Date of Award:

5-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Ecology

Committee Chair(s)

Timothy E. Walsworth

Committee

Timothy E. Walsworth

Committee

Sarah E. Null

Committee

Sarah Klain

Abstract

Management programs that aim to reduce the consequences of invasive species are often challenged by populations that can rapidly recover from removal efforts. Selectivity, the relative impact of harvest on different size classes, can contribute to population recovery when younger fish are not effectively targeted. In Utah Lake, the location of one of the world’s largest freshwater fish control programs, managers have been attempting to control the common carp (Cyprinus carpio, hereafter “carp”) population since 2009 but efforts have been hindered by the use of selective fishing gears. I conducted a lake-wide field study to gain insights into the distribution of juvenile and small adult carp in time and space and to identify fishing gears that can be incorporated in control efforts. I evaluated factors influencing the presence and abundance of juvenile, small adult, and all ages of carp in survey samples, and identified strong temporal trends across years, with carp catch being 125 to 270 times more likely in 2023 than 2021. While the highly variable nature of Utah Lake impacted my study and additional sampling might provide further insights, it is important to assess which age classes are the most critical to capture. To do this, I used a simulation framework that integrates age-based gear selectivity and the widely implemented commercial fisheries metric of maximum sustainable yield (MSY) to evaluate the effect of improving selectivity among younger carp. I found that improving selectivity on younger, but mature, age classes achieved the control program’s biomass target with only 2.5 times maximum historic effort, while further improving juvenile selectivity had minimal benefit. The historic level of fishing effort was below that required to achieve MSY regardless of selectivity scenario, suggesting the control program would be harvesting at a sustainable rate even if gear selectivity were improved. Controlling invasive species becomes much more feasible if an approach that targets all adult age classes can be identified and incorporating sustainable harvest metrics into simulation models of invasive species populations provides a framework for evaluating a harvest control program’s ability to achieve management objectives.

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