Gilmer Reservoir - 2004 Survey Report

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Prepared by Michael W. Brice
Inland Fisheries Division
District 3-A, Marshall, Texas

This is the authors' summary from a 25-page report. For a copy of the complete report, use the download link in the sidebar.

Gilmer Reservoir was surveyed using gill nets (spring; 2002-2004), trap nets (fall; 2001-2004), and electrofishing (fall; 2001-2004) to monitor the fish community. Habitat, vegetation, and access surveys were also conducted in 2004. Additionally, an access creel survey was conducted September 2001 through August 2002 (36 days). This report summarizes the results of the surveys and contains a management plan for the reservoir based on those findings.

Reservoir Description

Gilmer Reservoir is located on Kelsey Creek in the Cypress River Basin. It was constructed by the City of Gilmer in 1995 for municipal water, a water supply for a downstream gas-fired electric power plant, and public recreation. The dam was closed in 2000 and the reservoir filled to its conservation pool of 315 ft msl. The reservoir inundates 1,010 acres and has a maximum depth of 28 ft. Shoreline length is 7.5 mi and the shoreline development ratio is 1.6. The reservoir lies within the East Texas Timberlands Land Resource Area and has a drainage area of approximately 40 square miles. Annual water level fluctuation is unknown and will be better understood after the downstream power plant is on line. The reservoir opened to the public September 29, 2001. Boating access is available at one county park. A two-lane boat ramp equipped with loading piers and parking for 100 vehicles is provided. Structural habitat is comprised of inundated timber, brush, and creek channels. Most of the timber was removed during the construction phase; however most of the basin contained brush and native grasses prior to dam closure. Aquatic macrophyte growth is moderate with hydrilla, chara, and coontail being the dominant species.

Fish Community

• Prey species: Efforts to increase prey fish diversity in Gilmer Reservoir were successful by stocking threadfin shad in 1997 (2,000 fish), 2001 (200 fish), and 2002 (6,000 fish). Threadfin shad were collected during 2002 and 2004 fall electrofishing surveys at 60.0 and 124.0 fish/hour, which indicated this species was reproducing naturally in the reservoir. Index of vulnerability (IOV) for gizzard shad in 2004 indicated only 21% of the population was available to existing predators, compared to 2001 (84%) and 2002 (45%). Electrofishing catch rate of gizzard shad has declined from 436 fish/hour in 2001 to 151 fish/hour in 2004. The catch rate of combined sunfish species (green sunfish, warmouth, bluegill, longear sunfish, and redear sunfish) in 2004 was 602.0 fish/hour with many available in preferred sizes as prey. Prey fish populations in Gilmer Reservoir were adequate judged by good body condition of largemouth bass (Wr >90; 2003 and 2004).
• Catfishes: The relative abundance of channel catfish caught in gill net collections has steadily declined in recent years. Catch rates of channel catfish were at their highest in 2001 (6.0 fish/net night), but have declined to 1.8 fish/net night in 2002 and 1.2 fish/net night in 2005. All channel catfish collected in 2005 were > 25 inches. There was no evidence of natural reproductive success or subsequent recruitment of individuals into the population. Creel surveys (2001-2002) indicated the majority (93%) of the channel catfish harvested were >20 inches. Possible competition with flourishing populations of black and yellow bullhead could be keeping the channel catfish population from expanding. In 2005, black bullhead and yellow bullhead catch rates were 16.2 fish/net night and 13.2 fish/net night, respectively, with the majority of the bullhead ranging from 12-14 inches. Growth of channel catfish was not assessed in 2005 due to low sample size. In 2003-20004, angling effort directed towards channel catfish (1.07 hours/acre) accounted for 2.4% of the total angling effort. Anglers targeting channel catfish caught and harvested 0.91 and 0.14 fish/hour, respectively.
• Sunfishes: Electrofishing surveys indicated several sunfish species were present and potentially available for harvest. Bluegill was the dominant sunfish species in 2004 (440.0 fish/hour). Historical data (Ryan and Brice 2001) indicates bluegill grow to 6.0 inches by age 2. The catch rate of redear sunfish increased from 13.0 fish/hour in 2002 to 112.0 fish/hour in 2004. Redear sunfish up to 9 inches were collected in 2004.
• Largemouth bass: The catch rate of largemouth bass was 102.0 fish/hour in 2004 fall electrofishing samples, which was similar to 2001 (107.0 fish/hour) and 2002 (112.0 fish/hour). The catch rate of stock-size (> 8 inch) individuals was 79.0 fish/hour and has steadily increased over the past several years (2001; 30.0 fish/hour, 2002; 32.0 fish/hour, 2003; 55.0 fish/hour). The largemouth bass population can be characterized as one of moderate abundance, exhibiting good condition (Wr > 95) and growth. Largemouth bass attain 14 inches during their third growing season and reach legal-size (>18 inches) in 4 or more growing seasons. Only one legal-size largemouth bass was captured in electrofishing surveys each year in 2003 and 2004. Electrophoretic testing of largemouth bass (age 0; n=67) collected during 2004 electrofishing showed 33.6% Florida alleles were present. In 2001-2002, angling effort directed towards largemouth bass (27.39 hours/acre) accounted for 61.8% of the total angling effort. Anglers targeting largemouth bass caught and harvested 0.99 and 0.002 fish/hour, respectively.
• Crappie: No crappie were collected during fall trap netting in 2004; however, both white and black crappie were colleted during 2005 spring gill netting collections at 0.8 and 8.6 fish/net night, respectively. Black crappies attain legal size (> 10 inches) between age 2 and age 3 (Ryan and Brice 2001). Creel data (2001-2002) indicated that anglers targeting crappie (3.8% of total effort) fished 1.70 hours/acre, caught 3.58 fish/hour, and harvested 0.15 fish/hour.

Management Strategies

The relative abundance of largemouth bass, crappie, and many sunfish species has increased in the time since sampling was initiated (2001) following impoundment of Gilmer Reservoir. The relative abundance of channel catfish, however, has declined and the population is represented only by low numbers of larger (>25 inches) adult fish. Supplemental stockings of advanced-size channel catfish need to be conducted until natural recruitment occurs to maximize quality fishing opportunities. The fish community should be surveyed every 4 years using electrofishing, frame netting, and gill netting techniques. Additionally, an access creel survey will be conducted June 2005 through May 2006 to monitor angling effort and success. Fishing information should be disseminated to the public through media outlets to keep anglers aware of fishing opportunities.

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