River dolphin

Taxobox
name = River Dolphins


image_width = 225px
image_caption = Chinese River Dolphin
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Cetacea
subordo = Odontoceti
superfamilia = Platanistoidea
subdivision_ranks = Families
subdivision =
See text

River dolphins are four living species of dolphin which reside in freshwater rivers and estuaries. They are classed in the Platanistoidea superfamily of cetaceans. Three species live in fresh water rivers. The fourth species, the La Plata Dolphin, lives in salt-water estuaries and near-shore marine environments. However, it is scientifically classed in the river dolphin family rather than the oceanic dolphin family.

Ecology

River dolphins are now facing extinction due to habitat loss, hunting by humans, and naturally low numbers. Also, many river dolphins possess very poor eyesight -- some are considered blind -- which can lead to unfortunate encounters with humans or human-made objects (boats or fishing nets, for example).

Some dolphin species can live in marine or riverine environments. The Tucuxi, for example, is equally at home in both ecotypes. However, these are not classified in the Platanistoidea superfamily and are therefore not regarded as true river dolphins. Juvenile river dolphins are grey and turn pink at maturity.

Taxonomy

In the most recent classification (Rice, 1998) there are currently four extant families that make up the river dolphins. However, a December 2006 survey found no members of "Lipotidae" (commonly known as the Yangtze River dolphin) and declared the species functionally extinct, [ [http://www.journals.royalsoc.ac.uk/content/15782wq480207749/ Turvey "et al"] , "Journal of the Royal Society, Biology Letters" (2007 Aug. 7).] [ [http://www.allheadlinenews.com/articles/7005844811 All Headline News] , Dec. 2006.] Platanistidae is listed as the only extant family of the Platanistoidea superfamily. The previously accepted classification treated all four families as belonging to this family and treated the Ganges and Indus River Dolphins as separate species.

Classification by Rice (1998)

*Superfamily Platanistoidea
**Family Platanistidae
***Ganges and Indus River Dolphin, "Platanista gangetica"
**Family Iniidae
***Amazon River Dolphin (or Boto), "Inia geoffrensis"
**Family Lipotidae
***Chinese River Dolphin (or Baiji), "Lipotes vexillifer" (possibly extinct, since December 2006)
**Family Pontoporiidae
***La Plata Dolphin (or Franciscana), "Pontoporia blainvillei"

Previous classification

*Family Platanistidae
**Ganges River Dolphin, "Platanista gangetica"
**Indus River Dolphin, "Platanista minor"
**Amazon River Dolphin (or Boto), "Inia geoffrensis"
**Chinese River Dolphin (or Baiji), "Lipotes vexillifer" (presumed extinct as of 2006
**La Plata Dolphin (or Franciscana), "Pontoporia blainvillei"

Extinction

On Dec. 13th, 2006, the Yangtze River Dolphin, or Baiji, was declared "functionally extinct", after a 45-day search by leading experts in the field failed to find a single specimen [http://www.allheadlinenews.com/articles/7005844811] . The last verified sighting of the beak-nosed dolphin was in September of 2004. [http://www.baiji.org/fileadmin/pdf/1206_release_YFDE.pdf] However, in August, 2007, reports surfaced that a man saw and videotaped what appears to be a baiji in the Yangtze River. A team of scientists attempted to verify the sighting beginning in September, 2007. [http://www.usatoday.com/tech/science/2007-08-29-china-dolphin_N.htm]

It is believed that overfishing, damming and sub-aquatic sonar pollution (which interfered with the dolphin's sonar-based method of locating food), led to the extinction. Reuters news reported this their first record of a mammalian extinction in 50 years.

Notes

References

*Reeves, Randall R. et al. (2002). National Audubon Society guide to marine mammals of the world. Alfred A. Knopf. 527 pp.
*Rice, Dale W. (1998). Marine mammals of the world: systematics and distribution. Society of Marine Mammalogy Special Publication Number 4. 231 pp.