Hydrilla Management Plan

hydrillaplanWhat is hydrilla?
Hydrilla (Hydrilla verticillata) is an aquatic plant native to Asia and Africa introduced to the United States during the 1960’s as an aquarium plant.  Because hydrilla plants sprout from small fragments, it is easily transported from lake to lake by boaters.  Hydrilla’s other reproductive structures (tubers, turions, and seeds) are consumed and spread by waterfowl.  Once firmly established, hydrilla is not easily eliminated due to its many ways of reproducing.  In addition to reproducing using two seed like structures, hydrilla expands by producing tubers (tiny potato-like bulbs) in lake soils and by breaking into fragments.  Both of these reproductive techniques result in new hydrilla plants.  Hydrilla can be controlled but never completely eliminated.  Hydrilla tubers can live in lake soils for years, sprouting and growing new plants each year.  Hydrilla is considered the number one aquatic weed problem in the United States.  Because it performs and expands so well, Kenneth Langeland, a weed control specialist at the University of Florida, calls hydrilla the “perfect aquatic weed”[1].  A common quote is that “hydrilla can grow an inch per day”.  One study showed that a four inch piece of hydrilla grew to 3,200 inches in 35 days.  This non-native weed quickly reaches the surface, forming a canopy that shades out and displaces native plants. 

The Virginia Department of Game and Inland Fisheries aquatic biologists who documented the hydrilla infestation at Claytor Lake estimated it covered about 40 acres in September 2003.   Today, the best estimate is 400 acres and that acreage is climbing every year.  Left unchecked, hydrilla could eventually cover about 1,000 of Claytor Lake’s 4,633 total acres.  Hydrilla’s potential impact on the recreational uses of Claytor Lake may be significant.  Homeowners, boaters, anglers, swimmers, and other lake recreationists will be affected by its unchecked growth.  Because it quickly grows from the bottom to the surface, displacing other plants by shading, hydrilla can choke off entire coves and shallow areas of the lake.  Hydrilla can become the primary aquatic plant in Claytor Lake in areas where it finds suitable soils.  Hydrilla is found in up to 20 feet of water in Claytor Lake.  Initially, anglers love hydrilla and do not want to see it destroyed, because catching fish along the edges of large hydrilla beds is often easier than catching them in other habitats.  Left untreated, hydrilla spreads quickly, choking out available fish habitat and interfering with predators feeding on prey, resulting in unbalanced fish populations.  Hydrilla can also cause oxygen sags in the back ends of coves, resulting in fish kills.  In some cases, hydrilla serves as a surface for a species of toxic blue green algae that can kill waterfowl that eat the plant or predatory birds (like bald eagles) that eat waterfowl.  Finally, hydrilla traps trash, resulting in unsightly conditions.  Clearly, the unchecked growth of hydrilla in Claytor Lake has potential long-term impacts on many lake users.  If we fail to address this resource management problem, the use of this important southwest Virginia reservoir will be impacted for years to come.  We must determine ways to control this “Hydrilla Gorilla” before it overpowers Claytor Lake.

What is the Claytor Lake Technical Advisory Committee?
The Claytor Lake Technical Advisory Committee (CLTAC) was formed by the Pulaski County administrator to advise the county on long-term management of Claytor Lake.  The CLTAC is composed of the following public and private sector members with an interest in Claytor Lake:

