divergences and downstream of sharp meanders. They have been seen in the same area as finless porpoises in coastal waters of Bangladesh and Myanmar (Smith et al. 2005), and Ganges River dolphins in the waterways of the Sundarbans mangrove forest (Smith et al. 2006).

Systems
  • Freshwater
  • Marine

Threats


Major Threats
The estuarine and freshwater occurrence of this species makes it particularly vulnerable to threats from the human activities that occur in these environments. Threats include direct mortality from fisheries interactions (particularly gillnet entanglement), vessel strikes, and habitat loss and degradation (e.g. declining or altered freshwater flows due to dam and embankment construction, environmental contamination). Live captures for aquarium display also have been a conservation issue in some local areas. Irrawaddy dolphins have been hunted directly in the past, at least in the Mekong and Mahakam Rivers, but are revered by local people in many areas of Asia.

Irrawaddy dolphins are caught accidentally in fishing nets in almost all areas where they have been studied (Smith et al. 2007-b). The most detailed information on bycatch comes from the Mekong River where, of 15 confirmed human-caused deaths 2001-2005, 13 (87%) were due to gillnet entanglement (Beasley et al. 2007). Based on reports from local fishermen and the retrieval of eight carcasses along the Mahakam River between 1995 and 2005, Kreb et al. (2007) documented 48 deaths, 66% of them from entanglement in large-mesh (10 –17.5 cm) gillnets. Mortality also has been recorded in drift gillnets targeting elasmobranchs in coastal waters of Bangladesh (Smith et al. 2005) and bottom-set gillnets targeting crabs in Malampaya Sound (Smith et al. 2004). Fishermen in some areas report the dolphins are released if found still alive (Smith and Hobbs 2002, Kreb et al. 2007), but in the case of drowned animals, the oil may be used for medicinal purposes or the flesh eaten (Smith et al. 2004).

There have been no systematic observer schemes in freshwater or coastal regions, but evidence of bycatch and increased use of gillnets is cause for concern (IWC 2000). Fishing with electricity is considered a dire threat to the Ayeyarwady subpopulation (Smith et al. 2007-a).

Many dams have been proposed that are likely to degrade the channels inhabited by Irrawaddy dolphins in the Mekong River Basin. Of greatest concern are the large run-of-the-river dams (dams without a reservoir that generally preserve a relatively natural flow regime) proposed for the Mekong mainstem near Stung Treng and Sambor (Perrin et al. 1996; Mekong Secretariat 1995). Dam projects in Lao PDR, Cambodia and Viet Nam threaten not only dolphins but also fisheries and therefore human livelihoods (Smith et al. 2007-b). A recent report of a high dam planned for the headwaters of the Ayeyarwady River, Myanmar, in Myitsone just below the confluence of the Mali Hka and N’Mai Hka tributaries, provides reason for concern about its effects on the population of Irrawaddy dolphins downstream (Anon. 2007).

Deforestation and gold, sand and gravel mining are causing major changes to the geomorphologic and hydraulic features of rivers and marine-appended lakes where Irrawaddy dolphins occur (Smith et al. 2007-b). Increased sedimentation resulting from deforestation in surrounding watersheds has resulted in declining water depths in Songkhla, Chilika and Semayang Lakes. The last of these water bodies is appended to the Mahakam River and previously supported dolphins throughout most of its breadth. Now it contains suitable habitat only in a small area near the channel connecting it with the mainstem (Kreb et al. 2007). Between 1992 and 1997 the maximum depth of Chilika Lake declined from 3.4 to 1.4 meters and the accumulation of sediments led to shrinkage of the opening channel and a dramatic decline in salinity. A new channel dredged in the northern portion of the lake in 2000 apparently has mitigated at least some of the problems caused by sedimentation (Pattnaik et al. 2007).

Habitat loss and population fragmentation in several areas have resulted from the proliferation of fixed fishing gears. In the middle and southern portions of Songkhla Lake about 27,000 Sai nong or sitting traps and 13,000 Sang sai or barrier traps create more than 8000 linear km of barrier in multiple rows. These fishing structures are left in place year-round and restrict dolphin movements such that their habitat is substantially reduced and the potential for demographic interaction with individuals in the Gulf of Thailand is eliminated (Smith et al. 2004).

