Long-term monitoring reveals the success of salmonid habitat restoration

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Louhi, Pauliina, Vehanen, Teppo, Huusko, Ari, Mäki-Petäys, Aki, Muotka, Timo
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2016
• Subjects: Northern Finland
• Online Access: http://dx.doi.org/10.1139/cjfas-2015-0546; http://www.nrcresearchpress.com/doi/full-xml/10.1139/cjfas-2015-0546; http://www.nrcresearchpress.com/doi/pdf/10.1139/cjfas-2015-0546

The growing concern on declining salmonid populations has resulted in numerous restoration projects with variable responses worldwide. In this spatially replicated multiyear study, we assessed the long-term (12 years postrestoration) effects of in-stream habitat restoration (i.e., addition of boulders or large woody debris (LWD) together with boulders) on densities of three age-classes of juvenile brown trout (Salmo trutta) in six forest streams in northern Finland. LWD combined with boulders was more beneficial, particularly for the larger trout (age-2 and older), than were boulder structures alone, indicating that the more diverse habitat created by LWD may have provided a safeguard against drought for the larger fish. Density of age-0+ trout showed a significant long-term increase in boulder-restored sections, providing evidence that log structures may need to be complemented by stony enhancement structures to guarantee the availability of suitable stream habitat for all trout age-classes. As trout densities are known to exhibit inherently wide interannual variability that tracks climatically induced hydrological variation, long-term postrestoration monitoring that encompasses extreme hydrological events is critical for evaluating the success of restoration projects.