  • Pete Huber                            Pulaski County
  • Teresa Rogers                      Appalachian Power Company
  • Mark McGlothin                 Appalachian Power Company
  • Wayne Alexander               Appalachian Power Company
  • Mike McLeod                       Virginia Department of Environmental Quality
  • Chris Doss                            Claytor Lake State Park
  • Bill Kittrell                            Virginia Department of Game and Inland Fisheries
  • John Copeland                    Virginia Department of Game and Inland Fisheries
  • Brian Watson                      Virginia Department of Game and Inland Fisheries
  • Troy Phillips                        Virginia Department of Game and Inland Fisheries
  • David Peake                         Virginia Department of Game and Inland Fisheries
  • Mike Burchett                      Rock House Marina Owner and Angler
  • David Gruber                        Biological Monitoring and Coast Guard Auxiliary
  • Laura Bullard                       Friends of Claytor Lake and Property Owner
  • Cheri Strenz                          Friends of Claytor Lake and Property Owner
  • Laura Walters                      Friends of Claytor Lake and Property Owner
  • Mike Hoffman                     Friends of Claytor Lake
  • Darla Jennings                   Friends of Claytor Lake
  • Jim Kelly                               Property Owner
  • Danny Morris                      Ducks Unlimited and Homebuilder
  • Larry Bandolin                    Retired Biologist and Property Owner

What is the CLTAC doing about hydrilla?
Since September 2010, the Claytor Lake Technical Advisory Committee (CLTAC) has explored options for controlling the increasing footprint of hydrilla at Claytor Lake.  CLTAC met on a bimonthly basis, addressed the hydrilla problem with other lake communities (Lake Gaston and Smith Mountain Lake), chemical companies, a commercial weed control specialist, Virginia Tech and N.C. State weed control specialists, the Virginia Department of Environmental Quality, the Pulaski County Board of Supervisors, and other interested parties. The purpose of this process was to yield a workable plan for hydrilla control.  CLTAC’s hydrilla control plan during 2011 is outlined in the Friends of Claytor Lake’s Hydrilla Business Plan (available upon request from info@focl.org).

The Claytor Lake Hydrilla Management Plan will guide the hydrilla control process during the next 10 years.  It includes pros and cons of mechanical, chemical, and biological control options and a recommendation for using triploid grass carp in Claytor Lake.  Elements of this 10-year plan are borrowed from hydrilla management plans prepared by James P. Kirk, PhD (U.S. Army Corps of Engineers, Vicksburg, MS).  Appendix A outlines a grass carp research project to assess movements and effectiveness of grass carp in Claytor Lake.  Appendix B is a Management Plan Outline in the format developed by James P. Kirk[2] for Lake Norman.  Appendix C is a time line detailing major events required during implementation of this management plan.

What are CLTAC’s goal and objectives for managing hydrilla?

Limit hydrilla’s impact on the recreational and ecological services of Claytor Lake and surrounding waters.

1. Limit hydrilla transport to and from nearby waters.
2. Decrease hydrilla’s negative impact on Claytor Lake’s recreational uses and their economic value.
3. Communicate CLTAC hydrilla management actions to the Claytor Lake community.
4. Control hydrilla in a manner that limits its ecological impact on Claytor Lake.
5. Limit the spread of hydrilla to uninfested areas of Claytor Lake to protect native aquatic vegetation beds.

What are the options for managing hydrilla?
Managing hydrilla in a reservoir is as much an art as it is a science.  Aquatic plant managers have three viable control options in their bag of tricks: mechanical, chemical, and biological.  Selecting the best control option or options is a process of eliminating possibilities based on physical and financial limitations.  For example, mechanical harvesting has been used in many flowing water systems, but its use can be limited by underwater obstructions that cause expensive equipment breakdowns.  Chemical treatment is frequently used to improve recreational access to hydrilla impacted waters, but may be limited in applicability due to the amount of time needed for chemical contact on plants, concerns about chemical control impacts on water uses, and the expense of lake-wide chemical controls.  Biological control includes a consideration of off-site impacts of biological control agents.  Following is a summary of typical costs and limitations of hydrilla control options investigated for use at Claytor Lake. 

Mechanical Control
Mechanical harvesting equipment costs $200,000 to $300,000 for each harvester, representing a major capital expense.  The Washington Council of Governments, based on their experience operating mechanical harvesters on the Potomac River, estimates their operating costs at $2,000/acre.  Mechanical harvesting requires repeated operations during the growing season.  Harvested plants have no commercial value, so they present a disposal problem.  The harvesting process produces stem fragments, which foster new hydrilla plant growth.  Harvesting hydrilla kills aquatic species living in the plant growth.  Harvesting impacts on juvenile bass and bluegill may be significant.

