Limestone Reservoir - 2004 Survey Report

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Prepared by John E. Tibbs and Michael S. Baird
Inland Fisheries Division
District 2-B, Waco, Texas

This is the authors' summary from a 45-page report. For a copy of the complete report, use the download link in the sidebar.

Limestone Reservoir was surveyed in fall 2004 by boat electrofishing, winter 2004 by trap netting, and spring 2005 by gill netting. A year-long creel survey was conducted from June 1 2004 to May 31 2005. This report summarizes survey results and contains a management plan for the reservoir based on those findings.

Reservoir Description

Limestone Reservoir is a 13,680-acre reservoir within the Navasota River system in Limestone, Robertson and Leon counties, Texas. The reservoir was created in 1978 and is operated by the Brazos River Authority. Primary land use surrounding Limestone’s 130 miles of shoreline is agriculture. The reservoir is eutrophic with water transparencies ranging from 1 to 2 feet, and average and maximum depths of 16.5 and 43 feet respectively. Water uses include power plant cooling and recreation. Shoreline habitat 53consisted of native emergent and submergent vegetation, flooded timber, and man-made bulk heading at the time of sampling. Bank fishing is limited to a few day-use areas on the reservoir. Boat access remains adequate and handicap facilities remain poor. Further information about Limestone Reservoir and its facilities can be obtained by visiting the Texas Parks and Wildlife web site and and navigating within the fishing link.

Aquatic Vegetation

Limestone reservoir contains a high diversity of aquatic vegetation species. Although vegetation coverage of 20 to 30% is considered beneficial to fisheries, a few exotic plant species are known for their ability to spread rapidly and inundate a water body. Limestone reservoir has two of these species: hydrilla and water hyacinth. Hydrilla coverage was extensive in the early to mid 1980’s, but has been less in recent years. Hydrilla was the only species of concern within the reservoir in 1997, covering an estimated 19 surface acres. From 2000 through 2005, only trace concentrations of hydrilla were observed.

Water hyacinth was observed upstream of the FM 3371 bridge during the August 2000 survey, and its coverage was estimated at 7.0 acres. Coverage was 3.5 acres in April 2001, however numerous individual plants were observed drifting within the main stem reservoir at this time. In 2002, 37.5 acrs were observed throughout the reservoir. In 2003 and 2004, 35 acres were observed throughout the reservoir. During periods of wind, large numbers of plants can be observed drifting across the lake. Water hyacinth was previously a problem in the reservoir in 1983, but was eradicated by the following severe winter.

Water hyacinth is the most serious threat to Limestone reservoir currently because of its floating nature and ability to colonize any stretch of shoreline. To date, no aquatic vegetation control has been slated for Limestone reservoir, despite communications with the Brazos River Authority (BRA) and frequent complaints from landowners. A well-attended public meeting was held in 2003 to present options for private citizens wishing to control vegetation along their shoreline. Annual vegetation surveys are recommended to further monitor these two problematic plant species.

