Canyon Reservoir - 2003 Survey Report

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Prepared by Stephan J. Magnelia and Craig C. Bonds
Inland Fisheries Division
District 2-C, San Marcos, 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.

Canyon Reservoir was surveyed in 2003 using trap netting and electrofishing. Gill netting, access and habitat surveys were conducted in 2004. Canyon Reservoir was surveyed using random sites in accordance with standardized procedures. This was the first year randomly selected gill netting sites were used, because of the ongoing evaluation of an experimental white bass length limit regulation enacted September 1, 1995. The change to random gill net sites in 2004 should be considered whenever catch-per-unit-effort (CPUE) comparisons are made with data collected before 2004 when fixed sites were used. The 2003-2004 CPUE for species in this summary was compared with CPUE collected in previous Canyon Reservoir surveys. This report summarizes the results of those surveys and contains a fisheries management plan for the reservoir based on those findings.

Reservoir Description

Canyon Reservoir is an 8,308-acre impoundment of the Guadalupe River located in Comal County. It was constructed in 1964 by the U.S. Army Corp of Engineers (USACE) for purposes of flood control, water conservation and recreation. Canyon Reservoir has a drainage area of approximately 1,452 square miles and a shoreline length of 90.5 miles. The basin is steep-sided with only a few shallow coves and shoal areas. The reservoir lies within the Edwards Plateau ecological area and land use is predominately ranching.

• Angler access: Boat angler access was excellent. Eighteen improved public boat ramps were available. Seven USACE parks were available for bank anglers. Shoreline access at many of the parks was excellent. One public fishing pier was available at Cranes Mill Park, on the upper end of the reservoir. White bass anglers could access the Guadalupe River above the lake using the Rebecca Creek boat ramp. There were no specific provisions made for increasing fishing access to physically challenged anglers.
• Aquatic habitat: The presence of aquatic vegetation was severely limited in this reservoir due to water-level fluctuations, wave action, and rocky substrate. Littoral fish habitat was limited to marinas, rock ledges and boulders. Pelagic (open-water) habitat was abundant.

