Different life histories of brook trout populations invading mid-elevation and high-elevation cutthroat trout streams in Colorado

Brook trout (Salvelinus fontinalis), native to eastern North America, have invaded many montane cold-water systems of Western North America, and these invasions are implicated in the decline of native cutthroat trout (Oncorhynchus clarki). If fisheries biologists are to be effective in managing brook trout invasions, demographic models that predict invasion success will need to incorporate life history variation in different environments. We tested whether brook trout populations invading streams at 2 different elevations varied in life, history characteristics that influence population dynamics and potential invasion success. In the high-elevation stream (3195 in), water temperatures were colder and brook trout apparently grew more slowly (i.e., had shorter lengths-at-age), became sexually mature 2 years later. and had life spans 2 to 3 times longer than those in the mid-elevation stream (2683 in). This flexibility in life history may allow brook trout to maximize their chance of establishment and invasion success among elevations. We propose that in mid-elevation streams fast growth and early maturity maximize fitness and can lead to rapid establishment and high population growth rates. In high-elevation streams, slow growth, later maturity, and a long reproductive life span may allow brook trout to successfully establish populations in these marginal habitats where recruitment is often poor.