Management agencies documented a decline in the mountain whitefish (Prosopium williamsoni) population on the Big Lost River, and unscreened diversions were recognized as a potential factor for this decline. Research suggests the Big Lost River mountain whitefish population is genetically unique, and it has been petitioned for protection under the Endangered Species Act. In 2007, a basin-wide synopsis of diversions was conducted to describe relative entrainment and identify diversions that entrained the most mountain whitefish. This larger scaled synopsis facilitated a more precise assessment of entrainment by a subset of diversions in 2008. In 2008, the volume that was diverted and the available stream-flows were assessed to identify correlations between discharge and increased entrainment. Lastly, a stage-structured population matrix model was used to describe the potential effect that entrainment is having on the mountain whitefish population. Entrainment was evaluated in canals using multiple-pass electrofishing depletions in conjunction with block-nets. Entrainment was estimated using simple or stratified random population estimates. Entrainment varied widely among diversions and between water years. Variations in entrainment were attributed to seasonal patterns, population densities, and the physical characteristics of the diversion. A positive correlation was identified (R2 = 0.81) between the number of mountain whitefish entrained and the volume of water diverted annually. I observed substantial numbers of fish entrained by two diversions on the upper Big Lost River. I illustrate how reducing entrainment at these diversions will increase recruitment to adulthood and increase the viability of the population overall.

European whitefish (Coregonus lavaretus) forms reproductively isolated sub-populations with different body sizes in the lakes where northern pike (Esox lucius) exists. It has been hypothesized that the initial reproductive isolation between ecotypes arises through size-assortative mate choice or because small and large individuals arrive to the spawning grounds at different times. To test these hypotheses, I caught and measured both breeding whitefish pairs and singular whitefish on the spawning grounds over the spawning season. There was no correlation between the lengths of males and females in breeding pairs, indicating that mate selection was random with respect to body size. There were no significant differences in body length between sampling dates during the field period in November 2021, suggesting that there is no divergence in spawning time between large and small individuals. Thus, neither of the two hypotheses were supported. Interestingly, males have significantly higher amount of breeding tubercles than females according to my results, which could be a selective factor in mate selection. However, the function of the tubercles is yet poorly understood.

Electrophoretic patterns on polyacrylamide gels of blood serum proteins from 74 mountain whitefish (Prosopium williamsoni Girard) were examined for differences as they pertained to two geographically isolated populations, age, and sex. Serum samples were acquired from two supposedly isolated populations, the lower Provo River and the lower Weber River. Comparisons among gels were made on the basis of protein distribution as indicated by number of fractions and their density. Serum proteins showed marked intraspecific differences between the males as well as the females of each population. No variations were found which could be attributed to degree of maturity. Definite pattern differences were observed between the sexes of each population. Individual pattern variations within each group studied were observed.

Comprehensive population studies in the field of fisheries are in great demand. Many of our fishable waters are being changed, and we need to be able to predict the results of these habitat alterations. We must know how to include beneficial modifications in readjustments of habitat in order to create a fishery or prevent destruction of an existing one. The acceptable situations for good fish production in large mountain streams are not well-knowno A fishery can be properly managed only if the manager has sufficient knowledge of the carrying capacity of the habitat, the survival and mortality of the population, and the movements of the fish within the population. My study is an attempt to answer some of these questions about the self-sustaining populations of brown trout (Salmo trutta fario Linnaeus) and mountain whitefish (Prosopium williamsoni Girard) in a 5-mile section of Logan River, Utah.

Ecological traits of the endemic Bear Lake whitefish Prosoopium abyssicola and the Bonneville whitefish prosopium silonotus were investigated. Spatial distributions indicated distinctive differences in depth contour preference. Catch per unit effort data indicated that Bonneville whitefish prefer shallow depths and warmer water temperatures, whereas Bear Lake whitefish prefer deep, cold water. Diet differences between the two species were large. Differences in both age distribution and growth rate patterns were also observed. The Bonneville whitefish population was predominantly composed of juvenile age classes. Very large adults reached ages of 12-14 years. Bear Lake whitefish exhibited a different population structure with few young fish and larger proportions of older age classes. Some of these fish were aged over 35 years old. Both analyses suggest that the population structure of each species is the result of a stable or growing population.

