Lady Bird (Town) Lake - 2003 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 31-page report. For a copy of the complete report, use the download link in the sidebar.

Town Lake was surveyed in 2003 using trap netting and electrofishing. Gill netting, access and habitat surveys were conducted in 2004. A creel survey was conducted in 2002. An aquatic vegetation survey was conducted in 2003. Town Reservoir was surveyed using random sites in accordance with standardized procedures. The 2003-2004 catch-per-unit-effort (CPUE) for species in this summary was compared with CPUE collected in previous Town Lake surveys. This report summarizes the results of those surveys and contains a fisheries management plan for the reservoir based on those findings. Randomly selected sampling sites have been used since 1996, and the change to randomly selected sites should be considered whenever catch-per-unit effort (CPUE) comparisons are made with data collected prior, when fixed sites were used. When largemouth bass data were combined, and compared before and after implementation of a slot length limit on September 1, 2000, electrofishing data collected in November 2000 were considered pre-regulation.

Reservoir Description

Town Lake is a stable-level, 469-acre impoundment of the Colorado River located in the city of Austin, Travis County, Texas. The reservoir runs through the mid-section of the city and was constructed in 1960 for purposes of flood control, municipal and industrial water supply and recreation. The reservoir also serves as a cooling source for steam-electric power generation and is owned and operated by the City of Austin (COA). The reservoir lies within the Edwards Plateau ecological area and has shoreline length of 18.3 miles and a drainage area of approximately 38,240 square miles. Some of the land bordering the reservoir has been developed into city parks. Other shoreline areas have been developed by private businesses. A fish consumption advisory was placed on the reservoir by the Texas Department of Health from 1985 to 1999 because of elevated levels of the pesticide chlordane.

• Angler access: Access for boats launched with trailers was inadequate. Two unimproved boat ramps were available in the lower end of the reservoir. A third ramp (Red Bud Island) in the upper end of the reservoir was improved by the City of Austin in 2000, but was subsequently closed. This ramp was reserved for emergency use only. The closure of this ramp impeded boat angling on the upper end of the reservoir, since gasoline powered motors could not be used as a source of propulsion. The use of gasoline-powered motors was prohibited by city ordinance; however, the use of electric trolling motors was permitted. Accessing the upper end of the reservoir from lower reservoir ramps with an electric motor was impractical. Shoreline access was excellent, although no public fishing piers were available. Improvements in both the condition and location of boat ramps; and, the addition of fishing piers were needed to increase fishing opportunities. This has been a recommendation to the City since 1994 (Terre and Magnelia 1994).
• Aquatic habitat: Only a few acres (6-13 acres, mean = 2% total coverage) of aquatic plants were found in annual vegetation surveys from 2000-2003. Aquatic plant coverage was also sparse in 1993 (Terre and Magnelia 1994) and 1989 (TPWD, unpublished data). Submerged species included water stargrass (Heteranthera dubia) and Eurasian water milfoil (Myriophyllum spicatum). The paucity of aquatic vegetation in this reservoir was puzzling, since the upstream reservoir Austin (Tennant and Magnelia 2001) and downstream Colorado River (Magnelia et al. 2003) had dense stands of aquatic plants. Upstream Austin reservoir had dense stands of the exotic plant hydrilla (Hydrilla verticullata) and the possible establishment of this aquatic plant in Town Lake was of concern. Other habitat of value to cover seeking fishes was overhanging brush, which was found along 68% of the shoreline.

