Do in-stream restoration structures enhance salmonid abundance? A meta-analysis Sarah L. Whiteway, Pascale M. Biron, Andre ´ Zimmermann, Oscar Venter, and James W.A. Grant Abstract: Despite the widespread use of stream restoration structures to improve fish habitat, few quantitative studies have evaluated their effectiveness. This study uses a meta-analysis approach to test the effectiveness of five types of in- stream restoration structures (weirs, deflectors, cover structures, boulder placement, and large woody debris) on both sal- monid abundance and physical habitat characteristics. Compilation of data from 211 stream restoration projects showed a significant increase in pool area, average depth, large woody debris, and percent cover, as well as a decrease in riffle area, following the installation of in-stream structures. There was also a significant increase in salmonid density (mean effect size of 0.51, or 167%) and biomass (mean effect size of 0.48, or 162%) following the installation of structures. Large dif- ferences were observed between species, with rainbow trout (Oncorhynchus mykiss) showing the largest increases in den- sity and biomass. This compilation highlights the potential of in-stream structures to create better habitat for and increase the abundance of salmonids, but the scarcity of long-term monitoring of the effectiveness of in-stream structures is prob- lematic. Re ´sume ´: Malgre ´ l’utilisation re ´pandue de structures de restauration des cours d’eau pour ame ´liorer les habitats des pois- sons, peu d’e ´tudes quantitatives ont e ´value ´ leur efficacite ´. Notre e ´tude emploie une me ´thode de me ´ta-analyse pour tester l’efficacite ´ de cinq types de structures internes de restauration des cours d’eau (seuils, de ´flecteurs, structures de couvert, blocs de pierre et grands de ´bris ligneux) sur a ` la fois l’abondance des salmonide ´s et les caracte ´ristiques physiques de leur habitat. La compilation des donne ´es provenant de 211 projets de restauration de cours d’eau montre une augmentation sig- nificative de la surface des fosses, de la profondeur moyenne, des grands de ´bris ligneux et du pourcentage de couvert, ainsi qu’une re ´duction des zones de courant apre `s l’installation des structures dans le cours d’eau. Il y a aussi une augmen- tation significative de la densite ´ (importance moyenne de l’effet 0,51, ou 167 %) et de la biomasse (importance moyenne de l’effet 0,48, ou 162 %) des salmonide ´s apre `s l’installation des structures. Il y a d’importantes diffe ´rences entre les espe `- ces, mais c’est la truite arc-en-ciel (Oncorhynchus mykiss) qui connaı ˆt les augmentations les plus importantes de densite ´ et de biomasse. Cette compilation souligne le potentiel que pre ´sentent les structures internes pour fournir un meilleur habitat pour les salmonide ´s et pour augmenter leur abondance; il reste cependant le proble `me qu’il y a peu de surveillance a ` long terme de l’efficacite ´ de ces structures internes. [Traduit par la Re ´daction] Introduction It is widely acknowledged that humans are negatively af- fecting the aquatic systems on which our survival depends (Richter et al. 1997; Ricciardi and Rasmussen 1999; Lake et al. 2007). In response to this degradation, the number of stream restoration projects has grown exponentially since the 1980s (Kondolf and Micheli 1995; Bash and Ryan 2002) and spending on restoration in the United States alone exceeds US $1 billion per year (Bernhardt et al. 2005; Roni et al. 2008). Despite over a century of restoration activity, many unanswered questions remain regarding the effective- ness of various restoration approaches, which is in part due to the lack of project monitoring, and inconsistent results from studies that have been monitored (Bernhardt et al. 2005). A number of literature reviews conclude that salmonid abundance typically increases following restoration (Bayley 2002; Roni et al. 2002, 2008), even if some case studies were not successful (e.g., Johnson et al. 2005; Rosi-Marshall et al. 2006; Klein et al. 2007). However, traditional litera- ture reviews, while qualitatively describing the results of Received 23 July 2009. Accepted 10 February 2010. Published on the NRC Research Press Web site at cjfas.nrc.ca on 16 April 2010. J21317 Paper handled by Associate Editor Jordan Rosenfeld. S.L. Whiteway 1 and P.M. Biron. Department of Geography, Planning and Environment, Concordia University, 1455 de Maisonneuve Blvd. W, Montreal, QC H3G1M8, Canada. A. Zimmermann. Northwest Hydraulics Consultants, Ltd., 30 Gostick Place, North Vancouver, BC V7M3G3, Canada. O. Venter. School of Biological Sciences, University of Queensland, Brisbane, Queensland 4072, Australia. J.W.A. Grant. Department of Biology, Concordia University, 7141 Sherbrooke Street West, Montreal, QC H4B1R6, Canada. 1 Corresponding author (e-mail: sarahwhiteway@gmail.com). 831 Can. J. Fish. Aquat. Sci. 67: 831–841 (2010) doi:10.1139/F10-021 Published by NRC Research Press