Genetic Investigation of Snake River and Yellowstone Cutthroat Trout

The relationship between Yellowstone cutthroat trout, Oncorhynchus clarki bouvieri, and Snake River finespotted cutthroat trout, 0. clarki behnkei, was examined with two mitochondrial DNA fragments, COl and ND5. No variation was found within either subspecies, and just one (out of 1069) nucleotide differed between subspecies. Thus, these subspecies are very closely related. Samples for this study were obtained from hatcheries, and may not be representative of the subspecies. 0. c. bouveri were sampled from the Clark Fork Hatchery, in Powell, WY, and 0. c. behnkei were sampled from the National Fish Hatchery in Jackson, WY. Further sampling, preferably from natural populations, is needed to more thoroughly survey the variation within subspecies, and to measure the differences between subspecies.

Greater predation by Double-crested Cormorants on cutthroat versus rainbow trout fingerlings stocked in a Wyoming river

We studied the relative vulnerability of Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri) versus rainbow trout (Oncorhynchus mykiss) stocked as fingerlings in the North Platte River, Wyoming, to Double-crested Cormorant (Phalacrocorax auritus) predation. Cutthroat fingerlings decreased as a fraction of the population from stocking in late June to electrofishing surveys in the following October and March. In contrast, the fraction of cutthroat fingerlings among tagged fingerlings eaten by cormorants collected on the river was significantly greater than that in the population when originally stocked. More limited data from pellets regurgitated by adult cormorants at a nearby colony and in American White Pelicans (Pelecanus erythrorhynchos) collected on the river showed the same trend toward greater percentages of cutthroat trout being consumed than were present among trout stocked. There were no differences in cormorant predation rates on the Eagle Lake strain of rainbow trout reared under shaded versus partially shaded conditions, or between Auburn and Bar BC strains of Snake River (Yellowstone) cutthroat trout. On the North Platte River, cutthroat trout fingerlings were more susceptible to cormorant predation than rainbow trout of similar size that were stocked simultaneously.

Life-History Organization of Yellowstone Cutthroat trout (Oncorhynchus clarki bouvieri) in Yellowstone Lake

Life-history organization of the cutthroat trout (Oncorhynchus clarki) may be viewed at various levels, including species, subspecies, metapopulation, population, or individual. Each level varies in spatial scale and temporal persistence, and components at each level continually change with changes in environment. Cutthroat trout are widely distributed throughout the western United States, occurring in such diverse environments as coastal rivers of the Pacific Northwest and interior streams of the Great Basin. During its evolution the species has organized into 14 subspecies with many different life-history characteristics and habitat requirements. Within subspecies, organization is equally complex. For example, life-history traits, such as average size and age, migration strategy, and migration timing, vary among individual spawning populations of Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri) in tributary streams of Yellowstone Lake. Understanding the effects of human perturbations on life-history organization is critical for management of the cutthroat trout and other polytypic salmonid species. Loss of diversity at any hierarchical level jeopardizes the long-term ability of the species to adapt to changing environments, and it may also lead to increased fluctuations in abundance and yield and increase the risk of extinction.