Lake Somerville - 2004 Survey Report

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Prepared by Jeff Henson and Mark Webb
Inland Fisheries Division
District 3-E, Bryan, Texas

This is the authors' summary from a 32-page report. For a copy of the complete report, use the download link in the sidebar.

Lake Somerville was surveyed during the period June 2004 to May 2005 using electrofishing, trap netting, gill netting, 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

Lake Somerville is an 11,460-acre flood control reservoir constructed by the U.S. Army Corps of Engineers on Yegua Creek in Burleson and Washington Counties, Texas. Principle tributaries are Middle Yegua, West Yegua, and Nails Creeks. Lake Somerville has a drainage area of approximately 1,006 square miles, a shoreline length of 104 miles, and a shoreline development ratio of 5.7. The reservoir has a mean depth of 11 feet and a maximum depth of 38 feet. Average rainfall in the watershed is 39 inches per year. The reservoir lies within the Post Oak Savannah Land Resource Area with soils consisting of Falba-Burlewash, Kaufman-Gowen, and Tabor-Axtell associations. Land uses around the reservoir are primarily agricultural and recreational.

Fish Community

• Prey species: In past years, threadfin shad were the predominant prey species in Lake Somerville. In 2004, the electrofishing catch rate for threadfin shad was down to 174.0 fish/hour, the lowest since 1994. The electrofishing catch rate of gizzard shad was 304.0 fish/hour. Most individuals in the sample are less than 8 inches and available as prey. Bluegill and longear sunfish make up the bulk of sunfish prey with catch rates in 2004 of 313.5 fish/hour and 134.0 fish/hour, respectively. Other prey species include bullhead minnow, inland silverside, blacktail shiner, green sunfish, warmouth, and redear sunfish.
• Catfishes: Gill net catch rates of blue catfish have increased since 1994. The catch rate in 2005 was 2.7 fish/net night; an increase from 0.6 in 2001 and 1.7 in 2004. Length frequency data indicates a recruiting population with high growth potential. One individual in the 2005 sample was 42 inches. The sample PSD was 53. Lake Somerville supports a substantial population of channel catfish. The gill net catch rate in 2005 was 11.1 fish/net night, down from 2001 (20.3 fish/net night) but still higher than 9.9 fish/net night captured in 1997. Fish in inch groups from 7 through 22 inches were captured, suggesting adequate recruitment. The PSD was 20 and the RSD-12 was 96, indicating that the population contains good numbers of quality-sized fish. Creel results from 2001-2002 indicate low directed effort for catfishes (0.7 angler hours/acre), yet angler catch rates are very high at 3.3 fish/angler-hour.
• White bass and palmetto bass: Gill net CPUE of white bass was much lower in 2005 (5.8 fish/net night) than in 2004 (17.7 fish/net night). Proportional Stock Density was 100 in both years, and RSD-P was 97 in 2005 and 67 in 2004. Gill net CPUE of palmetto bass was 2.5 fish/net night in 2005 and was similar to that of 2004 (2.3 fish/net night). However, the relative abundance of legal-length fish was much lower in 2005 than it was in 2004 or 2003. The RSD-18 was 3 in 2005; a decrease from 65 in 2004 and 48 in 2003. This is probably the result of missing year classes in 2001 and 2003. The creel survey in 2001-2002 indicates a popular fishery for temperate basses. Directed effort by anglers seeking palmetto bass was 0.3 hours/acre and 1.4 hours/acre for anglers seeking white bass. The angler catch rate of white bass was the highest for all species at 6.7 fish/angler-hour. Anglers seeking that species harvested an estimated 19,195 white bass. This estimate is presumed to be low being based solely on anglers targeting white bass in the creel survey. It does not account for anglers targeting temperate basses as a species group. Over 7,000 additional hours were reported for anglers seeking temperate basses.
• Black basses: The electrofishing CPUE of largemouth bass increased greatly since 2000 from 7.0 fish/hour to 76.5 fish/hour. The low catch in 2000 was probably due to low water conditions. The 2004 catch rate is the highest since 1992. The sample was distributed across sizes from 3 to 21 inches TL. The PSD was 47 and RSD-P was 23. Electrophoretic analysis of 50 age-0 largemouth bass resulted in a Florida largemouth bass allele frequency of 58.0% with 20% pure Florida largemouth bass genotypes. The results of the 2001-2002 creel survey indicate that the largemouth bass fishery is very popular with anglers. Directed angling effort for largemouth bass was 2.1 hours/acre and an estimated total of 24,982 bass were caught by anglers seeking that species.
• Crappie: The trap net CPUE for white crappie was high in 1997 (9.5 fish/net night) and even higher in 2001 (17.7 fish/net night), the highest we have ever recorded. However, by the fall of 2004, the catch decreased to 1.6 fish/net night. Though relative abundance was low, the catch was well distributed across lengths from 4 to 12 inches with PSD=96 and RSD-10=57. The low CPUE is evidence of a decline in relative abundance possibly due to a succession of poor recruitment years beginning in 2000 when water levels were low during spring and summer. Also, the creel survey from 2001-2002 revealed that crappie were the most targeted species at Lake Somerville resulting in an estimated total harvest of 14,900 crappie that year alone. The total angler catch of crappie in 2001-2002 was estimated to be 55,000. Only one black crappie was caught in the fall 2004 trap netting survey; a decrease from 35 in 2000. Again, poor recruitment classes from 2000 and subsequent years is probably the reason for the decline in relative abundance of black crappie. The growth rate of crappie is high in Lake Somerville. White crappie reach legal size (10 inches) by age 1 and black crappie by age 2.

Management Strategies

• TPWD will continue to monitor the temperate bass populations annually with gill nets.
• The centrarchid and ictalurid fisheries will be monitored again in 2008-2009.
• The creel results from 2001-2002 indicate that the crappie fishery is heavily exploited and numbers of crappie in our 2004 trap netting survey were much lower than they were in the 2000 survey. We will survey the crappie population again with trap nets in the fall of 2005.
• The abundance of hydrilla has decreased in the past two years and is no longer a serious problem. TPWD will work with the U.S. Army Corps of Engineers to continue monitoring and, if necessary, control this species should it become a problem again. TPWD will also consider the feasibility of enhancing the diversity of the native plant community in the reservoir.

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