TEXAS FRESH-WATER FISH ASSEMBLAGES FOLLOWING 3 DECADES OF ENVIRONMENTAL-CHANGE

In 1953, C. Hubbs and colleagues surveyed fishes from a large number a nd variety of freshwater habitats throughout the state of Texas. Thirt y-three years later, he replicated sampling at 129 of these sites with in the Red, Sabine, Neches, Trinity, Brazos, Colorado, Guadalupe, San Antonio, Nueces, and Rio Grande drainages. Care was taken to match ori ginal sampling effort, times, and dates at each location. Relative pro portional abundances of families showed numerous changes from 1953 to 1986 within the ten basins. Mantel tests comparing family abundances i n 1953 and 1986 datasets showed little overall change statewide. Sites in the eastern half of the state that did not contain marine species showed less significant positive covariation between early and recent datasets than those in western Texas. Rank plots of species diversity (H') for the two regions of the state showed a consistent trend of dec reased diversity over time in eastern Texas. A similar plot for west T exas showed decreased diversity with time, but only within species-poo r assemblages. The analyses reveal reductions in biological diversity on a local scale, but also reveal relative stability in statewide and regional ichthyofaunas. Despite the encouraging large-scale trends, se veral Texas fishes went extinct and others are threatened as a result of local habitat disturbances, including alteration of instream flow, eutrophication, and exotic species introductions.