Buchanan Reservoir - 2003 Survey Report
Prepared by C. Craig Bonds and Stephan J. Magnelia
Inland Fisheries Division
District 2-C, San Marcos, Texas
This is the authors' summary from a 34-page report. For a copy of the complete report, use the download link in the sidebar.
Buchanan Reservoir was surveyed in 2003 using trap netting and electrofishing, and in 2004 using gill netting. Structural habitat and angler access surveys were conducted in 2004. Caution should be used when comparing 2004 gill netting catch rates with previous years because sampling location strategies were altered following the white bass length limit evaluation in 2003. This report summarizes the results of these surveys and contains a fisheries management plan for the reservoir based on those findings.
Buchanan Reservoir is a 23,060 acre impoundment of the Colorado River located in Burnet and Llano counties. It was constructed in 1937 by the Lower Colorado River Authority (LCRA) for purposes of hydroelectric power, water supply, flood control, and recreation. The reservoir lies within the Edwards Plateau ecological area. Its drainage area is approximately 31,250 square miles of which 11,900 square miles are probably non-contributing. Shoreline length is approximately 140.6 miles.
- Angler access: Three public boat ramps were available at county parks located in Burnet and Llano counties. Several other privately-owned boat ramps were available to the public for a fee. Public access to shoreline areas was limited; however, access was available at Burnet and Llano County parks, two LCRA-controlled parks, and in some privately-owned lodges.
- Aquatic habitat: The presence of aquatic vegetation was severely limited in this reservoir due to water-level fluctuations, wave action, and rocky substrate. Littoral fish habitat was limited to boat docks, rock ledges and boulders. Pelagic (open-water) habitat was abundant.
- Prey species: Gizzard shad electrofishing catch-per-unit-effort (CPUE) in 2003 was 132.0/hour, which was less than the previous two surveys in 1996 (186.0/hour) and 1999 (262.0/hour), but greater than in 1993 (105.0/hour). The index of vulnerability (IOV) for the gizzard shad sample was 38, which suggested the majority of gizzard shad measured greater than 8 inches, making them less susceptible to predation by most sport fish. The 2003 IOV value was less than previous surveys. Threadfin shad were present in low numbers (2003 = 19.0/hour). This compared similarly to surveys conducted in 1996 (17.0/hour) and 1999 (33.5/hour). Most sunfish species were collected in greater numbers in the 2003 electrofishing survey compared to the previous two surveys conducted in 1996 and 1999. Relative abundance (187.5/hour) of bluegill was much greater compared to previous surveys (average CPUE for 1996 and 1999 = 19.3/hour). Redbreast sunfish were the most abundant species collected (259.0/hour), with fish measuring up to 8 inches present in the sample. Longear sunfish were also collected frequently (187.0/hour). Other sunfish species were sampled in low or moderate numbers: green sunfish, 15.5/hour; redear sunfish, 1.5/hour; and warmouth, 2.0/hour.
- Catfishes: The gill netting catch rate for channel catfish in 2004 (2.7/net night) was less than the average value for survey years 1997 – 2002 (4.8/net night). Sizes ranged from 7 to 25 inches in length, and Wr values typically increased with size above 13 inches. Wr values for larger fish (> 16 inches) averaged greater than 100. Blue catfish were stocked in 1989 and 1990 to further take advantage of this reservoir’s pelagic habitat and preyfish, as well as to diversify angling opportunities. Although blue catfish have developed a self-sustaining population, it can be characterized as one of low abundance. The gill netting catch rate in 2004 (0.7/net night) was similar to previous years (average for years 1997 – 2002 = 0.5/net night; range = 0.2 – 1.1/net night). Fish measuring up to 34 inches in length have been sampled in recent surveys. Flathead catfish were also present in low abundance (0.7/net night), but catch rates in 2004 were consistent with previous years (average for years 1997 – 2002 = 0.6/net night).
