KCI’s ongoing work in water quality restoration has identified a hidden problem that may be contributing far more to the deterioration of water quality than previously recognized. Large populations of common carp can directly and indirectly affect water quality, water clarity, aquatic habitat, and species richness within a lake system. These fish are a resilient species that can thrive and breed in the worst water quality conditions, which they help create as their populations increase to dramatic proportions within a system. On average, a large female carp can lay 100,000-500,000 eggs in a single spawn. The fish also have a long life span, have no natural predators, and are rarely sought by anglers. The effects that this invasive species has within lake and various freshwater systems can be significant. These impacts on ecosystem processes fall into three categories:
Nutrient Inputs – Direct input and conversion of nutrients in the system through metabolic processes
Common carp are known to be an omnivorous species, and their diet is diverse and flexible given available resources. They can consume zooplankton, worms, insect larvae and organic plant matter, which they then digest into soluble nutrients. As the species grows in size and their population increases, nutrients are directly affected within the water column.
Foraging Behavior and Bioturbation – Alteration of habitat and ecosystem processes
Carp are known to vigorously roil the water and bottom substrate in search of food and during spawning seasons. With large numbers of carp spawning and swimming, the effects of large populations can alter the physical bottom stratus and water column within a lake, making it difficult for any native fish or vegetative species to thrive over time. These activities stir up the sediment at the bottom of the lake causing turbidity and bioturbation, which also reduces subsurface light needed for plant growth.
Fish Assemblage and Diversity – Domination of modified habitat and reduction of predation
As carp muddle and cloud the water they live in, they can have significant impacts on fish assemblages within lake systems. Sight-feeding species, such as walleye, bluegill and black bass, populations are reduced when a clear lake becomes turbid. In addition, carp uproot submerged aquatic plants needed for other native fish and waterfowl species for reproduction and feeding. Fish species such as black crappie, bluegill, pumpkinseed and yellow perch and waterfall populations see a reduction in growth when large populations of carp are present.
Management and treatment of these species is common within lake systems to improve water quality. One such example is Grand Lake St. Marys in Ohio, which has a population estimated between 250 to 500 pounds of carp per acre. Annually, participants compete in the “Get the Carp Outta Here” tournament which rewards fishers who remove the largest and most amount of carp. In 2014, over 6,000 pounds of carp were removed from the lake during the tournament. KCI has worked with the local counties to develop a restoration plan for the lake, and last year water quality continued to rise while recreational activity increased.
Click here to review my full paper and works cited on this topic: A Review of the Impacts, Effects of Common Carp on Freshwater Lake Systems through Nutrient Contributions and Ecological Thresholds