|
|
Orcaella brevirostris (Mahakam subpopulation)
– Critically Endangered
Taxonomy
|
Kingdom:
|
ANIMALIA
|
|
Phylum:
|
CHORDATA
|
|
Class:
|
MAMMALIA
|
|
Order:
|
CETACEA
|
|
Family:
|
DELPHINIDAE
|
|
Scientific Name:
|
Orcaella brevirostris (Mahakam subpopulation)
|
|
Species Authority:
|
(Owen in Gray, 1866)
|
|
Common Name/s:
|
| English | — | IRRAWADDY DOLPHIN, SNUBFIN DOLPHIN |
| French | — | ORCELLE |
| Spanish | — | DELPHÍN DEL IRRAWADDY |
|
Assessment Information
|
Red List Category & Criteria:
|
CR D ver 2.3 (1994)
|
|
Year Assessed:
|
2000
|
|
Assessor/s:
|
Kreb, D. & Smith, B.D. (Cetacean Specialist Group)
|
|
Evaluator/s:
|
Reeves, R. & Taylor, B.L. (Cetacean Red List Authority)
|
|
Justification:
|
According to criterion D, the Irrawaddy Dolphin subpopulation in the Mahakam River qualifies as Critically Endangered because there are less than 50 mature individuals.
|
Geographic Range
|
Range Description:
|
The freshwater subpopulation of Irrawaddy Dolphins (Orcaella brevirostris) in the Mahakam River of East Kalimantan, Indonesia, ranges in the mainstem from about 180 km above the mouth until 600 km upstream, seasonally inclusive of several tributaries and Semayang and Melintang lakes (Kreb 2000).
During five sighting surveys of the entire Mahakam River conducted during high, low, and medium water stages in 1999 and 2000, no sightings were made below 180 km upstream of the mouth.
|
|
Countries:
|
Native:
Indonesia (Kalimantan)
|
Population
|
Population:
|
The total subpopulation is estimated to be 33–50 individuals based upon eight sighting surveys covering the entire known range in the Mahakam system. Sightings in the main river were confined to a 190 km segment in the middle reaches, starting from 180 km above the mouth, inclusive of the Kedang Kepala, Kedang Rantau, Belayan and Kedang Pahu tributaries, and in the Ratah tributary of the upper reaches, located about 500 km upstream from the mouth (Kreb 2000).
|
|
Population Trend:
|
|
Habitat and Ecology
|
Habitat and Ecology:
|
Dolphins concentrate in deep pools located near confluences and meanders, and they are occasionally found in appended lakes and connecting tributaries. These areas are also primary fishing grounds and subject to intensive motorized vessel traffic.
|
|
System:
|
Freshwater
|
|
List of Habitats:
|
| 5.1 | Wetlands (inland) - Permanent Rivers/Streams/Creeks (includes waterfalls) |
|
Threats
|
Threats:
|
During 1997–99, 16 deaths were recorded (10 dolphins from gillnet entanglement, three probably from vessel strikes, and three deliberately killed for unknown reasons) (Kreb 2000). During 1997–98 at least seven dolphins were also illegally live-captured in the river and taken to oceanaria. Plans exist to capture more animals for a new oceanarium to be built in Tenggarong (D. Kreb, pers. comm.). Intensive fishing with gillnets, electricity and poison (Kreb 2000), and the accidental introduction of an exotic piscivorous fish, locally known as ikan toman (Kreb, pers. comm.), may have depleted the dolphins’ prey. The high density of gillnets used in Semayang and Melintang lakes physically obstructs dolphin movements, thereby reducing available habitat. This problem, together with high sedimentation caused by devegetation of the surrounding shorelines, has probably resulted in the elimination of these lakes as primary areas of occupancy as reported by Tas’an and Leatherwood (1984). Leaks from dams in the upper reaches that retain chemical wastes from gold mining industries, including mercury and cyanide, occurred in 1997 and resulted in a massive fish kill (D. Kreb, pers. comm.). High concentrations of mercury were found in water samples taken from the upper reaches in 1997 (WQMMM/GTZ 1998).
|
|
List of Threats:
|
| 1 | Habitat Loss/Degradation (human induced) (ongoing) |
| 4.1.1.3 | Accidental mortality - Bycatch - Fisheries-related - Entanglement (ongoing) |
| 4.2.2 | Accidental mortality - Collision - Vehicle collision (ongoing) |
| 6.3 | Pollution (affecting habitat and/or species) - Water pollution (ongoing) |
| 8.3 | Changes in native species dynamics - Prey/food base (ongoing) |
|
Conservation Actions
|
Conservation Actions:
|
No conservation measures have been formally implemented, but there are some local initiatives towards establishing conservation areas (Kreb 2000).
|
Bibliography
|
Bibliography:
|
Kreb, D. 1999. Observations on the occurrence of Irrawaddy Dolphin, Orcaella brevirostris, in the Mahakam River, East Kalimantan, Indonesia. Zeitschrift für Säugetierkunde 64: 54-58. Kreb, D. 2000. Abundance and distribution of the pesut, Orcaella brevirostris in the Mahakam River, lakes, and coast of East Kalimantan, Indonesia. Paper submitted to the International Whaling Commission. SC/52/SM32. MacKinnon, K., Hatta, G., Halim, H. and Mangalik, A. 1997. The ecology of Kalimantan. The ecology of Indonesia series 3. Oxford University Press. Reeves, R.R., Smith, B.D., Crespo, E.A. and di Sciara, G.N. (compilers) 2003. Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World's Cetaceans. IUCN/SSC Cetacean Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK. Tas’an and Leatherwood, S. 1984. Cetaceans live-captured for Jaya Ancol Oceanarium, Djakarta, 1974-1982. Report to the International Whaling Commission 34:485-489. WQMMM, GTZ. 1998. Concept for water quality management- Mahakam, phase 2, March 1996.
|
|
|
