Date of Award
12-1-2024
Degree Name
Master of Science
Department
Biological Sciences
First Advisor
Whitledge, Gregory
Abstract
Grass Carp (Ctenopharyngodon idella) is a species of concern in areas they have invaded, such the Laurentian Great Lakes, due to their potential to substantially reduce aquatic macrophyte coverage. Efforts to control Grass Carp in the Great Lakes have primarily been focused on two tributaries to the western basin of Lake Erie (i.e., Sandusky and Maumee rivers, Ohio) where reproduction has been documented, although other Great Lakes tributaries are known to have thermal and hydrological regimes suitable for Grass Carp spawning. Knowledge of sources contributing to the expanding population of invasive Grass Carp in the Great Lakes is key to allocating control efforts aimed at curbing further introductions, reducing natural recruitment, and limiting potential for further range expansion. A recent study demonstrated that otolith microchemistry is an effective tool for identifying the natal environment of Grass Carp in the Great Lakes. Increased captures of Grass Carp in Lake Erie and Lake Michigan indicates an ongoing need to determine which tributaries are supporting Grass Carp recruitment. Therefore, the objectives of this study were to use otolith stable oxygen isotope (δ18O) analysis to determine whether diploid and unknown ploidy Grass Carp collected from the Great Lakes during 2019-2022 were wild or of aquaculture origin, analyze Sr:Ca and Ba:Ca ratios of water samples collected from known and potential Grass Carp spawning tributaries to assess persistence of differences in water chemistry among tributaries observed in prior studies, use otolith core trace element ratios (Sr:Ca and Br:Ca) to infer natal rivers of wild Grass Carp, and estimate how many groups of aquaculture-origin Grass Carp (both diploid and triploid individuals) with distinct otolith chemistry profiles were present among fish collected during 2019-2022. Water Sr:Ca and Ba:Ca for Great Lakes tributaries were consistent with data from prior studies. Diploid and unknown ploidy Grass Carp (21%) were identified as aquaculture origin fish based on otolith core δ18O. Multiple clusters and broad ranges of otolith core Sr:Ca and Ba:Ca among aquaculture-source Grass Carp suggest multiple sources of introduced/escaped fish in the Lake Erie basin. Tributaries to the western basin of Lake Erie were identified as the primary sources of wild Grass Carp, although there was some evidence of recruitment from central or eastern basin tributaries to Lake Erie. There was no evidence of Grass Carp reproduction in the Lake Michigan basin; the one wild fish caught in the Lake Michigan basin had otolith core Sr:Ca consistent with origin in a western basin tributary of Lake Erie. Thus, efforts to control natural recruitment of Grass Carp should remain focused on tributaries to the western basin of Lake Erie, especially where reproduction has been documented. However, the relatively high percentage of aquaculture-source Grass Carp (including some fertile, diploid fish) captured during multi-agency response efforts indicates that curtailing natural recruitment, further introductions, and spread of Grass Carp is necessary for successful population control.
Access
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