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 independent data sets and analytical approaches. A monitoring study conducted by the Galveston District, U.S. Corps of Engineers, revealed lower croaker and brown shrimp abundances for 3 years following the diversion compared to their abundances during 3 pre-diversion years. No changes in the abundances of white shrimp, blue crabs and spot were evident in this monitoring study. The relative distributions of these common epifaunal organisms within the eastern arm of the bay, where the redirected river-mouth empties, did not change following the diversion. Analyses of data (1982–1995) from a long-term trawl-survey programme conducted by the Texas Parks and Wildlife Department (TPWD) indicated that the catches of common epibenthic organisms in the eastern arm of the bay following the diversion were also within the range of historic variation. Species richness decreased significantly at the eastern stations where salinities were lower following the diversion. Commercial fishery landings of most species in the post-diversion period were within the range of historic variation. Oyster landings, however, were consistently low for the 4 years for which post-diversion data were available, probably because previously harvestable reefs were lost to sedimentation and burial close to the redirected river mouth. Prior to the diversion (1970–1991), oyster landings were negatively associated with the same yearʹs maximum annual river flows and the duration of low flows (<14 m3 s−1) 2 years previous (r2=0•63,P<0•001). The regression results indicate that post-diversion increases in freshwater inflows during low flow periods will likely benefit oyster harvests 2 years later Increases to oyster yields may take several more years to be realized and will be contingent upon the success of harvests from the newly created oyster reefs along the northern bay arm.