Rainbow trout versus brook trout biomass and production under varied climate regimes in small southern Appalachian streams
Many Appalachian streams historically dominated by Brook Trout Salvelinus fontinalis have experienced shifts towards fish communities dominated by Rainbow Trout Onchorhynchus mykiss. We used empirical estimates of biomass and secondary production of trout conspecifics to evaluate species success under varied thermal regimes. Trout populations were sampled in 13 Appalachian streams from Maryland to North Carolina during summer 2012, and biomass and production of trout species were examined in relation to habitat and water temperature data. Rainbow Trout and Brook Trout were found co-occurring at three sites, Rainbow Trout populations were encountered at an additional five sites, and Brook Trout populations were also encountered at an additional five sites. Brook Trout co-occurred at one site with Brown Trout Salmo trutta. Biomass estimates for Brook Trout and Rainbow Trout ranged from 0.01 to 1.15 g·m-2 and 0.35 to 1.60 g·m-2, respectively. Secondary production estimates for Brook Trout and Rainbow Trout ranged from 0.12 to 1.09 g·m-2·yr-1, and from 0.06 to 7.48 g·m-2·yr-1, respectively; thus, Rainbow Trout tended to dominate production in study streams where both species co-occurred. Brown Trout was 1.14 g·m-2 and production was 1.20 g·m-2·yr-1; thus, it also dominated biomass and production compared to Brook Trout. Logistic regressions revealed percent production of Rainbow Trout had a positive relationship with mean minimum winter air temperature (P<0.05) and, conversely, percent production of Brook Trout had a negative relationship with mean minimum winter temperature (P<0.05). Thus, temperature coupled with interspecific competition could be influencing Brook Trout production in these mixed trout streams. Our results suggest that with increasing winter temperatures Brook Trout production could decrease, further highlighting the need to mitigate the effects of climate change on Brook Trout in their native range.