Biologists utilize a variety of tools to manage and conserve Montana's fisheries resources. In addition to restoring and protecting aquatic habitat, fish stocking is an important management tool for providing recreational fishing opportunities and conserving populations of native fish. While stocking is most commonly used to supplement fisheries in lakes with little or no natural reproduction, it may also be used to replace or "swamp out" introduced fish with native fish species.
Beginning in the 1920's and 1930's many high mountain lakes in the South Fork Flathead drainage were stocked with nonnative rainbow and/or Yellowstone cutthroat trout. Although these lakes are located above the barrier waterfalls and were historically fishless, they contain quality trout habitat and stocking was successful in establishing trout populations. After the creation of Montana Fish, Wildlife & Parks' (MFWP) westslope cutthroat trout broodstock in the mid-1980's, these lakes were stocked exclusively with native fish from this brood source. Frequent stocking (i.e. swamping) and successful natural reproduction of westslope cutthroat trout changed the genetic characteristics of fish in these lakes and, in some cases, resulted in populations of nearly genetically pure westslope cutthroat trout.
As a result, MFWP resumed swamping in Pyramid, George, Woodward and Pilgrim Lakes in summer 2009 and is evaluating this technique as an alternative method to chemical treatment for replacing nonnative trout with westslope cutthroat trout. Pending results from genetic sampling, swamping may also resume in Upper and Lower Three Eagles lakes in summer 2010.
View photos of treatment at Pyramid Lake: