Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Andrew Whiteley

Commitee Members

Lisa Eby, Elizabeth Metcalf, Jedediah Brodie, Erin Landguth

Keywords

Fisheries, Genetics, Human Dimensions

Abstract

Non-native freshwater fish are considered a significant threat to the survival of native freshwater fish populations. Traditional management strategies for dealing with non-native fish such as chemical or mechanical removal have limitations and can be unsuccessful. A novel method for the removal of non-native fish is a technique where the addition of non-native male fish with a YY genotype (MYY) theoretically results in a shift of the population sex ratio towards all or mostly all males, driving population extirpation. However, many aspects that affect the success of this method have not been thoroughly tested. My doctoral research incorporated multiple disciplines to enhance the management strategies for a non-native trout, the brook trout (Salvelinus fontinalis). Currently, in the Boundary Dam reservoir in Washington, an extensive management program of these non-native fish is underway, including suppression and chemical removal as well as introduction of MYY. I first used genetic monitoring to provide managers with information regarding the genetic structure of brook trout populations and provide information about population resilience in the face of management efforts. I found evidence of significant genetic substructure within the system and highlighted three populations that were most likely to be successfully eradicated due to limited gene flow. I also found evidence of isolation by distance within the largest Boundary tributary (Sullivan Creek) suggesting that partial eradication within this system would likely be followed by recolonization. Next, I performed a study of the reproductive performance of MYY brook trout compared to hatchery XY brook trout in a lab-based setting. My results indicate that MYY brook trout perform similarly to hatchery XY males at fertilization and their offspring survive similarly at early development stages suggesting they could be an effective tool in non-native brook trout eradication efforts. Simulation studies testing the effectiveness of MYY have suggested that eradication success and/or minimum population size of the non-native population may be affected by many different factors. However, no studies to date have looked at the possible consequences on the remaining population if MYY management plans result in failure to eradicate. Suppression and MYY

introduction cause reductions in the abundance of the population, essentially forcing these populations through a population bottleneck and increasing the chance of inbreeding depression (ID). I performed a simulation study that looked at the effects of ID on the bottleneck and recovery of the remnant brook trout population after suppression and MYY introduction if it does not result in eradication. I found that during MYY introduction, ID resulted in a decrease in the population abundance compared to models that did not include fitness effects. However, because of increased genetic variation due to hatchery MYY admixture, populations recovered to above pre-treatment levels for most simulations post-suppression and MYY treatment. This result suggests that even if populations are driven to very low abundance, managers should not rely on them going extinct due to the effects of ID. Finally, I conducted a survey of wildlife managers to determine how manager characteristics influence the likelihood that managers will implement two novel management methods (MYY implementation and genetic rescue) to conserve native headwater stream fish populations. Findings suggest that risk tolerance was a good indicator for managers willingness to implement novel strategies. Additionally, we found differences for managers from different states and regions in their willingness to implement novel strategies. These results show that understanding the individual characteristics of managers is important for identifying factors that hinder the implementation of novel methods in the conservation of species. Overall, this research demonstrates that genetic tools can be informative when managing non-native species. MYY may be an effective approach to the management of nonnative species, however, caution should be taken as incomplete eradication could result in full recovery of the population. Finally, understanding manager characteristics could be beneficial for determining whether managers are willing to implement novel management strategies.

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