Amistad Reservoir - 2018 Survey Report

Prepared by Randall A. Myers and Mitchell Nisbet
Inland Fisheries Division - San Antonio District

This is the authors' summary from a 35-page report. For a copy of the complete report, use the download link in the sidebar.

Fish populations in Amistad Reservoir were surveyed in 2018-2019 using electrofishing and gill netting since the last report (2017). Anglers were surveyed from January through June in 2018 using a creel survey. Historical data are presented for comparison. This report summarizes the results of the surveys and contains a management plan for the reservoir based on those findings.

Reservoir Description

Amistad Reservoir (63,680 acres when full) borders Mexico and was constructed in 1969 on the Rio Grande River. It is managed by the International Boundary and Water Commission to provide water for irrigation and hydro-electric power generation. Boat and angler access are excellent; the National Park Service (NPS) maintains 9 public boat ramps. Water level declined from full pool in 2011 to 61 feet low in 2013. Water level subsequently increased and remained 26-37 feet low since 2015 with water level fluctuating 12.9 feet annually on average. Aquatic vegetation occurrence decreased and hydrilla occurrence increased slightly in 2018 compared to in 2016. Three water samples from the reservoir tested positive for Zebra Mussel DNA in December 2018, further water tests have tested negative and monthly shoreline surveys have not found any adult mussels.

Management History

Important sport fishes include Largemouth Bass, Smallmouth Bass, catfishes, Striped Bass, and White Bass. Striped Bass were stocked in most years since 1974. Florida Largemouth Bass (FLMB) were stocked periodically from 1975 to 2006 and annually since 2010 to improve FLMB introgression and trophy Largemouth Bass potential. Angler harvest of all sport fishes has been regulated according to statewide size and bag limits. Since 2004, the NPS has regulated Largemouth Bass tournaments via a tournament permitting program.

Fish Community

• Prey species: Relative abundance of Gizzard Shad was lower than the previous survey in 2016, but their Index of Vulnerability (IOV) was comparatively higher in 2018. Bluegill, Redbreast Sunfish, and Redear Sunfish were other important forage species present in the reservoir. Overall, prey species relative abundance and size was sufficient to support existing predator species populations.
• Catfishes: Channel Catfish was the predominant catfish species present in the reservoir. Directed angling effort was lower than the previous survey in 2015, however angling success and harvest were higher in 2018 than in previous years. Fishing for catfishes accounted for 5.7% of the total angling effort occurring on the reservoir in 2018.
• Temperate Basses: White Bass and Striped Bass relative abundance has been consistently low since 2011. Fishing for temperate basses accounted for 3.7% of total angling effort occurring on the reservoir in 2018.
• Black basses: Relative abundance of Largemouth Bass has stayed constant in recent years. The population was mostly comprised of quality-sized fish (>12 inches) in 2018-2019. Directed angling effort was similar in 2018 compared to 2015; however, harvest was higher. Anglers caught and released an estimated 162,421 fish from January to June 2018. Catch of Smallmouth Bass has been constant since 2012, after increasing considerably since 2007.

Management Strategies

• Continue to provide a Striped Bass fishery supported by annual stockings.
• Continue stocking FLMB annually to maintain high FLMB introgression and trophy potential.
• Work cooperatively with Amistad Reservoir stakeholders to address issues that arise.
• Conduct electrofishing, gill netting, vegetation surveys every other year, and a creel survey every four years.

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