CHANGES IN FISH ASSEMBLAGES IN EAST TEXAS STREAMS FROM 1953 TO 1986

摘要

Fish assemblages from 58 sites in east Texas were sampled in 1953 and 1986. Change in assemblage structure over this one-third century time span was analyzed using Detrended Correspondence Analysis. Two sites in the lower reaches of Trinity River adjacent to Trinity Bay were distinct from all other east Texas sites in both years, and showed a large change in assemblage composition that corresponded with presence of large numbers of estuarine species in the 1986 collections. Analyses of the remaining 56 sites detected change in east Texas fish faunas at three spatial scales: regionally, within individual river basins, and at specific sites. At the regional scale, DCA revealed that fish assemblages in the five river basins (Red, Sabine, Neches, Trinity and Brazos) were relatively distinct in 1953, but showed almost complete overlap in 1986. This increased overlap was the result of increased variation in assemblage structure in 1986 within each river basin. Fifteen individual sites exhibited change equivalent to a 50% (or greater) turnover in assemblage composition. These changed sites were from all river basins sampled and their trajectories in multivariate space did not occur in any single direction, suggesting that changes were influenced by local rather than basin-wide conditions.