Conservation Actions


Conservation Actions
The species is listed in Appendix I of CITES.

The Action Plan for the Conservation of Freshwater Populations of Irrawaddy Dolphins (Smith et al. 2007-c) notes that multiple-use protected areas will play a key role for conserving freshwater populations of Irrawaddy dolphins. Protected areas could be a particularly effective conservation tool due to the fidelity of the species in freshwater systems to relatively circumscribed areas, as this can facilitate management. The Action Plan also provided details on strategies for mitigating bycatch that included (1) establishing core conservation areas where gillnetting is banned or severely restricted; (2) promoting net attendance rules and providing training on the safe release of entangled dolphins; (3) initiating a program to compensate fishermen for damage caused to their nets by entangled dolphins that are safely released; (4) providing alternative or diversified employment options for gillnet fishermen; (5) encouraging the use of fishing gears that do not harm dolphins by altering or establishing fee structures for fishing permits to make gillnetting more expensive while decreasing the fees for non-destructive gears; and (6) experimenting with acoustical deterrents and reflective nets.

Citation

Reeves, R.R., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. 2008. Orcaella brevirostris. In: IUCN 2013 . IUCN Red List of Threatened Species. Version 2013.1 . <www.iucnredlist.org>. Downloaded on 10 February 2014 .
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Threats

Major Threats
The estuarine and freshwater occurrence of this species makes it particularly vulnerable to threats from the human activities that occur in these environments. Threats include direct mortality from fisheries interactions (particularly gillnet entanglement), vessel strikes, and habitat loss and degradation (e.g. declining or altered freshwater flows due to dam and embankment construction, environmental contamination). Live captures for aquarium display also have been a conservation issue in some local areas. Irrawaddy dolphins have been hunted directly in the past, at least in the Mekong and Mahakam Rivers, but are revered by local people in many areas of Asia.

Irrawaddy dolphins are caught accidentally in fishing nets in almost all areas where they have been studied (Smith et al. 2007-b). The most detailed information on bycatch comes from the Mekong River where, of 15 confirmed human-caused deaths 2001-2005, 13 (87%) were due to gillnet entanglement (Beasley et al. 2007). Based on reports from local fishermen and the retrieval of eight carcasses along the Mahakam River between 1995 and 2005, Kreb et al. (2007) documented 48 deaths, 66% of them from entanglement in large-mesh (10 –17.5 cm) gillnets. Mortality also has been recorded in drift gillnets targeting elasmobranchs in coastal waters of Bangladesh (Smith et al. 2005) and bottom-set gillnets targeting crabs in Malampaya Sound (Smith et al. 2004). Fishermen in some areas report the dolphins are released if found still alive (Smith and Hobbs 2002, Kreb et al. 2007), but in the case of drowned animals, the oil may be used for medicinal purposes or the flesh eaten (Smith et al. 2004).

There have been no systematic observer schemes in freshwater or coastal regions, but evidence of bycatch and increased use of gillnets is cause for concern (IWC 2000). Fishing with electricity is considered a dire threat to the Ayeyarwady subpopulation (Smith et al. 2007-a).

Many dams have been proposed that are likely to degrade the channels inhabited by Irrawaddy dolphins in the Mekong River Basin. Of greatest concern are the large run-of-the-river dams (dams without a reservoir that generally preserve a relatively natural flow regime) proposed for the Mekong mainstem near Stung Treng and Sambor (Perrin et al. 1996; Mekong Secretariat 1995). Dam projects in Lao PDR, Cambodia and Viet Nam threaten not only dolphins but also fisheries and therefore human livelihoods (Smith et al. 2007-b). A recent report of a high dam planned for the headwaters of the Ayeyarwady River, Myanmar, in Myitsone just below the confluence of the Mali Hka and N’Mai Hka tributaries, provides reason for concern about its effects on the population of Irrawaddy dolphins downstream (Anon. 2007).

