M.E. Herbert and F.P. Gelwick, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843

Abstract. Fishes were collected seasonally (Feb, May, Aug, Dec) for one year in tributaries of the West Fork (13 sites) and East Fork (9 sites) of the San Jacinto River. All sites were within or bordering the Sam Houston National Forest. West Fork tributaries were isolated from each other by Lake Conroe. Fishes were collected in a 100-m stream reach by seining and backpack electrofishing. A total of 42 species were collected. Species distributions and assemblage structure were related to the seasonal variation in discharge and other instream habitat conditions and physico-chemical water conditions. Species richness decreased across sites with increasing seasonal variation in discharge in both forks. Preliminary analyses show that Spearman's Rank correlation and Morisita's index decrease with increasing seasonal variation in flow in the unimpounded East Fork system. West Fork sites above Lake Conroe show either no relationship or show increases with increasing variation in discharge. The coefficient of variation of population abundance estimates between seasons declined with variation in discharge in both forks, but showed a much stronger relationship in the East Fork streams. This suggests that patterns of seasonal assemblage stability and persistence have been influenced by the presence of Lake Conroe. Lake Conroe may buffer seasonal changes in assemblage structure in tributary streams through a stable source of potential colonizing fishes. Other results also indicate that the presence of Lake Conroe influences some species' presence or absence and relative abundance in tributary streams.