Whitefish populations around the world have long been difficult to categorize taxonomically. The whitefish of Bear Lake, Utah/Idaho are no exception. There are three recognized species of Prosopium that are endemic to the lake. Two of these species, Prosopium spilonotus and Prosopium abyssicota, have previously been indistinguishable outside of spawning times. Previous studies have proposed additional taxa within P. spi/onotus to further complicate the identification among these taxa. Morphological characteristics were quantified on wild whitefish from Bear Lake, as well as from progeny reared in the laboratory from the wild adult fish. The purported taxa were separated in the field using the best characteristics presented in previous studies, and the progeny were reared separately in these groups. Otolith aging was also done on the wild adult fish to understand the age structure of the spawning populations. Results from otolith aging and morphological analyses on the laboratoryreared fish indicated that there is only one taxonomic group of P. spilonotus. By using scale counts, it was determined that P. spilonotus and P. abyssicola can be distinguished from each other with considerable reliability.

The upper optimum temperature for embryonic development of mountain whitefish is 6 C, and for the post yolk sac stage is 9 to 12 C. The need to know effects on all stages in the life cycle in cases of thermal pollution is demonstrated. Abnormalities caused by thermal pollution in hatched larvae were agape jaws, coloboma or fissure of the eye, monophthalmia or the presence of only one eye, monomicrophthalmia or the presence of one small eye and one case of twinning. High mortalities of eggs occurred at 9 C and higher. Study of the energy expenditure, by the dry weight method showed an energy deficit at 6 and 9 Cat the time of hatching. The larvae are then fully capable of offsetting these deficits by feeding. The oxygen consumption method showed an energy deficit during hatching at 6 C, but failed to show any at 9 C. The efficiency of yolk conversion generally decreased as development progressed. No group effect in active metabolism was observed in the underyearlings. The electrochemical method of measuring oxygen consumption of embryos gave a cumulative value which was 6.8% higher than values obtained using the manometric method. This increase is attributed to the increase in activity of embryos caused by the nature of the experimental set up. Active metabolism and scope for activity were high at 9 and 12 C compared to 6 and 15 C. Standard metabolism steeply increased at 1:5 C. There was very little scope for activity at 15 C. The embryonic development was similar to that of other whitefishes. The mountain whitefish requires more thermal units to reach corresponding stages than does the lake whitefish, after the stage when the blastodisc is prominantly raised up on the yolk.

Broad whitefish, Coregonus nasus, is an important subsistence fish species in Arctic North America, yet virtually nothing is known regarding the genetic population structure of Nearctic populations of this species. In this thesis, microsatellite DNA variation was assayed among 1213 broad whitefish from 47 localities throughout North America, with emphasis on the Mackenzie River system, Northwest Territories. Specifically, I examined geographic variation in allele frequencies to assess how historical factors (Pleistocene glaciations) have shaped the current structuring of genetic variability and population differentiation. Microsatellite data was also used to resolve the relative contributions of broad whitefish populations to subsistence fisheries in the Mackenzie River system. Overall, broad whitefish exhibit relatively high intrapopulation microsatellite variation (average 12.29 alleles/locus, average HE = 0.58) and there were declines in these measures of genetic diversity with distance from putative refugia suggesting historical factors, namely post-glacial dispersal, have influenced current microsatellite variation. Interpopulation divergence was low (overall FST = 0.07), but the main regions assayed in this study (Russia, Alaska, Mackenzie River and Travaillant Lake systems) are genetically differentiated. Strong isolation-by-distance among samples was resolved when including only those populations occupying former Beringia, but not when assaying those at the periphery of the range in the Mackenzie River system, suggesting that broad whitefish in the Mackenzie system have not occupied the region long enough since their invasion post-glacially to have approached equilibrium between gene flow and drift. Mixture analysis indicated that most fish from the lower Mackenzie River subsistence fishery originated from the Peel River, highlighting the importance of this tributary. Additionally the mixture analysis provides evidence for a putative riverine life history form in the Mackenzie River. My results indicate that glaciation and post-glacial colonization have been important in shaping the current genetic population structure of North American broad whitefish. They also illustrate the utility of microsatellite DNA to delineate population structure and patterns of genetic diversity in recently founded populations in addition to resolving contributions to fisheries. My data also support the hypothesis that there are several designatable units of conservation among broad whitefish populations and that management strategies should be implemented accordingly.

