Evaluating the ability of tiger muskellunge to eradicate brook trout in Idaho alpine lakes

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.