Biology Reference
In-Depth Information
Additionally, such as Leatherwood (1996) and others demonstrated, river dolphins show
a significant attraction for river segments which contained confluences versus ones that
didn't. Thus, the dolphin concentrations in limited and circumscribed places make them
especially vulnerable to accidental entanglement in fishing nets (especially with nylon gill
nets; Reeves & Leatherwood, 1994, Leatherwood, 1996), directed killing dolphins, destroying
their habitat and providing local sources of pollution. Even in diverse parts of the Amazon,
although illegal, explosives and electricity are used in fishing (Goulding, 1983; Smith &
Smith, 1998). Best & da Silva (1989) claimed that fishermen, using explosives, commented
that they sometimes attempt to kill dolphins which prey on the stunned or dead fish. The
echolocation structures of the river dolphins are particularly vulnerable to the concussion
effects of these explosions and acoustical contamination (noise) caused by vessel traffic could
be another important risk for river dolphins.
Although Indian communities are afraid of the mythical and legendary ―powers‖ of the
dolphins, some Indians have traditionally hunted river dolphins. Such was the case of Mura in
the Negro River during the nineteenth century. The destruction of their own Indian cultures
by the ―colonos‖ (settlers) and the introduction of firearms are dangerous facts which affect
the ―mythical invulnerability‖ of the river dolphins (yacurana, water spirit in quechua; Luna,
1983). Another, maybe past problem, was the capture of specimens for export to aquaria.
Since 1956, over 100 pink river dolphins were caught for this task (Layne, 1958; Layne &
Caldwell, 1964; Brownell, 1984). Nevertheless, imports ceased because of expensive costs,
high mortality and new conservation laws.
Although the status of the pink river dolphin seems to be the most secure with regard to
all the other river dolphins, if the construction of hydroelectric dams in Brazil, and in other
countries of the Amazon basin, are carried out, this species may well join the list of
endangered cetaceans (Klinowska, 1991). The converging threats on the South-American
riverine dolphins are of sufficient magnitude for conservation action. For example, the
International Union for the Conservation of Nature (IUCN) proposed an action plan for the
conservation of biological diversity (1988-1992) concerning dolphins, porpoises, and whales
(Perrin, 1988), where 63,000 US dollars were diverted to conservation studies of the Amazon
river dolphins (the names of the projects were: 1- Monitor incidental kills of dolphins in
Amazon fisheries in Brazil, 2- Promote the establishment of river dolphin conservation areas
in Brazil, 3- Promote legislation to fully protect river dolphins in Peru, Ecuador, Colombia
and Venezuela, 4- Promote enforcement of existing laws protecting river dolphins in South
America, 5- Establish dialogue on river dolphin conservation and management among Brazil,
Peru, Venezuela, Colombia, Ecuador and Bolivia).
Furthermore, the effective protection of pink river dolphins could have beneficial
consequences on the protection of other species with similar conservation threats, being the
case of the two Amazon otter species ( Pteronura brasiliensis and Lontra longicauda ), the
Amazon manatee ( Trichechus inunguis ), some reptiles, such as the white and black caimans
and turtles ( Podocnemys ), and large fish such as certain species of big catfish and Arapaima
gigas .
To carry out successful conservation programs it is not enough to only undertake river
dolphin censuses and to promote enforcement laws but it is a necessity to also know the
evolutionary demographic history and colonization patterns of the species and if it is coming
from a stable, bottlenecked or original population that has expanded. This information
describes the species' evolutionary potential.
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