Chemical Control
Chemical control of hydrilla typically costs about $1,000 per acre.  A number of chemicals are approved for use in aquatic plant control.  The two chemicals typically used for hydrilla control are copper chelates and fluridone.  Copper chelates (product names include Cutrine Plus, StockTrine, Komeen, and K-Tea) are used where lake water turnover is high.  Copper chelates have no restrictions on water use for irrigation, fish consumption, livestock watering, swimming, or drinking water intakes.  Fluridone (product names include Sonar and Avast), is used where lake water turnover is low.  The use of fluridone limits water use for irrigation (7-30 days depending on the type of crop and maturity).  However, fluridone has no restrictions on water use for fish consumption, livestock watering, or swimming.  Fluridone cannot be used within a quarter mile of a water intake.

Biological Control
A number of biological control agents have been investigated for hydrilla control, but none of them offer the assurance of control in large systems as well as the use of plant eating grass carp (Ctenopharyngodon idella).  The grass carp, a large minnow native to eastern Asia, is widely cultured for food and was introduced into the United States in the 1960’s to control aquatic vegetation.  The development of the sterile or triploid grass carp during the 1980’s caused renewed interest in use of this species for aquatic plant control in many areas of the United States.  In Virginia, importation of grass carp requires a permit from the Virginia Department of Game and Inland Fisheries (VDGIF).  The VDGIF only allows sterile (triploid) grass carp to be used for aquatic plant control in Virginia.  Only Virginia approved suppliers are allowed to bring triploid grass carp into the state for sale.  Once grass carp are rendered triploid during a hatchery process, there is no chance of reversal.  Triploid grass carp remain sterile throughout their lifespan.

Sterile (triploid) grass carp readily eat hydrilla. Since they can control large areas of aquatic vegetation for up to 10 years when other treatment measures are not feasible or are too expensive, grass carp are a critical piece in integrated hydrilla control approaches.  The potential impacts of triploid grass carp must be clearly understood and tradeoffs evaluated[3].  Triploid grass carp should be used in reservoirs only if certain conditions are met.  Public support and a thorough appreciation of its biology and potential impacts are required.  Triploid grass carp should be stocked incrementally with the goal of achieving control of aquatic vegetation several years later[4].  This approach was used in the Santee Cooper reservoirs of South Carolina where thousands of acres of hydrilla were established during the late 1980’s.  A total of 768,500 triploid grass carp were stocked incrementally from 1989 to 1996.  Hydrilla declined dramatically, from a high of over 42,000 acres during 1994, to remnant stands by 1996[5].  Since then, hydrilla has been controlled without further stockings or use of herbicides.  In recent years, triploid grass carp were used to control hydrilla in other systems, like Lake Gaston, Lake James, and Lake Norman in North Carolina.

Grass carp tend to stay close to their food sources, but can move upstream or downstream.  Adult grass carp can make long movements and potentially leave a reservoir system[6]. Impacts on desirable aquatic plants, waterfowl, estuarine nursery areas, and fish communities are also considerations in utilizing this fish.  Some studies suggest that triploid grass carp move to stands of hydrilla and remain there[7]. In Claytor Lake, concerns about migration apply. Triploid grass carp are not prevented from downstream movement by Claytor Dam.  The grass carp stocked in Claytor Lake may move upstream as far as Buck Dam on the New River in Carroll County.  Since native aquatic vegetation beds in the New River are a primary source of river productivity[8], the use of grass carp for hydrilla control at Claytor Lake will involve a research component to document off-site movements and overall effectiveness of grass carp in Claytor Lake.  A pre-proposal for this research is located in Appendix A.Recommended triploid grass carp approach for Claytor Lake
The recommended approach to control hydrilla uses the minimum number of triploid grass carp incrementally stocked over at least three years. It is possible for hydrilla control to be achieved within a year of the first stocking, but this outcome is unlikely.  It is likely that triploid grass carp will not immediately control hydrilla because of a lag effect.  Regardless of initial results, stocking a maintenance number of fish over a 3-year period will allow estimates of mortality that will be important in projecting the decline of these sterile fish. During the first year, triploid grass carp will be stocked at a rate of 15 fish per vegetated acre.  For example, during 2010, approximately 400 acres of hydrilla were measured during fall surveys.  In May 2011, 15 fish per vegetated acre will be stocked (6,000 stocked fish).  During fall 2011, hydrilla may expand.  Stocking additional grass carp will be based on the fall 2011 hydrilla acreage estimate. A minimum of 3 years of stocking will be conducted with a goal of achieving a stocking density of 20 grass carp per vegetated acre.  This stocking will allow three year classes of grass carp to occupy Claytor Lake and the potential to develop reliable estimates of mortality.

