Riverine and fjord migration of wild and hatchery‐reared Atlantic salmon smolts

Abstract

Migration timing, speed, survival and effects of environmental parameters on migration, between wild and hatchery produced Atlantic salmon, Salmo salar L., smolts in the River Laerdalselva were studied. Hatchery-reared (n = 40) and wild pre-smolts (n = 40) were tagged with acoustic tags, and an array of receivers along the migration route was deployed. In all, 77 and 85% of the fish from the two groups, respectively, were recorded as migrating smolts, that is, predation rate and/or numbers of fish opting to remain in the river were low. Hatchery-reared smolts showed a migration pattern, speed and migration route similar to wild smolts, even though the time period between river release and onset of migration was relatively short. Both groups of smolt showed high migration speed through both the river and the fjord compared with other studies.

Does size matter? A test of size‐specific mortality in Atlantic salmon Salmo salar smolts tagged with acoustic transmitters

“…Urke et al . () although not specifically reporting on the effect of tag size, indicate high survival rates to sea for wild smolts (77% survival, mean L F 127 mm, mean mass 16·5 g) implanted with acoustic transmitters (7·3 mm diameter, 1·2 g in water) and hatchery S. salar (85% survival, mean L F 157 mm, mean mass 40·8 g) with transmitter mass to body mass ratios equating to c . 7%.…”

Release during night enhances survival of wild Atlantic salmon smolts

“…Similar results have been observed for other species and systems, where stocking during the day or night has not impacted survival (Stein, Carline & Hayward, ). Meanwhile, several studies have shown that downstream migration and estuary entry tends to be nocturnal (Hedger et al., ; Ibbotson, Beaumont, Pinder, Welton & Ladle, ; Martin et al., ; Thorstad, Whoriskey, et al., ; Urke et al., ), indicating that wild smolts prefer to migrate through areas of high predation with the camouflage of darkness. However, several studies have also reported a large proportion of salmon migrating during the daytime later in the season (Ibbotson et al., ; Moore, Potter, Milner & Bamber, ).…”

Diel migration pattern of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) smolts: an assessment of environmental cues

“…Some authors have maintained that smolt migrations are predominantly nocturnal (Antonsson & Gudjonsson, 2002;Greenstreet, 1992;Hesthagen & Garnås, 1986;Moore, Ives, Mead, & Talks, 1998;Urke, Kristensen, Ulvund, & Alfredsen, 2013;Urke, Kristensen, Arnekleiv, et al, 2013). Others report that a high proportion of the smolts migrate during daylight (Fängstam, Berglund, Sjöberg, & Lundqvist, 1993;Ibbotson, Beaumont, Pinder, Welton, & Ladle, 2006;Moore, Potter, Milner, & Bamber, 1995).…”