Trout biomass and stream habitat relationships in the white mountains area, east-central arizona

We surveyed stream habitats and lish populations at 243 stations among 21 highelevation trout streams in the Apache-Sitgreaves National Forest and White Mountain Apache Reservation in the White Mountains area, east-ccntral Arizona, from 1986 to 1990. The While Mountains urea makes up most of the historic habitat for Apache trout Oncorhynchus apache. listed by the U.S. federal government as a threatened species. A generalized linear model relating trout biomass and stream, riparian, and geomorphic habitat variables was developed (R² = 0.68). Among the significant variables in the systematic components of the model, bank damage by ungulates was the only variable solely influenced by land management practices. We attribute the bulk of the bank damage to domestic cattle grazing and conclude that better cattle management is necessary for improvement of trout habitats. Another significant variable, channel width, was partly dictated by geomorphology but was also correlated with bank damage by ungulates. Three significant variables in the model were completely geomorphic (station elevation, channel type, riparian area width) and thus not useful for management purposes. The model coefficient of determination was relatively low in comparison with some other trout-habitat models developed in the western USA. This result may indicate that trouts in our study area arc limited less by physical habitat than by climatic events or predation and competition influcnccs.