Population Characteristics of Brook Trout in Idaho Streams and Alpine Lakes

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In western North America, nonnative brook trout (Salvelinus fontinalis) frequently threaten native salmonids via competition and hybridization, so fisheries managers often implement eradication programs for conservation purposes. In conjunction with such programs, managers often construct population models to evaluate the effects of different management strategies designed to control the undesirable population, but such models require demographic data (e.g., age, growth, sex ratios, and survival), which are lacking for western brook trout populations. Brook trout were sampled from 12 alpine lakes and two streams in Idaho, with total length varying from 80 to 380 mm and age varying from 1 to 11 yrs. Across all waters, the von Bertalanffy growth parameters L∞ varied from 231 to 490 mm (mean = 345 mm) and K varied from 0.15 to 0.76 (mean = 0.37). Survival estimates, constructed from age-length keys, were corrected for streams with mark-recapture data; for alpine lakes, corrections were made via gill net selectivity data. Survival varied from 0.30 to 0.56 (mean = 0.45), and except for one waterbody, estimates were minimally affected by correcting for capture efficiency. The proportion of the population that was male varied from 0.34 to 0.75 (mean = 0.53). Our results indicate that brook trout population vital rates in Idaho were similar to those observed in their native range, and were surprisingly similar between alpine lake and stream environments.