A Review of Grass Carp in Iowa: Commercial Harvest Trends, Vegetation Response after Lake Renovation, and Recent Efforts Regarding Policies and Rules

Grass carp Ctenopharyngodon idella were first used as a management tool to control aquatic vegetation in Iowa in 1973 when they were imported and stocked into Red Haw Lake by the Iowa Conservation Commission.  Grass carp currently inhabit lakes, ponds, and rivers throughout most of the state. Commercial harvest of grass carp from the Mississippi River bordering Iowa has generally increased since 1987 with a low of 145 lbs in 1990 to a high of 63,400 lbs in 2009. Research in Iowa has documented grass carp over 30 years old, weighing over 50 lbs, having a biomass of 440 lbs/acre, and controlling vegetation from initial stockings for over 20 years.  The near complete elimination of aquatic macrophytes by grass carp in lakes has led the Iowa Department of Natural Resources (IDNR) to renovate lakes in order to reestablish aquatic macrophytes and improve fish habitat. The IDNR also developed a policy to no longer stock grass carp in public waters. No permits are required to stock grass carp, including diploids, into any waters of Iowa. Recent efforts by the IDNR to prohibit the stocking of diploid grass carp was met with resistance by the private aquaculture industry in Iowa.