Falcon Reservoir - 2017 Survey Report

Prepared by Mitchell Nisbet and Randall Myers
Inland Fisheries Division – San Antonio District

This is the authors' summary from a 39-page report. For a copy of the complete report, use the download link in the sidebar.

Fish populations in Falcon Reservoir were surveyed in 2016-2018 using electrofishing and gill netting since the last report (2016). Anglers were surveyed from January through June 2016 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

Falcon Reservoir (83,654 acres when full) borders Mexico and was constructed in 1954 on the Rio Grande River. The reservoir experiences extreme water level fluctuations due to variable rainfall and water releases for downstream agricultural irrigation. Water level declined about 10 feet during the survey period (06/2016-05/2018) before abruptly increasing about 20 feet in October 2017. This water level increase, however, was short-lived as water level declined about 13 feet from March through May 2018, and as of May 15, 2018 was 30 feet below conservation pool elevation. In September 2017, occurrence of flooded terrestrial vegetation was low (13%) by historic standards on the Texas-side of the reservoir.

Management History

Fish harvest is regulated according to the standard statewide restrictions, except for Alligator Gar. The daily bag limit for Alligator Gar is 5 fish/day. On the Mexico side, fish harvest is unregulated and a substantial commercial gill net fishery exists targeting primarily Blue Tilapia according to anecdotal reports. Florida Largemouth Bass (FLMB) fingerlings have been stocked annually in recent years to increase FLMB genetic introgression and in turn, Largemouth Bass trophy potential. Giant salvinia was found growing near a boat ramp in 2016 and was removed.

Fish Community

• Prey species:Relative abundance of Gizzard Shad and their index of vulnerability (IOV) was comparatively high in 2017. Threadfin Shad, Bluegill, and Blue Tilapia were other important species present in the reservoir. Overall, prey species abundance and size was sufficient to support existing predator species populations.
• Alligator Gar: Relative abundance and size structure in 2018 was similar to 2014 according to gill net sampling conducted in April of each year. From January to June 2016, anglers expended 1,668 h bow-fishing and harvested 187 Alligator Gar. Non bow-fishing effort has been observed, but was not captured in our surveys.
• Catfishes: Directed angling effort, angling success, and harvest were lower in 2016 than in previous years. Fishing for catfishes accounted for 3.5% of the total angling effort occurring on the reservoir in 2016.
• White bass: No angling effort directed towards White Bass occurred during the 2016 creel survey period. However, an estimated 507 White Bass were incidentally caught and harvested by anglers targeting other species.
• Largemouth bass: Relative abundance of Largemouth Bass has decreased in recent years. The population is mostly comprised of quality-sized fish (>12 inches) in 2017-2018. Directed angling effort was greater in 2016 than in previous years, however harvest was much lower. Anglers caught and released an estimated 108,278 fish from January to June 2016 and one of every 14 caught and released exceeded 4 lbs.
• Black crappie: Angling effort directed towards Black Crappie remained low in 2016, however it was greater than in 2011. Despite the increase in angling effort, harvest was considerably lower in 2016 (676 fish) than in 2011 (2,651 fish).

Management Strategies

Concerning Largemouth Bass, stock FLMB annually, frequently monitor the population, and continue to explore the potential effectiveness of alternative harvest regulations. Assess Alligator Gar population relative abundance, size and age structure to determine effects of daily bag limit increase which was implemented in 2015. Monitor for presence of invasive aquatic species and conduct control activities 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