Biologists use new tools to battle northern pike in Alaska

ANCHORAGE, Alaska (AP)  Biologists are trying new techniques to combat the spread of northern pike, invasive fish that are wiping out rainbow trout, salmon and other species in some Alaska lakes.

In some hard-hit lakes, biologists have used an organic compound that deprives fish of oxygen to eradicate pike. They're also exploring the best uses for a tool similar to a high-pressure water gun and another device that works like a low-voltage electric fence.

Northern pike prefer shallow, vegetated waters where they can hide and ambush pray. They're native to some parts of the state, but they've been introduced to waterways in south-central Alaska since the 1950s. In the area's shallow waters, native water species can't dive deep to escape and haven't evolved other defenses against the pike.

The fish have pointed snouts with teeth, and they have a capacity to devour a large amount of prey, Ken Marsh, a spokesman for the Alaska Department of Fish and Game, told KNBA-FM.

"They will literally, and have literally, in scores of lakes in the valley, eat every rainbow trout, every salmon in sight,'' Marsh said. "And they've actually eradicated rainbow trout from many lakes where they used to be native and abundant.''

Northern pike also prey on water fowl, especially chicks, and amphibians.

To combat the problem, biologists have used an organic compound that deprives gilled creatures of oxygen. It has no effect on mammals, birds or humans, but it kills all fish. In many cases, that's not a problem because the pike have already wiped out most or all of the other fish species, biologists said.

The compound, rotenone, has been used in four lakes since 2008, and biologists are planning to use it in Stormy Lake, near Nikiski, this fall. After the chemical evaporates, the state restocks lakes with new fish or with fish removed earlier.

"The cost for that is going to be just about $100,000 to buy the rotenone to treat that lake,'' said Robert Massengill, a fisheries biologist for the Fish and Game Department. "And there's a lot of other costs associated with applying the rotenone, too.''

They're also looking at using a gun that shoots a high-pressure wave of water. Biologists spray the water at pike from different distances and evaluate the damage sustained. Bigger guns have bigger blasts but are harder to transport, so researchers are trying to find the most effective balance between size and power, officials said.

One other option under consideration is a sort of low-voltage electric fence. The fence could be attached to two boats and used to corral pike into one end of a lake, where other tools could be used, said Pat Shields, a biologists from the wildlife agency's commercial fisheries division.

Biologists are also experimenting with aggressive netting of pike at Alexander Creek and Alexander Lake in the Mat-Su Valley water bodies. Officials say the water bodies were once prolific king salmon fisheries but have been taken over by pike.

Despite all the problems with pike, Massengill said people are continuing to illegally stock waterways with the fish. Transport, possession or release of live fish or fish eggs in Alaskan waters without a permit is a misdemeanor.

"Hopefully with the education that we're doing, and the penalties that people can face when they do it, that's becoming less of a problem,'' Massengill said. "I think we're making some headway there.''

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