What’s up with the carp and hydrilla?Posted February 11, 2013 at 3:45 PM, Filed Under: BCA News, Front Page, Village Mill
By Wendy Parker
Mandatory water-use restrictions were lifted for all county water customers last month, and the reservoir has recovered from extremely low water levels. Reservoir Management Group Chair Bob Malek recently corresponded with Chesterfield County Utilities Director Roy Covington to get an update on the triploid carp and hydrilla situation. In April 2010, approximately 10,500 sterile triploid carp were introduced into the reservoir to control the invasive hydrilla plant.
Covington responded to Malek’s questions.
Questions & Answers
Did the last survey continue to show low hydrilla presence?
Yes, we are very fortunate the carp continue to do an excellent job keeping the hydrilla in check.
How large are the carp these days and is the general health of the carp OK?
Scott Herrmann of Virginia Department of Game & Inland Fisheries this past fall noted: “The collected grass carp ranged in size from 27.04 inches to 31.18 inches with a mean total length of 29.52 inches. The weight range was from 8.47 pounds to 12.36 pounds with the mean weight of 10.62 pounds.” Both Herrmann, in his limited survey in the fall, and Bill Kirkpatrick of Aquatic Environment Consultants Inc. in the previous year survey, found the grass carp to be in good health.
What are the carp eating?
Dr. Kenneth Wagner has discussed grass carp and hydrilla consumption in the past. He notes that the grass carp are essentially keeping “the lawn mowed.” The hydrilla has not disappeared as grass carp rarely uproot the plant, and tubers are abundant and not digested when consumed.
Low hydrilla biomass does not mean low hydrilla production. Dr. Wagner compared it to a bank account and income. While we may now have a low bank account (plant biomass) our income (potential plant growth) is still high. It won’t be a perfect balance, but the plants are still growing and the fish are still consuming.
Herrmann noted: “Grass carp will continue their best to forage along the bottom in hopes of finding any species of aquatic plant even if they have to turn to eating less than desirable filamentous algae.”
Are there any plans to add more carp this year?
No, currently the carp are keeping up well with the hydrilla. Some carp will continue to survive up to a decade, but due to mortality and being less vigorous, grazing effectiveness can be expected to decline in the future. This is why we will continue to monitor the situation.
I think it is fair to say that in general if no hydrilla is being observed in the reservoir, then the carp are doing their job, and there will be nothing new or exciting to report. The Utilities Department will continue to monitor the situation as recommended by Dr. Wagner.