Genetic evaluation of walleye (Stizostedion vitreum vitreum) stock structure and recruitment in Claytor Lake, Virginia

Walleyes from several geographic areas have been stocked in Claytor Lake since 1940. Fish presently in the reservoir may have originated from the stocking of Kansas, Nebraska, or Pennsylvania walleyes, or may possibly be descended from a native New River walleye strain. Recent stockings (1974, 1975, 1977, 1979) utilized walleye fingerlings of primarily Kansas origin. A biochemical genetic approach was used to evaluate the present stock structure of Claytor Lake walleyes. Electrophoretic phenotypes for skeletal muscle malate dehydrogenase (MDH) and parvalbumin were identified (using starch and polyacrylamide gel electrophoresis techniques, respectively) for 217 walleyes from three Claytor Lake sites. MDH-B² allelic frequency was significantly higher in stocked than in unstacked cohorts. Muscle parvalbumin frequencies were independent of cohort, but were dependent upon collection site and sex. Parvalbumin-a allelic frequency was higher in male than female walleyes from Claytor Lake. Sex of Claytor Lake walleyes was dependent upon both collection site and cohort, with unstocked cohorts containing more female fish than the stocked cohorts (independence. G-tests). At least two genetically distinct stocks of walleyes presently survive in Claytor Lake. Allelic frequencies of Claytor Lake walleyes were compared (heterogeneity G-test and STP) to those of 428 walleyes collected from Kansas, Nebraska, and Pennsylvania in an effort to identify existing Claytor Lake stocks and to evaluate the effectiveness of recent stockings. Phenotypic frequencies for both MDH and muscle parvalbumin conformed to expected Hardy-Weinberg proportions in samples from all geographic areas, confirming assumptions of genetic control by two co-dominant alleles. Kansas, Nebraska, and Pennsylvania walleyes were different from one another, as were stocked and unstocked Claytor Lake cohorts. Unstocked Claytor Lake cohorts were similar to Nebraska walleyes. Stocked Claytor Lake cohorts were different from all three brood fish sources, probably because stocked cohorts contain both stocked Kansas fish and fish originating from natural reproduction by some other stock in Claytor Lake (probably Nebraska fish). Based on allelic frequency differences between stocked and unstocked cohorts, the stocking of Kansas fingerlings in Claytor Lake during 1975 - 1978 contributed approximately 53 percent of the recruitment to those cohorts in years during which stocking occurred, and approximately 36 percent of the total recruitment to the 1975 - 1978 cohorts. The effectiveness of the present Claytor Lake stocking program is similar to that reported for other walleye stocking programs. Based on 1975 replacement costs for walleye fingerlings, each stocked walleye caught by a Claytor Lake angler during 1976 - 1978 cost approximately $14.78. Low levels of angler harvest may make the continuation of a fingerling walleye stocking program on the reservoir economically unjustifiable. Multiple genetic stocks of walleyes can exist in a relatively small reservoir ecosystem, particularly in mainstream impoundments where very diverse habitats are often spatially isolated due to the large size of these reservoirs. The existence of these multiple stocks is an important consideration for effective management. Particular management strategies may not impact all genetic stocks in the reservoir equally (particularly if they are spatially isolated), and therefore may not produce the desired or expected results if the population is treated as being homogeneous.

Ph. D.