Spatial and Temporal Variation in Fish Distributions and Assemblage Structure in the Upper San Jacinto River System

M. E. Herbert and F. P. Gelwick, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas 77843-2258

Fishes were collected seasonally (February, May, August, December) for 1 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 flow. 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.

Copyright © 1999
Texas Chapter of the American Fisheries Society
Last modified: 03/03/04 04:15:38 PM