Deforestation and gold, sand and gravel mining are causing major changes to the geomorphologic and hydraulic features of rivers and marine-appended lakes where Irrawaddy dolphins occur (Smith et al. 2007-b). Increased sedimentation resulting from deforestation in surrounding watersheds has resulted in declining water depths in Songkhla, Chilika and Semayang Lakes. The last of these water bodies is appended to the Mahakam River and previously supported dolphins throughout most of its breadth. Now it contains suitable habitat only in a small area near the channel connecting it with the mainstem (Kreb et al. 2007). Between 1992 and 1997 the maximum depth of Chilika Lake declined from 3.4 to 1.4 meters and the accumulation of sediments led to shrinkage of the opening channel and a dramatic decline in salinity. A new channel dredged in the northern portion of the lake in 2000 apparently has mitigated at least some of the problems caused by sedimentation (Pattnaik et al. 2007).

Habitat loss and population fragmentation in several areas have resulted from the proliferation of fixed fishing gears. In the middle and southern portions of Songkhla Lake about 27,000 Sai nong or sitting traps and 13,000 Sang sai or barrier traps create more than 8000 linear km of barrier in multiple rows. These fishing structures are left in place year-round and restrict dolphin movements such that their habitat is substantially reduced and the potential for demographic interaction with individuals in the Gulf of Thailand is eliminated (Smith et al. 2004).
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The major threat to the Irrawaddy dolphin is incidental entanglement in gillnets (5) (9), but it is not believed to be at risk of imminent extinction (2). In the Ayeyarwady River it is also at risk from electrocution and prey depletion from electric fishing (10). Other issues affecting this dolphin include increasing pollution, construction of dams and the build-up of silt and sedimentation following severe erosion (2). Fishing with explosives also results in dolphin casualties (4). Most live captures are for the oceanarium trade in Asia (4), and hunting of this species is rare, occurring only in parts of India to harvest oil for the treatment of rheumatism (2).
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Management

Conservation Actions

Conservation Actions
The species is listed in Appendix I of CITES.

The Action Plan for the Conservation of Freshwater Populations of Irrawaddy Dolphins (Smith et al. 2007-c) notes that multiple-use protected areas will play a key role for conserving freshwater populations of Irrawaddy dolphins. Protected areas could be a particularly effective conservation tool due to the fidelity of the species in freshwater systems to relatively circumscribed areas, as this can facilitate management. The Action Plan also provided details on strategies for mitigating bycatch that included (1) establishing core conservation areas where gillnetting is banned or severely restricted; (2) promoting net attendance rules and providing training on the safe release of entangled dolphins; (3) initiating a program to compensate fishermen for damage caused to their nets by entangled dolphins that are safely released; (4) providing alternative or diversified employment options for gillnet fishermen; (5) encouraging the use of fishing gears that do not harm dolphins by altering or establishing fee structures for fishing permits to make gillnetting more expensive while decreasing the fees for non-destructive gears; and (6) experimenting with acoustical deterrents and reflective nets.
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Conservation

Very few provisions have been made to conserve the dolphins or their habitat. The Irrawaddy dolphin is protected by law in Laos, Vietnam and Cambodia. Direct taking of cetaceans is prohibited in Bangladesh, India, Laos, Malaysia, Myanmar and Thailand. (9). In December 2005, the Department of Fisheries in Myanmar, established a protected area for Irrawaddy dolphins along a 74 kilometre segment of the Ayeyarwady River. Protective measures in the area include requiring fishermen to immediately release dolphins if found alive and entangled in their nets, and prohibiting the trade and catching or killing of dolphins and the use of electricity fishing and gill nets that obstruct the water-course, are more than 300 feet long, or spaced less than 600 feet apart (11). The problem of live captures for the aquarium trade has largely been solved by the uplisting of the species to Appendix I of the Convention on International Trade in Endangered Species (CITES) which prohibits international trade. Some captive breeding of this species has been successful (2).
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

The only way that Irrawaddy dolphins may have a negative economic impact on humans is that they share a common food source. Some fisherman believe the dolphins are pests because they reduce their catch, although this is unlikely.

