Laboratory feeding experiments showed that sympatric Dolly Varden charr (Salvelinus malma) were able to locate and consume prey targets at lower irradiance levels than sympatric cutthroat trout (Salmo clarki clarki) but their acuity was poorer. Reaction distance (RD) of both species to artificial and natural prey targets increased as irradiance level increased from a visual irradiance threshold (VIT), an irradiance level below which prey targets were not detected visually (3.0 x 10¹⁴ photons m⁻²s⁻¹ for charr and 3.0 x 10¹⁵ photons m⁻² s⁻¹ for trout) to a saturation irradiance level (SIL) which produced the maximum RD (3.0 x 10¹⁶ photons m⁻² s⁻¹ for charr and 6.6 x 10¹⁸ photons m⁻² s⁻¹ for trout). The VIT and SIL were independent of prey type and prey characteristics in both species. At all irradiance levels greater than the VIT of trout, the RD of trout exceeded that of charr for the same prey type. At a given irradiance level the largest RD in both species occurred in the presence of red irradiance followed in decreasing order by green, yellow and blue irradiance. Reaction distance of trout and charr increased with increases in prey size, movement and contrast. The percent increase in RD was greatest in trout. Between the VIT and the SIL the percent increase in RD was greater at higher irradiance levels in both species. At or above the SIL the percent increase in RD was constant. The central portion of retinas of trout and charr from sympatric and allopatric populations were examined by light microscopy. The two trout populations had a similar density of cone cells and higher than either charr population. Sympatric charr had the lowest cone cell density and allopatric charr intermediate density. Rod cell density showed the opposite trend, being highest in sympatric charr, lowest in sympatric and allopatric trout and intermediate in allopatric charr. The cone cell mosaic, consisting of a regular array of double and single cones, was the same in all four populations. Both cone types were smallest in the two trout populations, largest in the sympatric charr population and intermediate in allopatric charr. The degree of retinal summation was greatest in sympatric charr, least in the trout populations and intermediate in allopatric charr. In summary, histological studies indicated that sympatric and allopatric trout possessed the highest level of visual acuity while sympatric charr were the most sensitive to low irradiance conditions. Foraging velocity of sympatric trout and charr increased as irradiance increased reaching a maximum at the SIL of each species. From foraging velocity, RD and information on the diel irradiance regime in Loon Lake I estimated the volume of water searched visually for two natural prey types by trout and charr on a mid-summer day. Below the VIT, only charr were able to locate and consume buried prey targets, presumably by employing their chemosensory system. Differences in visual and non-visual feeding behaviour in sympatric trout and charr and in retinal structures of sympatric and allopatric trout and charr are generally as expected based on field studies of their vertical distribution and feeding habits. / Science, Faculty of / Zoology, Department of / Graduate

Sympatric populations of Dolly Varden (Salvelinus malma) and cutthroat (Salmo clarki clarki) are spatially and food segregated in Loon Lake, British Columbia. Dolly Varden are found mainly in the lower water column, while cutthroat are found in the middle and upper water column. Zooplankton, the only major prey type found in both diets, appear more important to the cutthroat. The purpose of this study was to determine whether this segregation was due to behavioural interactive processes or genetically based selective processes. This was investigated by the segregation and transferral of the members of the two populations to separate fishless lakes. In addition, field studies examined selective feeding on zooplankton and laboratory studies compared the feeding behaviour and abilities of Dolly Varden and cutthroat on three different types of zooplankton. Little change occurred during the two year sampling period in either the diet or the vertical distribution of the two species, an indication that the fish were not interactively segregated. However, the physical and biological characteristics of the lakes may have reinforced, at least initially, previous behaviour patterns. As a result, more time may be required to properly assess the final results. Laboratory results indicate that primarily Chaoborous larvae and secondarily Daphnia pulex were the preferred prey types to both fish predators, mainly because of their poor escape response when compared to that of Diaptomus kenai. The abundance of these prey types in the diet of lake-caught fish was generally in accordance with the laboratory preferences. These results also demonstrated that cutthroat were more efficient planktivores than were Dolly Varden. / Science, Faculty of / Zoology, Department of / Graduate