Fish Community

• Prey species: Major prey species captured during fall electrofishing consisted of gizzard shad, threadfin shad, and bluegill. The catch per unit of effort (CPUE) for gizzard shad during fall 2004 electrofishing was 215.5 fish/hour, which was within the range of the previous four surveys (94.0 fish/hour in 2001 to 264.5 fish/hour in 1997. The index of vulnerability (IOV) (i.e., the percentage of individual gizzard shad less than 8 inches total length, thought to be vulnerable to largemouth bass predation) was 62, well below the average for the previous four surveys (89) (DiCenzo et al. 1996). However, the majority of the gizzard shad population was still available as prey. Threadfin shad CPUE was 1,608.5 fish/hour, indicating high availability of small clupeid prey. The bluegill catch rate was 56.0 fish/hour, similar to the average for the four previous surveys (50.5 fish/hour). The size structure of the bluegill population remains skewed toward smaller individuals, with a proportional stock density (PSD) and relative stock density of eight-inch fish and greater (RSD-8) both zero. In fact, bluegill greater than six inches in length have not been collected in Limestone reservoir in the past five surveys.
• Catfishes: Channel catfish are the most abundant ictalurid species found in Limestone Reservoir. The gill netting catch per unit of effort (CPUE) for channel catfish in spring 2005 was 3.3 fish/net night, similar to the 2001 (3.6 fish/net night) and 1997 (4.1 fish/net night) surveys. Channel catfish PSD was 33 and RSD-12 was 96, indicating good numbers of legal fish in the population. Relative weights (Wr’s) for most size classes ranged between 95 and 105 indicating good condition. Age structures showed most of the fish to be between 4 and 8 years old, with very few younger than 4. Catfishes, all species combined, were the third most sought-after group, with 0.7 hours/acre of directed effort in the 2005 creel survey. Those anglers seeking catfish caught fish at a rate of 0.7 fish/hour and harvested fish at a rate of 0.3 fish/hour. FAST modeling for this species yielded questionable results, likely because of extreme fluctuation in year class strength, numerous year classes, and high variability in growth within year classes. Some results are available in Appendix C. The blue catfish gill netting catch rate (2.1 fish/net night) was similar to the 2001 sample (2.3 fish/net night) and higher than the three surveys previous to that. It appears that fish from the stockings in 1996 and 1998 have not spawned yet. Condition was good overall with Wr’s ranging from 90 to 100. Most collected fish ranged from 6 to 9 years of age. FAST modeling for this species yielded questionable results, likely because of extreme fluctuation in year class strength, numerous year classes, and high variability in growth within year classes. Some results are available in Appendix C.
• White bass: The gill netting catch rate for white bass in spring 2005 samples was 6.2 fish/net night, which was within the range of previous surveys (4.3 fish/net night in 2001 to 18.1 fish/net night in 1994). Size structure continues to be dominated by larger individuals, with a PSD of 98 and an RSD-12 of 67. Relative weights calculated for the 2005 sample ranged from 95 to 105, indicative of average condition. Growth rates were determined from a total sample of 369 fish. Fish reached legal size early in their second year of life. Recruitment appears consistent. Anglers spent 0.4 hours/acre seeking white bass in the 2005 creel survey, the least of any game fish species in the reservoir. White bass were caught at a rate of 2.0/hour and harvested at a rate of 0.9/hour. A total of only 0.78 fish/acre were harvested, indicating low exploitation. Modeling using FAST (Appendix C) determined that total annual mortality was 48.6%, but that fish could reach a theoretical maximum age of 9 years. Recruitment was fairly consistent as determined by catch-curve analysis.
• Largemouth bass: The largemouth bass catch rate for the fall electrofishing sample was 51.5 fish/hour, which was withing the range of previous surveys (37.0 fish/hour in 1991 to 129.0 fish/hour in 1994). A PSD of 63 and an RSD of 39 were similar to previous surveys. Most relative weights were around 105, indicating better than average condition. The percentage of Florida largemouth bass (FLMB) alleles (31.7) was similar to the average of the previous three surveys (28.5) for which there were electrophoretic results. The percentage of pure Florida bass was 3.3, higher than any of the previous three surveys. Early growth rates are good, with fish exceeding legal size on average at the end of their second year of life. However, growth appears to plateau by age-4 at about 18.5”. Whether this is real or a result of gear bias is not known. Recruitment appears consistent. Anglers spent 2.0 hours/acre seeking largemouth bass, catching 0.7/hour and harvesting 0.2/hour. It should be noted here that all of the largemouth bass marked as harvested in the creel were actually being held by tournament anglers prior to weigh-in. In fact, not a single largemouth bass was harvested by an angler with the purpose of taking it home to eat. Interestingly, l;argemouth bass was the most sought after species in the reservoir. Still, modeling using FAST (Appendix C) determined that total annual mortality was 50.8%, and that the theoretical maximum age was only 7.8 years. Recruitment was very consistent, as determined by catch curve analysis.
• Crappie: The catch rate of white crappie in trap nets has varied widely in recent surveys. In 2004, CPUE was 5.1 fish/net night, down from 9.9 fish/net night in 2000. Crappie are known to experience variable year-class strength and this was shown to occur from age data (Appendix C). For example, 214 age-1 fish were collected, but only 1 age-2 fish. The relative weights ranged from 100 to 110, indicating better than average condition. Growth was good as fish reached the minimum length limit of 10”, on average, by the end of their second year of life. Anglers spent 1.4 hours/acre seeking crappie, making it the second most sought after species group. Crappie were caught at the relatively high rate of 5.2/hour and harvested at a rate of 1.6/hour. Modeling using FAST (Appendix C) determined that total annual mortality was high at 66.2%, with a theoretical maximum age of only 4.4 years. Recruitment was quite variable as determined by catch curve analysis.

Management Strategies

Limestone Reservoir should continue to be managed with the existing bag limits and minimum length regulations. The 2005 creel indicated low to nonexistent harvest on major gamefish species.

Performance Report as required by Federal Aid in Sport Fish Restoration Act Texas Federal Aid Project F-30-R-30 Statewide Freshwater Fisheries Monitoring and Management Program