Re‐building brown trout populations in dredged boreal forest streams: in‐stream restoration combined with stocking of young trout

Abstract

Summary 1. Rivers in boreal forested areas were often dredged to facilitate the transport of timber resulting in channels with simplified bed structure and flow fields and reduced habitat suitability for stream organisms, especially lotic fishes. Currently, many streams are being restored to improve their physical habitat, by replacing boulders and gravel and removing constraining embankments. The most compelling justification behind stream restoration of former floatways has been the enhancement of native fish populations, specifically salmonids. 2. We examined the success of a stream management programme aimed at re‐building diminished brown trout (Salmo trutta) populations by monitoring densities of young‐of‐year and older trout in 18 managed and three reference streams during 2000–2005. Rehabilitation included in‐stream restoration combined with a 5‐year post‐restoration period of stocking young brown trout. Our space‐for‐time substitution design comprised four pre‐management, four under‐management, 10 post‐management and three reference streams. 3. Densities of young‐of‐year brown trout, indicating population establishment, were significantly higher in post‐ compared with pre‐management streams. However, density of young‐of‐year brown trout in post‐management streams was significantly lower compared with near‐pristine reference streams. Furthermore, success of managed brown trout population re‐building varied, indicating stream‐specific responses to management measures. Density of burbot (Lota lota), a native generalist predator, was associated with low recruitment of brown trout. 4. Stream‐specific responses imply that rehabilitation of brown trout populations cannot be precisely predicted thereby limiting application. Our findings support the importance of adaptive stream restoration and management, with focus on identifying factor(s) limiting the establishment of target fish populations.

Demonstration Restoration Measures in Tributaries of the Vindel River Catchment

“…One reason for stream restoration in northern Europe is the rehabilitation of brown trout populations, which are popular game fish. Reconstruction of lost spawning beds and retention of added spawning bed substrate is key for success in this matter (Rosenfeld et al 2011, Luhta et al 2012) and these goals are more likely to be reached in slow-flowing, boulder-rich stream reaches like the demonstration sites. Another reason for stream restoration is increasing water retention during heavy rains and flood-erosion events, predicted to become more frequent as a result of climate change (Nilsson et al 2013).…”

“…Growing awareness of the value of healthy ecosystems and the need to adapt to future changes in climate has put a focus on restoration of ecosystems, especially rivers (Bernhardt et al 2005, Palmer et al 2008, Arthington et al 2010. Recent river restoration approaches include renaturalization of flows; that is, environmental flows (Tharme 2003) and flood protection (Nardini and Pavan 2012); reconfiguration of channels (Nilsson et al 2005a); defragmentation, that is, dam removal (Bednarek 2001, Lejon et al 2009), and rebuilding of populations (Luhta et al 2012). There is a dearth of detailed, scientifically based guidelines for stream restoration.…”

Resource use by juvenile brown trout andAlpine bullhead: influence of interspecific versus intraspecific competition

“…Some field studies have indicated that the numbers of brown trout are reduced in areas preferred by bullheads (Gaudin & Caillere 1990;Hesthagen et al 2004;Luhta et al 2012), yet other studies have concluded that bullheads have no significant effects on densities of juvenile trout or Atlantic salmon (Pihlaja et al 1998;Jørgensen et al 1999), and even opposite results, a salmonid being superior to bullheads, have been reported. In fact, the presence of yearling, but not of smaller, trout forced ABs to shift to microhabitats with higher current velocities.…”

Riparian and in‐stream restoration of boreal streams and rivers: success or failure?

“…Luhta et al, 2012) if they included other measures, such as fish stocking, that enhanced natural recovery after physical restoration. We only excluded studies (e.g.…”