Georgetown Reservoir - 2017 Survey Report

Prepared by Mukhtar Farooqi and Marcos J. De Jesus
Inland Fisheries Division
Austin/San Marcos District

This is the authors' summary from a 36-page report. For a copy of the complete report, use the download link in the sidebar.

Fish populations in Georgetown Reservoir were surveyed in 2017 using electrofishing and in 2018 using gill netting. Historical data are presented with the 2017-2018 data for comparison. This report summarizes results of the survey and contains a fisheries management plan for the reservoir based on those findings.

Reservoir Description

Georgetown Reservoir is a 1,297-acre impoundment (when full) of the North San Gabriel River located in Williamson County, Texas. The dam was constructed in 1980 by the U.S. Army Corps of Engineers (USACE) for flood control, municipal water supply and recreation. Georgetown Reservoir is mesotrophic with a mean TSI chl-a of 57.06, and a 10-year change of +7.11 (Texas Commission on Environmental Quality 2018). Water level varies widely and is replenished via an intra-basin transfer from Stillhouse Hollow Reservoir.

Management History

Important sport fish included White Bass, Largemouth Bass, and Hybrid Striped Bass (Palmetto Bass and Sunshine Bass). Since 2003, Palmetto Bass were stocked annually, except in 2010, 2012, and 2014. Sunshine Bass were stocked instead of Palmetto Bass in 2014. Smallmouth Bass were first stocked in 1978 and more recently from 2006 to 2008, and from 2010 to 2011. However, stocking ceased in 2012 to reduce potential impact to the genetically pure Guadalupe Bass population in the San Gabriel River. Stockings of Blue Catfish were conducted in 2000 and 2001 in an attempt to establish a fishery for this species. Florida Largemouth Bass were stocked in 1986 to improve trophy fish potential. Largemouth Bass have been managed since 1993 with a 14- to 18-inch slot-length limit. An evaluation of that length limit suggested it had been successful in increasing density and angler catch rate of Largemouth Bass greater than 14 inches in length. Angler harvest of sub-slot bass was not sufficient to improve growth under the slot length limit.

Georgetown Reservoir has never been reported to support aquatic vegetation. Since 2007, 30 fish habitat sites were installed and are maintained in partnership with SCHFC to provide cover for fish and allow anglers the opportunity to increase their catch rate by targeting these known sites. In 2017, all 30 existing fish attractor sites were supplemented with Mossback fish habitat structures in partnership with the Sun City Hunting and Fishing Club (SCHFC) and funded by the Brazos River Authority (BRA). Structural shoreline habitat consisted primarily of rocky shoreline and gravel shoreline.

In collaboration with BRA, fish habitat availability, river/reservoir connectivity, and access were assessed at various lake levels at Georgetown Reservoir as a component of the controlling authority’s operating plan for the Brazos River Basin. Threshold recommendations were provided to decrease potential impacts to the fishery during future basin-wide water level manipulations. The Georgetown Reservoir management threshold recommendation was 787 ft above mean sea level (MSL). Overall, littoral areas and woody habitat are significantly compromised below 787 ft above MSL. Two of three public ramps on the reservoir remain functional below 772 ft MSL. All boat ramp functionality is lost below 769 ft MSL, which is 22 ft below conservation pool.

In 2017, Georgetown Reservoir was classified as infested with zebra mussels by Texas Parks and Wildlife Department (TPWD) biologists after discovering larvae in routine water samples and young zebra mussels were found attached to rocks along the shoreline by BRA and TPWD.

Fish Community

• Prey species: Redbreast Sunfish, Gizzard Shad, Bluegill, and Threadfin Shad were the predominant prey species in 2017. Green Sunfish were also available as forage. Catch rates for Redbreast Sunfish and Threadfin Shad had increased since the 2013 survey.
• Catfishes: Blue Catfish, Channel Catfish, and Flathead Catfish were present in low abundance.
• Temperate basses: White Bass and Hybrid Striped Bass were present in the reservoir. White Bass were present in low abundance, fish up to 13 inches in length were present. The catch rate of Hybrid Striped Bass was also low. Individuals collected in 2018 ranged from 7- to 22-inches in length and reached harvestable-size (18 inches) between ages three and four. Body condition of harvestable-size Hybrid Striped Bass was poor.
• Black basses: Largemouth Bass abundance was moderate and population size structure had improved since the 2009 and 2013 surveys. Body condition was low for fish over 14 inches in length. Growth was below average. The largest fish caught was 19 inches in length. Smallmouth Bass and Guadalupe Bass were present in low abundance.

Management Strategies

Most sport fish should continue to be managed with existing regulations. However, as a result of a review of existing harvest regulations for Largemouth Bass statewide, the 14- to 18-inch slot length limit will be replaced by the statewide 14-inch minimum length limit, effective September 1, 2018. Largemouth Bass daily bag will remain at five fish. Hybrid Striped Bass stocking will be terminated in 2018 due to the failure of the establishment of a viable fishery despite consistent stocking since 2003. Standard electrofishing will be conducted in 2021-2022. Fish structural habitat sites should continue to be replenished with brush and artificial habitat structures as needed.

Performance Report as required by Federal Aid in Sport Fish Restoration Act Texas Federal Aid Project F-221-M-3 Inland Fisheries Division Monitoring and Management Program