Date of Award:

12-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Timothy E. Walsworth

Committee

Timothy E. Walsworth

Committee

Karin Kettenring

Committee

Phaedra Budy

Abstract

Shallow lake ecosystems and their associated wetland habitats globally are subject to non-native species introductions, nutrient loading, and water level fluctuations, each of which can decrease vegetated habitat availability, exposing vulnerable native aquatic species to predation. Managers are frequently tasked with mitigating native species declines by restoring vegetation considered crucial for their survival. However, restoring vegetation can be challenging in the presence of multiple stressors, requiring managers to assess the relative importance of the different stressors limiting vegetation recovery.

Utah Lake is a large shallow lake subject to multiple stressors and has shifted from a mesotrophic lake with abundant aquatic vegetation to a hypereutrophic lake dominated by phytoplankton. The threatened, endemic June sucker Chasmistes liorus demonstrates extremely limited natural recruitment, and limited vegetated refuge habitat availability likely contributes to their low juvenile survival. Currently, removal efforts are underway to eliminate invasive common carp Cyprinus carpio and Phragmites australis, with the goal of restoring the aquatic vegetation considered critical to June sucker recovery. The objectives of this study were to (1) evaluate the response of vegetation to removal efforts and lake level variability at the lake-wide scale, and (2) determine how fish community composition and size-structure differs between vegetated and unvegetated habitats in Utah Lake. Addressing these objectives will describe the relative importance of stressors limiting vegetation and inform managers of fish habitat use.

My results indicate changes in lake level across years drive vegetation coverage at the lake scale in Utah Lake, affecting fish community composition and structure. Submerged vegetation decreased under elevated lake levels, while emergent vegetation increased under elevated lake levels. Interestingly, vegetation coverage demonstrated no response to changes in carp biomass or Phragmites treatment extent. Small-bodied and juvenile fish were more abundant in vegetated habitats, suggesting these habitats represent predator refugia. However, no juvenile June sucker were captured in any of my samples. My study demonstrates that, as non-native fishes also depend on vegetation for refuge, competition with non-native fishes may limit the benefits of vegetation restoration realized by June sucker. The implications of my results suggest managers must prioritize both lake level management and non-native fish control to support June sucker recovery.

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