The effect of physiological and environmental conditions on smolt migration in Atlantic salmon Salmo salar

Abstract

Hydropower development has negatively influenced Atlantic salmon (Salmo salar)populations. Compensatory hatchery-rearing programmes exist, but released fish suffer from high mortality that may be related to the lack of experience from natural environments in hatchery-reared smolts and their large body size and high energetic state. Here, we used acoustic telemetry to test how body size, energetic state, and the environmental conditions of the river affect migration in hatchery-reared smolts.The study was conducted in three consecutive years between 2011 and 2013 in the lower part of the River Umeälven, Sweden. For individual fish, there was no effect of body size but the energetic state of the fish had a negative effect on sea entry. The most important factor affecting sea entry rate was the water discharge in the old river bed that differed among years. Smolts were more likely to enter the sea in years when the discharge was high or when the discharge increased substantially shortly after release. Hatchery-reared fish had higher migration speed at a slower flowing section compared with a faster flowing section, which was likely a result of large hesitation to enter the rapid section. The increase in water discharge led to an increase in fish migration speed disproportional to the increase in water velocity. Our results highlight the importance of water discharge for the smolts during smolt migration, and we argue that concern should be given to migrating fish when managing regulated rivers. K E Y W O R D Sbody length, condition factor, discharge, river migration, sea entry, water velocity

Development of an accurate model to predict the phenology of Atlantic salmon smolt spring migration

“…Nevertheless, Zydlewski et al (2014) The results also suggest an effect of the hydrological conditions on smolt spring migration. Similar observations have been reported in field studies, where a sharp increase in river flow can stimulate smolt migration activity (Aldvén et al, 2015;Antonsson & Gudjonsson, 2002;Hvidsten et al, 1995;Jonsson & Jonsson, 2011;Karppinen et al, 2014;Persson, Kagervall, Leonardsson, Royan, & Alanärä, 2019). In the West River basin, Whalen et al (1999) found variability in the influence of river discharge peaks throughout the migration season; responsivity was highest during the mid-season until the physiological status of smolts declined.…”

“…Thus, the discharge peaks are not indispensable for initiating fish migration, but they can promote massive downstream movements during increased river flow. Moving in a group can provide protection against predation (Berdahl, Westley, & Quinn, 2017) and migration during high flow is energetically beneficial (Persson et al, 2019), as also proposed for silver eels Anguilla anguilla (Barry et al, 2016). Nevertheless, smolt activity was not affected by discharge peaks before the spring equinox, suggesting that the sensitivity to hydrological change occurred only after the photoperiod cue had been received.…”

Synchrony and multimodality in the timing of Atlantic salmon smolt migration in two Norwegian fjords

“…We show here that migration timing in these populations seems to be primarily influenced by the timing of river spring floods, though temperature seems more important as the season progresses. The importance of water discharge and temperature in triggering migration has been observed many times elsewhere 3 , 22 , 24 – 26 , 49 , 50 . Here, the degree to which river conditions control the phenology of migration timing is the likely cause of the observed synchronization among rivers with similar hydrological properties.…”

Atlantic salmon living on the edge: Smolt behaviour and survival during seaward migration in River Minho

“…The statistical analyses revealed that larger sized smolts were more likely to successfully move down through the study area. Recent literature reports both cases where estimated survival is positively associated with length (Chaput et al, 2019; Davidsen et al., 2009; Flávio et al., 2019; Jepsen, Aarestrup, Økland, & Rasmussen, 1998), negatively associated with length (del Villar‐Guerra, Larsen, Baktoft, Koed, & Aarestrup, 2019) and where no effect of smolt length was detected (Dempson et al., 2011; Persson, Kagervall, Leonardsson, Royan, & Alanärä, 2019; both of which tagged larger smolts on average), seemingly indicating that the impact of size on survival may be site‐specific (Gregory, Armstrong, & Britton, 2018). Importantly, while it is not possible to entirely rule out tagging effects on survival, this difference in survival rates between fish lengths is expected to reflect a true difference in fitness, as Newton et al.…”