Mass Extinction of
Freshwater Creatures
HALIFAX, Nova Scotia, Canada (ENS) - The first estimate of extinction rates of North America's freshwater animals, just released, has found they are the most endangered species group on the continent. The Canadian study warns that the U.S. could lose most of its freshwater species in the next century if steps are not taken to protect them.
"A silent mass extinction is occurring in our lakes and rivers," says author Anthony Ricciardi of Dalhousie University in Halifax. Ricciardi,s study with coauthor Joseph Rasmussen of McGill University in Montreal is published in the October issue of "Conservation Biology."
Northern shore of Lake Superior in Minnesota (Photo by Dave Hansen courtesy Great Lakes National Program Office) Relatively little media attention has been given to freshwater species, the authors say, but these animals are in at least as much danger as land species. Since 1900, at least 123 freshwater animal species have been recorded as extinct in North America.
Common freshwater species, from snails to fish to amphibians, are dying out five times faster than land species, and three times faster than coastal marine mammals, the researchers found. Their estimate of the loss of freshwater biodiversity "is probably conservative," the researchers say, "because there have likely been extinctions of species that we did not know existed, as suggested by the fact that several extinct fishes are known from only a few specimens."
Freshwater animals are dying out as fast as rainforest species, considered by many to be the most imperiled on Earth. The authors predict that about four percent of freshwater species will be lost each decade if nothing is done to conserve them.
Worldwide the situation is even more perilous for these creatures. The World Wide Fund for Nature (WWF) said in September that 51 percent of freshwater species, from fish and frogs to river dolphins, are declining in numbers. The 1999 Living Planet Report, an annual index on the state of the world's natural wealth, presents the most reliable data available on forest area and populations of marine and freshwater species worldwide. It also examines consumption of critical resources in 151 countries and its consequences.
"This report is a graphic call to reduce these negative trends as the world enters the 21st century," said Claude Martin, director general of WWF. "The observed declines in populations of freshwater species is particularly alarming as they indicate the extent of deterioration in the quality of the world's rivers, lakes and other wetlands."
Toad in Britain (Photo by Ian Britton courtesy <
Freshwater amphibians are hard hit. The disappearance of the golden toad and other amphibians in Costa Rica has been attributed to climatic changes. Many losses have been recorded in national parks and nature reserves, indicating pervasive threats even in protected areas. In Australia, Panama and the US, about 20 frog species have been decimated by a previously unknown fungus. Deformities are also widespread, caused by pollutants such as pesticides and other factors.
The report, produced by WWF in collaboration with the New Economic Foundation and the World Conservation Monitoring Centre (IUCN), found that the total of marine and inland fish caught reached a record level of 95 million tonnes in 1996, up 11 million tonnes from the annual average in the preceding five years.
To get a picture of how rapidly species extinction is accelerating, the Canadian researchers compared current extinction rates with those from the fossil record. They calculate that the background rate of extinction for freshwater fish species is about one species every three million years.
The modern extinction rate in North America, the study says, is about one extinction every 2600 years - about 1,000 times higher than the background rate.
Ricciardi and Rasmussen predict that many species considered at risk will disappear within the next century. At risk species account for 49 percent of the 262 remaining mussel species, 33 percent of the 336 crayfish species, 26 percent of the 243 amphibian species, and 21 percent of the 1,021 fish species.
Sea lampreys on lake trout (Photo courtesy U.S. Fish & Wildlife Service)
Non-native species pose a serious threat to indigenous freshwater animals. European zebra mussels are outcompeting native mussels in North American lakes and rivers. Sea lampreys invade lakes and attach themselves to native fish, killing them. Even sport fish transplanted from one lake to another can take over an ecosystem, driving less aggressive native fish toward extinction.
Dams that obstruct river flow are also threats. Of 5.2 million kilometers (3.2 million miles) of stream habitat in the lower 48 states, less than two percent, or about 100,000 kilometers, is pristine enough to be federally protected, Ricciardi and Rasmussen say. Excess sediment, toxic contaminants and organic pollutants from agriculture threaten most U.S. waterways.
Only 40 rivers longer than 200 kilometers (125 miles) remain free flowing in the lower 48 states. "Such massive habitat deterioration threatens some of the world,s richest freshwater faunal assemblages," the study says. Ricciardi and Rasmussen note that hundreds of U.S. dams are coming up for federal relicensing soon, providing an opportunity to reestablish natural flows in many rivers.
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