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In hydropeaking rivers, flow regulation typically follows demands in electricity consumption. One hundred and twenty one adult salmon were tagged with radio transmitters to study their spawning run migration patterns in hydropeaking conditions. The fish were released in small groups into the rivers Kemijoki and Iijoki, in Finland. Typically, salmon made subsequent up‐ and downstream movements ascending upstream to the tailrace of the power station and then descending again downstream to lower water velocities. The rate of these migration attempts was higher in mid‐summer and at relatively high flows. On an hourly basis, the pattern of migration attempts followed a trend of increasing attempts at dawn and higher discharges and a decreasing trend towards dusk and low flows. It was concluded that day length and discharge were the most important environmental factors, while temperature had less effect on the pattern of migration attempts. [ABSTRACT FROM AUTHOR]

Abstract: Three‐dimensional distribution of adult upstream‐migrating Atlantic salmon, Salmo salar L., was studied in three power plant tailrace channels on the large, regulated River Kemijoki in northern Finland using novel pressure sensor radio telemetry. The salmon swam mostly at depths of 1–4 m below the surface, with the salmon‐specific averages ranging from 1.3 to 6.4 m. When approaching a power plant, no change in swimming depth was observed. The horizontal locations of salmon in the two regularly shaped tailrace channels peaked at 5–10 m distance from the shoreline and showed a positively skewed distribution with a tail towards the central part of the tailrace. A graphical presentation of salmon locations in the tailrace channel and data on swimming depth and distance from the shoreline may prove useful in determining the location and design of a fishway entrance and in dimensioning attraction flow. [ABSTRACT FROM AUTHOR]

Studies on the effectiveness of in-stream restoration have generally reported increased habitat heterogeneity, but biological responses have been more variable. One hypothesis states that the restored habitat structure does not persist through time, resulting in fading biological responses. We studied the durability of in-stream restoration in northern and central Finland by assessing short-term (0-1 years) and long-term (≥10 years) changes in habitat structure after restoration. In 2010, we repeated the field surveys first conducted in the 1990s in 27 stream reaches. We also made similar habitat measurements in ten near-pristine sites. Restoration caused significant changes in the stream habitat that either remained unaltered or were reinforced through time, with several of the restored sites resembling closely the near-pristine reference sites 10-20 years post-restoration. Cover of aquatic mosses initially decreased sharply but recovered close to near-pristine level within about 15 years. However, substrate variability still remained somewhat lower in the restored than in near-pristine streams. Individual restoration structures had changed little over time. The most evident failures were the disappearance and entrenchment of gravel beds. Restoration of our study sites had shifted the sites to a trajectory towards more natural habitat conditions, and our results do not support the hypothesis that gradual destruction of the restored habitat might partly explain weak biological responses. From the perspective of channel evolution, the restorations were still fairly recent, and only long-term monitoring will tell if the sites will continue on the trajectory to hydromorphological and ecological recovery. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Temporal coherence or spatial synchrony refers to the tendency of population, community or ecosystem dynamics to behave similarly among locations through time as a result of spatially-correlated environmental stochasticity (Moran effect), dispersal or trophic interactions. While terrestrial studies have treated synchrony mainly as a population-level concept, the majority of freshwater studies have focused on community-level patterns, particularly in lake planktonic communities. We used spatially and temporally hierarchical data on benthic stream invertebrates across six years, with three seasonal samples a year, in 11 boreal streams to assess temporal coherence at three spatial extents: 1) among regions (watersheds), 2) among streams within a region, and 3) among riffles within a stream, using the average of correlation coefficients for stream/riffle pairs across years. Our results revealed the primacy of strongly synchronized climatic factors (precipitation, air temperature) in inducing temporal coherence of macroinvertebrate assemblages across geographically distinct sites (i.e. Moran effect). Coherence tended to decrease with increasing spatial extent, but positive coherence was detected for most biological variables even at the largest extent (about 350 km). The generally high level of coherence reflected the strong seasonality of boreal freshwater communities. A hydrologically exceptional year enhanced the synchrony of biological variables, particularly total macroinvertebrate abundance. Regionally low precipitation in that year led to a substantial decrease in benthic densities across a broad spatial extent, followed by a rapid post-drought recovery. Coherence at the among-riffle (within-stream) extent was lower than expected, implying that local-scale habitat filters determine community dynamics at smaller spatial extents. Thus, temporal coherence of stream benthic communities appears to be controlled by partly different processes at different spatial scales. [ABSTRACT FROM AUTHOR]