Incremental stocking of triploid grass carp will eventually control hydrilla in Claytor Lake.  Preventing reestablishment of hydrilla in the future is important due to triploid grass carp mortality.  A second level of stocking should be the next management goal.  This goal will prevent the reestablishment of hydrilla.  This density is not clearly defined in the scientific literature, but results from the Santee Cooper reservoirs suggest this level is approximately one fish for every two to four formerly vegetated acres. Thus, by maintaining a very low density of triploid grass carp, control of hydrilla can be maintained indefinitely using supplemental stocking.  Using longevity information in the literature, stocking numbers, and generated mortality estimates specific for Claytor Lake, these stocking densities can be rapidly determined.  These grass carp densities, sufficient to control hydrilla, but too low to control other forms of aquatic vegetation, may allow less palatable forms of aquatic vegetation to become established.

How will the CLTAC manage hydrilla at Claytor Lake?
The CLTAC recommends a four pronged approach to controlling hydrilla in Claytor Lake. 

1. Perform chemical treatments with copper chelates, principally Komeen.  In public use areas, treatments will be funded by Appalachian Power.  Homeowners, landowners, and business owners affected by hydrilla may treat their shoreline areas as specified below.
2. Introduce sterile grass carp during May 2011and two subsequent years.
3. Monitor grass carp movement and hydrilla control effectiveness.
4. Based on annual estimates of hydrilla acreage as a measure of effectiveness, repeat the plan each year using an adaptive management approach.

How will the hydrilla management plan be implemented?

The initial sterile grass carp stocking occurred in May 2011.  Pulaski County obtained a triploid grass carp stocking permit from the VDGIF, then purchased and stocked 6,000 triploid grass carp that were a minimum of 13 inches long.  Pulaski County stocked these grass carp with the assistance and guidance of VDGIF aquatic biologists.  VDGIF aquatic biologists tagged 34 of these fish with radio transmitters to track them and monitor their effectiveness.

Monitoring grass carp movement and effectiveness

The VDGIF is funded a grass carp research project through the Virginia Tech Department of Fish and Wildlife Conservation to track the movement and effectiveness of the sterile grass carp.  Virginia Tech is providing recommendations for continuing use of grass carp and maintenance stocking levels based on control effectiveness.  A pre-proposal for the Virginia Tech grass carp study is located in Appendix A.

Evaluating the impacts of hydrilla on Claytor Lake fisheries

Uncontrolled hydrilla growth is likely to disrupt fish ecology in Claytor Lake in two ways.  First, because hydrilla forms high density plant beds in shallow areas, it may interfere with ecological relationships of near-shore fish species like the predatory fishes largemouth bass (Micropterus salmoides), smallmouth  bass (Micropterus dolomieui), and spotted bass (Micropterus punctulatus), and their primary prey, bluegill (Lepomis macrochirus).  Second, large hydrilla beds in the upper third of Claytor Lake may disrupt nutrient transport to the lower lake as these beds absorb nutrient inputs from the New River.  As a result, phytoplankton and zooplankton production may decline, disrupting energy transfer through prey fishes like gizzard shad (Dorosoma cepedianum) and alewife (Alosa pseudoharengus) to large open-water predatory fish like striped bass (Morone saxatilus), striped bass hybrids (Morone saxatilus x Morone chrysops), and walleye (Sander vitreum).  If hydrilla growth is reduced within the next 3 to 4 years, these potential impacts are likely to be minimal.  The impacts of hydrilla on near-shore Claytor Lake fish species will be monitored using shoreline electrofishing in hydrilla infested areas and in areas without hydrilla.  The impact of hydrilla on Claytor Lake’s open-water fish species will be monitored using annual gill net surveys.