Fish Community

• Prey species: Gizzard shad, bluegill and redbreast sunfish electrofishing CPUE were 70/hour, 255/hour and 131/hour, respectively, which were large increases over previous surveys. All gizzard shad collected in 2003 were of a size too large (>12 inches) for the reservoir’s primary predator fish, largemouth bass, to consume. Size ranges of sunfish species indicated good availability to existing predators. Other prey species included threadfin shad, longear sunfish, spotted sunfish and inland silversides. Few sunfish of quality size (>7 inches) were collected electrofishing, although anglers reported catches of large sunfish from this reservoir. There was some directed fishing effort for sunfishes (3.1%) documented in the 2002 creel survey. Of the fish harvested from the reservoir in spring 2002, 66% (1,988) were sunfish.
• Catfishes: Since the early 1990s Town Lake has had a low-density channel, blue and flathead catfish population (Tennant and Magnelia 2000). In an effort to provide better bank fishing opportunities for catfish species, fingerling (29,988) and advanced fingerling (24,974) channel catfish were stocked in 2000 and 2001, respectively. Gill netting CPUE of channel catfish in 2003 and 2004 was disappointing (2003 = 0.6/net night, 2004 = 0.4/net night), considering the large number of channel catfish stocked. These catch rates were below the mean of the three surveys prior to the stockings (1993, 1996, 1999 mean CPUE = 0.8/net night). Channel catfish CPUE in two gill netting surveys in the 1980’s (1986, 1989) had a mean CPUE of 4.5/net night. The channel catfish population probably suffered from lack of recruitment due to predation from larger largemouth bass, whose density has increased since 1989. The high water clarity (secchi = 4-6 feet) and lack of cover for juvenile channel catfish may have exacerbated predation by largemouth bass. Directed fishing effort for channel catfish in spring 2002 was low (6.6%) and no catch of any catfish species was documented. Based on the poor return of stocked channel catfish additional stocking of channel catfish was not considered.
• Largemouth bass: Largemouth bass were the most sought after sport fish on Town Lake, with 67% of the fishing effort directed at this species. The 2003 largemouth bass total electrofishing CPUE of 127/hour was similar to the previous two surveys (2001, 2002 mean CPUE = 120/hour), but much lower than the mean for surveys from 1986 to 2000 (mean CPUE = 188/hour, N=8). The reduction in total electrofishing CPUE was attributed to decreased numbers of juvenile largemouth bass (<8 inches) (mean CPUE<8 1986-2000 = 117/hour, mean CPUE<8 2001-2003 = 39/hour). Population structure and electrofishing CPUE >14 improved since implementation of the 14- to 21-inch slot length limit. The proportion of adult largemouth bass ≥14 inches increased from a mean of 33% in the three samples (1996, 1999, 2000) prior to implementation of the slot length limit regulation to a mean of 50% in the three samples post-regulation (2001, 2002, 2003). Similarly, post-regulation electrofishing CPUE ≥14 increased from a mean of 26/hour in the three samples pre-regulation to a mean of 41/hour in the three samples post-regulation (Appendix C). The combination of sparse juvenile cover and increased predation, due to increased density of bass >14 inches, may have been responsible for the reduction in juvenile electrofishing CPUE. Eighty-one percent of the bass caught by anglers in spring 2002 were released. Of the legal size bass caught 30% were harvested, which was higher than other area reservoirs with slot length limits (TPWD, unpublished data). The largemouth bass growth rate in 2003 was slower than previous estimates. Largemouth bass reached 14 inches between ages 2 and 3. In previous samples, bass typically reached 14 inches by age 2. Slower growth may have been a result of increased intraspecific competition among adult bass under the slot length limit regulation. In 2003 electrophoresis indicated that 61.9% of the alleles in the largemouth bass population were from the Florida subspecies. Florida largemouth bass (FLMB) influence has steadily increased since 1988, when FLMB influence was only 12.7%. This is the result of reproduction of Kemp’s bass (F1 Florida x Northern largemouth bass) stocked in 1984, 1987, and 1988, (Terre et al. 1993) or the influence of FLMB stocked in 1998. Guadalupe bass are also available to anglers. This species was present in low density.

Management Strategies

Based on current information, the reservoir should continue to be managed with existing harvest regulations. Angler access deficiencies existed on this reservoir and the controlling authority should be made aware of these. Because channel catfish stockings were not successful in increasing gill netting CPUE further stockings were not warranted. Largemouth bass growth was slower than previous samples. Slow growth may decrease the effectiveness of the slot length limit. Growth of this species should be monitored more frequently.

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