Assessing Habitat Suitability for Juvenile Atlantic Salmon in Relation to In‐Stream Restoration and Discharge Variability

Abstract

In-stream restoration often aims at increasing the availability of the stream habitat suitable for salmonid fishes, thus creating potential for increased fish abundance. We assessed the success of in-stream restoration of River Kiiminkijoki, northern Finland, by combining River2D habitat hydraulic modeling and fish density monitoring at the same sites, with data from multiple restored and reference reaches for 3 years both before and after restoration. We modeled the effects of restoration on the area suitable (weighted usable area, WUA) for juvenile Atlantic salmon from post-hatching to age-1 fish. Wetted width in the restored reaches increased by 8.1% on average compared with only −0.2% change in the reference reaches. Habitat time series across 10 years showed significant increases in the amount of suitable habitat under summer conditions for both age-0 and age-1 salmon. However, improvement of overwintering habitats was marginal or nonexistent. Densities of age-1 salmon showed no response to restoration. Low river discharge during the winter was correlated with low salmon densities the following summer. It thus appears that variability in wintertime discharge, and associated high interannual variation of WUA values, overrode the almost 20% increase in average post-versus pre-restoration summertime WUA. Our study shows that the combination of hydraulic modeling and biological monitoring is a promising approach to stream restoration assessment.

Long‐term performance of in‐stream restoration measures in boreal streams

“…Quantitative analyses of substrate composition after restoration also showed scarcity of bed material suitable for salmonid spawning. Lack of spawning gravel may restrict the recovery of salmonid populations (Palm et al, 2007), although the effects of gravel addition on fish populations are not always obvious (Koljonen et al, 2012). Therefore, if spawning grounds are to be added as part of stream enhancement projects, careful design is needed to avoid failures in gravel placement (Barlaup et al, 2008).…”

Seamless Mapping of River Channels at High Resolution Using Mobile LiDAR and UAV-Photography

“…While small reaches of shallow rivers can be surveyed using tachymetry [32] or a pole-mounted Real Time Kinematic Global Navigation Satellite System (RTK-GNSS), the limits of these methods are reached fairly quickly as the size of the area to be surveyed or the water depth increases. Furthermore, the accuracy of the terrain model that can be created based on points surveyed in this fashion depends largely on the density of the point pattern, which is directly proportional to time spent surveying.…”

Modelling changes in trout habitat following stream restoration

“…The objectives of this study were (1) to evaluate initial changes in habitat quality using a two‐dimensional (2D) hydrodynamic modelling approach and (2) to compare multiple metrics of habitat quality. This 2D modelling approach has been successfully applied to quantify changes in fish habitat for other stream restorations (Boavida, Santos, Cortes, Pinheiro, & Ferreira, ; Gard, ; Koljonen, Huusko, Mäki‐Petäys, Louhi, & Muotka, ). As fish populations may take five or more years to respond to restoration (Binns, ; Hunt, ), biological monitoring targets were not evaluated for this initial investigation.…”