Conflicting effects of woody debris on stream fish populations: implications for management

• Published in: Freshwater Biology
• Main Authors: LANGFORD, T. E. L., LANGFORD, J., HAWKINS, S. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: Minnows; Anguilla anguilla
• Online Access: http://dx.doi.org/10.1111/j.1365-2427.2012.02766.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2427.2012.02766.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2427.2012.02766.x

Summary 1. Coarse woody debris (CWD) in stream channels causes changes in flow, sedimentation and ratios of pool to riffle areas. There is a consensus among fishery managers and scientists that CWD is beneficial to stream fish communities because of its enhancement of habitat diversity, invertebrate production and cover. Our hypothesis was that CWD accumulation or introduction would not increase in‐stream habitat capacity for all species and their ontogenic stages at reach and stream scales. 2. The study used a system of gravel‐bed streams with naturally dynamic CWD accumulations and a fish community consisting of Salmo trutta , Cotttus gobio , Phoxinus phoxinus , Lampetra cf planeri , Nemacheilus barbatulus and Anguilla anguilla . Cotttus gobio and L . cf planeri are protected by an EU Directive and S. trutta is exploited for angling. Riffles, pools and CWD matrices, considered as the basic habitat/spatial units of channel structure, were sampled separately and abundance of each fish species quantified seasonally at each spatial scale. 3. Multiple‐pass electric fishing techniques were used. Capture efficiencies were calculated for species, habitat and season. Areal densities (number m −2 ) were compared for habitat types and season using nonparametric anova . Canonical analysis and stepwise multiple regression were used to show the most influential physical variables on fish density. Densities were also compared by unit volume (numbers m −3 ) for pools and CWD matrices to investigate direct three‐dimensional use for cover. Reach‐scale densities for each fish species in relation to habitat composition were made using Spearman rank correlation of habitat‐scale densities with proportionate areas of the different habitat units in the reach. 4. Habitat‐scale densities of bullheads and age 0+ trout were negatively correlated with depth and CWD areas for some seasons. Densities of lampreys, older trout, eels and minnows were positively correlated with depth in some seasons. Water depth had the most consistent ...