LONGITUDINAL DISTRIBUTION OF FISHES IN AN EAST TEXAS STREAM

The fish populations of Big Sandy Creek were investigated from June 1974-Jan. 1976 to evaluate longitudinal changes. A total of 46 fish species were collected by seining, electrofishing and gillnetting. The number of species per station from 7 stations increased regularly.sbd.by addition of species.sbd.from 22 in the headwaters to 33 at the downstream limits of the study area. Relative abundance for individual species increased in some cases, decreased in others or remained roughly constant in relation to longitudinal position. Among the 24 abundant species, longitudinal change in size composition was detected by length-frequency analysis only in Erimyzon oblongus, which had high percentages of small individuals in headwater streams. Diversity per individual (.hivin.H) was generally greater at downstream stations, but the relationship between fish diversity and longitudinal position was not precise. An unusually diverse headwater assemblage may have been related to soil characteristics of the watershed. Diversity in general seemed to be more highly correlated with depth than with longitudinal position. Calculated heterogeneity (IH) showed that changes in community structure were gradual along a longitudinal continuum. These changes were not related to increase in stream order.