River dolphins are small, aquatic mammals which belong to the order Cetacea. Scientists today classify river dolphins as endangered species because many populations have declined in recent years as a result of widespread habitat degradation and habitat loss. River dolphins once ranged widely throughout the rivers and coastal estuaries of Asia and South America. Today river dolphins live only in limited portions of the Yangtze, Mekong, Indus, Ganges, Amazon and Orinoco river basins and coastal estuaries in Asia and South America. River dolphins flouish in zones of quiet water typically found near river confluences. River dolphins prefer to swim alone or in groups of two and three. They feed on fish and crustaceans. Several species lack the ability to see.
All river dolphins use a sophisticated system of sonar clicks’ called echolocation to identify mates and prey. In the past river dolphins and people coexisted peacefully along the Mekong, Ganges, Yangtze and Amazon rivers. People traditionally shared the fish and water of the rivers with river dolphins and included river dolphins in myths and stories. These traditional beliefs used to helped river dolphins survive. Today however, people sometimes do not observe taboos against harming river dolphins directly and wound or kill river dolphins in greater numbers than before.
River dolphins are threatened critically by widespread habitat degradation and habitat loss caused by pollution, deforestation, dam construction and other destructive river development, and over-fishing. Chemical pollution from urban, industrial and agricultural wastes and runoff weakens the immune systems of river dolphins, leaving river dolphins vulnerable to infectious diseases. Noise pollution disrupts the direction-finding abilities and reproductive systems of river dolphins. Deforestation reduces the numbers of fish in rivers, depriving river dolphins of their primary fish prey. Deforestation also changes rainfall runoff patterns, often causing the water level in rivers to drop. The water levels of the rivers sometimes fall further after water is drawn from them for irrigation. The lowered water levels strand river dolphins in drying pools. River dolphins are sometimes hit by logs which logging companies transport down rivers directly. Over-fishing has caused world river and ocean fisheries to decline, placing river dolphins in direct competion with people for food. River dolphins are losing the competion because they often become fatally entrapped in gillnets and on fishing hooks or stunned by explosives used sometimes to harvest fish.
Dams and other destructive river developments affect river dolphins by reducing the numbers of fish in rivers and lowering levels of dissolved oxygen. Dams sometimes reduce flows of fresh water by trapping freshwater in their reservoirs and irrigation canals. Dams also fragment river dolphin populations into small and genetically-isolated populations that become highly vulnerable to extinction because populations downstream of dams can not migrate across dams to interbreed. Dams change river sedimentation patterns, causing rivers to undergo major changes in morphology which reduce the likelihood river dolphins’ preferred habitats, bars and sandy islands, will form. Destructive river developments like pumping stations and irrigation projects further fragment river dolphin habitat and affect the abilities of river dolphins to reproduce and survive. Oil exploration, development and extended river developments which are often financed by international lending agencies also degrade wide areas of habitat, adversely affecting river dolphins.
Measures for protecting river dolphins are underway along rivers and coasts worldwide. Conservation efforts include research projects, relocation and captive breeding efforts, dolphin reserves and laws banning the killing and disturbing of river dolphins. Scientific research and relocation and captive breeding efforts are underway in areas both in and out of the wild. Researchers have established natural, semi-natural and artificial reserves to breed Chinese river dolphins in captivity. Sanctuaries for river dolphins have been established or proposed for areas of the Amazon basin and rivers and coastal estuaries in Asia. Community initiatives are presently underway to promote sustainable fishing alternatives and develop local conservation programs which will allow people and river dolphins to share the resources of rivers. National and international laws also legislate against the killing or harming of river dolphins worldwide. The degrees of protection vary.
Nonetheless, despite human awareness of the endangered status of river dolphins and present conservation efforts, river dolphins continue to decline worldwide. In many cases the declines are critical. Some populations are losing the genetic variability necessary to survive short and long term threats including climate change and fluctuations in prey. Other populations are presently composed of high numbers of young animals, limiting the population’s ability to reproduce adequately and withstand mortality factors like habitat destruction. Today’s plight of river dolphins has prompted many environmentalists to call for a concerted international effort to save river dolphins from extinction, to manage human activities along rivers so people and all aquatic wildlife can coexist.