Hydrilla chemical treatment

Treatment will be done by Appalachian Power, homeowners, land owners, and business owners affected by hydrilla.  All treatments must be done by a licensed pesticide applicator in the state of Virginia, and must meet the requirements of Virginia laws and regulations. In 2011, Appalachian Power furnished 50,000 for the chemical treatment of hydrilla from a priority list based on consultation with VDGIF, Claytor Lake State Park, and FOCL.  Appalachian Power’s annual financial commitment will be based on an annual review of chemical control needs in priority one areas.  Priority one is public ramps, fishing piers, public beaches, and designated bank fishing areas operated by the state or local government including Claytor Lake State Park and Harry DeHaven Park, and all of the VDGIF boat access sites.  Priority two is homeowners and lake business owners.  Priority three is property owners with no homes.  Any monies not used for priority one will be placed in a pool by FOCL to be used as rebates based on treatment costs of all applying homeowners that show proof of treatment by the licensed applicator. The amount of reimbursement will vary based on the total dollar value of requests versus the dollar balances available.  Hydrilla treatment account balances will vary from year to year, due to funding changes by Appalachian Power and/or other interested parties and donations.  Homeowner reimbursements can range from 0% to 75% with a 75% cap regardless of funds available.  Those receiving reimbursement have the option to return any or all of the funds received to FOCL earmarked to increase the amount for treatment in the future and receive a tax donation receipt.  When a homeowner has their property treated, a receipt from the applicator to include the dollar amount and acreage treated will be considered proof of treatment.  A downloadable form for the rebate request will be posted on FOCL’s website and must be mailed in with the proof of treatment to FOCL, P.O. Box 815, Pulaski, Virginia, 24301, post marked between November 1 and November 31 annually.  Funds will be dispersed in the month of December by FOCL based on a percentage of money in the pool divided by the total money spent by applying homeowners.  Some homeowners work through neighborhood organizations, such as road committees, or home owner associations to receive better pricing from the licensed applicator.  Payment of the rebate will be paid to the person or organization based on proof of treatment.


Outreach Plan

The CLTAC will work with Friends of Claytor Lake, Claytor Lake State Park, the U.S. Coast Guard Auxiliary, and the Department of Game and Inland Fisheries to increase public awareness of hydrilla and the hydrilla management plan being implemented at Claytor Lake.  Outreach efforts will use the “Hydrilla Gorilla” posters developed by Friends of Claytor Lake as the face of the hydrilla problem at Claytor Lake.  These posters will be placed in businesses in the Claytor Lake area and at all boat access sites on Claytor Lake.  Claytor Lake State Park and Department of Game and Inland Fisheries interpretive programs will use hydrilla as an example of an invasive exotic plant.  Department of Game and Inland Fisheries conservation police officers will distribute hydrilla postcards developed by Friends of Claytor Lake during routine boat patrols.   The Claytor Lake Flotilla of the U.S. Coast Guard Auxiliary will be asked to distribute hydrilla postcards during their boating safety work.  Annual updates on hydrilla management will be delivered to local media contacts.

What are the next steps in the hydrilla management plan at Claytor Lake?

  1. Provide notification to homeowners and business owners of the parts of the homeowner rebate program that apply to them.
  2. Develop an educational brochure featuring the Hydrilla Gorilla.
  3. Define the process and people to work with and through to have hydrilla declared a noxious aquatic weed in the Commonwealth of Virginia.
  4. Define the process and people to work with and through to seek and receive outside funding for hydrilla control.
  5. Educate anglers, waterfowl hunters, and other constituents about the need for hydrilla control at Claytor Lake.

