Austin Reservoir - 2004 Survey Report
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Prepared by Stephan J. Magnelia and C. Craig Bonds
Inland Fisheries Division
District 2-C, San Marcos, Texas
This is the authors' summary from a 20-page report. For a copy of the complete report, use the download link in the sidebar.
Austin Reservoir was surveyed in 2004 and 2005 using gill netting, trap netting and electrofishing. Access and habitat surveys were completed in 2004. The 2004-2005 catch-perunit-effort (CPUE) for species in this summary was compared with CPUE collected in previous Austin Reservoir surveys. This report summarizes the results of those surveys and contains a fisheries management plan for the reservoir based on those findings.
Austin Reservoir is a stable level 1,599 acre riverine type impoundment of the Colorado River located in the heart of the City of Austin (COA). It was constructed in 1893 for purposes of hydro-electric power, municipal water supply, water conservation and recreation. The reservoir is used to pass water from Travis Reservoir downstream. The reservoir is operated by the Lower Colorado River Authority (LCRA) and COA. The reservoir lies within the Edwards Plateau vegetational area and has a drainage area of approximately 38,240 square miles. Land surrounding the reservoir is highly developed with commercial and residential property bordering most of the shoreline.
Aquatic Vegetation Management
Aquatic vegetation management has been a part of the Austin Reservoir ecosystem for over fifty years. A history of aquatic vegetation management efforts through 2000 are found in Tennant and Magnelia (2001). The reservoir has been drawn down 12 feet annually from December to February since 2001 in an attempt to control aquatic vegetation. In 2003 and 2004 triploid grass carp (8,125) were stocked as part of a plan to control hydrilla (Hydrilla verticullata). The effects of these control measures on total aquatic vegetation and hydrilla coverage are currently being assessed.
- Prey species: Gizzard shad and bluegill electrofishing catch rates were 109.3/hour and 97.3/hour, respectively. Twenty seven percent of the shad were vulnerable to predation, as expressed by the index of vulnerability (IOV), which calculates the percentage of gizzard shad <8 inches in length (DiCenzo et al. 1996). This is higher than previous years. Threadfin shad are also available as forage. Both gizzard and threadfin shad catch rates were higher in 2004 than those historically encountered on this reservoir. The bluegill population was mainly composed of small individuals with 76% £4 inches, indicating good availability to predators. The redbreast sunfish catch rate was 142.7/hour with 49% of the individuals £4, which indicated good availability as forage.
- Catfishes: Gill net catch rates for channel (0.4/net night) and blue (0.2/net night) catfish were extremely low. Blue, flathead and channel catfish have historically been present in low density.
- Black basses: Austin Reservoir contained a high quality, moderate density largemouth bass population. Many large bass have been caught in this reservoir since the early 1990’s, including six bass over 13 pounds, which were entered into the Texas Parks and Wildlife Sharelunker program. Based on these catches, it is regarded as the area’s best trophy bass fishery. Total electrofishing catch rate (110.0/hour) and population structure have remained similar since 2001. In 2004, 30% of the adult largemouth bass collected were 14 inches or greater, compared with 40% in 2003 and 34% in 2002. Growth has remained almost constant over time with fish reaching legal size between age 2 and 3. Largemouth bass body condition is good with relative weights typically above 90. In 2002, only 19.2% of the individuals sampled were pure Florida largemouth bass. Florida largemouth bass were stocked in 2003 and 2004 in an attempt to increase Florida bass influence. Guadalupe bass are present in extremely low density.
Aquatic vegetation coverage in the 10-40% range will be important for maintaining the quality largemouth bass fishery that currently exists. Aquatic vegetation coverage will be evaluated at least annually. This reservoir has been designated a trophy bass fishery. Florida bass stocking will be recommended when the percentage of pure Florida bass in the population falls below 20%.
Performance Report as required by Federal Aid in Sport Fish Restoration Act Texas Federal Aid Project F-30-R-29 Statewide Freshwater Fisheries Monitoring and Management Program