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Economic Importance for Humans: Positive

In the Irrawaddy River these dolphins engage in cooperative fishing with cast-net fishermen. Irrawaddy dolphins increase the amount of fish the fishermen catch; therefore, they are of economic value.  Additionally, Irrawaddy dolphins have brought ecotourism to communities in Indonesia and India.

Positive Impacts: food ; ecotourism

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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

Irrawaddy dolphin

The Irrawaddy dolphin (Orcaella brevirostris) is a euryhaline species of oceanic dolphin found in discontinuous subpopulations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia.

Etymology and taxonomic history[edit]

Irrawaddy mum skeleton specimen exhibited in Museo di storia naturale e del territorio dell'Università di Pisa

One of the earliest recorded descriptions of the Irrawaddy dolphin was by Sir Richard Owen in 1866 based on a specimen found in 1852, in the harbour of Visakhapatnam on the east coast of India.[3] It is one of two species in its genus. It has sometimes been listed variously in a family containing just itself and in Monodontidae and in Delphinapteridae. There is now widespread agreement to list it in the Delphinidae family.

Genetically, the Irrawaddy dolphin is closely related to the killer whale (orca). The species name brevirostris comes from the Latin meaning short-beaked. In 2005, genetic analysis showed the Australian snubfin dolphin found at the coast of northern Australia forms a second species in the Orcaella genus.

Overall, the dolphins' color is grey to dark slate blue, paler underneath, with no distinctive pattern. The dorsal fin is small and rounded behind the middle of the back. The forehead is high and rounded; the beak is lacking. The front of its snout is sort of blunt.The flippers are broad and rounded. The species found in Borneo, the finless porpoise, Neophocaena phocaenoides, is similar and has no back fin; the humpback dolphin, Sousa chinensis, is larger, has a longer beak and a larger dorsal fin.[3]

Vernacular names for O. brevirostris include the following:

  • Burmese: ဧရာဝတီ လင်းပိုင် eyawadi lăbaing
  • Chilika dialect: baslnyya magar or bhuasuni magar (lit. oil-yielding dolphin)[3]
  • Filipino: lampasut[4]
  • Bangladesh: shushuko
  • Indonesian: pesut
  • Khmer: ផ្សោត ph’sout
  • Lao: ປາຂ່າ pha’ka
  • Malay: dolphin empesut
  • Oriya: khem or khera
  • Thai: โลมาอิรวดี pla loma hua bat ("alms-bowl dolphin", due to the shape of their heads)[5]

Description[edit]

Specimen in Cambodia

The Irrawaddy dolphin is similar to the beluga in appearance, though most closely related to the killer whale. It has a large melon and a blunt, rounded head, and the beak is indistinct. The dorsal fin, located about two-thirds posterior along the back, is short, blunt, and triangular. The flippers are long and broad. It is lightly coloured all over, but slightly more white on the underside than the back. Adult weight exceeds 130 kg (290 lb) and length is 2.3 m (7.5 ft) at full maturity. Maximum recorded length is 2.75 m (9.0 ft) of a male from Thailand.[5]

Reproduction[edit]

1878 illustration of a foetus in the uterus

These dolphins are thought to reach sexual maturity at seven to nine years. In the Northern Hemisphere, mating is reported from December to June. Its gestation period is 14 months; cows give birth to a single calf every two to three years. Length is about 1 m (3.3 ft) at birth. Birth weight is about 10 kg (22 lb). Weaning is after two years. Lifespan is about 30 years.

Behavior[edit]

Communication is carried out with clicks, creaks, and buzzes at a dominant frequency of about 60 kilohertz, which is thought to be used for echolocation. Bony fish and fish eggs, cephalopods, and crustaceans are taken as food. Observations of captive animals indicate food may be taken into the mouth by suction. Irrawaddy dolphins sometimes spit streams of water, sometimes while spy-hopping and during feeding, apparently to expel water ingested during fish capture or possibly to herd fish. Some Irrawaddy dolphins kept in captivity have been trained to do spyhopping on command. The Irrawaddy dolphin is a slow swimmer, but swimming speeds of 20–25 km/hour were reported when dolphins were being chased in a boat.[6]

