Brook Trout Supression

Brook Trout are a nonnative species present throughout many western states. Brook Trout have been shown to negatively affect or displace many native fishes where they have been introduced. For example, Brook Trout have been shown to hybridize with, and out compete, threatened Bull Trout. Brook Trout have also been shown to displace a variety of Cutthroat Trout subspecies. As a result of the negative effects of Brook Trout on native species, resource managers have expended substantial effort on suppression or eradication of nonnative Brook Trout populations.

Traditional methods of Brook Trout suppression (e.g., mechanical removal, chemical removal) are labor intensive or may result in significant negative results to non-target species. Recently, researchers have suggested that M_YY Brook Trout may be a valuable tool for eradicating unwanted populations of nonnative Brook Trout. M_YY Brook Trout are hatchery-reared Brook Trout that have two Y chromosomes. When M_YY Brook Trout spawn with wild female Brook Trout, the resulting progeny are all males. Analytical models suggest that stocking M_YY Brook Trout into a wild population of Brook Trout can result in an increasingly male-skewed sex ratio. Under ideal conditions, continued M_YY Brook Trout stocking may result in demographic collapse and extirpation of the nonnative population of Brook Trout.

Although modeling exercises have demonstrated that M_YY Brook Trout show promise for managing nonnative Brook Trout populations, field-based studies on the efficacy of this technology are limited. As part of a broader effort organized by the Western Association of Fish and Wildlife Agencies, Oregon Department of Fish and Wildlife has initiated an M_YY Brook Trout study in the Upper South Fork Sprague River, a headwater subwatershed in the Klamath River Basin. Nonnative Brook Trout occupy about 35 kilometers of stream habitat in the Upper South Fork Sprague River, and occur at densities in excess of two Brook Trout per meter in some areas with a population abundance of about 32,000 Brook Trout.

The objective of this study is to evaluate the efficacy of using M_YY Brook Trout as a novel means to suppress or eradicate a nonnative Brook Trout population. Project activities include 1) annual removal of wild Brook Trout, 2) annual stocking of M_YY Brook Trout, 3) annual monitoring of M_YY Brook Trout relative abundance, distribution, and survival, and 4) semi-annual assessment of the sex ratio of the Upper South Fork Sprague River Brook Trout population.

For More Information

Project Contact: Mike Meeuwig