Averhoff Reservoir - 2004 Survey Report

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

This is the authors' summary from a 21-page report. For a copy of the complete report, use the download link in the sidebar.

Averhoff Reservoir was surveyed from June 2004 to May 2005 using electrofishing, trap nets, gill nets, 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

Averhoff Reservoir (174 acres) is a riverine reservoir located on the Nueces River, near Crystal City, TX, in Zavala County. It was constructed by the Zavala-Dimmit Water Improvement District Number 1 in 1948 to provide water for agricultural, recreational, and flood control purposes. Water level records are currently not recorded. Access was fair with only one public ramp and there were no handicap specific facilities. The primary shoreline habitat feature was overhanging brush. Aquatic vegetation occupied about 4 acres of the reservoir with Illinois pondweed, Egyptian paspalidium, and stargrass being the predominant species.

Fish Community

• Prey species: Electrofishing catch rate of gizzard shad ranged from 30.0-50.0/h in 2004, 2000, and 1998. Gizzard shad Index of vulnerability (IOV) was 24, indicating a low availability of gizzard shad as forage for predators. Threadfin shad were not collected in 2004 and 2000 and only one threadfin shad was collected in 1998. Electrofishing catch rate of bluegill was similar in 2004, 2000, and 1998, ranging from 100.0-122.0/h. Bluegill Proportional Stock Density (PSD) was low (5-16) in 2004, 2000, and 1998 indicating a high proportion of the population was of suitable size to be prey for predators. Electrofishing catch rate of all other sunfishes combined was 110.0fish/h. Sunfish are the dominant forage in this reservoir.
• Catfishes: Gill net catch rate of channel catfish was 3.6/NN, similar to the 2002 catch rate of 3.2/NN, but lower than the 2001 catch rate of 6.0/NN. Relative weights (Wr) were above 80 for all fish in all three sample years. PSD was high in 2005, 2002, and 2001 (ranging from 72-95) indicating the majority of the population is larger sized fish. Two flathead catfish were collected (one 24-inch and one 25-inch, total length). No blue catfish were collected in 2005.
• Largemouth bass: Electrofishing catch rate of largemouth bass in 2004 (50.0/h) was similar to the catch rate of 46.0/h in 2000 and higher than the catch rate of 27.0/h in 1998. Largemouth bass PSD ranged from 22 in 2004 to 28 in 1998. Largemouth bass average Wr ranged from 80 to 103. Electrophoretic analysis of age-0 and age-1 fish collected in 2004 indicated a 52.6% frequency of Florida largemouth bass alleles with 6.9% of the sample having the Florida largemouth bass genotype.
• White crappie: Trap net catch rate of white crappie was low in 2004 (1.6/NN) and similar to in 1998 (0.4/NN) and 2000 (1.4/NN).

Management Strategies

• Based on survey results all species should continue to be managed under current harvest regulations.
• Monitor fish populations with standard sampling conducted every fourth year.
• Stock threadfin shad.
• Prepare a press release detailing availability of water body fish records to be set in the reservoir.

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