It surfaces in a rolling fashion and lifts its tail fluke clear of the water only for a deep dive. Deep dive times range from 70–150 seconds to 12 minutes. When 277 group dives were timed (time of disappearance of last dolphin in group to emergence of first dolphin in the group) in Laos, mean duration was 115.3 seconds with a range of 19 seconds to 7.18 minutes.[5] They make only occasional low leaps and never bow-ride. Groups of fewer than six individuals are most common, but sometimes up to 15 dolphins are seen together. [6] [7]

Interspecific competition has been observed when Orcaella was forced inshore and excluded by more specialised dolphins. When captive humpback dolphins (Sonsa chinensis) and Irrawaddy dolphins were held together, reportedly the Irrawaddy dolphins were frequently chased and confined to a small portion of the tank by the dominant humpbacks. In Chilika Lake, local fishers say when Irrawaddy dolphins and bottlenose dolphins meet in the outer channel, the former get frightened and are forced to return toward the lake.[3]

Habitat and subpopulations[edit]

Irrawaddy dolphin on Mekong River at Kratié, Cambodia

Although sometimes called the Irrawaddy river dolphin, it is not a true river dolphin, but an oceanic dolphin that lives in brackish water near coasts, river mouths and in estuaries. It has established subpopulations in freshwater rivers, including the Ganges and the Mekong, as well as the Irrawaddy River from which it takes its name. Its range extends from the Bay of Bengal to New Guinea and the Philippines.

It is often seen in estuaries and bays in Borneo Island, with sightings from Sandakan in Sabah, Malaysia, to most parts of Brunei and Sarawak, Malaysia. A specimen was collected at Mahakam River in East Kalimantan.[1]

No range-wide survey has been conducted for this vulnerable species; however, the worldwide population appears to be over 7,000, with over 90% occurring in Bangladesh. Populations outside Bangladesh and India are classified as critically endangered. Known subpopulations of Irrawaddy dolphins are found in eight places, listed here in order of population, including conservation status.

Chilka Lake, Odisha, India, habitat of Irrawaddy dolphins
  1. Bangladesh; 5,832 (VU) in coastal waters of the Bay of Bengal[8] and 451 (VU) in the brackish Sundarbans mangrove forest[9][10]
  2. India; 152 (VU) in the brackish-water Chilka Lake.[11] Presence recorded from Sundarbans National Park, India also.
  3. Laos and Cambodia; 78-91 (CR) in a 190-km (118-mi) freshwater stretch of the Mekong River[12]
  4. Indonesia; (CR), in a 420-km (260-mi) stretch of the freshwater Mahakam River
  5. Philippines; about 42 (CR) in the brackish inner Malampaya Sound.[13] Researchers are studying the recent discovery of 30-40 dolphins sighted in the waters of Bago City and Pulupandan town in the province of Negros Occidental, in Western Visayas [1]
  6. Burma; about 58-72 (CR) in a 370-km (230-mi) freshwater stretch of the Ayeyarwady River
  7. Thailand: less than 50 (CR) in the brackish Songkhla Lake.[1]

Interaction with humans[edit]

Irrawaddy dolphins have a seemingly mutualistic relationship of co-operative fishing with traditional fishers. Fishers in India recall when they would call out to the dolphins, to drive fish into their nets. [14] In Burma, in the upper reaches of the Ayeyawady River, Irrawaddy dolphins drive fish towards fishers using cast nets in response to acoustic signals from them. In return, the dolphins are rewarded with some of the fishers' bycatch.[15] Historically, Irrawaddy River fishers claimed particular dolphins were associated with individual fishing villages and chased fish into their nets. An 1879 report indicated legal claims were frequently brought into native courts by fishers to recover a share of the fish from the nets of a rival fisher which the plaintiff's dolphin was claimed to have helped fill.[5]

Threats[edit]

Fishermen with fishnets in Bangladesh

Irrawaddy dolphins are more susceptible to human conflict than most other dolphins who live farther out in the ocean. Drowning in gillnets is the main threat to them throughout their range. The majority of reported dolphin deaths in all subpopulations is due to accidental capture and drowning in gillnets and dragnets, and in the Philippines, bottom-set crabnets. In Burma, electrofishing, gold mining and dam building are also serious and continuing threats. Though most fishers are sympathetic to the dolphins' plight, it is difficult for them to abandon their traditional livelihood.[1]

