Trends in Biomass and Relative Weight of Brook Trout in Response to Introduction of Non-native Brown Trout in an Appalachian Mountain Stream

Native brook trout (Salvelinus fontinalis) have been declining in many areas of their range partially because of introduction of nonnative salmonids. Brook trout biomass and relative weight in the Conway River, Virginia, were evaluated for 24 years using regression to discern trends po- tentially associated with colonization of brown trout (Salmo trutta). The Rapidan River is adjacent to the Conway River and has brook trout but not brown trout, and thus this river was sampled over similar time intervals and served as a reference stream for this case study. Brook trout biomass in the Conway River varied from 21.8 to 58.5 kg ha–1 but displayed no temporal trends throughout the study (r 2 = 0.01; P = 0.81). Concurrently, brown trout biomass varied from 5.5 to 59.9 kg ha–1 and increased during the study (r 2 = 0.63; P < 0.01). Total salmonid biomass increased from 44 to 61 kg ha–1 over 1995–2000 to 80 to 107 kg ha–1 over 2014–2019 (r2 = 0.39; P < 0.02) suggesting brown trout biomass was additive and did not replace brook trout biomass. Brown trout composed <25% of salmonid biomass in the Conway River from 1995 to 2003 but increased to 40%–55% from 2008 to 2019. Brook trout biomass in the Rapidan River was approximately double that of the Conway River but also displayed no temporal trends during the study (r 2 = 0.01; P = 0.76). Mean relative weight of brook trout was relatively stable through time in the Rapidan River but appeared to decline in the Conway River (r 2 = 0.28; P = 0.06), possibly from density-dependent factors due to the increase in total salmonid biomass. In systems such as ours where brook trout do not appear to be negatively affected by brown trout, resource management agencies in eastern North America may wish to consider forgoing intensive eradication of expanding brown trout populations in lieu of brook trout habitat protection measures.

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