Strawberry Reservoir, Utah is an 8.000 acre lake at the elevation of 7,550 feet; it has a maximum depth of 52 feet and an average depth of 18 feet. The supply of cutthroat trout eggs used to replenish and distribute this trout throughout the state are taken from two spawning traps located on reservoir tributaries. Because it has not proven economical to raise cutthroat to a larger size than newly hatched fry, it is at this site they are planted. Because of competition, predation, and lack of space the planting back of fry to maintain the fishery and spawning run presents a serious problem. Tributaries are at carrying capacity from being closed to fishing and the reservoir supports a tremendous population of trash fish; mainly the Utah chub, Gila atraria (Girard); yellow perch, Perca flavescens (Mitchell); redside shiner, Richardsonius balteatus (Cope); mountain sucker, Pantosteus delphinus Cope; and dace. Rhinichthys osculus Cope. The rainbow trout, Salmo gairdneri Richardson. and the cutthroat trout dominate the game fish population. It has been the policy of the Utah State Department of Fish and Game to trap and artificially spawn spawn every possible fish, leaving most of the spawning ground unused. This cost, plus the unknown advantage, if any, of artificial over natural reproduction led to the study of the possibilities of natural reproduction for replenishment of the cutthroat trout in the reservoir.

A study was undertaken to investigate the application of tissue culture and histochemical banding techniques normally used in mammalian studies to fish cells and to examine the mechanisms of chromosome evolution and speciation in salmonids by comparing the chromosomes of the hybrid to those of the parental types. The application of banding techniques was generally unsuccessful in revealing bands, though quinacrine staining did reveal the presence of two fluorescent spots in the vicinity of the centromere. These were thought to be heterochromatic blocks, possibly related to the high incidence of centric fusion or fission in salmonids. Results of chromosome analysis showerd a higher incidence of acrocentric chromosomes in the hybrid than in either parental type which together with evidence for tetraploidization in salmonids is consistant with some of the requirements for species diversification. Conditions of divergence in chromosome evolution and changes which would have to occur in the hybrid for divergence from the parental types to take place are discussed. The results of a preliminary electrophoretic examination of LDH and esterase activity tended to confirm hybridization.

Climate change and anthropogenic effects have vastly reduced Westslope Cutthroat Trout (Oncorhynchus clarki lewisi, WCT) habitat throughout their range, including the Colville National Forest in northeastern Washington where this study was conducted. Many native salmonid populations have declined in abundance since the early 1900s due to a variety of climate- and human-driven forces. Westslope Cutthroat Trout are especially sensitive to habitat loss or degradation and to climate change. Together, climate change, habitat degradation, and non-native salmonid invasions are contributing to increasingly fragmented WCT populations. Ongoing and predicted future warming trends are expected to further fragment these populations and isolate them in headwater stream reaches, with populations in the spatial margins of their distributions facing greater risk. Native salmonid populations are often separated or isolated by natural or artificial upstream migration barriers (i.e., waterfalls, culverts, etc.). Prior to continuing conservation and management actions targeting WCT, it is imperative to understand habitat requirements of this keystone species in fragmented areas. Field survey data were collected in the summer of 2015 on channel geomorphic characteristics and WCT presence/absence in 26 streams located in the Colville National Forest. A clear spatial separation was observed between Eastern Brook Trout (Salvenius fontinalis, EBT) and WCT above four culvert road crossings and the habitat in both of these areas was compared statistically to identify explicit differences. This dataset was also analyzed using logistic regression modeling to determine the best habitat predictors of the presence of isolated WCT populations existing upstream of these crossing. In general, stream habitat in the Middle and South Forks of Mill Creek had low large substrate, high fine sediments, and exhibited pool-riffle channel morphology. Pool habitat supporting isolated WCT was significantly smaller, in terms of volume and surface area, than pool habitat supporting sympatric populations of WCT and EBT, largely due to the headwater nature of channel units supporting isolated WCT populations. Additionally, due to the extreme drought conditions during 2015, stream flow was substantially diminished in the study area causing these reaches to be highly fragmented and largely disconnected from the rest of the stream channel. Fine sediments were generally higher in headwater reaches supporting isolated WCT, including in pools and riffles, which was unexpected, mainly because they exist above sediment delivery points in the longitudinal extent of the system. Logistic regression analysis indicated that the presence of isolated WCT populations was primarily positively associated with an increase in large wood and boulders, and negatively associated with increasing gravel, bedrock, habitat unit length, depth, and width (Significant x2, R2=0.174, misclassification rate = 14.9%, α=0.05). The final model correctly predicted 37.5% of isolated WCT presence observations and 96.5% of the WCT/EBT presence observations significantly better than by chance alone (k=0.81). This model, in fact, may be useful in identifying limited habitat due to the fragmented nature of the channel units supporting IWCT. Large wood and boulders were positively correlated to WCT presence, likely because both are important in the formation of pools and cascades. Channel unit length, width, depth, active channel width as well as gravel and bedrock substrates, were all negatively associated with WCT presence. This suggests that isolated WCT are primarily associated with small headwater cascades with complex shelter, which may provide greater thermal and predation refuge compared to shallow glide or large pool habitats. Future model analysis should include additional habitat variables such as water temperature, stream gradient, and species interactions to strengthen the prediction of Westslope Cutthroat Trout presence. Overall, I concluded that differences in stream habitat above and below blocking culverts are not driving Westslope Cutthroat Trout distributions in the study area due to confounding factors such as the presence of problematic barriers and small sample size. I also conclude that future conservation and management decisions specific to WCT should prioritize complex cascade habitat in headwater stream reaches because of the type and quantity of habitat they may provide, especially during severe drought or low flow conditions.

