Hydrilla threatens lake But using carp to eat weed could hurt other plants

February 28, 1993|By Mark Guidera | Mark Guidera,Staff Writer

Meet the spunky hydrilla, a leafy aquatic weed that replicates furiously and can take over an entire pond, lake or stream in just weeks.

While the plant has been the source for more than a few jokes among Howard County government officials lately, there's also serious concern about Lake Centennial, one of the county's premier recreation spots.

An infestation of the lake, spotted in 1987, is so serious that some Howard lawmakers are considering seeking an exemption to the state's ban on introducing any fish into Maryland waters that doesn't naturally occur here.

At issue is a species of carp, called a grass carp, which some believe could control the hydrilla. The grass carp, native to the Amur River along the China-Russia border, is a voracious eater. The problem is that the fish not only eats the hydrilla, but most other water plants.

Howard County has spent about $46,000 since 1987 attempting to control the hydrilla. which can grow more than 30 feet from the bottom to the water's surface, with chemicals. County officials surmise the plant may have been imported to the lake from a boat that had picked it up in the Potomac River, where it has been reproducing since the mid-1980s.

But out of concern for the long-term costs and consistent use of an herbicide in the lake, county officials want to explore other possibilities.

4 That's lead to humorous and serious suggestions.

One County Council member has suggested having a few friendly manatees sent up on loan from Florida. Another member has joked that health food enthusiasts from Columbia ought to be advised the hydrilla makes a tasty addition to salads.

Instead, the county has sought help from the Environmental Protection Agency. A $44,600 grant from the federal agency will help the county study how best to control the hydrilla and set up a long-range management plan for the lake, stocked annually with large-mouth bass, channel catfish and rainbow trout.

The grant was awarded, in part, because of EPA concern that the weed may soon start sprouting, if it hasn't already, in the Little Patuxent River, a vital part of the lower Patuxent drainage basin that feeds into the Chesapeake Bay, said Jeffrey Bourne, Howard's director of recreation and parks. The river flows into and drains out of the man-made lake, which opened in 1987.

The 54-acre lake is an economic magnet for the county, drawing almost 1 million visitors annually for boating, fishing and other recreational activities. County officials are concerned that if the hydrilla problem can't be controlled it could cut off the flow of visitors.

A genetically altered type of the fish, called a triploid grass carp, cannot reproduce. That strain has caught the eye of County Council Chairwoman Shane Pendergrass.

She believes use of the fish could prove more cost-efficient than controlling the hydrilla with the expensive herbicide the county Recreation and Parks Department is using to keep the weed in check in the summer when it flourishes.

The county is spending about $8,000 annually for spot control. Controlling the weed throughout the lake would cost $20,000 to $30,000 annually.

"I'm certainly no expert on this fish and the state, I guess, must have legitimate concern for not wanting it imported," said Ms. Pendergrass. "But my common-sense test tells me there must be a way of double-checking that the fish we get are the

kind that can't reproduce. That test couldn't be that expensive."

Ms. Pendergrass has asked county recreation and parks officials to research the testing method other states use to ensure fish purchased for placement in weed-infested waters aren't able to reproduce.

A testing system can ensure the fish are triploids, but Mr. Bourne said his staff found it was not fail-safe.

While Maryland's ban on nonindigenous fish bars the use of the grass carp, several southern states allow use of the fish to control water plants that often are used in golf course ponds.

Pennsylvania, which also bans importation of the grass carp, is considering lifting its ban and issuing permits for the carp.

Maryland's Department of Natural Resources opposes the Pennsylvania plan because of concerns the carp would wind up in the bay, reproduce and destroy aquatic vegetation that sustains so much of bay life. Research by the Pennsylvania's fisheries experts has concluded that while it is likely the fish could escape to larger bodies of water, including the Susquehanna River and the Chesapeake Bay, it is doubtful grass carp would be as destructive to aquatic plants as Maryland officials contend.

"It's likely that carp capable of reproducing would be in some of the batches from the vendors and would escape and reproduce," said Del Graff, chief of Pennsylvania's Fisheries Division.

"But it's unlikely the escaped fish would ever be able to establish the extensive populations needed to destroy the bay's aquatic plant life. We really see use of the fish as an acceptable risk."

Mr. Bourne, the Howard recreation and parks director, said introducing the grass carp into Centennial Lake may have at least one negative effect.

"We've found that the hydrilla has been good for the largemouth bass population. It gives the bass fry a place to hide while growing. The grass carp would wipe out that habitat. We're hoping the study shows us a natural way to control the hydrilla and create good habitats for the fish."

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