Promote the CLTAC’s 10 year master plan for hydrilla control.

Appendix A – Grass Carp Research Pre-proposal

Grass Carp Growth, Mortality, and Movement in a Riverine Reservoir System

Andrew L. Rypel (rypel@vt.edu) and Brian R. Murphy (murphybr@vt.edu)

Department of Fish and Wildlife Conservation, Virginia Tech, Blacksburg, VA 24061

Background:  Hydrilla (Hydrilla verticillata) has become established in Claytor Lake (Pulaski County, VA), and is rapidly expanding.  Stakeholders are lobbying VDGIF to stock triploid grass carp Ctenopharyngodon idella), in conjunction with presently ongoing chemical control.  While grass carp have been used successfully to control hydrilla in some southern reservoirs, little is known about the behavior of the fish in a large riverine system like Claytor Lake.  Being a riverine species that tends to migrate upstream during high-water periods, there is potential for grass carp to move into the upper New River and possibly impact native vegetation that is critical for native stream-fish life cycles.  Upstream migration would reduce the effectiveness of carp for control of hydrilla in the lower reservoir.  Carp also may potentially pass through Claytor dam and affect areas in the lower New River.  Radiotracking of stocked grass carp will allow evaluation of movements within the system, and their fidelity to targeted vegetation areas.  Radiotagging will also facilitate estimates of natural mortality in stocked grass carp, and calculation of growth rates in conjunction with aging work.  If initial stocking of carp does not seem to reduce hydrilla to desired levels, tracking and mortality data will help mangers to determine whether plant control failure is due to inadequate initial stocking densities or failure of fish to stay in the desired control areas.  Such information will be critical to prevent overstocking of fish, and potential unintentional impacts to non-target areas.

Goals and Objectives:  The overall goal of the project is to achieve control of hydrilla (surface coverage of less than 100 acres) in Claytor Lake by fall 2014, while not negatively impacting native vegetation through the overstocking of grass carp.  An ancillary goal is to obtain information on the behavior of stock grass carp in a large, riverine reservoir, to support a viable management plan for the use of grass carp to achieve control of hydrilla in such a system.  Objectives include: 1) determine long-range movements of stocked grass carp in a riverine reservoir adjacent to long stretches of unimpeded river miles; 2) estimate natural mortality and growth for stocked grass carp; 3) model stocked grass carp population dynamics, in conjunction with hydrilla growth dynamics, to optimize sequential stocking events over time to fine-tune grass carp biomass to control nuisance vegetation.

Methods:  Triploid grass carp will be stocked in May 2011 at an initial rate of 15 fish per vegetated acre (6,000 fish, >325 mm).  Twenty-five stocked carp will be equipped with mortality-sensing radio transmitters, to be provided by Virginia Tech.   Virginia Tech, VDGIF, and FOCL (Friends of Claytor Lake) will collaborate to locate fish monthly from boats and/or fixed wing aircraft.  Mortality of grass carp will be modeled from tracking data, and growth of fish will be monitored through electroshocking and other survey methods.  Model results will be combined with a vegetation survey in the fall of 2011 to proscribe subsequent stocking densities in 2012 and 2013, to reach an ultimate stocking density of approximately 20 fish per vegetated acre.  At least 25 fish in each stocking cohort will be tagged with radio tramsitters, to facilitate the collection of movement and mortality data from all three cohorts.  Expected battery life for transmitters is 2-3 years.

Anticipated Results:  Three year classes of triploid grass carp will be established in Claytor Lake, and reduction of hydrilla coverage should be achieved.  Information will be gained about the behavior of grass carp in a southern riverine system, which will improve management understanding and use of grass carp for hydrilla control.  Results of modeling will facilitate the effectiveness of limited future stocking events, by fine-tuning stocking rates based on periodic vegetation surveys.