Genetic diversity of two salmonid species, Dolly Varden (Salvelinus malma) and coastal cutthroat trout (Oncorhynchus clarki clarki) in Prince William Sound, Alaska were examined at multiple spatial scales with three molecular markers. Pleistocene glaciers covered what is now Prince William Sound 8,000- 12,000 years ago and both species colonized the region subsequently. Because these species have different migratory behavior and historic ranges I expected to see different patterns of genetic diversity within Prince William Sound. Haplotype frequency and nucleotide diversity in sixteen mitochondrial DNA (mtDNA) restriction fragment enzymes combinations in Prince William Sound were higher in Dolly Varden than in coastal cutthroat trout, which were close to fixation. Low estimates of these measures in coastal cutthroat trout may reflect a founder effect resulting from colonization of this region from a single glacial refuge (Cascadia) and low dispersal capacity. To examine if genetic diversity in coastal cutthroat trout was higher in areas of glacial refuge, three additional locations from throughout their distributional range were examined with the same restriction enzymes. Haplotype frequency and nucleotide diversity were lower in areas that were glaciated than estimates of the same measures in a glacial refuge. Again, founder effects during colonization of the three glaciated sites may account for these results. Genetic variation of Dolly Varden and coastal cutthroat trout was also examined within and among populations in Prince William Sound with microsatellites and allozymes. The pattern of genetic variation in coastal cutthroat trout was complex. There was lower genetic diversity within populations that were recently colonized following recent de-glaciation (150-350 ybp). Genetic diversity among some coastal cutthroat trout populations was high, which possibly reflects restricted migration. In other trout populations there was low diversity among populations, possible reflecting historic gene flow. In Dolly Varden, genetic variation among anadromous populations in Prince William Sound was low. There were large differences among resident and anadromous populations. These data provide information for the management for both species, which may reduce the risk of the loss of genetic diversity within local populations. / Graduation date: 2003

An intensive creel census and marking program was conducted in 1969 and 1970 to make possible population estimates and estimates of harvest of cutthroat trout in the Snake River in Teton County, Wyoming. Stock density determinations made in one of the five study areas provided an estimate of 400 and 992 cutthroat trout, eight inches or more in length, per mile of stream in 1969 and 1970 respectively. Harvest data provide an estimate of 5,207 and 5,903 cutthroat trout harvested in 1969 and 1970 respectively. The harvest estimates obtained in this study are not comparable to those made in 1967 and 1968 due to a difference in the methods used in obtaining these data. The catches of cutthroat trout per hour in 1969 and 1970 were calculated to be 0.31 and 0.30 respectively, These relatively low success rates are coincident with the fluctuating volume flows of the Snake River. Average lengths, condition factors, and catch per unit effort do not indicate significant changes in the fishery from past years.

