Impacts of Golden Alga on Fish Populations in Reservoirs of the Upper Colorado River and Brazos River Basins, Texas

Several reservoirs in the Upper Colorado River (UCR) and Brazos River (BR) basins have experienced toxic blooms of golden alga (GA) and associated fish kills since 2001, potentially impacting their popular fisheries. The objectives of the present study are to: 1) determine if fish populations are impacted by toxic GA blooms in a similar manner between river basins, 2) determine species differences in tolerance to toxic GA blooms, and 3) assist ongoing development of best management practices for impacted reservoirs. We used Before-After-Control-Impact analysis on catch-per-unit-effort (CPUE) data collected during TPWD fisheries surveys (1990-2010). This analysis determines whether fish populations have declined and not recovered following an impact, a pattern termed “sustained” disturbance. Unfortunately, the dissimilar sampling schedules among reservoirs did not allow determination of “pulsed” disturbances, where populations exhibit an initial decline and then recover. In the UCR, white bass, bluegill, river carpsucker, freshwater drum, and channel, flathead and blue catfishes all exhibited sustained disturbances; whereas gizzard shad, longnose gar and white crappie did not. In the BR, blue catfish was the only species that appeared to exhibit a sustained disturbance. Largemouth bass did not exhibit sustained disturbances in either system based on total CPUE; however, proportional size distribution showed a sustained disturbance in the UCR but not in the BR, indicating dominance by smaller size classes in the UCR that may be the result of stocking. Results from this study indicate that: 1) not all basins affected by GA are impacted in the same manner; namely, the incidence of sustained disturbances in the UCR are far greater than in the BR; 2) populations of certain species are more tolerant than others; and 3) current management plans may be sufficient to maintain populations of most species in the BR, whereas new management options may benefit recovery of fisheries in the UCR.