Appendix B – Recommended Claytor Lake Management Plan

  1. Problem aquatic plant species: Hydrilla
  1. Infestation coverage: 400 acres estimated in September 2010.
  1. 3.     Management objectives:
    1. Limit hydrilla transport to and from nearby waters.
    2. Decrease hydrilla’s negative impact on Claytor Lake’s recreational uses and their economic value.
    3. Communicate CLTAC hydrilla management actions to the Claytor Lake community.
    4. Control hydrilla in a manner that limits its ecological impact on Claytor Lake.
    5. Limit the spread of hydrilla to uninfested areas of Claytor Lake to protect native aquatic vegetation beds.
  1. 4.     Selected control methods:
    1. Triploid (sterile) grass carp used lake wide for long-term control.
    2. Registered and properly applied herbicides will be used in all public use areas with funding from Appalachian Power.
    3. Registered and properly applied herbicides may be used by home owners for spot treatments.
  1. 5.     Triploid grass carp stocking:
    1. Triploid grass carp will be released from boat ramps near the greatest concentrations of hydrilla.
    2. Triploid grass carp will be stocked at a rate of 15 per vegetated acre of hydrilla.  Stockings will be incremental and yearly for at least 3 years.  Should hydrilla be controlled before 3 years, further stocking will be based on discussions of the CLTAC.
    3. Stock triploid grass carp using standard techniques using fish from the Virginia approved vendors of triploid grass carp.
    4. When permitted by the Virginia Department of Game and Inland Fisheries, triploid grass carp will be released during the spring of 2011 and annually in the spring for three years. RESULTS FROM TRIPLOID GRASS CARP MAY NOT BE EVIDENT FOR TWO OR MORE YEARS.  After hydrilla control has been achieved, stocking rates will be based on discussions of the CLTAC.
    5. Triploid grass carp will be a minimum of 13 inches total length.  All shipments will be examined for condition and length specified in the contract with the vendor.
    6. Private entities are not permitted to stock additional triploid grass carp.  Private entities may use registered and appropriately applied herbicides for spot treatments.
    7. Triploid grass carp will be applied by the commercial vendor supervised by the CLTAC, funding agency, or individuals designated by the CLTAC.
  1. 6.     Aquatic herbicide control:
    1. Registered herbicides must be applied by licensed applicators in accordance with label instructions.
  1. 7.     Long-term management strategy:
    1. Manage hydrilla’s potential adverse impacts to the Claytor Lake ecosystem primarily using triploid grass carp stocked initially at a rate of 15 fish per vegetated acre.
    2. Maintain or enhance native aquatic vegetation by maintaining the lowest possible stocking rates of triploid grass carp, especially once major stands of hydrilla have been controlled.
    3. Seek to prevent further introduction and distribution of problem aquatic species through public education and enforcement of existing laws and regulations.
    4. Periodically revise the management plan and strategy as new environmental data becomes available.
    5. Plan for long-term control of hydrilla, once control has been achieved, by maintaining very low densities of triploid grass carp.  Stockings will be determined based on discussions of the CLTAC.
    6. Evaluate the impacts of hydrilla on Claytor Lake fisheries.

Appendix C – Time Line and Sequence of Events


2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
January – March 2, 4, 7 2, 3, 5 2, 3, 5 3, 5 3 3 3 3 3
April – June 4, 8 4, 5, 8 4, 5, 8 5, 6, 8 6, 8 6 6, 8 6 6,8
July – September 1 1, 5 1,5 1, 5 1 1 1 1 1 1
October – December 7 5, 9 5, 9 5, 9 9 9 9 9 9 9
  1. Estimate hydrilla acreage.
  2. Order triploid grass carp.
  3. Evaluate fisheries data for potential impacts of triploid grass carp.
  4. Stock triploid grass carp.
  5. Support Virginia Tech grass carp research project.
  6. Possible restocking of triploid grass carp to meet management objectives.
  7. Obtain management plan approval and identify funding sources.
  8. Sample Claytor Lake shoreline electrofishing sites.
  9. Sample Claytor Lake gill net sites.

