EFFECT OF THE COLORADO RIVER DIVERSION ON MATAGORDA BAY EPIFAUNA

The effect on epifauna of the Colorado River diversion, which restored river flow to Matagorda Bay, Texas, U.S.A. was assessed using three i ndependent data sets and analytical approaches. A monitoring study con ducted by the Galveston District, U.S. Corps of Engineers, revealed lo wer croaker and brown shrimp abundances for 3 years following the dive rsion compared to their abundances during 3 pre-diversion years. No ch anges in the abundances of white shrimp, blue crabs and spot were evid ent in this monitoring study. The relative distributions of these comm on epifaunal organisms within the eastern arm of the bay, where the re directed river-mouth empties, did not change following the diversion. Analyses of data (1982-1995) from a long-term trawl-survey programme c onducted by the Texas Parks and Wildlife Department (TPWD) indicated t hat the catches of common epibenthic organisms in the eastern arm of t he bay following the diversion were also within the range of historic variation. Species richness decreased significantly at the eastern sta tions where salinities were lower following the diversion. Commercial fishery landings of most species in the post-diversion period were wit hin the range of historic variation. Oyster landings, however, were co nsistently low for the 4 years for which post-diversion data were avai lable, probably because previously harvestable reefs were lost to sedi mentation and burial close to the redirected river mouth. Prior to the diversion (1970-1991), oyster landings were negatively associated wit h the same year's maximum annual river flows and the duration of low f lows (< 14 m(3) s(-1)) 2 years previous (r(2) = 0.63, P < 0.001). The regression results indicate that post-diversion increases in freshwate r inflows during low flow periods will likely benefit oyster harvests 2 years later Increases to oyster yields may take several more years t o be realized and will be contingent upon the success of harvests from the newly created oyster reefs along the northern bay arm. (C) 1998 A cademic Press.