In stochastic environments such as streams, fishes must persist under a range of environmental conditions. When factors in the stream environment suddenly change following a disturbance, a new environmental state is realized. Fishes generally respond at both the individual and population level, and biological systems with the capacity to survive under the new environmental conditions persist. These biological responses to the changed environment provide insights about the relative state of the ecosystem. For example, in headwater streams, isolated populations of coastal cutthroat trout reflect conditions in their environment. Growth of individuals and population demographics are two characteristics that can shift in response to environmental change.
Wildfire, a largely terrestrial perturbation, is broadly recognized as an agent
of disturbance and ecological change in forested biomes, but the links to subsequent
changes in aquatic systems are less well documented. Wildfire causes a number
of changes in stream environments, including increased solar radiation, increased
water temperatures, change in water chemistry, increased erosion and sedimentation,
and increased water yields. At the basin scale, the influence of wildfire is
theoretically most profound in headwater streams because of the tight linkage
between aquatic and terrestrial ecosystems. These abiotic changes resulting
from wildfire will elicit biological responses, many of which are poorly understood.
Current wildfire management plans are often based solely on theories, models, and extrapolation of forest management data. Studies that relate post-fire environmental conditions to ecological responses of stream fishes are lacking, although the two are hypothesized to be strongly connected. These gaps in understanding impede our ability to formulate comprehensive management plans. By observing growth and demographics of coastal cutthroat trout, we are attempting to understand how post-fire conditions influence fish in headwater streams at the basin scale. Specific objectives of this study are to investigate 1) the relationships between wildfire severity, abiotic stream characteristics, and relative growth rates of coastal cutthroat trout at the landscape scale, and 2) annual trends in the distribution, relative abundance, and population age structure of coastal cutthroat trout following wildfire.
