Date of Award:

2014

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Ecology

Advisor/Chair:

Phaedra Budy

Abstract

Through a myriad of practices, anthropogenic land and water use has caused the localized extirpation or complete elimination of many native fishes throughout North America. Specifically, native salmonids have seen substantial declines in population sizes and geographic distributions due to a number of factors, including habitat loss or degradation, overharvest, or the introduction of non-native competitors and predators. Among those affected, the 14 subspecies of cutthroat trout found across western North America have been subject to two extinctions and five listings as Threatened as per the Endangered Species Act.

Lahontan cutthroat trout Oncorhynchus clarkii henshawi have experienced marked reductions throughout their native range in the western Great Basin, U.S. In Pyramid Lake, Nevada, where they were once locally extirpated due to overfishing, water loss, and degraded spawning habitat, Lahontan cutthroat trout have been successfully stocked and managed, though they do not routinely reach their pre-extirpation sizes. With little research to determine the factors influencing Lahontan cutthroat trout in Pyramid Lake, I used a suite of modeling tools and empirical data to elucidate the influence of the current surrounding environment on Lahontan cutthroat trout in Pyramid Lake.

To identify important food web interactions that may affect the availability of food to Lahontan cutthroat trout, I used diet composition and stable isotope analyses of carbon and nitrogen to understand dietary trends. Large Lahontan cutthroat trout (>400 mm TL), along with non-native Sacramento perch Ambloplites interruptus, relied most heavily on fish prey, yet neither species showed signs of cannibalism or preying on the other species. Diet composition and stable isotope analyses also indicated that Lahontan cutthroat trout rely mostly on tui chub Gila bicolor and other fish for food. I also used results from bioenergetic and hydroacoustic analyses to compare the number of tui chub consumed by trout to the number of tui chub in the lake, during the time of this study. Results from these analyses suggest that trout consume well below the number of tui chub available in the lake, indicating that trout are not limited by the availability of tui chub. Lastly, I used a number of biotic and abiotic predictors to determine which factors influence the distribution, and subsequently abundance, of trout in Pyramid Lake and found that biotic factors were very weak predictors of trout distribution, further indicating that trout are not limited by food resources in Pyramid Lake.

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