Growth of Norris Reservoir Walleye during the First Twelve Years of Impoundment

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Abstract
Age and growth of 1210 Norris Reservoir, Tennessee, walleyes (Stizostedion v. vitreum) taken by various methods, 1942-1948, were studied by the scale method. These data extend previous information to cover the first 12 yrs. of impoundment. The ratio of avg. total length/standard length was 1.184. Walleyes reach legal size (15 in.) in summer as 1-yr.-olds. The largest and oldest male was 23.2 in. long, weighed 4.2 lb., and was 8 yrs. old; 33 females in the sample were 6-, 7-, and 8-yr.-olds. The largest and oldest female was 30.1 in. long, weighed 111.9 lb., and was 8 yrs. old; 13 females in the sample were 6-, 7-, and 8-yr.-olds. Larger known specimens were undoubtedly females and 10 or more yrs. old. Avg. lengths of females exceeded those of males by from 0.9 in. at 1 yr. of age to as much as 8.9 in. the 8th yr. Norris walleyes feed heavily on young of the gizzard shad (Dorosoma cepedianum) during most of their lives. Upon reaching a length of 20 to 23 in. the walleyes commence to feed on adult gizzard shad (8-10 in. and larger). This is near the max. length known for males whereas females attain this length in 3-5 yrs. Several females had adult shad 8-13.2 in. long in their stomachs while only the largest male of the sample is known to have eaten an adult shad. An ability of females to utilize adult shad at relatively early ages undoubtedly accounts for the repeated capture of prize-winning walleyes in Norris Reservoir. Avg. lengths attained in each successive yr. of life from the 1st through the 8th, sexes combined, were: 10.3, 16.4, 18.7, 19.9, 20.8, 21, 22.1, and 24.9 in. Rate of growth increment through the first 7-9 yrs. of impoundment probably correlated with increased food supply; it decreased more recently through the 12th yr. due to significant increases in population density. The present avg. growth rate remains as rapid as during the first 5 yrs. of impoundment. Intra-seasonal growth of fish of the first 4 age groups is rapid in spring and early summer (mid-May and June), virtually ceases at times in mid-summer (July), and is again rapid in late summer (mid-Aug. to mid.Sept.); autumn growth is slow. No increase in length occurs between the end of Nov. and the time of annulus formation in Spring. This irregular intra-seasonal growth probably results from the tendency of walleyes to frequent deep water in July and the proclivity of young fish for shallow water until late summer. Notable success of early and mid-summer deep-trolling for wall-eyes doubtless depends on these factors. Avg. "K" for 57 young-of-the-yr. was 1.38; for all other fish used (1087) it was 1.5. Length-wt. relationship (1151 fish up to 26 in. and 7 lb.) was described as W = 0.85276 x 10-5 L3T097; increase in wt. vary about as the 3.1 power of increase in length. Population dominance by walleyes of the 1942 yr.-class (7th yr. of impoundment) was indicated, and significant increase in population density (at possible expense to the black crappie, Pomoxis nigro-maculatus) occurred in the 9th-llth yrs. of impoundment (1944-1946). This was probably due to the long-term cycle of spring-and-early-summer water levels which results in periodic improvement in food and survival conditions. Water management practices, abundant available food, and long growing seasons are important factors in maintaining rapid growth of Norris walleyes despite several-fold incr. in population density. Increased fishing pressure, following removal of the closed season in 1944, had an unknown, probably beneficial, effect.

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