 |
|
 |
|
 |
|
 |
|||||||||||||||||||||||||||
|
In China, snakeheads are prized as a food fish with special nutritional benefits. Two years ago a man in Crofton, Md., evidently ordered a couple of live northern snakeheads from a New York fish market to make a soup for his ailing sister. But she had recovered by the time the fish arrived, and he dropped the fish into an aquarium. (Snakeheads come in a number of sizes, and some are valued by tropical-fish collectors.) The snakeheads outgrew the guy's aquarium — in captivity, they can grow nearly an inch a month. So he dumped them into a nine-acre pond near Crofton two years ago. The snakehead presence was not discovered until recently, when a fisherman caught one. He reported his catch to game wardens and the sirens went on. Snakeheads, which look like the native dogfish, are real survivors. If their pond dries up, they can burrow into the mud and remain there, breathing air, for several months. If they run out of food, they can crawl out of the water and survive for up to three days while searching for a new body of water. The Little Patuxent River is only 75 feet away from the pond where these snakeheads were found. These critters could devastate the native ecosystem and be almost impossible to control. The discovery of snakeheads in Maryland led the Department of the Interior to admit that snakeheads have been found in six other states. Interior Secretary Gale Norton will soon announce a government import-and-trade ban on 28 species of snakeheads. Everyone is concerned about illegal aliens these days. We have a similar problem with illegal critters. According to the Sea Grant, over 350 species of non-indigenous plants and animals have recently entered the U.S. When a foreign species enters a new ecosystem, it will seek out a niche it can fit into — either one that's empty, or one it can compete for with native species. Sometimes, of course, introductions work out. The ringneck pheasant from Asia, for instance, has been an appreciated addition to America's wildlife. Most others unfortunately are not. A U.S. Fish and Wildlife Service study estimated that the total cost to the U.S. of invasive species is more than $100 billion a year. Before you wonder where they got that figure, keep in mind that invasive species include starlings, wild boar, nutria, and Norway rats, as well as West Nile virus and plants like water hyacinth and kudzu. And let's not forget the MSX parasite that has devastated oyster beds in Maryland and Virginia, bringing the harvests down to one percent of their original size. Some exotics, like the South American water hyacinth, are valuable in moderation. Water hyacinths, plants with bulbous stems that float on the surface, are efficient at water filtration and are used in some sewage-treatment plants. They are virtually indestructible, and in the wild can clog a whole river with a bank-to-bank carpet of vegetation, curtailing boating and smothering the native plants and animals to death. Since the 28-mile-long Welland Canal was constructed in 1829, at least 130 non-indigenous species have slipped into the Great Lakes. The most dramatic invader was the sea lamprey, a parasitic, snake-like creature with a suction-cup mouth filled with sharp curved teeth. The adults feed by latching onto the side of a fish and sucking the life out of it. When the fish dies, they detach and move on. First reported in Lake Erie in l927, it was breeding in all the Great Lakes by l947. In two decades, lampreys devastated the lake trout and white fish, and destroyed the Great Lakes fisheries. Fortunately, lampreys have been controlled by a selective pesticide that can be applied to feeder streams where they breed, and the fishery has bounced back. Then there was the alewife — a shiny fat minnow that came roaring in through the canal and took up the plankton-eating niche once filled by the chubs, whitefish, and cisco that the lampreys had decimated. Alewives breed quickly and are too oily to be a food fish. Before the Great Lakes were restocked with salmon and trout, the alewife populations used to roar up and down according to plankton blooms. When they exceeded their food supply they would die off, and waist-high piles of alewives would wash up on beaches, fouling the water. Recently, two small exotic fish (the Eurasian ruffe and the round goby) and a large zooplankton (the spiny waterflea) have slipped in, presumably by way of the bilge waters of foreign boats. The ruffe was first observed in 1986 in Lake Superior at Duluth, Minn. According to Sea Grant research, between 1988 and 1991 the population of ruffe exploded from about 100,000 to over two million. In this period, the forage-fish population decreased two- to threefold, and the yellow perch and walleye populations plummeted. If the ruffe spreads to other Great Lakes the impact on sport fishery and tourism could be catastrophic. Exotic plants and animals are invading us from all around the world. Two plant species, the purple loosestrife and the European watermilfoil, are rapidly spreading through American waters. Along the East Coast the European green crab threatens the tasty blue-crab fishery, as well as shellfish. One green crab can consume 40 half-inch clams a day, as well as blue crabs its own size. Then there is the zebra mussel, a little fingernail-size mollusk with zebra stripes. No one is quite sure how zebra mussels got here from Europe — probably from the bilge of a foreign ship, or even locked onto a ship's hull. In the embryonic stage, they are only about the size of a pencil point. Adults are about as big as your thumbnail. Zebra snails reproduce like gangbusters. In no time at all they can cover boats, foul beaches with stinky razor-sharp shells, and clog water-intake pipes. Millions of dollars are being spent annually by Great Lakes cities and industries to unclog intake pipes. Zebra mussels now inhabit the waters of 20 states and the Canadian provinces of Ontario and Québec. The weak link in our law-enforcement system is the "Thin Green Line," those officers who patrol vast expanses of wild country, usually without backup, and have the widest jurisdiction of any law-enforcement agents. Nationwide, there are around 7,000 state game wardens — about as many as the number of New York police force assigned to cover New Year's Eve celebration. The "birds and bees cops" police more unwanted aliens than any other branch of law enforcement.
— Mr.
Swan is the “Media Watch” columnist for North American Hunter
magazine. |
|
|
|
|||||||||||||||||||||||
<% dim printurl
printurl = Request.ServerVariables("URL")%>
ast
month, northern snakeheads were found in a pond between Baltimore and
Washington. The snakehead is a voracious predator fish from China's Yangtze
River. Some species grow to one meter in length, can breathe air and "walk"
— living out of water for three days — and will eat about anything
they can find. The people of northern Thailand believe snakeheads are
reincarnated sinners.