In several Asian countries, Irrawaddy dolphins have been captured and trained to perform in public aquariums. Their charismatic appearance and unique behaviors, including spitting water, spyhopping and fluke-slapping, make them very popular for shows in dolphinariums. The commercial motivation for using this dolphin species is high because it can live in freshwater tanks and the high cost of marine aquarium systems is avoided. The region within and near the species’ range has developed economically, and theme parks, casinos and other entertainment venues that include dolphin shows has increased. In 2002, there were more than 80 dolphinariums in at least nine Asian countries[16]

Collateral deaths of dolphins due to blast fishing were once common in Vietnam and Thailand. In the past, the most direct threat was killing them for their oil.

The IUCN lists five of the seven subpopulations as critically endangered, primarily due to drowning in fish nets.[1] For example, the Malampaya population, first discovered and described in 1986, at the time consisted of 77 individuals. Due to anthropogenic activities, this number dwindled to 47 dolphins in 2007.[17]'Italic text'

Conservation[edit]

Entanglement in fishnets and degradation of habitats are the main threats to Irrawaddy dolphins. Conservation efforts are being made at international and national levels to alleviate these threats.

International efforts
Listed as Critically Endangered in Laos, Malaysia, Burma, Philippines, and Thailand

Protection from international trade is provided by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Enforcement, though, is the responsibility of individual countries.[1] While some international trade for dolphinarium animals may have occurred, this is unlikely to have ever been a major threat to the species.

Some Irrawaddy dolphin populations are classified by the IUCN as critically endangered; in Lao PDR, Cambodia, Viet Nam (Mekong River sub-population), Indonesia (Mahakam River sub-population, Borneo), Burma (Ayeyarwady/Irrawaddy River sub-population), the Philippines (Malampaya Sound sub-population), and Thailand (Songkhla Lake sub-population). Irrawaddy dolphins in general however, are IUCN listed as a vulnerable species, which applies throughout their whole range.[1] In 2004, CITES transferred the Irrawaddy dolphin from Appendix II to Appendix I, which forbids all commercial trade in species that are threatened with extinction.[18]

The UNEP-CMS Action Plan for the Conservation of Freshwater Populations of Irrawaddy dolphins notes that multiple-use protected areas will play a key role for conserving freshwater populations. Protected areas in fresh water could be a particularly effective conservation tool and can facilitate management, due to the fidelity of the species to relatively circumscribed areas. The Action Plan provides details on strategies for mitigating by-catch that includes:

-establishing core conservation areas where gillnetting is banned or severely restricted
-promoting net attendance rules and providing training on the safe release of entangled dolphins
-initiating programs to compensate fishers for damage caused to their nets by entangled dolphins that are safely released
-providing alternative or diversified employment options for gillnet fishers
-encouraging the use of fishing gear that does not harm dolphins, by altering or establishing fee structures for fishing permits to make gillnetting more expensive while decreasing the fees for nondestructive gear
-experimenting with acoustical deterrents and reflective nets.[19]

The Irrawaddy dolphin is listed on both Appendix I[20] and Appendix II[20] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix I[20] as this species has been categorized as being in danger of extinction throughout all or a significant proportion of their range and CMS Parties strive towards strictly protecting these animals, conserving or restoring the places where they live, mitigating obstacles to migration and controlling other factors that might endanger them, as well on Appendix II[20] as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.[21]

The species is also covered by the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (MoU).[22]

National efforts

Several national efforts are resulting in the reduction of threats to local Irrawaddy dolphin subpopulations:

Bangladesh
Satellite image of the Sundarbans

Portions of Irrawaddy dolphin habitat in the Sundarbans mangrove forest of Bangladesh are included within 139,699 ha (539 sq mi) of three wildlife sanctuaries, which are part of the Sunderbans World Heritage Site. The Wildlife Conservation Society is working with the Bangladesh Ministry of Environment and Forests to create protected areas for the 6000 remaining dolphins[4][23]

