Upstream migration by adult salmonids is impeded by dams in many regulated rivers, as is the case for landlocked Atlantic salmon, Salmo salar, in the River Klarälven, Sweden. There, the salmon cannot reach the spawning grounds due to the presence of eight dams. Hence, hatchery-reared smolts are released downstream of the dams, and upstream migrating spawners are caught in a trap at the lowermost dam before transported by truck to the spawning grounds past the dams. To identify the spawning grounds and compare the behavior of wild and hatchery-reared Atlantic salmon during upstream migration and spawning, 34 wild and 28 hatchery-reared, radio-tagged Atlantic salmon were followed during their spawning migration from August to October 2011. Half (50%) of the hatchery fish, but only 11,8% of the wild fish ended up as fallbacks, i.e. they migrated past the first downstream power station, and did not spawn. A significantly higher proportion (21.4%) of hatchery- reared salmon moved in an erratic way, with several up and down stream movements, when compared to the wild salmon (5.9%). When looking at the salmon that stayed in the river (exc. fallbacks), wild individuals exhibited a holding behavior (little or no movements before presumed spawning) more often (86.7%) than the reared ones (50%). The wild salmon also held position (and presumably spawned) for longer time (25.4 days) than the reared salmon (16.1 days). Reared salmon held position, on average, 10 km further upstream than wild salmon, passing the presumed best-quality spawning habitat. The migration speed (average 17.4 km/day) between two logger stations did not differ between wild and reared fish or between sexes. Our results suggest that the reproductive success of hatchery-reared Atlantic salmon is relatively low and their capacity as supplementary spawners to the wild population in the Klarälven, is probably small.

The behavior of early (June-July) and late (August-September) migrating, adult Atlantic salmon, in The River Klaralven, Sweden, was analyzed using radio telemetry. River Klaralven is a regulated river without functioning fishways, instead upstream migrating salmon are trapped and trucked past eight hydropower plants before released back to the river. We distinguished two parts of the spawning migration, that is, one part being the migration from the place where the fish was released to the spawning grounds. The other part was a holding phase on the spawning grounds with little or no movements before spawning. The late salmon spent less of their total time on holding, 36.2%, and more on migration, 63.8%, compared with early migrating salmon, which distributed their time rather evenly between migration, 47.5%, and holding, 52.5%. In total, early salmon used 30% more time migrating and 156% more time holding than late salmon. Some Atlantic salmon (Salmo salar) fell back over the hydropower plant after release and got excluded from spawning. The fallback rates of transported, tagged spawners were higher in the early than in the late group in both years. The fallback rate in 2012 was 42.8% of the early group and 15.1% in the late. In 2013, there were 51.7 % fallbacks in the early group and 3.4% in the late. The salmon fell back on average 9days after being released in 2012 and 16days in 2013. A high mean daily discharge on the day of release increased the probability of becoming a fallback. Copyright (c) 2016 John Wiley & Sons, Ltd.

Passage of hydropower plants by upstream-migrating salmonid spawners is associated with increased mortality, delays, injuries and reduced migration success, and consequently the need for a more comprehensive understanding of fish behavior downstream of dams is widely recognized. Studies of passage typically involve tagging fish, and in many cases, the fish used in these studies are caught in the fishways, and hence have prior experience negotiating them. In this study, we studied fishway passage of tagged landlocked Atlantic salmon (Salmo salar) in the River Klarälven, Sweden and brown trout (Salmo trutta) in the River Gudbrandslågen, Norway, and the influence of prior experience on passage success in 2012 and 2013. In the River Klarälven, fishway efficacy varied from 18 (2012) to 88% (2013). Most salmon (81%) entered the fishway trap on days without spill, and salmon moved from the turbine area to the spill zone when there was spill, with small individuals showing a stronger reaction than large fish. Analysis of fish with and without prior trap experience showed that a higher percentage of the “naïve” fish (70% of salmon and 43% of the trout) entered the fishway traps than the “experienced” ones (25% of the salmon and 15 % of the trout). Delays for fish that entered the trap ranged from 3-70 days for salmon and 2-47 days for trout, and there was no difference in median delay between naïve and experienced fish for each species. Manual positioning of radio-tagged salmon revealed that 11% of the naïve fish and 50% of the experienced fish ceased migration after tagging and release. In addition, a greater percentage of the salmon that were captured, marked and released in the lake attempted to enter the fishway (70%) than lake-caught salmon that were also transported 10km to the stream before release (33%). The data based on manual positioning and lake caught salmon indicate that differences in behavior of naïve and experienced individuals are likely stress-related. Moreover, our results suggest that estimates of fishway efficacy using fish with prior fishway experience may be biased, and based on our study, efficacy is underestimated.

Worldwide declines in salmonid populations have generated major interest in conservation and restoration of wild populations and riverine habitats. Plans to re-introduce species to rivers where they previously occurred raises questions as to their potential impact on these systems after so many years. In the River Klarälven, Atlantic salmon (Salmo salar) has been extinct from the upper reaches of its former distribution for more than 50 years due to the construction of hydropower dams. Here we study competitive interactions between Atlantic salmon and two other salmonids, grayling (Thymallus thymallus) and brown trout (Salmo trutta), that presently occur in the upper reaches of the river. We examine foraging rates, aggression and activity of juvenile Atlantic salmon, grayling and brown trout in allopatry at three different densities and in sympatry with one or both potential competitors in laboratory flumes. We found that Atlantic salmon captured prey less frequently in the presence of brown trout and grayling, whereas grayling and brown trout affected each other, but were unaffected by Atlantic salmon. Rates of aggression initiated by salmonids in allopatry versus sympatry revealed differences between fish species, with grayling being the most aggressive and salmon the least. There was also a difference in activity, i.e. time spent cruising or holding position, between the species, with grayling being the most active and salmon the least. These results suggest that re-introduction of Atlantic salmon probably will have little impact on grayling and brown trout, whereas high densities of grayling and brown trout could affect the success of re-introducing Atlantic salmon.