Stream-dwelling salmonids and bullheads occupy similar resource niches in northern rivers. It is therefore tempting to assume that they might be involved in a competitive interaction, with potential implications for the habitat use and growth of brown trout ( Salmo trutta). We conducted artificial-stream experiments to test whether a putative competitor, Alpine bullhead ( Cottus poecilopus), had an effect on the habitat use of under-yearling (0+) and yearling (1+) trout. We hypothesised that (i) 1+ trout would be competitively superior to 0+ trout, forcing the younger fish to suboptimal habitats, and that (ii) bullhead might affect the habitat use and prey selection of 0+ trout but less so that of 1+ trout. Against our predictions, no effect of bullhead was found on the habitat use of either age class of brown trout. Instead, yearling trout seemed to force bullheads to suboptimal microhabitats with high current velocities. Presence of yearlings also decreased the growth of under-yearling fish and caused a shift in their diet composition. These findings suggest that competitive interactions may not limit the coexistence of brown trout and bullheads in boreal rivers. Intraspecific interactions between trout age classes may be more important, with potentially detrimental effects on the growth and overwintering success of 0+ trout. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The article presents a study which examines how restoration projects aimed at the enhancement of juvenile brown trout affects benthic macroinvertebrates. The study uses a before-after-control-impact (BACI) design and a space-time substitution design. Results show that community composition differed between restored and natural streams but not on channelized and restored streams. Also, assessing restoration success must focus on using multiple organism groups in stream and riparian ecosystems.

Growth of the body length in vertebrates is well known to be unidirectional, with organisms progressively increasing in body size as they become older. However, there is evidence that body length shrinkage is a survival strategy for some vertebrates under unfavourable environmental conditions. Here we report both experimental and field evidence that the body length of young stream-dwelling salmonids can decrease in winter. In examining how juvenile salmonid fish responded to harsh environmental conditions, we were faced with unexpected and previously undocumented observations in terms of growth performance, indicating that fish do shrink in harsh winter conditions. Young salmonids showed significant shrinking of individual body length, up to 10% of the body length, over the course of winter. The dynamics of the growth in length of these fish can be explained by a combination of anorectic stress and environmental conditions. Under stable, sheltered underwater conditions fish were best able to maintain positive growth in length. We propose that growth in body length of a vertebrate animal can be temporally negative, individuals suffering from nutritional deficits shrinking in their length in addition to losing their body mass. There is circumstantial evidence that subsequent compensatory growth can have unexpected and dramatic longer-term costs. Experimental approaches, both field- and laboratory based, are sorely needed to reveal how common a phenomenon negative structural growth is among animals, and what the consequences are for individual performance, and, furthermore, for population dynamics. [ABSTRACT FROM AUTHOR]

The effect of water source and removal of dead eggs by hand on egg survival of brown trout Salmo trutta and Atlantic salmon S. salar was studied experimentally in a hatchery trial, which started from fertilization in October and lasted until egg eye-up in early March; no antifungal chemical treatments were used. The experimental treatments were water source (surface water, filtered surface water, or groundwater), species, and hand-picking of dead eggs (used, not used); we used four replicates per treatment, resulting in 48 batches. Incubation of eggs in groundwater yielded higher egg survival to eye-up than incubation in surface water or filtered surface water. Hand-picking of dead eggs enhanced survival of eggs incubated in surface water but not those incubated in groundwater. The best combination for egg survival in both species was the use of groundwater incubation without hand-picking of dead eggs. [ABSTRACT FROM AUTHOR]

We examined microhabitat selection by age-0 brown trout Salmo trutta and grayling Thymallus thymallus in experimental flumes with channelized (monotonic configuration and low amount of stones) or restored (highly heterogenous substrate) streambed structures at low and high flows and at different times of year. Both brown trout and grayling used higher water velocities in summer high flows. Both species also occupied higher-velocity microhabitats in channelized than in restored flumes, but for grayling this difference was significant only in summer. Overall, brown trout used lower water velocities than grayling. In winter and in high-flow treatments, brown trout were more susceptible to downstream displacement in channelized compared with restored flumes. For grayling, the effect of flume type occurred only in winter when fish were located further downstream in channelized flumes. Both species were more aggregated in winter. Brown trout also exhibited a different spatial pattern among the flume types, being more aggregated in channelized flumes. The flume type did not affect the spatial pattern of grayling, but they were more contiguously distributed in high flows. Because both brown trout and grayling used lower velocities in winter, the potential for interspecific competition may increase in winter. The spatiotemporal differences in fish habitat preferences suggest that assessment of the physical carrying capacity of a stream in relation to species-specific habitat requirements is a prerequisite for effective management of brown trout and grayling populations. Preference curves indicated that the habitat requirements were narrowest in winter and that the crucial habitat factor was the availability of flow refuges; thus, the curves helped identify the timing of, and the key factor underlying, a potential habitat bottleneck in northern boreal streams. [ABSTRACT FROM AUTHOR]