Date of Award:

2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Advisor/Chair:

Brett Roper

Co-Advisor/Chair:

Phaedra Budy

Abstract

Watersheds are often managed without direct knowledge of how salmonid species use spatially-distinct spawning habitats within their watersheds, and rarely take into account the relationship between fish movement and potential population structure when making management decisions. The population of native Bonneville cutthroat trout (Oncorhynchus clarki utah) within the Logan River is the largest documented population remaining for this imperiled species, and still maintains extremely high densities of native fish in the upper river. Currently, fishing is not allowed in the upper 20 kilometers of the Logan River watershed during spawning, based on the assumption that cutthroat trout migrate to and spawn primarily in this section. I redetected cutthroat trout tagged (2,271) during years 2008-2012 in seven mainstem and tributary reaches of the Logan River during spawning months (April-June) of 2013 using a combination of stationary detection systems and mobile scanning techniques. Cutthroat trout in both mainstem and tributary reaches exhibit a leptokurtic movement distribution, indicating most fish spawn near to their original tagging site; however, small percentages of trout moved long distances to seek out spawning sites throughout the watershed. Growth, length, and condition estimates between mobile and non-mobile tagged fish demonstrate that while mobile fish tend to growth faster, be slightly larger, and in some cases be in relatively poorer condition, these differences are often biologically insignificant and dependent on site location within the watershed. A genetic microsatellite DNA analysis conducted on trout sampled from each study site confirms the assumption of panmixia, and I observed very little evidence of sub-population structure. Using River Styles® to assess geomorphically distinct reaches, I created a large-scale population estimate of spawning individuals, which found approximately 61% of spawning cutthroat trout are not subject to angling during the spawning season, while 39% could be susceptible to harvest in the lower basin and its tributaries. Most trout within the Logan River likely spawned very close to initial tagging locations and microsatellite analyses confirmed the population is genetically well-mixed, indicating conservation efforts should promote risk-averse management throughout the watershed, rather than focus heavily on any one section of the river.

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