Cambodia

Irrawaddy dolphins are fully protected as an endangered species under Cambodian Fishery Law.[24] In 2005, The World Wide Fund For Nature (WWF) established the Cambodian Mekong Dolphin Conservation Project with support from government and local communities. The aim is to support the survival of the remaining population through targeted conservation activities, research and education.[25] In January 2012, the Cambodian Fisheries Administration, the Commission for Conservation and Development of Mekong River Dolphin Eco-tourism Zone, and WWF signed the "Kratie Declaration on the Conservation of the Mekong River Irrawaddy Dolphin", an agreement binding them to work together, and setting out a roadmap for dolphin conservation in the Mekong River.[26] On August 24, 2012 the Cambodian government announced that 180-kilometer-long stretch of the Mekong River from eastern Kratie province to the border with Laos has been stated as limit fishing zone which uses floating houses, fishing cages and gill nets are disallowed, but simple fishing is allowed.[27] This area is patrolled by a network of River Guards, specifically to protect dolphins.

India
Irrawaddy dolphin at Sundarbans National Park, India

The Irrawaddy dolphin (under the common name of snubfin dolphin, with the scientific name misspelled as Oreaella brevezastris) is included the Indian Wildlife Protection Act,[28] Schedule I,[29] which bans their killing, transport and sale of products.[4] A major restoration effort to open a new mouth between Chilika lake and the Bay of Bengal in 2000 was successful in restoring the lake ecology and regulating the salinity gradient in the lake waters, which has resulted in increases in the population of Irrawaddy dolphin due to increase of prey species of fish, prawns and crabs.[30]

Indonesia
Specimen in Kalimantan

At East Kalimantan Island, the Semayang National Park has been proposed as an Irrawaddy dolphin sanctuary.[4] Local conservationists have also been pressing for protection of the lake and its watershed, the Berambai Forest.[31]

Laos

Canadian conservationist Ian Baird set up the Lao Community Fisheries and Dolphin Protection Project to study the Irrawaddy dolphins in the Lao part of the Mekong. Part of this project compensated fishers for the loss of nets damaged to free entangled dolphins. This project was expanded to include Cambodia, after the majority of the dolphin population was determined to have been killed or migrated to Laos' southern neighbour.[32] The Si Phan Don Wetlands Project has successfully encouraged river communities to set aside conservation zones and establish laws to regulate how and when fish are caught.[33]

Burma

In 2005, the Department of Fisheries established a protected area for Irrawaddy dolphins in a 74 km (46 mi)-km segment of the Ayeyarwady River between Mingun and Kyaukmyaung. Protective measures in the area include mandatory release of entangled dolphins, prohibition of the catching or killing of dolphins and trade in whole or parts of them and the prohibition of electrofishing and gillnets more than 300 feet (91 m) long, or spaced less than 600 feet (180 m) apart.[4] Mercury poisoning and habitat loss from gold mining dregding operations in the river have been eliminated[34]

Philippines

In 2000, Malampaya Sound was proclaimed a protected seascape. This is the lowest possible prioritization given to a protected area.[19] Malampaya Sound Ecological Studies Project was initiated by the WWF. With technical support provided by the project, the municipality of Taytay[disambiguation needed] and the Malampaya park management developed fishery policies to minimize the threats to the Irrawaddy dolphin from by-catch capture. Gear studies and gear modification to conserve the dolphin species were implemented. The project was completed in 2007.[35] In 2007, the Coral Triangle Initiative, a new multilateral partnership to help safeguard the marine and coastal resources of the Coral Triangle, including the Irrawaddy dolphin subpopulation in Malampaya Sound, was launched.[36][37]

Thailand

In 2002, the Marine and Coastal Resources Department was assigned to protect rare aquatic animals such as dolphins, whales and turtles in Thai territorial waters. To protect the dolphins, patrol vessels ensure boats stay at least 30 m (98 ft) away from dolphins and there is no chasing of or running through schools of dolphins. Many fishermen on the Bang Pakong River, Prachinburi Province, have been persuaded by authorities to stop shrimp fishing in a certain area and 30 to 40 fishing boats have been modified so they can offer dolphin sightseeing tours.[38] A total of sixty-five Irrawaddi dolphins have been found dead along the coast of Trat Province in the past three years.[39][40] The local fishing industry is blamed for the deaths of the dolphins.[41]

