Falcon Reservoir - 2019 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 2018-2020 using electrofishing and in 2018 using gill netting. The reservoir sport fishery was quantified in 2019 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. Fisheries habitat was poor during the study period. Water level ranged from 22 to 38 feet below conservation pool elevation, and occurrence of flooded terrestrial vegetation was low (13%).

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

Fish Community

• Prey species: Relative abundance of Gizzard Shad and Bluegill was low in 2019, but Threadfin Shad abundance was much higher in 2019 than in previous years. Overall, prey species abundance and size was sufficient to support existing predator species populations.
• Alligator Gar: Abundance was higher in 2018 than 2014 and size structure was similar in both years. Spawning habitat availability was low in 2018-2019 resulting in only a 4% probability of strong year class formation. Angling for this species accounted for 3.4% of total angling effort occurring on the reservoir, 85 fish were harvested from April to September 2019.  
• Catfishes: In 2019, catfish angling comprised 4.6% of total angling effort and anglers harvested similar numbers of Blue Catfish and Channel Catfish. Catfish catch success (mean catch/h) was substantially lower in 2019 than in previous years.
• White Bass: In 2019, minimal angling effort was expended targeting White Bass, but anglers harvested substantially more fish than in previous years.  
• 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 2019, Largemouth Bass angling accounted for 87.2% of the total angling effort occurring on the reservoir. Tournament-angling comprised 31% of total Largemouth Bass angling effort. Largemouth Bass harvest and catch success were lower in 2019 than in previous years. Fish >4 lbs. represented 10% of all released Largemouth Bass in 2019.
• Black Crappie: More angling effort was expended targeting Black Crappie in 2019 than in previous years, however angling for this species accounted for only 1.9% of total angling effort.  Catch success was lower in 2019 than previous years and percent legal release was high for the species.  

Management Strategies

• Biennially monitor the Largemouth Bass population and annually stock Florida Largemouth Bass fingerlings.
• Annually assess Alligator Gar recruitment 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