Trophic Status, Energetic Demands, and Factors Affecting Lahontan Cutthroat Trout Distribution in Pyramid Lake, Nevada

The progression of human development across the landscape has caused declines to both terrestrial and aquatic fauna. Many fishes, specifically native salmonids, have seen reductions in both population size and geographic distribution resulting from reduced habitat, overharvest, and the introduction of non-native predators and competitors. A native North American fish particularly hard hit by these types of actions, Lahontan cutthroat trout, are now limited to less than 10% of their historical habitat, and currently occupy only half of the lakes that they once occupied. In Pyramid Lake, Nevada, where Lahontan cutthroat trout were once locally extinct, due to overfishing, water loss, and loss of spawning habitat, stocking and proper management have helped to maintain a healthy fishery. However, since their reintroduction, little research has been conducted to determine which, if any, factors limit the production of Lahontan cutthroat trout in Pyramid Lake, one of their last remaining strongholds. For my thesis, I used a number of analytical tools, accompanied with field data, to assess whether Lahontan cutthroat trout in Pyramid Lake are potentially limited by food availability. To understand dietary trends of Lahontan cutthroat trout and other prey fish in the lake, I used diet composition from three different seasons throughout the year, as well as stable isotope data, which give insight to long-term dietary trends. These results suggest that trout, and other predatory fish, primarily rely on tui chub, an abundant native prey fish, for food. I combined these dietary data with temperature and growth rate data to estimate the number of tui chub consumed by trout on an annual basis. These results, coupled with abundance estimates from acoustic sampling, allowed me to compare the number of chub consumed by trout to the number of chub available within the lake. Consumption and abundance estimates indicated that trout consume less than one third of the standing biomass of tui chub on an annual basis. Results from these analyses suggest that trout consume well below the number of tui chub available in the lake, and indicate that trout are not limited by the availability of tui chub. In addition, I used data on physical and biological characteristics of the Pyramid Lake environment to understand which factors influence trout distribution and abundance. This approach confirmed the previously described results that suggest trout do not appear to be limited by food resources. These results will help aid in the management and conservation of this important sport and subsistence fishery, and add to the existing body of research on Lahontan cutthroat trout throughout their native range