Federal Aid to Fish Restoration Annual Performance Report, Man-Made Lakes Investigations, July 1999

(1999) Federal Aid to Fish Restoration Annual Performance Report, Man-Made Lakes Investigations, July 1999. Natural Resources, Department of

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Abstract

This investigation documented the changes in the walleye population at Rathbun Lake since 1984 when it was characterized by low recruitment, low density and large fish. The goal of the study was to triple population abundance by 1995 through a regimented stocking schedule of 2,000 fry per acre (1984-1995), 10 extensively-reared fingerlings per acre (1984-1990) and 5 intensively-reared fingerlings per acre (1991-1995). Fry stocking was most influential in establishing strong year classes at Rathbun Lake in 1985, 1986, 1993, 1995, 1997 and 1998. Densities of these year classes in November were 9-27 fish per acre. Intensively-reared fingerling survival was greater than those raised extensively 4 out of 5 years. On the average, overwinter survival of intensively-reared fingerling survival was 11 times greater than extensively-reared fish. The primary reason for better survival of intensively-reared walleye was size at stocking; mean length was 7.4 inches as opposed to 5.0 inches for extensively-reared walleye. Another factor influencing survival of extensively-reared fingerlings was the hauling stress involving a 6 hour, 300 mile trip. In 1991-1997 a comparison of survival was made between fall-stocked and overwintered, spring-stocked intensively-reared fingerlings. Six sample years out of eight yielded valid test statistics. Spring-stocked fingerling walleye survived better than fall-stocked fingerlings in 1994, 1995, 1997 and 1998, while fall-stocked fish survived better in 1992 and 1993. In July 1997 and 1998, fingerlings marked with oxytetracycline (OTC) were stocked in watershed streams to assess their contribution to the lake population. Summer sampling with seine and backpack electrofishing showed good survival and excellent growth. Fall otolith samples in the lake showed no OTC marked fish had moved to the lake proper. Cost of stocking various groups of walleye and benefits, based on survival, were analyzed to provide alternatives for stocking strategies. The goal of tripling the walleye population at Rathbun Lake was attained by increasing recruitment through a regimented stocking schedule, and most importantly, the angler was not penalized by harvest regulations.