- Temperate basses: This reservoir supports a popular white bass fishery (Betsill and Pitman 2002), especially during spring months in the upper reservoir and upstream Colorado River. An experimental 12-inch minimum length limit on white bass was implemented on Buchanan Reservoir (along with several other Texas reservoirs) in 1995. The regulation was intended to provide added harvest protection to fast-growing white bass, thereby increasing population numbers and average sizes of white bass caught by anglers. An intensive evaluation of fisheries data collected from all reservoirs regulated with the 12-inch length limit was conducted in 2002. This evaluation concluded the experimental regulation did not result in increased population numbers or average size of white bass caught by anglers. Additional analysis supported by recent scientific literature indicated that white bass reproductive success was highly correlated with springtime reservoir inflow rates (DiCenzo and Duval 2002; Schultz et al. 2002). The experimental regulation was rescinded in favor of the 10-inch, statewide minimum length limit in 2003. Gill netting catch rate of white bass in 2004 (6.3/net night) was the highest observed since 1997 (8.1/net night). The majority of white bass sampled measured 11 to 13 inches in length. Stronger than average year classes were produced in three successive years (2000 – 2002), contributing to fish numbers within the 11-to 13-inch groups. White bass grew similar to ecoregion averages through age 5, except ages 2 and 3, which exceeded typical growth rates. Striped bass were first stocked into this reservoir in 1977 to introduce a large, pelagic (openwater) sportfish which could fill an ecological niche underutilized by littoral fishes (i.e., black basses and sunfishes). A popular fishery was developed and has been maintained with annual stockings of approximately 250,000 fingerlings. Stockings were interrupted in 2001 because golden alga toxins decimated hatchery production. Due to exceptional hatchery production and an effort to compensate for the previous missing year class, more than double the number of fingerlings were stocked in 2002 (580,900 fingerlings). Striped bass gill netting catch rate in 2004 (CPUE = 2.7/net night) was lower than the average for the previous five surveys (3.9/net night) conducted from 1997 – 2002. Doubling the stocking rate in 2002 did not result in greater catches or suppressed growth of age-2 fish in 2004 compared to prior surveys. Mortality of stocked fingerlings may be density-dependent (Sutton et al. 2000), negating the justification for future stockings at rates greater than normal (10 fingerlings per surface acre). For an unknown reason, survival of stocked fingerlings in 1999 was higher than in most years. Fish from the 1999 year class were the most frequently sampled of all striped bass collected in 2000, 2002, and 2004. Striped bass growth lagged behind ecological region averages in all ages collected. Body condition of adult striped bass has improved slightly since the late 1990s, but relative weights (Wr) continued to indicate thinner than average fish. This relationship was evidenced primarily in fish measuring 20 to 26 inches. Slow growing and thinner than average striped bass suggested that either stock densities of predators were too high or that deficiencies in prey abundance may have existed.
- Black basses: This reservoir historically contained a low-density largemouth bass population (average electrofishing CPUE for years 1996 and 1999 = 29.5/hour). The largemouth bass 2003 electrofishing catch rates for all sizes (94.0/hour) and for stock (> 8 inches) sizes (77.5/hour) were higher than any previous year’s survey. The size structure was dominated by 10-to 13-inch fish, but largemouth bass measuring up to 22 inches were collected. Legal size (> 14 inches) fish were sampled in greater numbers (15.0/hour) compared to past surveys (average CPUE>14 for years 1996 and 1999 = 6.8/hour). Largemouth bass growth rates exceeded eco-region averages for all age classes collected. Two to three years were required for most largemouth bass to reach 14 inches. Florida bass were only stocked in 1978, but their genetic influence continued to persist in the population. Electrophoresis samples collected in 2003 indicated 57% of the alleles represented Florida largemouth bass introgression, and 13% of the sample were pure Florida bass. Guadalupe bass were collected in the 2003 electrofishing survey at a greater rate (21.0/hour) compared to 1999 (7.0/hour), but similar to 1996 (18.5/hour). Sizes collected in these surveys typically ranged from 3 to 15 inches.
- Crappie: Buchanan Reservoir supports a low-density white crappie fishery. The 2003 trapnetting catch rate was 0.3/net night, which was similar to previous years (average CPUE for years 1996 and 1999 = 0.3/net night). The frequency, duration, and magnitude of reservoir water-level fluctuations likely limit crappie production.
Based on current information, the reservoir should continue to be managed with existing regulations. The white bass 12-inch regulation evaluation was completed in 2002, and the length limit decreased to 10 inches. Striped bass angling at this reservoir is popular enough to support several full-time fishing guides. Gill netting surveys should continue to be conducted every two years to monitor population characteristics of these fisheries. Annual stockings of striped bass should be continued, but at a reduced rate of 5 fingerlings per acre.
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