In this study we plan to assess, for the first time, the impacts of hybridization on stream ecology. We will test the hypothesis that hybrids will exhibit a metabolic rate intermediate to rainbow trout, Oncorhynchus mykiss (relatively high), and cutthroat trout, Oncorhynchus clarki lewisi (relatively low). From this we will investigate whether a physical barrier is required to maintain a pure O. clarki lewisi population or can a higher metabolism also limit the upstream movement of hybridization providing headwater refuges.

In cases where hybrids are not limited in movement, are the O. clarki lewisi populations adaptive enough to allow for co-existence to evolve through a combination of resource partitioning and reproductive isolation.

In addition we will assess the degree to which morphological assessment can be used to distinguish between O. clarki lewisi, O. mykiss and hybrids and determine the status of pure O. clarki lewisi populations within this study area.