Endangered Species Handbook

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It's Too Late

Fish Extinctions

     The 2000 IUCN Red List lists a total of 81 species of fish that have become extinct over the past 400 years.  In addition, a large number of fish have been extinguished in Central and South American lakes ‒ scientists are still compiling information.  About 20 percent of the world's freshwater fish are indeed either extinct or in steep decline (Wilson 1992).
 
     No version of the IUCN Red List has listed many species reported as apparently extinct by biologists around the world.  In peninsular Malaysia, where 266 freshwater species were known to exist, a search found only 122 (Wilson 1992).  In the Philippines, where massive environmental destruction has taken place, Lake Lanao on Mindanao is famous for its diversity of endemic cyprinid fish.  Yet out of 18 species of three genera, an investigation found only three species of one genus (Wilson 1992).  These extinctions were apparently caused by overfishing and competition from introduced species (Wilson 1992).
 
     During this century, several mass extinctions of endemic fish have taken place when the creatures’ sole habitat was destroyed.  Lakes in East Africa, the Americas and Russia have either been drained ‒ as in the Russia’s Aral Sea ‒ or native species have been crowded out or preyed upon by introduced exotic fish. 
 
     Africa's Great Rift Valley, a product of movement in the Earth's crust eons ago, is home to several lakes of great biological diversity.  Lake Tanganyika has more than 140 endemic species of fish, Lake Victoria has more than 200 and Lake Malawi has at least 500 (McNeeley et al. 1990). These three lakes, home to hundreds of members of the colorful cichlid family, rank three, two and one respectively in the world for their diversity of fish (Myers 1979).  The lakes have been separated for millions of years, and although Lake Malawi and Lake Tanganyika are only 320 kilometers apart, they have not a single cichlid fish species in common (Myers 1979).  Each of these three lakes empties into great rivers; Lake Tanganyika flows into the Zaire, Lake Victoria into the Nile and Lake Malawi into the Zambezi (Kingdon 1989).  Most ancient is Lake Tanganyika, 3 to 6 million-years-old and twice the age of Lake Malawi, which is half as old as Lake Victoria (Kingdon 1989).  Lake Tanganyika is the second deepest lake in the world at 1,500 meters; only Siberia's Lake Baikal is deeper (Kingdon 1989).
 
     Lake Victoria is a shallow, enormous lake, covering an area the size of Ireland or the state of Maine (Kingdon 1989).  Evolution of cichlid fish in these lakes over the ages produced an extremely rich fauna.  From a few ancestor species, these fish flourished into an extraordinary diversity, each species filling a different ecological niche.  Their diets are extremely varied and may include plankton, crustaceans, mollusks or fish eggs (larvae) and even other fish (Kingdon 1989).  Cichlids brood their eggs in their mouths ‒ up to a thousand at a time ‒ protecting them from their many natural enemies.  They exhibit a great range in color, including silver, sapphire and turquoise blue, orange and yellow, and they are patterned in stripes, bars, dots or circles.  Resembling the fish one might see in a coral reef, many are popular in home aquariums (Kingdon 1989).  Various kinds of tilapia, which are also cichlids, form a major part of the diet of Africans living around these lakes, and they are being raised in aquaculture projects around the world.
 
     These beautiful fish and their ancient ecosystems are now disappearing.  The major cause is the Nile perch (Lates niloticus), Africa's largest freshwater fish, at more than 6 feet in length.  Since 1960, the Uganda Game and Fisheries Department has introduced thousands of these fish as a food source for the local people, despite objections from the East African Fisheries Research Organization (Simon 1995).  Even as a food fish, the Nile perch is not rated highly by the local Africans, who prefer the smaller tilapia, which they preserve by drying in the sun (Simon 1995).  The flesh of the Nile perch is so oily that it must be smoked, and more and more trees must be cut down for this purpose (Simon 1995).  An ecological disaster occurred after its introduction; although intended to increase the lake's productivity of fish, the opposite happened.  Gradually, this predatory fish became the dominant species in the lake, and completely destroyed the endemic cichlid fish fauna and fishery (Simon 1995).  Of the more than 300 varieties of Haplochromis genus cichlid fish (including subspecies) endemic to Lake Victoria, almost two-thirds died out, and the rest became endangered (Simon 1995).  Fifty known extinctions have beset Lake Victoria's endemic cichlids.  One species, Haplochromis pyrrhocephalus, has become extinct in the lake ‒ it exists only as a captive colony in the Horniman Museum in London (Simon 1995).  Extinctions of the surviving cichlids continue because of predation by the Nile perch and siltation of the lake from erosion of farmland soil on its shores.  This prevents these fish from mating because they are not able to recognize the brilliant colors and patterns of their potential mates (Yoon 1997).    
 
     The introduction of exotic fish threatens many freshwater species, and overfishing is virtually eliminating a large number of saltwater species.  Research on the latter is lacking, but it is likely that many of the 156 species listed as “critical” in the 2000 IUCN Red List will be listed as extinct in the near future.


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