Swimming depth of sea trout
Data on swimming depth of sea trout Salmo trutta (L.) in Icelandic waters was extracted and collated into a suitable format for use in marine renewables risk assessment. The data shows that the fish are close to the surface much of the time, with some time being spent at greater depths.
5. Other available information on sea trout swimming depth
Four other studies document the swimming depth of sea trout during their migration in sea, and all show results consistent with the present study (Sturlaugsson and Johannsson 1996; Rikardsen et al 2007; Hantke et al 2011 and Davidsen et al 2014).
Studies in coastal waters of Iceland in 1995 showed that during the sea migration sea trout tagged with data storage tags spent vast majority of their time in coastal waters within the uppermost 5 m (Sturlaugsson and Johannsson 1996).
Rikardsen et al (2007) tagged eight sea trout with data storage tags in Alta Fjord in northern Norway in 2002. The fish were recaptured 1-40 days later. The sea trout spent more than 50% of their time between 1 and 2 m depth and more than 90% of their time in water no deeper than 3 m from the water surface. However, deeper dives (to a maximum of 28 m) were also recorded. These deep dives were most frequently performed at the end of the sea migration.
Hantke et al (2011) give swimming depth information for tagged sea trout in coastal waters in northern Germany. They include in their abstract that "The majority of the tagged sea trouts (64%) migrated at the uppermost water level at about 1.5 m. Common behaviour of sea trouts was occasional deep dives up to 13 m water depth. Two patterns of vertical movements have been observed, rapid dives down from the surface layers or continuous movements in the upper layers."
Davidsen et al (2014) give swimming depth information for tagged sea trout in a fjord in Central Norway. They include a summary that "Average swimming depth in the period from April to September (1.87 m) varied significantly among habitats. In littoral (2.11 m) and cliff habitats (2.53 m) the average swimming depth was significantly deeper than in pelagic areas (1.26 m). The average swimming depth was significantly deeper during day (1.98 m) than night (1.28 m). The sea trout had a progressively deeper swimming pattern from April towards late summer, which was positively correlated with water temperature, suggesting that the sea trout actively regulated its internal body temperature."
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