The effects of stream canopy management on macroinvertebrate communities and juvenile salmonid production in a chalk stream

Abstract

The effects of changes in shading (through riparian canopy removal and re-growth) on juvenile salmon, Salmo salar L., trout, Salmo trutta L., and grayling, Thymallus thymallus (L.) populations, and macroinvertebrate biomass and species composition in a chalk stream in southern England were examined. Low levels of in-stream weed growth, because of shading by closed tree canopy, diminished macroinvertebrate production and diversity. 0+ salmon and trout had lower densities under closed canopy, relative to adjacent open sites with substantial weed cover, where fish were also found to be larger. Canopy removal positively affected the growth of aquatic macrophytes and the availability of potential prey for juvenile salmonids. The findings have implications for the management of chalk streams, in particular, that riparian tree canopy should be managed to prevent complete closure, and excessive cutting of weed should be avoided where salmon production is below sustainable levels.K E Y W O R D S : canopy, chalk stream, grayling, macroinvertebrate, salmon, trout.

Autumn microhabitat breadth differs between family groups of Atlantic salmon parr (Salmo salar) in a small chalk stream

“…Juvenile salmon in chalk streams prefer areas with weed cover, which provide shelter from predation risk, particularly at night (Riley et al. , ). The highest electivity value observed for weed cover was by Family 2 for proportions of 30–50%, which was the most infrequently encountered category in samples (Table ).…”

Do triploid Salmo trutta stocked into a chalk stream in the spring prey on wild Salmo salar smolts?

“…2) was 200 m long with a mean width of 12.5 m and was located between the discharges of the Blackbridge and Falloden carrier streams into the main river (see Riley et al 2009b). Stocking site A (51°03′14″N; 01°18′49″W) ( Fig.…”

Quantifying the effect of semi‐natural riparian cover on stream temperatures: implications for salmonid habitat management

“…Likewise, deeper water and more complex in‐stream components would provide cover from predators so the advantages of riparian canopy would be diminished (Riley et al . ). Larger watercourses convey larger volumes of water; therefore, the temperature regulation effect of riparian cover is less apparent than in their smaller equivalents (Larson & Larson ; Quinn & Wright‐Stow ).…”