Falcon Reservoir - 2021 Survey Report

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

This is the authors' summary from a 38-page report. For a copy of the complete report, use the download link in the sidebar.

Fish populations in Falcon Reservoir were surveyed in 2020-2022 using electrofishing. The reservoir sport fishery was quantified in 2022 using a creel survey. Historical data are presented for comparison. This report summarizes the results of these surveys and contains a management plan for the reservoir based on those findings.

Reservoir Description

Falcon Reservoir (83,654 acres when full) was constructed in 1954 on the Rio Grande River and forms the border with Mexico. The reservoir experiences extreme water level fluctuations due to variable rainfall and water releases for downstream agricultural irrigation. Fisheries habitat was poor during the study period. During the study period, water level ranged from 37 to 48 feet below conservation pool elevation, and occurrence of flooded terrestrial vegetation was low (8%).

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. In 2019, the commercial sale of catfishes was legalized by the Texas Legislature in Starr and Zapata counties, which encompass Falcon Reservoir (Parks and Wildlife Code, Title 7, Chapter 351). On the Mexico side, fish harvest is unregulated, and a substantial commercial gill net fishery exists primarily targeting Blue Tilapia. Florida Largemouth Bass (FLMB) fingerlings were stocked annually in recent years to maintain high FLMB genetic introgression and Largemouth Bass trophy potential.

Fish Community

• Prey species: Relative abundance of Gizzard Shad and Bluegill was low in 2021 and similar to previous years. Threadfin Shad abundance was much higher in 2019 than in 2021. Overall, prey species abundance and size was sufficient to support existing predator species populations.
• Alligator Gar: Spawning habitat availability was low in 2020 and 2021 resulting in less than a 35% probability of strong year class formation in each year. Angling for this species accounted for 5.3% of total angling effort occurring on the reservoir, and few fish were harvested (87 fish) from January through June 2022.   
• Catfishes: In 2022, catfish angling comprised 11.3% of total angling effort and anglers harvested more Channel Catfish than Blue Catfish. Catfish catch success (mean catch/h) was improved compared to 2019 but was lower than the historical average.
• White Bass: In 2022, minimal angling effort was expended targeting White Bass, and anglers harvested substantially fewer White Bass compared to 2019.  
• Largemouth Bass: Abundance of Largemouth Bass was decreased during the study period due to low and declining water level. The population was mostly comprised of quality-length individuals and their condition was good. In 2022, Largemouth Bass angling accounted for 73.5% of the total angling effort occurring on the reservoir. Tournament-angling comprised 4% of total Largemouth Bass angling effort. Largemouth Bass harvest was lower in 2022 than in previous years. Angler catch success was improved in 2022, but was still below the historical average. Fish >4 lbs. represented 18% of all released Largemouth Bass in 2022.
• Black Crappie: Angling for this species accounted for 6.6% of total angling effort and more angling effort was expended targeting Black Crappie in 2022 than in previous years. Catch success rebounded in 2022 and harvest was substantially higher than previous surveys. Percent legal release was low for the species.

Management Strategies

• Biennially monitor the Largemouth Bass population and annually stock Florida Largemouth Bass fingerlings.
• Annually assess Alligator Gar recruitment potential using the spawning habitat availability-year class strength model in Myers et al. (2020). 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