The timing of seaward migration is a key life‐history trait for many anadromous fish species, with growth and survival at sea depending on a match/mismatch scenario between the timing of the sea entry and optimal conditions. Based on a 25‐year study with 15,226 individually tagged brown trout ( Salmo trutta ) in a Norwegian river, we analysed how the within‐season timing of sea migration impacted growth and survival. In both f...

Sea trout face growth–mortality trade‐offs when entering the sea to feed. Salmon lice epizootics resulting from aquaculture have shifted these trade‐offs, as salmon lice might both increase mortality and reduce growth of sea trout. We studied mortality and behavioural adaptations of wild sea trout in a large‐scale experiment with acoustic telemetry in an aquaculture intensive area that was fallowed (emptied of fish) synchronic...

Despite satisfactory reactions to seawater challenge tests indicative of appropriate physiological state, hatchery‐reared Atlantic salmon Salmo salar smolts stocked in the Eira River in Norway between 2001 and 2011 performed less well at sea in terms of growth, age at maturity and survival than smolts of natural origin. The mean rates of return to the river for hatchery‐reared and naturally produced S. salar were 0·98 and 2·35...

The impact of salmon lice on the survival of migrating A tlantic salmon smolts was studied by comparing the adult returns of sea‐ranched smolts treated for sea lice using emamectin benzoate or substance EX with untreated control groups in the R iver D ale in western N orway. A total of 143 500 smolts were released in 35 release groups in freshwater from 1997 to 2009 and in the fjord system from 2007 to 2009. The adult recaptur...

Release strategies of hatchery‐reared Atlantic salmon, Salmo salar L., smolts were compared by studying survival and migration of smolts ( n = 99) and their predators (Atlantic cod, Gadus morhua L., n = 8; and saithe, Pollachius virens (L.), n = 2) during the first 37 km of the marine migration using acoustic telemetry. Survivorship was higher in smolts released at the river mouth (30%) compared with smolts released in the riv...

The anadromous life cycle of Atlantic salmon Salmo salar involves long migrations to novel environments and challenging physiological transformations when moving between salt‐free and salt‐rich waters. In this article, (1) environmental factors affecting the migration behaviour and survival of smolts and post‐smolts during the river, estuarine and early marine phases, (2) how behavioural patterns are linked to survival and (3)...

To study the migratory behaviour in wild northern European silver eel Anguilla anguilla during sea entry and early marine migration, 32 individuals were tagged with acoustic transmitters and registered at four automatic listening station arrays from the mouth of the north Norwegian River Alta and throughout the Alta Fjord. The A. anguilla entered the fjord during all parts of the tidal cycle and did not seem to utilize the out...

The early marine migratory behaviour of two populations of hatchery‐reared Atlantic salmon Salmo salar was compared in a common‐garden experiment. Post‐smolts from a river in a long fjord (Lærdal River, 144 km from the open coastline, n = 79) and a short fjord (Flekke River, 20 km from the open coastline, n = 80) in western Norway were tagged with acoustic transmitters and released during the spring of 2005 and 2006 in the inn...

Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean ± s.e . 0·15 ± 0·01 sea lice Lepeophtheirus salmonis g −1 fish mass) (HI), medium (0·07 ± 0·00 sea lice g −1 fish mass) (MI) or no [control (C)] sea‐lice infection during early stages of gonad development (June to July). Infection with sea lice resulted in increased plasma cortisol concentrations and...

The abundance of returning adult Atlantic salmon Salmo salar , in the River Orkla in mid‐norway (1 sea‐winter, SW, fish) and River Hals in north Norway (1–3 SW fish), was tested against the early marine feeding and the seawater temperature experienced by their corresponding year classes of post‐smolts immediately after entry into the Trondheimsfjord (Orkla smolts, 22 years of data) and Altafjord (Hals smolts, 17 years of data)...

The migratory behaviour of hatchery‐reared Atlantic salmon, Salmo salar L., post‐smolts during the first phase of the marine migration was examined to assess their susceptibility to salmon lice, Lepeophtheirus salmonis (Krøyer), infestations. Swimming depths of eight post‐smolts relative to the measured salinity and temperature were monitored for an average of 11.4 h following release outside the mouth of the River Eio using d...

The long and narrow Hardanger fjord in western Norway has a high density of salmon farms and has had severe salmon lice, Lepeophtheirus salmonis, problems. In the years 2004–06, salmon lice numbers were recorded in selected salmon farms in the fjord as part of a larger research project. Most farm sites participated in a strategic control programme and were deloused between November and January in each year. The aim of the prog...

Eight hatchery‐reared Atlantic salmon Salmo salar post‐smolts, implanted with acoustic depth sensing transmitters and manually tracked for 5–12 h in the Hardangerfjord (Norway), spent most of their time (49–99%) at 1–3 m depth during the day, whereas four of seven fish tracked were found close (

Three tagged Atlantic salmon Salmo salar were recaptured as subadults or adults (1·4–3 kg) between 70·5 and 78° N in the western Barents Sea, two of which originated from the Alta Fjord region in northern Norway and one from the Drammen River, south‐eastern Norway. An additional tag was recovered from the stomach of a Greenland halibut Reinhardtius hippoglossoides captured south‐west of Bear Island at >600 m depth; this tag wa...

A synthesis of results from two projects was assessed to analyse possible influence of sea lice Lepeophtheirus salmonis on marine Atlantic salmon Salmo salar survival. During the years 1992–2004, trawling for wild migrating post‐smolts was performed in Trondheimsfjord, a fjord in which no Atlantic salmon aquaculture activity is permitted. Prevalence and intensity of sea lice infections on migrating wild post‐smolts differed be...

The marine feeding pattern of anadromous brown trout (sea trout) Salmo trutta and Arctic charr Salvelinus alpinus was studied during June to August in 1992–1993 and 2000–2004 in a fjord in northern Norway. In general sea trout fed proportionally more on fishes than on crustaceans and insects (81, 1 and 18% by mass, respectively) by comparison with Arctic charr (52, 25 and 22% by mass, respectively). Herring Clupea harengus dom...