[1] Kirk, J. P., K. J. Killgore, J. V. Morrow, Jr., S. D. Lamprecht, and D. W. Cooke. 2001. Movements of triploid grass carp in the Cooper River, South Carolina. Journal of Aquatic Plant Management 39:59-62.

[1] Hill, B.H. and J.R. Webster. 1983. Aquatic macrophyte contribution to the New River organic matter budget. Chapter 13 in Fontaine, T.D. and S.M. Bartell, editors, Dynamics of Lotic Ecosystems, Ann Arbor Science Publishers, Ann Arbor, Michigan.


Key Points about Hydrilla in Claytor Lake 

• The Claytor Lake Technical Advisory Committee (CLTAC) was formed by the Pulaski County Administrator to advise him on issues affecting the sustainability of Claytor Lake. 

• CLTAC’s hydrilla management goal for Claytor Lake is to limit its impact on the recreational use and ecological services of Claytor Lake and nearby waters.  We will control hydrilla expansion, not eliminate it.  CLTAC will prevent hydrilla transport to other waters by controlling it at public access sites, since boats and trailers often spread hydrilla fragments to nearby waters. 

• Native aquatic plants rarely cause problems.  Hydrilla is an invasive non-native plant considered the number one aquatic weed problem in the United States, using multiple modes of reproduction (tubers, turions, seeds, and fragmentation) to increase its footprint.  It initially creates good fish habitat, but quickly reaches the surface, forming a canopy that shades out and displaces native plants, negatively impacting aquatic species. 

• In an October 2011 Virginia Tech Department of Fish and Wildlife Conservation survey, hydrilla covered an estimated 394 acres of Claytor Lake’s 4,633 acres.   

• The grass carp (also known as white amur) (Ctenopharyngodon idella) being stocked today are triploid grass carp.  Triploid grass carp are rendered sterile so they cannot reproduce.  The Virginia Department of Game and Inland Fisheries (VDGIF) restricts stocking non-sterile grass carp in Virginia. 

• Pulaski County is paying for the 3,200 sterile grass carp being stocked today.  VDGIF biologists and hatchery staff are participating in an advisory and research capacity. 

• Virginia Tech and VDGIF biologists will attach radio transmitters to 45 grass carp and T-bar anchor Floy tags to an additional 1,000 grass carp today to follow their movements.  Virginia Tech’s Department of Fish and Wildlife Conservation is a partner with VDGIF on this study.  The knowledge gained from this research will guide future grass carp stocking.

• Six thousand sterile grass carp were stocked in Claytor Lake on May 26, 2011, with 3,000 grass carp released at the Claytor Lake State Park boat ramp and 3,000 grass carp released in equal numbers at Lowman’s Ferry Bridge and Old Hurst Road. 

• On May 26, 2011, 34 sterile grass carp, averaging 19 inches long and ranging in size from 17 to 22 inches, were fitted with radio transmitters, then stocked at each of the 3 stocking locations.  Grass carp tracking immediately after stocking showed movement throughout the lake, indicating that grass carp engaged in a search period, looking for suitable habitat and a preferred food source.  By August 2011, grass carp movement slowed, with most fish remaining in hydrilla beds in both the upper and lower portions of Claytor Lake for the remainder of the fall. 

• The average size of the sterile grass carp stocked on May 26, 2011 was 15 inches, with fish ranging in size from 13 to 18 inches.  In March 2012, a total of 27 grass carp were collected from Claytor Lake and measured.  They ranged from 21 to 28 inches, an increase of 6 to 13 inches from the 15 inch average length at stocking.  The weights of March 2012 grass carp ranged from 3 to 11 pounds, an increase of 2 to 9 pounds from their 1 pound average at stocking. 

• Although the 2011 hydrilla acreage estimate remained unchanged from the 2010 estimate at close to 400 acres, the significant growth of the grass carp indicates high hydrilla consumption rates by the stocked grass carp.  Prior grass carp studies have shown a one season lag period before effects from grass carp are measurable, which will most likely be the case in Claytor Lake