Assessing the consistency of stream ecosystem characteristics in accounting for variation in trout abundance between summers with low versus high flow conditions
Water availability is a controlling factor in stream ecosystems with direct influences on habitat and aquatic ecosystem process, but little work has been done evaluating how biota respond to natural variations in low flow conditions during summer, and which biotic or abiotic features in the system may link most closely to aquatic vertebrates. I focus here on differences in biomass and abundance of salmonids in 16 streams in western Oregon across two years with distinctly different flow regimes that fall within the natural range of variation for summer flows in this region. Habitat is expected to be particularly important under low-flow conditions, so under higher flow conditions that provide adequate coastal cutthroat trout habitat, other factors such as food resources may be more limiting, and therefore more closely associated with local fish abundances. I found weak support for our hypotheses, but overall, the responses were not consistent across abundance or biomass density. Based on these results, I conclude that the lack of a shift towards or from any clear associations with changes in flow indicates that the system is resilient to the range of flows observed here, and/or that factors not included in my assessment are influencing trout populations.Keywords: summer low flow, coastal cutthroat trout, abiotic characteristics, biotic
characteristics, forested streams, headwater stream
