UBC Theses and Dissertations
Stream habitat, and rainbow trout (Oncorhynchus mykiss) behavioural, physiological, and population responses to streamside timber harvesting in the central interior of British Columbia Mellina, Eric
Interactions between forestry practices and the physical and biological processes occurring in small streams are numerous and potentially complex. There exists a relatively large body of literature, consisting of studies conducted primarily in coastal regions, that has shown how streamside timber harvesting can affect the physical habitats of streams and their fish populations. Although much of the future timber supply from the northern hemisphere is expected to come from interior, temperate regions, there is a relative dearth of knowledge about fish/forestry interactions in these regions. This thesis seeks to address some of these gaps in our knowledge by reporting on fish/forestry research conducted in north-central B.C., a temperate region characterized by moderate hillslopes and a continental climate. I examined stream habitat, and population and physiological stress responses of rainbow trout (Oncorhynchus mykiss) to streamside clear-cut logging. Increased stream temperatures and sedimentation, and decreased habitat complexity (which have all been associated with streamside harvesting), could be stressful to stream-dwelling fish. Data on stream habitat and trout physiological and population responses were collected in 1996 from 15 streams classified into 3 categories: unharvested (control), "newly logged" (clear-cut to both stream banks within the last 5-10 years), and "older logged" (clear cut more than 25 years ago). I could detect no effects of timber harvesting on stream habitat variables (the number and size of pools, and the size of undercut banks), nor on rainbow trout density, biomass, or acute stress responses (comprising plasma Cortisol, glucose and chloride concentrations). The only chronic stress response that was apparent was that trout from streams in the two logging categories had higher condition indices when compared to trout from streams in the control category. Multiple regression analyses using streams from all categories revealed that trout density, biomass and stress levels were related to habitat variables. Differences between coastal and interior regions (steep versus moderate hillslopes, maritime versus continental climates) may have resulted in harvesting impacts that were less severe than those found in coastal streams, and may have contributed to the general lack of physical and biological responses to streamside harvesting. During 1997-2001,1 examined the temperature responses of two small, lake-headed streams to clear-cut logging, and assessed the role of temperature on the emergence and growth of juvenile rainbow trout. Lake-headed streams cooled as they flowed downstream, whether the adjacent riparian canopy was intact or had been harvested. Changes in daily maximum and minimum temperatures, as well as daily fluctuations, were relatively modest in response to streamside harvesting. Furthermore, emergence of rainbow trout fry was accelerated, and growth was enhanced, in the two warm treatment streams when compared to a colder, unharvested stream. The observed cooling trends were likely due to groundwater inputs and the presence of headwater lakes, and this was supported by predictions from an empirical model constructed using data from 11 independent streams. Lastly, during 1997-1999 I examined seasonal long-range movement patterns of streamdwelling rainbow trout in the same three lake-headed streams that were used as part of the temperature study. My objectives were to determine if stream-dwelling trout in this region are sedentary or move long distances, and to assess if any linkages existed between these behaviours and environmental characteristics. Trout undertook long-range (>370 m) dispersions towards lakes primarily during the spring seasons. The cessation of long-range movements generally coincided with the onset of summer low flow conditions. Trout remained largely sedentary during the summer and fall seasons, despite temperatures that approached lethal levels for this species and recent streamside harvesting which resulted in increased suspended sediment concentrations. The management implications are that sedentary trout may remain fully exposed to harvesting-mediated alterations to stream habitats. Based on size distributions and movement patterns, these trout appeared to remain within stream environments for approximately 1-2 years before dispersing to larger waterbodies.
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