Date of Award
Master of Science
1st Chapter:Controlling invasive fishes is a pressing issue in fisheries management. Commercial harvest and bounty programs are often used as a control method to reduce abundance and lessen the destructive impacts of an invasive species. One group of species that may be controlled with harvest are invasive carps [Black Carp (Mylopharyngodon piceus), Grass Carp (Ctenopharyngodon idella), Bighead Carp (Hypophthalmichthys nobilis) and Silver Carp (H. molitrix)]. To reduce source populations and propagule pressure of invasive carps near the Laurentian Great Lakes, an enhanced contract commercial fishing program was started on the Peoria Pool of the Illinois River in September 2019. Commercial fishers received compensation of $0.10 for every pound of invasive carps caught in the Peoria Pool of the Illinois River on top of the price they were paid at the fish processing plant. My thesis used mobile hydroacoustic sampling to evaluate the effects of the enhanced contract fishing program by evaluating changes in invasive carp densities, biomass, and size structure from February 2020 to August 2021. The enhanced contract fishing program did increase fishing effort in the Peoria Pool of the Illinois River, which in turn increased harvest from 1,284,931 kgs of invasive carp in 2020 to 1,515,575 kgs of invasive carp in 2021. The average of hydroacoustic densities was 1.19 kgs/1000m3 and there was not a significant change throughout the duration of the project. It will be important to continue evaluating the enhanced contract fishing program as commercial fishing programs can take years to have effects. This study serves as a unique case study for future management by allowing us to assess how bigheaded carp abundances change due to commercial fishing pressure.2nd Chapter:Understanding the effects and having accurate estimates of demographic rates of an invasive species is important for management. Commercial harvest/removal is a common method of invasive species management. Quantifying mortality rates can be useful in informing population models for future management decisions for Silver Carp removal efforts. The objective of this study was to compare Silver Carp total annual mortality between the Wabash and Illinois Rivers, where additive mortality due to fishing and other factors likely differs. With the necessity of increasing additive mortality to bring down populations, these estimates are important to more accurately parameterize future control models as well as to differentiate between rivers with different management methods and other sources of mortality. For this study, survival and detection probabilities were determined in Program MARK using a Cormack-Jolly-Seber Models of acoustically tagged Silver Carp over 8 years and were compared between the upper and lower Illinois River and the Wabash River. The survival estimate for Silver Carp in the Wabash River (0.97±0.02) was higher than those in the Illinois River (0.22±0.14 to 0.77±0.07). Harvest and perhaps commercial barge traffic are leading to higher mortality in the Illinois River as there was much higher harvest and mortality in the Illinois River than there was in the Wabash River. Higher overall mortality in the Illinois River appears to be affecting densities differently in the upper and lower river due to the differing harvest strategies in these stretches of river. Previous estimates of annual mortality for the Illinois River were similar to our estimates. The Wabash River Silver Carp mortality was much lower than previous published estimates. This study serves as a unique method for evaluating the impacts of large-scale removal efforts and may also be useful in informing the Spatially Explicit Invasive Carp Population (SEICarP) modeling effort on how best to develop future management actions and harvest efforts.
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