Choke Canyon Reservoir - 2003 Survey Report

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Prepared by John Findeisen and Aaron Walters
Inland Fisheries Division
District 1-E, Mathis, Texas

This is the authors' summary from a 28-page report. For a copy of the complete report, use the download link in the sidebar.

Choke Canyon Reservoir was surveyed in fall 2003 using trap nets and electrofishing and in 2004 using gill nets. A creel survey is conducted annually. This report summarizes the results and contains a management plan for the reservoir based on those findings.

Reservoir Description

Choke Canyon Reservoir is a 25,989-acre reservoir located on the Frio River, in the Nueces River Basin, approximately 80 miles south of San Antonio. It receives water from the Frio River and several smaller tributaries and is used for water supply and recreation. The reservoir has a history of substantial water level fluctuations. The reservoir averaged 25,895 acres in size in 2003-2004. Shoreline, boat and handicap access are adequate. Water is typically clear. Substrate is composed primarily of clays, deep loams, saline soils, sand and small rock. Littoral habitat consists of dead timber, periodically flooded live and dead terrestrial vegetation, native aquatic vegetation, and hydrilla. The water level of the reservoir average 20-23 feet below conservation pool until July 2002, when it filled. Native aquatic vegetation and hydrilla reestablished in the reservoir shortly after the reservoir filled and has expanded since.

Fish Community

• Prey species: The 2003 electrofishing catch rates for gizzard shad and threadfin shad were 97.0/h, and 498.0/h, respectively. The Index of Vulnerability (IOV), for gizzard shad was 10%, indicating that only 10% of the gizzard shad population is less than 8 inches in length and available to predation. The high electrofishing catch rate for threadfin shad indicates that this species provides readily available foraging opportunities. The 2003 electrofishing catch rates for bluegill and redear sunfish were 156.0/h and 34.5/h, respectively. Sampling indicated too few quality sunfish present to support a fishery. Size ranges of sunfish species were suitable for predator fishes.
• Blue catfish: The gill net catch rate for blue catfish was 16.3/NN, similar to 2002 but down from 2003. Blue catfish growth rates were good as fish reached 12 inches by age 3. Condition of fish greater than 12 inches in total length was good as mean relative weights were near 95. Directed effort (h/acre) for blue catfish peaked in 2000-2001 and appears to decline since. This decline is probably due to the fact that many catfish anglers target catfish in general rather than just one species and and are treated as two different groups under current creel survey protocol. Angler catch rate (#/h) for blue catfish has increased since 2000-2001, while angler harvest rate (#/h) of blue catfish has remained similar.
• Channel catfish: The gill net catch rate for channel catfish was 0.7/NN, which is similar to 2002 and 2003. The consistency of low gill net catch rates of channel catfish may be an indicator of being outcompeted by blue catfish. Very few anglers are targeting channel catfish as the directed effort was only 0.01 h/acre in 2003-2004. Catch rate and harvest rate of anglers targeting channel catfish was zero but channel catfish were harvested anglers targeting other species.
• White bass: The gill net catch rate for white bass was 0.9/NN, down from 2002 but similar to 2003. The lower catch rates are probably due to sampling at the higher water levels, as white bass could swim around the nets set in the river. Historically, white bass reach 10 inches in length by age 1. Condition of stock size fish was excellent as mean relative weights were greater than 100. Directed effort for white bass was 0.2 h/acre, steadily declining from 2001-2002. This decline may be an artifact of the same number of anglers fishing a reservoir that doubled in size (when reservoir filled in July 2002) versus a true decrease in the amount of effort. Both angler catch and harvest rate declined in 2003-2004.
• Largemouth bass: The electrofishing catch rate for largemouth bass was 93.5/h, similar to 2001. Growth rates in 2002 and 2003 were slightly higher than in 2001. Fish reached legal size, 14 inches, between ages 1 and 2. Condition of stock size fish was above average as mean relative weights were near 100. Electrophoresis indicated an 87% frequency of Florida largemouth bass alleles, with 57% of the population having the Florida largemouth bass genotype. Directed effort for largemouth bass was lower than 2000-2001 but has gradually increased since 2001-2002. Angler catch rate of largemouth bass peaked in 2003-2004, while the angler harvest rate remained similar.
• White crappie: The trap net catch rate for white crappie was 4.7/NN, up from previous years. Growth rates were similar to previous years as fish reached 10 inches by age 1. Condition of stock size and greater fish was good; mean relative weights were near 100. Directed effort remained relatively stable since 2001-2002, well below the peak in 2000-2001. Angler catch rate and harvest rate have steadily decreased since 2001-2002.

Management Strategies

• Based on current information, the reservoir should continue to be managed with existing regulations.
• Hydrilla has spread throughout the reservoir and has the potential to create access problems. Work with the City of Corpus Christi on controlling problematic areas.
• Angling success has increased since the reservoir filled. Write press releases promoting the fisheries.
• Currently, annual creel surveys are only conducted on Choke Canyon Reservoir. Change the creel survey schedule at Choke Canyon Reservoir from every year to every other year in order to conduct creel surveys on other reservoirs in the district.

Performance Report as required by Federal Aid in Sport Fish Restoration Act Texas Federal Aid Project F-30-R-29 Statewide Freshwater Fisheries Monitoring and Management Program