Medina Reservoir - 2004 Survey Report

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Prepared by Randall A. Myers and John A. Dennis
Inland Fisheries Division
District 1-D, San Antonio, Texas

This is the authors' summary from a 30-page report. For a copy of the complete report, use the download link in the sidebar.

Medina Reservoir was surveyed from June 2004 to May 2005 using electrofishing, trap nets, gill nets, creel, a littoral zone habitat survey, an aquatic vegetation survey, and an angler access and facilities survey. This report summarizes the results of the surveys and contains a management plan for the reservoir based on those findings.

Reservoir Description

Medina Reservoir (5,410 acres) was constructed in 1913 and is located on the Medina River in Medina County, Texas. It was built primarily for irrigation water supply. The water level increased about 25 feet in 2000 to near conservation pool elevation and remained within 5 feet of that level until May 2005. Angler access is adequate with one public boat ramp and four private ramps open to the public. Bank angling access is fair and available adjacent to the boat ramps. The reservoir is deep, having an average depth of 46 feet, and relatively infertile with a secchi depth that exceeds 6 feet. Most of the shoreline (75%) is characterized as rock bluff or rocks and gravel. Boat docks occur along 24% of the shoreline. The reservoir contains very little aquatic vegetation with native emergent species occurring along only 1.5 miles of the shoreline.

Fish Community

• Prey species: Electrofishing catch rate of gizzard shad in 2004 (56.7 fish/hour) was similar to in 2000 (49.3 fish/hour) and greater than in 1997 (32.0 fish/hour). Gizzard shad population size structure was similar in 1997, 2000, and 2004, with most fish being too large (>8 inches) to be suitable prey for predators. In 2004, electrofishing catch rate of threadfin shad (113.3 fish/hour) was about double that of gizzard shad (56.7 fish/hour). Because of smaller size and greater relative abundance, threadfin shad likely contribute more to the forage base than do gizzard shad. Electrofishing catch rate of bluegill was greater in 2004 (143.3 fish/hour) than in 2000 (63.3 fish/hour), but lower than in 1997 (318.7 fish/hour). Electrofishing catch rate of redbreast sunfish was greater in 2004 (317.3 fish/hour) than in 2000 (138.0 fish/hour) and 1997 (195.3 fish/hour). Bluegill, redbreast sunfish, and green sunfish, because of their small size and abundant populations are important prey for predator species in the reservoir.
• Catfishes: Gillnet catch rate of blue catfish was lower in 2005 (0.7 fish/NN) than in 2000 and 2001 (1.9 and 2.4 fish/NN, respectively), whereas catch rate of channel catfish was similar in 2000, 2001, and 2005 (1.0-1.4 fish/NN). The majority of blue and channel catfish captured in gillnets were longer than the 12-inch minimum length. According to 2003-2004 creel surveys, catfish angling effort accounted for 19% of the total angling effort in the reservoir. Of the total estimated angler catch of catfish (1,663), about half (879 fish) were harvested with channel catfish accounting for the majority of the total catfish catch and harvest. Average rate of angler catch and harvest of catfish in the reservoir was <0.15 fish/angler-hour.
• Temperate basses: Gillnet catch rate of white bass in 2005 (1.0 fish/NN) was slightly less than in 2001 (1.9 fish/NN) and slightly greater than in 2000 (0.5 fish/NN). White bass population size structure was similar in 2000, 2001, and 2005, with most of the fish being >12 inches long. Gillnet catch rate of palmetto bass in 2005 (1.2 fish/NN) was similar to in 2001 (1.6 fish/NN) and much lower than in 2000 (8.6 fish/NN). Thus, according to gill net sampling, palmetto bass stockings in 2002 and 2004 were not as successful as stockings conducted prior to 2000. Palmetto bass population size structure was similar in 2000, 2001, and 2005, with about half of the sampled fish being longer than 18-inch minimum size limit. Average age of 17-19 inch palmetto bass was 3.8 years (N = 9) in 2005. According to 2003-2004 creel surveys, angling effort directed towards temperate basses (7,819 angler-hours) accounted for 21% of the total angling effort expended at the reservoir. An estimated 949 white bass and 1,944 palmetto bass were caught by anglers at an average rate of 0.318 fish/angler hour and 1,106 fish/angler-hour, respectively. Angler-harvest of white bass and palmetto bass was estimated to be 399 and 816 fish, respectively.
• Black basses: Electrofishing catch rate of largemouth bass in 2004 (60.0 fish/hour) was similar to 2000 (59.3 fish/hour), but lower than in 1997 (122.0 fish/hour). Largemouth bass population size structure was similar in 1997, 2000, and 2004, with preferred size fish (>15 inches) accounting for a very small proportion of stock size fish (RSD-P = 2). Average age of 13-15 inch largemouth bass was 2.9 years (N = 10). Florida largemouth bass allele frequency in 2004 (63.3%), as determined from electrophoretic analyses of age-0 individuals, was similar to 2000 (66.7%) and greater than in 1997 (44.2%). According to 2003-2004 creel surveys, angling effort directed towards black basses (18,959 anglerhours) accounted for 52% of the total angling effort in the reservoir. Largemouth bass catch and harvest was estimated to be 19,642 fish and 1,361 fish, respectively. Although the reservoir’s largemouth bass population is primarily composed of sub-14 inch fish, average angling success was considered good at 0.536 fish/angler-hour. An estimated 16 and 214 smallmouth and guadalupe bass, respectively, were caught from the reservoir.
• Crappie: Both white and black crappies are present in the reservoir; however white crappie dominate. Black crappie were not captured during 2004 trap-net sampling. Trap-net catch rate of white crappie in 2004 (0.50 fish/NN) was lower than in 2000 (4.7 fish/NN) and similar to 1997 (0.6 fish/NN). According to 2003-2004 creel surveys, angling effort directed towards crappies accounted for 6% of the total angling effort expended at the reservoir. Catch and harvest of white crappie was estimated to be 1,033 and 229 fish, respectively. No black crappie were observed harvested by anglers interviewed during creel surveys.

Management Strategies

All species should continue to be managed under current harvest regulations. Biennial electrofishing, gill-netting, and trap-netting will be conducted to monitor primary sport and prey species and evaluate the success of palmetto bass and largemouth bass stockings. Every fourth year age-0 largemouth bass will be collected and analyzed to assess the genetic composition of the population. To increase public awareness of angling opportunities, a press release regarding palmetto bass stockings will be prepared and signs depicting fish harvest regulations will be posted at boat ramps.

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