Evaluating Strategies for Controlling Invasive Crayfish Using Human and Fish Predation

Invasive species cause significant ecological and economic impacts in a variety of ecosystem types around the world. Preventing the introduction of new invasive species is usually the economically optimal management. However, since prevention is rare, typical management practices rely on reducing the abundance of invasive species populations or maintaining populations at low abundance to mitigate the ecological and economic impacts of the invasion. However, the costs of controlling invasive species are often prohibitively high. Populations of invasive crayfish have been successfully reduced using a combination of mechanical harvest (baited traps) and biocontrol (enhancement of predatory fish populations by using conservative fishing regulations). The large scale application of these management strategies is currently unlikely due to the high costs associated with conducting long term trapping which require a substantial investment in personnel. Furthermore, the optimal fish species for controlling crayfish populations has never been rigorously identified. This thesis investigates ways to improve both crayfish trapping techniques and the manipulation of predatory fish communities to control crayfish populations. Our analyses show that small changes in trapping techniques (protecting the bait and increasing the size of the trap) can greatly increase the effectiveness of trapping and significantly lower the amount of effort necessary to reduce crayfish populations. In addition to manually removing crayfish, the manipulation of fish communities to consume more crayfish is an essential part of any program designed to reduce populations of invasive crayfish. Bioenergetics modeling, informed by a literature review of diet composition, shows smallmouth bass (Micropterus dolomieu) consume the most crayfish when younger (ages 2-9), while rock bass become the best crayfish predators when older (ages 10+). When analyzed at the community scale, our analysis suggests that community wide crayfish consumption decreases with increasing piscivore abundances, indicating that enhancement of piscivore populations, a common practice of fisheries managers, may harm crayfish control efforts. Furthermore, analysis of inter-water body diet composition suggests that certain predatory fishes may be ideal for controlling abundant (smallmouth bass, rock bass and yellow perch) while others (Lepomis spp. and rock bass) may be more effective in controlling sparse crayfish populations. The integration of empirical experiments, theoretical ecology and economics in this thesis yielded results which could directly inform cost effective management of invasive species. A similar multi-disciplinary approach could be used to inform the management of other invasive species where current technology is prohibitory costly to implement on a large scale.