Granger Reservoir 2016 Survey Report (PDF 954.8 KB)
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Granger Reservoir - 2016 Survey Report
Prepared by Muhktar Farooqi and Marcos J. De Jesus
Inland Fisheries Division
San Marcos/Austin District
This is the authors' summary from a 30-page report. For a copy of the complete report, use the download link in the sidebar.
Fish populations in Granger Reservoir were surveyed in 2016 using electrofishing and trap netting, and in 2017 using gill netting. Historical data are presented with the 2016-2017 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
Granger Reservoir is a 4,009-acre impoundment of the San Gabriel River in Williamson County, Texas. The reservoir is located approximately 40 miles northeast of Austin, Texas, within the Brazos River drainage basin. It was constructed in 1980 by the U. S. Army Corps of Engineers (USACE) for purposes of flood control and water conservation. Granger Reservoir has a drainage area of approximately 709 square miles and a shoreline length of about 28 miles. High turbidity and fluctuating water levels have deterred the establishment of aquatic vegetation. Reservoir bank slope is relatively flat and small changes in water level (1-2 feet) can have a large impact on the abundance of shoreline habitat and river/reservoir connectivity.
Management History
Important sport fish include White Crappie, White Bass, and Blue Catfish. A creel survey conducted in the spring of 2005 showed White Crappie was the most sought-after species (61.5% directed angler effort) followed by catfishes (16.8%), White Bass (5.1%), and Largemouth Bass (2.5%; Bonds and Magnelia 2005). Blue Catfish were stocked in 1995 and 1996 to provide additional angling opportunities and utilize an abundant shad population. No additional stocking has been conducted since 1996.
In collaboration with the Brazos River Authority (BRA), a fishery assessment (habitat availability, river/reservoir connectivity, and access at various lake levels) was conducted at Granger Reservoir for a multi-year system operating plan for the Brazos River Basin (Farooqi and De Jesus 2013). Based on these multiple assessments, threshold recommendations were provided to decrease potential impacts to the fishery during future basin-wide water level manipulations. The Granger Reservoir management threshold recommendation was 504 ft. above mean sea level (MSL), which is the same as conservation pool. A critical threshold for fisheries applications was set at 498 ft. MSL. As a consequence, other than under exceptional circumstances, water level fluctuations at Granger Reservoir will be minimal and therefore have little impact on the fishery. Low to negligible vegetative coverage has been descriptive of Granger Reservoir.
Fish Community
- Prey species: Gizzard Shad, Threadfin Shad, and Bluegill were the predominant prey species in 2016. Catch rates for Gizzard Shad and Bluegill had increased since the previous survey.
- Catfishes: Blue Catfish was the predominant catfish species. Total catch rate was higher than in the previous two surveys and most fish were above harvestable size. Channel Catfish and Flathead Catfish were present in low numbers.
- White Bass: Total catch rate for White Bass had increased since the previous survey; fish up to 15 inches in length were present.
- Largemouth Bass: Largemouth Bass were present in low numbers, as has been the case in the previous three surveys. Only two harvestable-size fish were caught.
- White Crappie: White Crappie were abundant and the population size structure was good. On average, White Crappie reached harvestable size (10 inches) between age 1 and 2.
Management Strategies
- Based on current information, the reservoir should continue to be managed with existing regulations.
- White Crappie is by far the most sought-after species at this reservoir; therefore, trap net surveys will be conducted biennially to monitor the population dynamics of this species.
- Conduct general monitoring surveys with electrofishing and gill nets in 2020-2021.
- Access, shoreline structural habitat, and vegetation surveys will be conducted in 2020.
- Using funding from BRA under the Interlocal Agreement, install a network of 10 Fishiding Stakeout vertical crappie stake beds complexes around the reservoir to help improve crappie habitat availability and angler success. Use print and social media to inform the public about these habitat structures and their location (GPS coordinates and map).
Performance Report as required by Federal Aid in Sport Fish Restoration Act Texas Federal Aid Project F-221-M-2 Inland Fisheries Division Monitoring and Management Program