Grass carp movement and space use in Lake Erie : implications for management efforts

Grass Carp (Ctenopharyngodon idella) is an invasive species to the Laurentian Great Lakes that was first detected in the 1980s. The current invasion front for the Great Lakes is believed to be the western basin (WB) of Lake Erie, with spawning occurring in at least two WB tributaries. Targeted control is being used to reduce population densities in Lake Erie and lessen the risk of spread to other lakes. The effectiveness of this control strategy is hindered by two significant information gaps: the extent of intra- and inter-lake movements of Grass Carp and knowledge as to where in Lake Erie fish might aggregate. I used acoustic telemetry technology to quantify broad-scale movements of Grass Carp in Lake Erie, including movement to other Lake Erie basins and other Great Lakes. I additionally quantified movement and identified aggregation areas in the Sandusky River, which is a prime area for control due to it being the tributary with the most consistent annual spawning. Grass Carp dispersed up to 236 km from release locations, with approximately 25% of fish dispersing more than 100 km. Mean daily movement was as high as 2.49 km/day, with the highest movement occurring in the spring and summer. The Sandusky, Detroit, and Maumee rivers and Plum Creek were the most heavily used WB tributaries. In the Sandusky River, Grass Carp aggregated between river kilometers (RKMs) 34 and 36, and at RKM 45. During spawning conditions, fish also aggregated near RKM 48.6, close to the suspected spawning location for Grass Carp in the river. Based on my results, I believe past assessments have underestimated the risk of inter-basin and inter-lake spread of Grass Carp. I recommend focusing Grass Carp control efforts on Sandusky River and Plum Creek, and secondarily on Maumee and Detroit Rivers. Control efforts in the Sandusky River should be targeted for 20 RKMs below the former location of Ballville Dam; control policies should consider the use of passive capture gear during spring and summer months when movement in the Sandusky River is the greatest.