Fish Community

• Prey species: Gizzard shad and sunfishes were the dominant prey species available. Gizzard shad electrofishing CPUE was 116.7/hour, much higher than in 1999 (19.3/hour). Increased densities of gizzard shad in 2003 may have been the result of increased primary productivity from elevated water levels in summer 2002 (Appendix B). Gizzard shad from 2- to 15-inches in length were collected. The electrofishing CPUE of redbreast sunfish in 2003 was 234.0/hour, which was similar to 1999 (235.3/hour) and more than double the 1998 CPUE (108.7/hour). The electrofishing CPUE of bluegill was 324.0/hour, which was much higher than the previous two surveys (1999=83.3/hour, 1998=84.7/hour). High water levels in summer 2002 (Appendix B) probably increased recruitment of bluegill. Length frequency distributions of sunfish species indicated that most individuals were of a size available to predators. A few redbreast sunfish reached quality size (>7 inches). Other prey species included blacktail shiners, bullhead minnows, green sunfish, longear sunfish and threadfin shad.
• Catfishes: Channel catfish were the dominant catfish species present. Gill netting CPUE for this species in 2004 (1.7/net night) was very similar to that recorded in 2002 (1.3/net night) and 2000 (1.7/net night). Directed fishing effort for this species has been variable (1999 =5.9%, 1998 = 4.3%, 1997 = 22%), but on average was less than 10% of the total fishing effort during the 90’s (Magnelia and Bonds 2000). Blue catfish captured in the 2004 gill netting survey ranged from 25 to 31 inches. The CPUE (0.9/net night) was similar to previous surveys, and slightly greater than the historical average of 0.7/net night. As in 1999 (Magnelia and Bonds 2000), reproduction and recruitment of blue catfish was not documented. Several small specimens were captured in the 2000 gill net survey; unfortunately, these fish were not aged to determine if they were the result of natural reproduction. Based on their large size, blue catfish caught in 2002 and 2004 gill netting surveys appeared to be fish stocked in 1991 and 1992. In 1999 only 0.5% of the directed fishing effort was for blue catfish (Magnelia and Bonds 2000). Canyon Reservoir supported a low density flathead catfish population. The 2004 gill netting CPUE (1.0 net/night) was similar to previous surveys (Magnelia and Bonds 2000).
• Temperate basses: White bass were a popular sport fish in Canyon Reservoir, especially during spring months in the upper reservoir and the upstream Guadalupe River (Magnelia and Bonds 2000). In 1999 white bass was the second most sought-after species comprising 24.8% of the total directed fishing effort (Magnelia and Bonds 2000). In 2004 white bass were captured gill netting at a rate of 0.9/net night, which is much lower than the previous two surveys (2002 = 5.4/net night, 2000 = 3.5/net night). The decline in the gill netting CPUE may be attributed to the random sampling design implemented in the 2004. All gill netting prior to this survey was conducted at fixed sites as part of the 12-inch minimum length limit evaluation. An experimental 12-inch minimum length limit on white bass was implemented on Canyon Reservoir (along with several other Texas reservoirs) in 1995. The regulation was intended to provide added harvest protection to fast-growing white bass, thereby increasing population numbers and average sizes of white bass caught by anglers. An intensive evaluation of fisheries data collected from all reservoirs regulated with the 12-inch length limit was conducted in 2002. This evaluation concluded the experimental regulation did not result in increased population numbers or average size of white bass caught by anglers. Additional analysis supported by recent scientific literature indicated that white bass reproductive success was highly correlated with springtime reservoir inflow rates (DiCenzo and Duval 2002; Schultz et al. 2002). The experimental regulation was rescinded in favor of the 10-inch, statewide minimum length limit in 2003. The 2004 gill netting CPUE (0.5/net night) for striped bass was the lowest since 1994 (0.7/net night) and well below the historical average of 2.2/net night. The decline in the gill netting catch rate might be due to the random sampling design implemented in the 2004. Another contributor to the low catch rate may be that only one stocking (2002) of this species was made since 2000. Striped bass stockings were requested annually for Canyon Reservoir, but hatchery production did not meet demand. Since 2001 golden alga toxins have often decimated Texas Parks and Wildlife Department (TPWD) striped bass hatchery production, limiting the number of reservoirs stocked. Directed fishing effort for this species during the 90’s was generally only about 1-2 hours/acre, although this has often been 8-16% of the total directed fishing effort. (Magnelia and Bonds 2000). As in previous surveys striped bass captured gill netting in 2004 continued to exhibit poor body condition, even though gizzard shad densities were higher than previous surveys.
• Black basses: Largemouth bass CPUE (203.3/hour) was the highest since 1997 (242.0/hour). Extremely elevated water levels in summer 2002 (Appendix B) contributed to a strong 2002 year class of largemouth bass. Above average electrofishing catch rates were also recorded in other years when water level greatly exceeded the conservation pool level (1992 and 1997, mean CPUE = 191.5/hour). Higher CPUE during these years may be attributed to better conditions (flooded terrestrial vegetation) for survival of age-0 largemouth bass. During years when the reservoir was near or below conservation pool (1990, 1991, 1993, 1994, 1995, 1996, 1998 and 1999) largemouth bass electrofishing CPUE was generally much lower (mean CPUE = 69.6/hour). Largemouth bass reach legal length by age 2-3. Numbers of legal length fish in this population have historically been low. The percentage of adult fish exceeding 14 inches from 1994-2003 has ranged from 7-16%. Unlike 1997, when it appeared growth increased as a result of the elevated water level, growth in 2003 was average. Despite its reputation among anglers as a poor largemouth bass lake, this was the most sought after sport fish, with 46% of the total fishing effort directed toward this species in 1999 (Magnelia and Bonds 2000). Electrophoresis indicated that 72% of the alleles in the largemouth bass population were from the Florida subspecies. This is the highest level of Florida bass influence ever documented for Canyon Reservoir. Guadalupe and smallmouth bass are also available to anglers. These species are present in low densities and do not provide significant fisheries.
• Crappie: Canyon Reservoir supported a low density white crappie population. Trap netting CPUE during 2004 was 0.5/net night, which is similar to 1999 (0.6/net night). Trap netting CPUE has historically been better in the upper end of the reservoir. During 1999, white crappie angling activity accounted for only 3.6% of the total directed fishing effort, or 0.5 hours/acre (Magnelia and Bonds 2000).

Management Strategies

Based on current information, the reservoir should continue to be managed with existing harvest regulations. The lack of small blue catfish in the population was of concern. All blue catfish collected in future fish monitoring surveys should be aged to document natural reproduction. Annual requests for stockings of striped bass should be continued. Stocking of this species is necessary to support this fishery.

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