Effects of Timber Production on Coastal Cutthroat Trout Distribution and Genetic Heterozygosity

Joshua J. Latterell, Master's Project

To protect stream habitat quality, timber production activities in Washington State are restricted near streams bearing salmonids. State and federal management agencies, conservation groups, tribal authorities, and representatives of the private timber industry are currently examining cost-effective approaches to accurately delineate salmonid distribution across large spatial scales. The most feasible approach to date utilizes a logistic regression model based on remotely-sensed drainage characteristics to predict the upstream extent of salmonid distribution (Fransen et al. 1997). This model was developed with data from streams draining land managed for timber production. Since timber production activities are known to alter habitat variables related to salmonid distribution, model predictions may not be accurate for unmanaged streams. Further research is needed to determine whether similar interactions of stream-scale physical habitat parameters limit the upstream extent of salmonid distribution in streams draining ancient forests and land managed for timber production.

Allopatric coastal cutthroat trout Oncorhychus clarki clarki typically represent the upstream extent of salmonid distribution in the Pacific Northwest. Habitat fragmentation currently threatens the long-term persistence of a majority of isolated coastal cutthroat trout populations, which are important to the genetic diversity of the subspecies (Shiozawa and Evans 1994; Hilderbrand 1999). Genetic characteristics of headwater populations are poorly understood. By altering population size and connectivity, timber production activities may alter the genetic heterozygosity (H) of headwater populations. These alterations may affect the long-term population viability.

This project is intended to fill significant gaps in our understanding of the effects of timber production on the distribution and genetic characteristics of coastal cutthroat trout in headwater streams of the Pacific Northwest. Specifically, this research will determine 1) whether the upstream limit of coastal cutthroat trout distribution is associated with similar combinations of channel gradient and drainage area in managed and wilderness drainages, 2) whether timber production activities alter processes that regulate the genetic heterozygosity of coastal cutthroat trout, and 3) whether headwater stream populations of coastal cutthroat trout in a common basin represent single or multiple gene pools.

Using a GIS, 80-100 study sites with similar geology and elevations are being selected from the two major sub-basins of the Snohomish River (Snoqualmie and Skykomish Rivers). Electrofishing surveys will be used to delineate the upstream extent of fish distribution, where habitat surveys will be conducted upstream and downstream. We will also estimate coastal cutthroat trout abundance, and take fin-clips for genetic analyses of populations in managed and wilderness streams. Microsatellite analyses may be used to estimate genetic heterozygosity.

Our field season will last from mid-March to late July 2000.

• Fransen, B., S. Needham, G. McWethy, and V. Kim. 1997. Development of a process to delineate potential fish habitat based on physical characteristics measured at the upper extent of known fish distributions. Unpublished manuscript.
• Hilderbrand, R. H. 1999. Movements and conservation of cutthroat trout. Dissertation Abstracts International Part B: Science and Engineering 59(8), 3846 pp.
• Shiozawa, D. K. And R. P. Evans. 1994. Mitochondrial haplotype diversity in cutthroat trout. 1994 Annual Symposium of the Desert Fishes Council. Hendrickson, D. A. ed.