Many times, pond owners ask if they can use grass carp to solve their excessive aquatic plant growth problem. The answer is “no,” as they are an illegal species to possess in the state of Michigan, except under a Michigan Department of Natural Resources permit for education or research purposes. This is often confusing to Michigan residents as the neighboring states of Illinois, Indiana and Ohio allow the use of grass carp under certain conditions with the proper permit.

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When the commercial fishing operator operating near La Crosse saw what he thought were invasive carp, he contacted the DNR. The DNR invasive carp field crew assisted in removing and identifying the fish. The DNR identified 39 silver carp and 11 grass carp caught in Pool 8 of the Mississippi, just south of La Crosse, and one silver carp caught in Pool 6, about 20 miles farther upstream. All invasive carp recovered have been given to the U.S. Fish and Wildlife Service to determine their age, size and gender.

Previous captures of invasive carp in Minnesota have been individuals or small numbers of fish. This capture indicates an increase in the abundance of invasive carp in the Pool 8 portion of the river between Minnesota and Wisconsin.

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Hydrilla, which is native to Africa, Australia, and parts of Asia, forms dense mats of vegetation that interfere with recreation and destroy fish and wildlife habitat.  This plant is able to survive freezing temperatures and can grow in very low sunlight which is a huge advantage over native aquatic plants.  Hydrilla grows early in the season and quickly shoots to the water’s surface blocking the sunlight and absorbing nutrients native plants need to survive.

No lake is immune since a fragment of the plant, often transported from lake to lake via boats, is capable of regenerating new plants.  Lake Pinehurst, a 200-acre manmade lake is owned by Pinehurst Resort in North Carolina; a premiere golf and recreation resort. Power boats are not permitted making it an ideal lake to host cocktail cruises, sail, swim, and fish.  Well, maybe not fish – not anymore.  Residents and resort guests trolled for largemouth bass and other fish that were once plentiful in the lake.  Pinehurst Resort advertised a well-stocked lake and provided fishing guide services for guests.  That is until hydrilla was discovered, Pinehurst Resort and members of the homeowners association quickly ordered herbicide spraying to combat the aquatic invasive species.

Aquatic vegetation had always been a problem in shallow parts of the lake and years of limited spraying kept the vegetation under control.  Three years ago an intensive annual program of spraying herbicides to kill the hydrilla began.  The program costs $20,000 annually and has proved to be successful, at least if near complete obliteration of plant life was the goal.  Very little aquatic vegetation remained after the spraying program, and native vegetation is necessary to keep lakes healthy, filter pollutants, and create fish habitat.  The annihilation of the aquatic vegetation has led to an unproductive fishery in poor shape; there is lack of forage fish which has resulted in stunted and unhealthy game fish.

According to the North Carolina Agricultural Extension Service, heavy hydrilla infestations (those that cover more than 25 to 30 percent of the surface in a lake) eliminate fish habitat, cause stunting, and reduce the number of harvestable fish.  Also, low oxygen levels under the mats make them unsuitable for the growth and survival of sport fishes and most other aquatic animals.  It’s interesting to note that the results from the treatment plan sounds hauntingly familiar to a hydrilla infestation.  Of course the hydrilla is gone now.

At the urging of fishermen in 2011, a study was conducted by Foster Lake & Pond Management, to include an analysis of the health of the current fish population in the lake, analysis of the food chain, survey of the lake’s bottom, study of aquatic plants, water quality and the negative effects of the lake’s population of grass carp.  The report concluded that the aquatic vegetation proved to be bladderwort, a carnivorous plant that is native to North Carolina; no hydrilla was found actively growing, but that tubers from the weed could be present in the hydro soil.  The grass carp were found to be healthy and actively feeding on what little aquatic vegetation remained.  The main problem in the lake now is a shortage of forage fish, those upon which the game fish feed; resulting in stunted and unhealthy game fish.

Recommendations were made on how to help fix the problem that the herbicide treatment caused.  These included harvesting certain fish, forage fish restocking, a feeding program and habitat enhancement.  In an effort to add habitat, discarded Christmas trees were submerged as a type of artificial habitat.

So although there is not funding to aid the “unproductive fishery that is in poor shape” there is money to continue with chemical treatments.  A small group of sportsmen and homeowners are hoping to find a way to compromise with those who find any aquatic vegetation a nuisance.  Aquatic vegetation can be controlled without killing all of the aquatic vegetation which is necessary to keep Lake Pinehurst healthy; it is a lake after all and not a 200-acre chemically treated pool.