Nine hemoglobins have been isolated from the blood of cutthroat trout. All nine hemoglobins bind oxygen cooperatively and appear to be tetramers with molecular weights of -64,000. The oxygen equilibria and subunit structures of the purified hemoglobins were studied. In addition, the red blood cells of cutthroat trout were examined for the presence of ATP and GTP, which are known to be physiological modulators of hemoglobins in fishes. Five hemoglobins with isoelectric points from 9.1 to 7.0 are classified as cathodal hemoglobins. These five hemoglobins have identical oxygen binding properties by the criteria tested. All have oxygen equilibria which are unaffected by protons and ATP and essentially independent of temperature, with overall enthalpies of oxygenation ~0. Two hemoglobins with isoelectric points near 6.5, classified as a nodal hemoglobins, have oxygen binding properties distinctly different from those of the cathodal hemoglobins. Both are characterized by a Root effect, displaying non-cooperative oxygen binding and low oxygen affinity at pH 6.2. ATP causes a large reduction in the oxygen affinity without affecting the cooperativity of oxygen binding. GTP has a similar but slightly larger effect on both hemoglobins. The oxygen equilibria of the anodal hemoglobins are temperature dependent, with the oxygen affinity being reduced as temperature increases. The overall enthalpy of oxygenation is -14 kcal/mol for both hemoglobins. The two remaining hemoglobins represent only a small percentage of the total hemoglobin. These hemoglobins are tentatively designated as embryonic hemoglobins based primarily on a comparison of their properties to those observed for hemoglobins from newly-hatched rainbow trout (Iuchi, I. (1973) Comp. Biochem. Physiol. 44B, 1087-1101). These two hemoglobins have isoelectric points near 5.9 and oxygen binding properties similar to those of the cathodal hemoglobins. With the possible exception of one of the embryonic hemoglobins (for which globins were not obtained), all the hemoglobins are composed of two different types of globin chains. Six are ∝_2 β_2 tetramers, while two of the cathodal hemoglobins are hybrid tetramers of the type 〖∝∝'β〗_2 and ∝∝'ββ. Red blood cells of cutthroat trout contain both ATP and GTP, suggesting that, in contrast to rainbow trout, both nucleotides may be important physiological modulators of hemoglobin oxygen affinity in this fish.

Stream restoration has become a popular management tool for attempting to increase and/or restore fish populations by improving habitat. A section of the Strawberry River, Utah recently underwent a stream restoration project, where the main goals of the project included increasing spawning activity, rearing potential, and resident populations of Bear Lake cutthroat trout Oncorhynchus clarkia utah. The impact of the restoration project on cutthroat trout was investigated by first characterizing preferred habitat for different life stages, investigating habitat as a limiting factor in the system, and then assessing the quality of available habitat by comparing restored/unrestored sections of stream and pre-restoration/post-restoration of the same sections of stream. Results indicated cutthroat trout in the Strawberry River preferred faster water velocities, shallower depths, moderate substrates sizes, and riffle habitat types for spawning. In contrast, juvenile and adult life stages preferred deeper sections of stream, the presence of cover, and pool habitat types. Limiting factor analyses suggested spawner abundance may be limiting in the Strawberry River and maximum daily temperatures during the summer may be the strongest limiting habitat factor for juvenile and resident adult cutthroat trout. Restoration generally appeared to initiate a shift towards more favorable habitat, especially in terms of increasing near-bed velocity and increasing the proportion of preferred substrate sizes for spawning, and increasing the percentage of pools for juvenile and resident adult life stages. The potential benefits of the restoration remained somewhat ambiguous, a result of relatively small differences observed between study reaches, limited pre-restoration data, high spatial and inter-annual variability within and among control study reaches, and the inherently delayed reaction of ecological responses to physical changes from restoration. However, these issues can be resolved through continued monitoring. Long-term monitoring would allow for the accounting of natural variability to further tease out differences resulting from restoration and differences resulting from natural fluctuations. Additional monitoring would also capture long-term responses, which has the potential to be significant considering the relatively slow response of riparian vegetation to restoration. This study also provides a baseline dataset and template for future long-term monitoring efforts.

The distribution of Lahontan cutthroat trout Oncorhynchus clarki henshawi was assessed in a high-desert stream in southeastern Oregon where beaver Castor canadensis are abundant. Longitudinal patterns of beaver ponds, habitat, temperature, and Lahontan cutthroat trout age group distribution were identified throughout Willow Creek. Three distinct stream segments were classified based on geomorphological characteristics. Four beaver-pond and four free-flowing sample sections were randomly located in each of the three stream segments. Beavers substantially altered the physical habitat of Willow Creek increasing the depth and width of available habitat. In contrast, there was no measurable effect on water temperature. The total number of Lahontan cutthroat trout per meter was significantly higher in beaver ponds than free-flowing sections. Although density (fish/m��) showed no statistically significant (P<0.05) increase, values in beaver ponds were two-fold those of free-flowing sections. Age-1 and young-of-the-year trout were absent or in very low numbers in lower Willow Creek because of elevated temperatures, but high numbers of age-2 and 3 (adults) Lahontan cutthroat trout were found in beaver ponds where water temperatures reached lethal levels (>24��C). Apparently survival is greater in beaver ponds than free-flowing sections as temperatures approach lethal limits. / Graduation date: 2003