Crossville Chronicle, Crossville, TN

June 26, 2013

Grass carp used to control lake weeds


CROSSVILLE — Fairfield Glade residents are always concerned about the vegetation growing in the lakes. This vegetation can be unsightly, can restrict use of the lakes and generally can be seen as giving the lakes an unkempt look. It is important to accept that vegetation is an major contributor to the health and stability of the lakes' ecosystems. It is necessary that the lakes have some vegetation. That said, what are the options to keep the plant population from reaching the point that it interferes with the enjoyment of the lakes? The sad reality is that there are few options available for the control of vegetation and each option is seriously flawed.

At this time, the Community Club is choosing to depend on fish as the plant control of choice in our lakes. There are two finned grazers that are stocked in the lakes, tilapia and grass carp. As far as vegetation is concerned, tilapia are excellent at ridding the lakes of filamentous algae which the carp will not eat. However, the workhorse for plant suppression is the grass carp. For years, the Community Club used a mass stocking program. That is, when the plant population of a lake became problematic, a significant number of small carp were added and over time they would grow and would graze down the plants, sometimes to the point of damaging the lake habitat. In about 15 years, the carp population becomes old and, over a short period of time, dies off. At that point the plants return in massive amounts. The cycle of too many plants, too few plants, too many plants seemed self defeating.

In 2008, the Lakes Committee recommended, and the Board of Directors approved changing to an incremental stocking system for grass carp. With this approach the carp are stocked in the lakes in small numbers every other year. By using this system, a population of varying age carp is built up in the lakes over time. Once the population plateaus, (when the number being add equals the number dying) the average age of the population will be constant, the amount of vegetation being consumed will be constant and the roller coaster plant population cycle will be broken. The draw back to this is that patience is needed while the carp populations are being built.

In 2007, the carp in Lake St. George came to the end of their lives and the lake's plants took off. The new stocking system was put in place the next year. For the next several years St. George had unacceptable amounts of vegetation, residents were rightfully unhappy and the stocking quietly continued. Early observations this spring indicate that finally the fish may be overtaking the plants and the long suffering residents will be rewarded for their patience. This year, Lake Sherwood has been found to be in the same situation that St. George was in back in 2008. The draining of the lake killed off the carp and opened the door for the plants. A starter population of carp was stocked last spring and more will be added as scheduled. As the young carp grow and the population is increased, the vegetation explosion should subside and, like St. George, suppression will be achieved.  

The temptation is to say that a lake has too much vegetation so let's add a few more carp now to speed along the process of grazing down the plants. Doing this will delay the point where a desirable equilibrium is reach and brings into play the possibility of overstocking and damaging the ecosystem. If the carp are mistakenly over stocked it is a 15 year mistake because correction of the situation can only take place after the carp die. The important point is that sticking with the incremental schedule is the most certain way to get to the point where our lakes have a healthy ecosystem with a stable and reasonable amount of vegetation. Residents sometimes feel that if they do not see something being done, the problem is not being addressed. In the case of lake vegetation management, the problem is understood by those in charge and progress is being made. Patience will be rewarded.