An Evaluation of Rainbow Trout Strains in the Sport Fishery of Three Wisconsin Lakes and for Trout Ranching in Minnesota Winterkill Lakes

Various strains of rainbow trout (Salmo gairdneri) were stocked at legal size in spring in three Wisconsin lakes containing warm water fish populations, and angler harvest was determined by creel surveys. One lake, Sunset (26 ha), received the typical pattern of fishing pressure, i.e. high peak effort on opening weekend of the fishing season in early May, and an exponential, irregular decline in effort to a low level before the end of the first month. Two lakes, Keshena (9.9 ha) and LaBelle (9.3 ha), which were controlled by the Menominee people and which had no closed season, were subject to low, irregular angling pressure throughout summer. Estimated percentage of stocked rainbow trout harvested at Sunset Lake in May of 1975, 76, 78, and 79 was 41, 64, 67, and 50, respectively. Only 10 and 4% of the stocked trout were estimated to be harvested during summer 1978 in the other two lakes. Estimated harvest of the Nevin strain in Sunset Lake varied significantly from year to year, making between year comparison of strains impossible when only one strain was stocked in a lake. Variation in harvest of the Nevin strain was the result of differences in catchability and not to differences in fishing pressure or number of trout stocked. When more than one strain was stocked in a lake in the same year, the Nevin strain was found to be the most vulnerable to angling under both observed patterns of fishing pressure. The Nevin strain was more vulnerable (caught more rapidly and more caught) than a Hybrid strain (Desmet ♂ X McConaughy ♀) to both shore and boat anglers in Sunset Lake in 1979. It was more vulnerable (more caught) than another Hybrid strain (Manchester X Wytheville) and the Erwin strain in the Menominee lakes in 1978. The ratio of estimated percentages of stocked trout harvested was the same in the Menominee lakes, 3:2:1, for the Nevin, Hybrid, and Erwin strains, suggesting that differences in catchability were genetically determined. Three strains of spring-spawning rainbow trout were stocked as fingerlings in five winterkill lakes, 430-483 trout/ha, on the Red Lake Indian Reservation, Minnesota in June 1978. Estimated percentages of stocked trout that survived to October were 37, 18, 11, 4, and O for a hybrid strain (Desmet ♂ X McConaughy ♀) in Fox Lake, the Erwin strain in Lakes Little Shell and Little Bass, and the Wisconsin Spring Spawning strain in Lake McCall and Muerlin, respectively. Temperature, dissolved oxygen, and food supply appeared to be adequate for survival in all lakes, and the major cause of mortality was believed to be predation, especially from birds. Because predacious birds or fish were more abundant at the lakes stocked with the Wisconsin Spring Spawning strain, its survival could not be compared with that of the other strains in the other lakes, which were similar in physical and biological characteristics. The Hybrid may have survived better because it was less domesticated and, therefore, perhaps more wary of predators. Growth varied among lakes, mean weight in October ranging from 112 g to 164 g, and the differences were caused by environmental rather than genetic differences. Success of trout ranching on the Reservation was limited by small size of trout (mean of 131 gin all lakes combined in October), "muddy flavor", and low yield, 11.2 kg/ha. These problems probably could be solved. Future research would be needed to determine the manner and extent to which yield could be increased, to identify and assess causes of mortality, and to determine if "muddy flavor" could be masked by smoking or removed by harvesting later in fall. Without such research, the incentive for investment and labor in trout ranching will not develop.Wisconsin Cooperative Fishery Research Unit and College of Natural Resource