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Thesis (Ph. D.)--Montana State University--Bozeman, 2004. / Title from PDF t.p. (viewed on June 12, 2006). Chairperson, Graduate Committee: Thomas McMahon. Includes bibliographical references.

Since their discovery in Yellowstone Lake in 1994, Lake Trout (Salvelinus namaycush) have been the object of an intensive gillnet suppression program due to their predation on native Yellowstone Cutthroat Trout (Oncorhynchus clarkii bouvieri). Managers are also interested in targeting early life stages to augment suppression. A benthic sled was used to sample for Lake Trout eggs at 24 locations, hypothesized to be spawning sites, that encompassed a range of depths, slopes, and substrate composition to determine the location and characteristics of spawning sites in Yellowstone Lake. Lake Trout eggs were collected at seven sites, five of which had not been previously confirmed as spawning sites. Habitat characterization at these sites indicate Lake Trout spawning in Yellowstone Lake is limited to areas with rocky substrate, but is not constrained to areas with interstitial spaces or contour breaks as is seen within the species' native range. Lake Trout fry were captured around Carrington Island, an additional spawning site in Yellowstone Lake, in 2014 and 2015. These fry were significantly larger at each developmental stage, consumed more food beginning at earlier stages, and were captured much later into the summer than fry captured at a spawning site in Lake Champlain. The lack of potential egg and fry predators in Yellowstone Lake could be driving these differences in spawning site selection and fry behavior. This information will allow managers to identify additional spawning locations for suppression and evaluate the impact their efforts might have on the Lake Trout population in Yellowstone Lake.

I examined the relationship between landscape attributes and population differentiation among lake trout (Salvelinus namaycush) populations inhabiting a hierarchically structured dendritic freshwater system in northern Labrador, the Kogaluk River system. Samples were collected from a total of 10 lakes which differed in size, elevation, level of connectivity, and position within the system. STRUCTURE analysis provided evidence of significant population structure within the system likely attributed to a varying degree of asymmetric gene flow. Gene flow estimates were generally low and appear to be influenced by the presence of waterfalls as well as geographic distance. Isolation by distance tests coupled with decomposed pairwise regression analysis suggest a significant influence of geographic distance on population differentiation. Mantel testing also showed that population differentiation is significantly correlated with the position of waterfalls. Estimates of effective population size reveal significantly smaller population sizes in headwater lakes, a pattern not attributed to lake size.

One-hundred and three bottom samples taken at Fish Lake, Utah from July, 1969 to June, 1970 were analyzed to determine the abundance, distribution, and standing crop of the bottom fauna species and to relate their availability to the amount of food eaten by the trout. Twenty-three taxa, representing three phyla and 19 families were collected. An amphipod, Gammarus limnaeus, in the littoral zone, and a tubificid worm, Rhyacodrilus coccineus, in the sublittoral and profundal zones, were the most abundant species. All 23 species were unevenly distributed in the littoral zone, whereas, only eight were found in the sublittoral and five in the profundal zones. Standing crop of invertebrates was greatest in the littoral zone in November, 1969. Analysis of the stomach contents of 135 lake trout and 1105 rainbow trout revealed that bottom invertebrates contributed only small amounts to the diet; differing from previous studies where bottom invertebrates were of major importance in the trout's diet.