On the importance of ichthyoplankton monitoring for invasive grass carp control in the Laurentian Great Lakes

Grass carp (Ctenopharyngodon idella) is an invasive herbivore observed in small numbers in the Laurentian Great Lakes since the 1980 s with records from all lakes except Lake Superior. Identification of diploid, age-1 + grass carp from the Sandusky River, a Lake Erie tributary, in 2012, prompted targeted efforts to evaluate the status of grass carp reproduction in the Lake Erie Basin. In 2014, researchers from the U.S. Geological Survey and University of Toledo began surveys to assess grass carp spawning in the Great Lakes, with the first fertilized eggs discovered in 2015 in the Sandusky River. Eight Great Lakes tributaries in the United States have been surveyed for evidence of grass carp spawning, identifying three confirmed spawning tributaries (Sandusky, Maumee, and Huron Rivers in Ohio). Initial work identified specific flow and temperature conditions that likely stimulate spawning. Egg and larval drift modeling estimated spawning locations based on egg development and flow characteristics, which helped removal crews locate and target spawning fish in the Sandusky River and later, the Maumee River. The research synthesized herein demonstrates the value of ichthyoplankton research to inform control of emerging invasive species and could inform management of other invasive carps with similar reproductive life histories, should they enter the Great Lakes.