Amistad Reservoir - 2003 Survey Report
Prepared by Wilfred J. Dean
Inland Fisheries Division
District 1-D, San Antonio, Texas
This is the authors' summary from a 23-page report. For a copy of the complete report, use the download link in the sidebar.
Amistad Reservoir was surveyed using frame nets and electrofishing in 2003 and gill nets in 2004. This report summarizes the results of the surveys and contains a management plan for the reservoir based on those findings.
Amistad Reservoir is a 65,000-acre reservoir, at conservation pool, on the Rio Grande River constructed by the International Boundary and Water Commission and Mexico in 1969 to provide water for irrigation and hydroelectric power generation purposes. Amistad is located near Del Rio in Val Verde County. Principal tributaries are the Rio Grande River, Devils River and the Pecos River. The Conchos River in Mexico joins the Rio Grande near Presidio, Texas and is another major source of water for Amistad.
The fisheries in Amistad have been impacted by drought conditions which began in 1993. Amistad has a history of substantial water level fluctuations. At the beginning of this survey period Amistad was near elevation 1067 ft msl (50 feet low) and covered approximately 25,900 acres. Good rains the latter part of 2003 and early 2004 now have the elevation at 1090.2 ft msl and the reservoir covers approximately 42,494 surface acres. Access at normal pool elevation is adequate. Handicap specific facilities are available and maintained by the National Parks Service at Diablo East and Rough Canyon Marinas. Other launch sites include Air Force Marina, Blackbrush Point, Box Canyon, Spur 454 and Spur 406. Habitat present includes hydrilla, flooded terrestrial vegetation and rocky points and shoreline.
- Prey species: Bluegill, redbreast sunfish and gizzard shad were the main forage species found in the reservoir. Catch rates from electrofishing were 518.0/h, 259.5/h, and 65.5/h respectively. Other forage included redear sunfish and threadfin shad. Size distribution of most prey species was suitable for major predators. However, IOV (DiCenzo et al 1996) for gizzard shad was only 2.
- Catfishes: Gill net catch rates of blue catfish decreased from 0.73/NN in 2003 to 0.13/NN in 2004. Gill net catch rates of channel catfish decreased from 1.47/NN in 2003 to 0.47/NN in 2004. Historically, blue catfish and channel catfish reached legal size around age 3.
- Temperate basses: Gill net catch rates of white bass increased from 1.13/NN in 2003 to 1.20/NN in 2004. Historically white bass reached legal size at age 1. Gill net catch rates of striped bass increased slightly from 0.60/NN in 2003 to 0.67/NN in 2004. Historically striped bass reached legal size by age 3.
- Largemouth bass: Electrofishing catch rates decreased from 128.0/h in 2001 to 64.5/h in 2003. This is probably an affect of the drought period. Largemouth bass reach legal size between age 2 and 3. Electrophoresis indicated 46% Florida bass genotype and 81% Florida alleles.
- White crappie: White crappie trap net catch rates increased from 0.08/NN in 1999 to 0.20/NN in 2003.
Based on current information, the reservoir should continue to be managed with existing regulations. Monitor the success of introduced native largemouth bass. Based on success or failure, either the stocking of Florida largemouth bass or northern largemouth bass should be made to take advantage of expanded habitat.
Performance Report as required by Federal Aid in Sport Fish Restoration Act Texas Federal Aid Project F-30-R-28 Statewide Freshwater Fisheries Monitoring and Management Program