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The Mackenzie Delta region, NWT, has a short growing season and highly seasonal climate, and brown bears (Ursus arctos) there face many challenges obtaining their nutritional requirements. Consumption of meat by brown bears is linked to increases in population density, fecundity, growth and body size. I examined the use of Arctic ground squirrels (Urocitellus parryii), and broad whitefish (Coregonus nasus) as meat sources by Mackenzie Delta brown bears. As a preliminary step, I built an Arctic ground squirrel habitat model, using field-surveyed ground squirrel burrow locations. Using this model, I examined bears selection for Arctic ground squirrel habitat as a population, by sex and as individuals, and linked this to results of stable isotope analysis and site investigations. Bears showed little evidence of Arctic ground squirrel use at the population and sex level, but some individual bears appeared to prey heavily on ground squirrels, particularly during hyperphagia. I also described observations of a brown bear using broad whitefish in autumn, and used telemetry locations to show that other bears may also feed heavily on broad whitefish during hyperphagia. My research provides prey-specific evidence for intrapopulation niche variation among Mackenzie Delta brown bears. / Ecology

Estimates of production and related parameters (growth rate, density, standing crop) were made for populations of mountain whitefish in altered and "unaltered" areas of the Glacksmith Fork and Logan River, UtJh from spring 1975 through summer 1976. Capture records of marked whitefish were also analyzed to describe fish movement and check on assumptions implicit in the population estimator. Mean weights and instantaneous growth rates of whitefish were similar at all sites for comparable size/age groups. Among sites, differences in production per sampling interval and annual production were due mainly to differences in standing crop and/or age structure. Estimates of mountain whitefish density varied by site and season and ranged from 0 to 3,467 fish/ha, with the highest densities occurring during the fall and winter (spawning season) and the lowest during the summer when streamflows were low. Estimates of standing crops of whitefish followed a pattern similar to density. In the sites where fish remained during the summer most production occurred during the spring and summer. A bulldozed reach of the Logan River (including an "unstable" section) had the highest annual production of mountain whitefish (51.85 kg/ha/yr)--almost double the annual production for the same reach when the unstable section was not included (31.85 kg/ha/yr). The highest annual production of whitefish in sites in the Blacksmith Fork River (51.23 kg/ha/yr) occurred in a reach that had been recently dredged but still contained a riffle and pool structure. Annual production of whitefish was low in a recently bulldozed reach (5.47 kg/ha/yr) and an old bulldozed reach (10.08 kg/ha/yr) of the Blacksmith Fork River where suitable habitat (pools and glides) was lacking, especially during the summer months. Mountain whitefish remained or returned to reaches after channel alterations as long as water depth remained sufficient. This study illustrated the necessity of frequent sampling when attempting to evaluate the effects of perturbations on fish populations or in production studies in general.

No description available.

Top predators in aquatic ecosystems often have strong top-down effects on the ecosystem. Northern pike (Esox lucius) has been documented to cause whitefish (Coregonus lavaretus) populations to diverge into different ecomorphs. This can facilitate piscivory in other predators as a novel resource becomes available to them in the form of dwarf whitefish. The aim of this study is to examine whether the presence of pike causes Eurasian perch (Perca fluviatilis) to shift their diet from insectivory to piscivory, and whether this is directly driven by whitefish polymorphism. Stomach contents of 147 perch from lakes with and without pikes were analyzed. The results show that the presence of pike has a clear influence on the diet of the perch. In lakes without pike, perch are mostly insectivorous, and in lakes with pike, they are mostly piscivorous. This diet shift appears to be driven by whitefish availability, as a majority of the diet of perch in pike lakes consisted of whitefish, while none of the fish eaten by perch in non-pike lakes was whitefish. In addition, the results showed that perch undergo the diet shift from insectivory to piscivory at a smaller size when coexisting with pike. This study can be added to the growing body of evidence for the ecological significance of pike.

An important question in determining species composition in a lake is what species has had the chance to reach the lake in the first place. The aim of this study was to examine natural stream connectivity limitations for whitefish (Coregonus lavaretus) between lakes, and to contribute to the development and evaluation of GIS-based methods to answer this question. 497 lakes with identified downstream source lakes, were classified as naturally colonized or introduced whitefish populations, reflecting the possibilities for whitefish to reach the lake naturally. Data of maximum stream slope and stream length between each lake pair was generated by Stefan Blumentrath, NINA. Maximum stream slope was measured on two different resolutions of stream length for comparison, one on slope over 10 m and one over 150m. A subset of lakes was manually examined in geographic information systems and compared to maps and aerial photos to evaluate the data and compare the results with the full dataset. False slope maximums were corrected and streams with much human alteration around a possible natural slope maximum was removed from the small dataset. The two datasets were analyzed using logistic regression models. Akaikes information criterion (AIC) showed that the optimal model, for both datasets, was the one using only slope maximum as predictor, and slope over 150m gave better results than 10m. A k50-coefficient, the value of a predictor that results in 50% probability of colonization, was introduced as an approximate of when the predictor forms a connectivity hinder. The k50-corefficient was estimated to 2,08±0,22° (±standard error) for slope over 150m for the big dataset and 2,58±0,20 for the small. Weaknesses in the data were distinguished and improvements for future fish connectivity studies are suggested.