Midwest Fish & Wildlife Conference 2019

AUTHORS. Patrick M. Kocovsky, US Geological Survey; Nicole R. King, University of Toledo; Eric Weimer, Ohio Department of Natural Resources; Christine M. Mayer, University of Toledo; Song S. Qian, University of Toledo

ABSTRACT. Spawning of Grass Carp Ctenopharyngodon idella in the Great Lakes basin was verified when eight genetically-confirmed, fertilized eggs were collected in the Sandusky River, a tributary to Lake Erie, in June and July 2015. Researchers predicted the fertilization location for those eggs was ~3.9 ± 1 km downstream of Ballville Dam between the State Street and Hayes Avenue bridges within the city limits of Fremont, Ohio. In June 2018, two pieces of evidence permitted verification of the model-predicted spawning location. First, fertilized Grass Carp eggs were collected at several sites from 3.3 km to 18 km downstream of the predicted spawning area 11-14 June. We used water temperature measured in the field at time of capture, developmental stage (± 1 stage) determined by microscopic examination, and published curves relating developmental time to water temperature to estimate time since fertilization for several hundred eggs. We then subtracted developmental time from capture time for each egg to determine the time the egg was fertilized and created a histogram of fertilization times. Second, two mature, diploid female and 14 mature, diploid male Grass Carp were captured by electrofishing conducted within the predicted spawning area during a prescribed management action conducted 12-14 June. Histograms of egg fertilization times overlapped with collection times for mature Grass Carp in the model-projected spawning area, providing additional evidence of the location of the spawning area and validating the modeling method used.