No abstract

Increased growth, improved survival, and genetic protection of wild stocks have been suggested as benefits of stocking triploid (i.e., sterile) salmonids for recreational fisheries. We examined the return rates and growth of mixed‐sex diploid (2N), mixed‐sex triploid (3N), and all‐female triploid (AF3N) rainbow trout Oncorhynchus mykiss across 28 alpine lakes. Equal numbers of each treatment group were stocked in 2001 and 2003 and sampled 3–4 years later. During 2004 and 2005, a total of 75 2N and 36 3N marked rainbow trout were recaptured. Taken together, the 2N fish accounted for an average of 0.68 of the total marked fish caught, and the combined proportions of test fish (including netting and angling) differed significantly between the test groups and were consistent across survey years. During 2006 and 2007, a total of 60 2N, 31 3N, and 208 AF3N marked rainbow trout were recaptured. The mean length of the test fish was similar between test groups within sampling years. Overall, the return of 3N rainbow trout to alpine lakes in Idaho was low compared with that of 2N trout, whereas AF3N trout appeared to return in higher proportions than both of the other groups. The triploid stocks studied in this evaluation did not show any growth advantages over the duration of the study. Study design limitations may have contributed in part to some of the differences in the number of 2N and 3N rainbow trout captured. However, our results suggest that fisheries managers should consider all‐female triploid rainbow trout as a low‐risk option for maintaining alpine lake fisheries while minimizing the impact on native stocks.Received January 27, 2010; accepted November 16, 2010

In western North America, nonnative Brook Trout Salvelinus fontinalis in alpine lakes threaten the persistence of native trout and often offer limited sport fishing opportunity as they are prone to stunting. Stocking tiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy), which are reproductively sterile, may be an option to eradicate Brook Trout in some alpine lakes. We used floating gill nets to survey 17 alpine lake Brook Trout populations, then stocked 13 lakes with tiger muskellunge, with four additional lakes serving as controls. Tiger muskellunge were stocked at a mean TL of 317 mm and a density of 40 fish/ha. Brook Trout were resampled for 4 or 5 years after stocking to evaluate changes in Brook Trout TL and CPUE (fish/net‐night). Declines in CPUE were substantial for both treatment and control lakes but were significantly greater in treatment lakes. Mean Brook Trout CPUE in treatment lakes declined from 23.1 fish/net‐night to 2.3 fish/net‐night 5 years after stocking tiger muskellunge, whereas in control lakes, CPUE declined from 25.5 fish/net‐night to 7.8 fish/net‐night 5 years later. Complete eradication appeared to occur in two lakes within 2 years, and in two more lakes by year 5. In lakes where tiger muskellunge were stocked, the proportion of Brook Trout ≥250 mm TL in the catch increased significantly in years 1, 2, and 4 after stocking (compared with prestocking data), whereas no increase occurred in control lakes. Tiger muskellunge were most successful in reducing Brook Trout CPUE in lakes with no inlets or outlets, while elevation and lake area may also have played a role. Our results suggest tiger muskellunge can improve the size structure and potentially eradicate Brook Trout populations from some alpine lakes. However, we recommend combining any tiger muskellunge stocking with other conventional removal methods to increase the likelihood of successful eradication. Received October 27, 2014; accepted March 22, 2015

No abstract