Malaysia

In 2008, the Department of Forestry and Sarawak Forestry Cooperative in Sarawak established a protected area for Irrawaddy dolphins in Santubong and Damai (Kuching Wetland).[4] Furthermore, they plan to establish more beaches in Miri as protected areas for them. The protection measures in the area include prohibition of catching or killing of dolphins and trade in whole or parts of them, and prohibiting the use of gillnets. The government may also start small and medium scale research of this species at Sarawak Malaysia University with sponsorship from Sarawak Shell.

See also[edit]

References[edit]

  1. ^ a b c d e f g Reeves, R. R., Jefferson, T. A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E. R., Slooten, E., Smith, B. D., Wang, J. Y. & Zhou, K. (2008). "Orcaella brevirostris". IUCN Red List of Threatened Species. Version 2011.1. International Union for Conservation of Nature. Retrieved 26 June 2011.  Database entry includes a brief justification of why this species is of vulnerable.
  2. ^ a b William Perrin (2010). "Orcaella brevirostris (Owen in Gray, 1866)". In W. F. Perrin. World Cetacea Database. World Register of Marine Species. Retrieved May 11, 2012. 
  3. ^ a b c d Sinha, R. K. (May–August 2004). "The Irrawaddy Dolphins Orcaella of Chilika Lagoon, India". Journal of the Bombay Natural History Society (Mumbai, India: online edition: Environmental Information System (ENVIS), Annamalai University, Centre of Advanced Study in Marine Biology, Parangipettai - 608 502, Tamil Nadu, India) 101 (2): 244–251. Archived from the original on 2009-04-10. 
  4. ^ a b c d e f "Proposal for inclusion of species on the appendices of the convention on the conservation of migratory species of wild animals". PROPOSALS. ENEP/CMS. 2008-08-27. Retrieved 2008-12-26. 
  5. ^ a b c d Stacey, Pam J.; Peter W. Arnold (1999-05-05). "Orcaella brevirostris". Mammalian Species (American Society of Mammalogists) (616): 1–8. 
  6. ^ a b "Irrawaddy dolphin (Orcaella brevirostris)". Arkive. Wildscreen. 2008. Retrieved 2008-12-26. 
  7. ^ Culik, Boris; Kiel, Germany (2000). "Orcaella brevirostris (Gray, 1866)". Review of small Cetaceans Distribution, Behaviour, Migration and Threats. UNEP/CMS Convention on Migratory Species. Retrieved 2008-12-26. 
  8. ^ "Large population of endangered dolphins found in Bangladesh". Times of India, Flora and Fauna (2008 Bennett Coleman & Co. Ltd.). 2008-10-11. Retrieved 2008-12-29. 
  9. ^ Smith, Brian D.; Graulik Gill (2) ; Strindberg Samantha (1) ; Ahmed Benazir (3) ; Mansur Rubaiyat (4) (2006). "Abundance of irrawaddy dolphins (Orcaella brevirostris) and ganges river dolphins (Platanista Gangetica gangetica) estimated using concurrent counts made by independent teams in waterways of the sundarbans mangrove forest in Bangladesh". Marine Mammal Science (Oxford, UK: Blackwell) 22 (no3): 527–547. doi:10.1111/j.1748-7692.2006.00041.x. ISSN 0824-0469. 
  10. ^ Associated Press (2009-04-01). "Study: Bangladesh hosts 6,000 rare dolphins". PR-Inside.com. Retrieved 2009-04-01. 
  11. ^ "Dolphin population rises to 152 in Chilika lake in Orissa". Times of India. 2013-01-22. Retrieved 23 January 2013. 
  12. ^ Ryan, G.; Dove, V.; Trujillo, F.; Doherty, P.F. (2011). "Irrawaddy dolphin demography in the Mekong River: an application of mark-resight models.". Ecosphere 2 (5): art58. doi:10.1890/ES10-00171.1. 
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