Presence of Triaenophorus crassus Forel in the flesh of lake whitefish (Coregonus clupeaformis (Mitchill)) and cisco (C. artedi Lesueur) can be an important economic problem for commercial coregonine fisheries. This study was initiated during the development of native fisheries in northern Quebec. Coregonine populations from 6 lakes of the Nottaway watershed were sampled to determine infection patterns of T. crassus in relation to age and size of fish, and to document interlake differences in prevalence and number of T. crassus. Interspecific and interlake differences in the infection dynamics of T. crassus were described in relation to capsule types, sizes and plerocercoid conditions. Infection dynamics were also investigated with age of fish. All coregonine populations were infected with T. crassus, and cisco more so than lake whitefish where the two species co-occurred. Prevalence and number of T. crassus were independent of fish age and size in most lake whitefish populations. Number of T. crassus increased with fish age and size in all cisco populations, but prevalence increased only in the populations from the largest lakes. Interlake differences in prevalence and number of T. crassus were detected for both coregonine species, and were related to feeding behaviour of the fish and lake biophysical characteristics. Heavy infections in one lake whitefish population were mainly associated with piscivory. Interspecific and interlake differences in the infection dynamics of T. crassus were also observed. Differences in the proportions of capsule types, sizes, and plerocercoid conditions suggest that population turnover of T. crassus in cisco is faster than in lake whitefish. In contrast to previous studies, plerocercoid condition was found to be independent of capsule size. Coregonine populations, which did not differ in prevalence and number of T. crassus, showed some differences in the proportions of capsule types, sizes and plerocercoid conditions, suggesting

Broad whitefish, Coregonus nasus, is an important subsistence fish species in Arctic North America, yet virtually nothing is known regarding the genetic population structure of Nearctic populations of this species. In this thesis, microsatellite DNA variation was assayed among 1213 broad whitefish from 47 localities throughout North America, with emphasis on the Mackenzie River system, Northwest Territories. Specifically, I examined geographic variation in allele frequencies to assess how historical factors (Pleistocene glaciations) have shaped the current structuring of genetic variability and population differentiation. Microsatellite data was also used to resolve the relative contributions of broad whitefish populations to subsistence fisheries in the Mackenzie River system. Overall, broad whitefish exhibit relatively high intrapopulation microsatellite variation (average 12.29 alleles/locus, average HE = 0.58) and there were declines in these measures of genetic diversity with distance from putative refugia suggesting historical factors, namely post-glacial dispersal, have influenced current microsatellite variation. Interpopulation divergence was low (overall FST = 0.07), but the main regions assayed in this study (Russia, Alaska, Mackenzie River and Travaillant Lake systems) are genetically differentiated. Strong isolation-by-distance among samples was resolved when including only those populations occupying former Beringia, but not when assaying those at the periphery of the range in the Mackenzie River system, suggesting that broad whitefish in the Mackenzie system have not occupied the region long enough since their invasion post-glacially to have approached equilibrium between gene flow and drift. Mixture analysis indicated that most fish from the lower Mackenzie River subsistence fishery originated from the Peel River, highlighting the importance of this tributary. Additionally the mixture analysis provides evidence for a putative riverine life history form in the Mackenzie River. My results indicate that glaciation and post-glacial colonization have been important in shaping the current genetic population structure of North American broad whitefish. They also illustrate the utility of microsatellite DNA to delineate population structure and patterns of genetic diversity in recently founded populations in addition to resolving contributions to fisheries. My data also support the hypothesis that there are several designatable units of conservation among broad whitefish populations and that management strategies should be implemented accordingly.