Endangered Species Handbook

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Aquatic Ecosystems

Mangrove Destruction

     In the Americas, mangroves grow as far north as southern Florida and the Florida Keys, throughout the Caribbean region; and in South America, they  occur in a narrow band lining the Amazon River and on the coasts of French Guiana and northern Brazil.  Mangroves are also abundant in river deltas of West Africa, portions of the Middle East, east to Malaysia, Papua New Guinea, northern Australia and on many western Pacific islands.
     The Sundarban mangroves surround the Ganges Delta, extending along the coasts of eastern India and Bangladesh.  They cover 2,300 square miles and penetrate far inland along the Ganges River, forming an intricate maze of rivers, creeks and canals that are flooded daily by ocean tides (Dugan 1993).  Wildlife is abundant in these mangroves.  At least 35 species of reptiles, 270 bird species and 42 mammal species are native (Dugan 1993). The most famous of these is the magnificent Bengal tiger (Panthera tigris bengalus), whose largest population may be found here.  India has set aside a large reserve for tigers and other wildlife in its portion of the Sundarbans; as many as 350 to 400 tigers are present in Bangladesh's portion, with 250 to 300 in India's (Dugan 1993).  Even in this maze of mangroves, however, tigers are under siege from poachers, and since the early 1990s, their numbers have declined even here from habitat loss, poaching and loss of prey animals to hunters.
     The Sundarban mangroves are heavily exploited by the over 300,000 people who live here.  Each year 9 million cubic metres of timber and pulpwood and 106,400 tons of fuel wood are cut by Bangladeshi and Indian natives (Dugan 1993).  Overcutting has affected the fisheries habitat that provides about 150,000 tons of fish per year for the 10,000 fishermen in these mangroves (Dugan 1993).  So many of the outer island mangroves have been destroyed that storm surges caused by cyclones now move much further inland, leaving destruction and loss of life in their wake (Hauser 1992).  Fragile mangroves have been destroyed for a fishing jetty and prawn culture area inside the Indian Bhitarkanika Sanctuary for endangered Olive Ridley Sea Turtles (Lepidochelys olivacea).  These projects were funded by the World Bank. This prime wildlife area is vital to white-bellied sea eagles and threatened Indian smooth-coated otters of the same species as Maxwell's otter (see above).  The Olive Ridley sea turtles experienced a major die-off in February 2000.
     The cutting of mangroves in southeast Asia has destroyed thousands of acres to supply paper mills in Japan (Collins 1990).  Prior to the Vietnam War, scientists estimate that at least 1,000 square miles of the Mekong Delta were mangrove and paperbark forest.  Eleven million gallons of herbicide defoliants (known as Agent Orange) were sprayed during the war, destroying half the delta wetlands, or 480 square miles of mangrove and 100 square miles of paperbark (Dugan 1993).  To compound the damage, the forests beyond the mangroves were burned and sprayed with herbicides, and canals were dug by the U.S. armed forces to drain the flooded areas (Dugan 1993).  Much of this land remains poisoned and infertile 35 years after the end of the war; replanting is taking place on non-poisoned acreage.  The human toll has been significant: thousands of Vietnamese died from the effects, and many children born since the war have had a high incidence of birth defects, serious skin disease and tumors; American soldiers exposed to these chemicals suffered a wide range of cancers and other major health problems.  Only recently has the US government acknowledged the full range of the effects of these herbicides and paid compensation to ailing servicemen. 
     The Mekong River delta is native to 260 species of fish, 35 reptile species, 6 amphibian species, 386 bird species and 23 mammal species (Simon 1995).  Among these are the endangered Estuarine crocodile (Crocodylus porosus), a species in decline throughout its southeast Asian range, and the threatened eastern Sarus crane (Grus antigone), which disappeared from Vietnam during the war but later returned (Simon 1995).  One of the rarest birds in the world, the giant ibis (Pseudibis gigantea), is the largest of all ibises, a silvery-gray bird with pink legs.  The Mekong Delta system in Cambodia was its stronghold in the 1920s, where it was commonly seen, but a 1994 survey found no giant ibis.  Wetland drainage for agriculture, hunting and deforestation have pushed it to the edge of extinction.  Extinct in Thailand, only two birds have been seen in southern Laos in recent years ‒ in 1993 near a proposed protected area (Collar et al. 1994).  Once native to the Mekong Delta in Vietnam, it was probably extinguished during the war.  Cambodia has some lowland wetlands and may have undiscovered populations of giant ibis, but at present the estimated total world population is 50 birds and declining (BI 2000).
     At present, the greatest threat to mangroves worldwide is the farmed shrimp industry.  Mangroves are natural nurseries for shrimp, and this industry destroys the mangroves by cutting them in wide swaths to make room for artificial ponds.  These ponds are closed off to prevent the shrimp from swimming back to the sea.  Without the natural cleansing of the tides, the ponds soon become polluted and laden with chemicals added by the farmers.  Although not all farmed shrimp are raised in this environmentally destructive manner, in some countries this type of farming predominates.  The worldwide shrimp farm industry is worth at least $8 billion (Mydans 1996) and produces 783,200 tons of shrimp per year, about 30 percent of the world's shrimp production (Nixon 1996).  Fifty countries now farm shrimp, many with aid from the World Bank.  The governments of India and Ecuador have banned the further cutting of mangroves for shrimp farms, but in Ecuador, 85 square miles of mangroves were illegally cut after the ban.  In the Philippines, 1,000 square miles of mangroves, 67 percent of the country's total, were destroyed between 1920 and 1980, most being converted to ponds for farming shrimp and milkfish (Dugan 1993).
     Grassroots environmental organizations have recently appealed to international conservation groups and lending banks to stop funding the farmed shrimp industry and to the public to boycott all farmed shrimp.  One such group, the Seattle-based Mangrove Action Project, has united with The Sierra Club of Canada and other organizations to lobby against tropical shrimp farms. The shrimp pond industry may die out on its own, however, because of disease outbreaks in the ponds.  Various types of virus and bacterial infections have spread through shrimp ponds because of their stagnancy and the crowding of shrimp.  More than 42,000 acres of ponds in Ecuador now lie fallow, having been swept by disease, and many fishermen and shrimp farmers now see the wisdom in protecting the mangroves because these trees are able to filter water and maintain a clean environment for shrimp far more efficiently than human-made holding ponds along the coasts (Nixon 1996).  High-technology aquaculture buildings have been constructed that use aerated and filtered water and operate independently of natural ecosystems.  Some of these facilities have been constructed in Thailand and elsewhere.  They are a far more environmentally friendly method of producing shrimp.  A key element is the captive-breeding of shrimp in such a facility, rather than removal of wild larvae from the ocean.

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