1. Insolent invaders

2. Slitherin' snakeheads

3. Got crabs?

4. Super swine

5. Too many blooms

6. Bogus buckthorn

7. Argentine ants

8. Weed of a 1,000 leaves

9. Weed-beater success story


The snakehead fish has invaded a Maryland pond. A delicacy in Asia, it's a feared menace over here, and state officials plan to eradicate it with a fast-acting insecticide. Courtesy USGS


Wanted dead, not alive INVADING SPECIES Northern Snakehead, <i>Channa argus</i> Alias UnknownMottled dark and light brown, with continuous fins running along top and bottom ofbody, the snakehead looks like a camouflaged warrior.


This homely, carnivorous fish from Southeast Asia is a delicacy in its home turf - and a menace in Maryland, where the fish are reproducing in a pond near a shopping center. Breathes air, but cannot walk overland for three days, as some have claimed.




Armed (with sharp teeth) and considered dangerous. Will defend nesting areas, but will not kill people who disturb them. (Phew!)


More information



Inadvertent introduction
About two years ago, a Maryland resident bought some snakeheads at a fish market to treat his sister (in Asian medicine, the fish are considered medicinal). Fortunately, his sister got better. Unfortunately, he dumped the fish in a pond. The snakeheads multiplied and began gobbling other fish. This June, when a fisherman brought in a snakehead, state authorities grew alarmed that the invader would spread through Maryland. They resolved to fight back while the fish was still in one pond.

In July, says Donald Boesch, president of the University of Maryland Center for Environmental Research, experts decided that the best way to deal with the fish was to deal death to it. Boesch headed a panel charged with deciding the fish's fate.

The weapon of choice, the insecticide rotenone, has widely been used to kill unwanted fish in other lakes. By the time you read this, eradication efforts may be under way.

Unwanted lesson
Like many other invasive fishes, the snakeheads spent some time in a fish tank. Nationwide, Boesch says the deliberate release of unwanted fish from aquariums is probably the largest single source of problem fish. In second place, he says, is the practice of stocking fish.

Such "fish improvement" schemes have distributed troublesome exotics like northern pike and grass carp.

If the quick attack on the snakehead succeeds, it will offer more evidence for the benefits of responding to invasive species before they can occupy considerable terrain. As a second example will show later in this story, the economic and ecological costs of dealing with a nascent invasion are minuscule compared to the cost of a statewide, let alone nationwide, campaign.

While the chances of success in this instance are good, the intense interest in the snakehead (the "Frankenfish" can supposedly hike overland and live out of the water) may have benefits. Boesch sees the storm of attention as "a teaching moment, a poster child for the problem" of invasives. Indeed, Gale Norton, Secretary of Interior, has proposed to ban importation of snakeheads.

But does that demonstrate that the lesson of the snakehead invasion has been learned? As we'll see in our focus on "least wanted" exotic species, the problem extends far beyond one "Frankenfish" that happened to be dumped in a pond that happens to be near the capital city.

For his part, Boesch wants far wider action against invasive exotics. "There are all sorts of avenues for introduction, and there needs to be a broader approach" to control, he argues.

In other words, why close only the retail drip when the wholesale spigot is gushing?

By the shipload
In the past decade, ecologists have begun to rank exotic species as one of humanity's most destructive impacts. While habitat changes - deforestation, urbanization and the like - can cause extinctions, invaders can also push aside native species, even in protected nature areas.

When we say invaders, we are thinking about lots of organisms:

Exotic insects like gypsy moths attacking trees

Emerging diseases like West Nile virus

Goats stripping trees and shrubs from natural landscapes

Invasive plants "stealing" sunlight, nutrients and water from native species.

The key advantage of invaders largely results from transportation. Typically, invaders don't have to face natural controls -- the insects, diseases, competitors and predators that establish the loose "balance of nature" in undisturbed ecosystems. Over centuries in the new location, new controls will evolve, but until then, invader populations can skyrocket, with disastrous results.

Pumpin' mussel
Ever since the zebra mussel reached the Great Lakes in the 1980s in ship ballast water, biologists have dwelled on the threat posed by the millions of tons of ocean water lugged around the world in ships. Ballast water stabilizes empty ships -- and transports untold quantities of fish, shellfish, and even microbes around the world.

Can we sell you an analogy? If the snakeheads were a retail invasion, ballast water invites wholesale invasions. While controls on ballast water now exist in the Great Lakes and elsewhere, they are unevenly enforced.

Bay held at bay by blasted ballast
Ballast water is a disaster in San Francisco Bay, which ranks among the most invaded ecosystems in the United States. Over the past two decades, a new species has become established there every 14 weeks.

Many parts of the Bay are dominated by invasives. Andrew Cohen, an environmental scientist at the San Francisco Estuary Institute, a nonprofit research and monitoring group, says, "In many components of the most important habitats, in biomass and in numbers of individuals, 90 to 95 percent" are exotics.

The scale of invasion beggars the imagination. "On almost all of the bay bottom, many tens of thousands of acres, more than 90 percent of the biomass was already exotic a few decades ago," says Cohen. He adds that similar dominance appears among zooplankton -- floating animals that are near the bottom of the food chain. Most species came from Asian hitchhikers carried in ballast water.

The situation is grim, says Cohen. "Could we restore the Bay to something resembling the native species? Probably not. We probably won't find methods to remove the well-established exotics."

However, he points out that slowing the invasions may help some relatively pristine ecosystems by shifting the balance toward natives in places like salt marshes, where plants are subject to mechanical or chemical killing.

That, in turn, would help other components of the ecosystem. "We may have lost the muddy bottom, but we could still save the saltwater fish as a natural community," Cohen concludes. But only if the wholesale invasion of exotics in ballast water is slowed, he adds.

What else invades the ocean?





  The Why Files  

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Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive.


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