If calculated, the journey made by salmon can reach more than 1,000 kilometers. from 46 to 85% overlap for the southern stock using only 2008 observations). For example, U.S. salmon leave Maine rivers in the spring and reach the seas off Newfoundland and Labrador, Canada, by mid-summer. The Atlantic salmon (Salmo salar) undertakes long migrations to feeding areas in the ocean, including in the northern Norwegian Sea and around the Faroe Islands (Jacobsen et al., 2012). The two key areas, south of the Faroes and in the southern Norwegian Sea, where there may be substantial changes in the direction of post-smolt migration, merit further study. Also, contrary to expectations based on free pelagic drift, some post-smolts caught west of Ireland were genetically assigned to the northern stock. Some Atlantic salmon spend a single winter at sea before returning to spawn in freshwater. The latter year was chosen because the post-smolt growth (Jensen et al., 2012) and the windforcing (and consequently the surface currents) were considerably different from those in 2008. It was assumed that hatchery-reared fish would undertake the same migration and would have the same swimming speed as wild fish. For each simulation, 50 000 particles were released at one location, randomly distributed within a 25-km radius from the centre of the location. The area of overlap between observed (2008/2009) and modelled (2008) distributions of post-smolts for (b) the southern and (c) the northern stock. Swimming speeds >2.0 body length s−1 did not increase the overlap or reduce the minimum distance between the observations and the modelled distributions for the southern stock, whereas a small improvement was seen for the northern stock. Sean A. Hayes, John F. Kocik, Comparative estuarine and marine migration ecology of Atlantic salmon and steelhead: blue highways and open plains, Reviews in Fish Biology and Fisheries, 10.1007/s11160-014-9348-8, 24, 3, (757-780), (2014). Atlantic salmon return to their native river, and even the same stretch of the river from which they were born, with amazing accuracy. Atlantic salmon are an anadromous fish, that begins their life in freshwater and migrates to the ocean to feed and grow, and returns to freshwater to spawn. This image shows the movement of a satellite tagged adult Atlantic salmon leaving the Miramichi River in New Brunswick and swimming towards Greenland. Guided by the earth’s magnetic fields and an incredible sense of smell, Atlantic salmon return to spawn in their home river, sometimes in the same gravel bed they hatched from. Tag information for the Irish tag recovery samples used in the model was made available from the Marine Institute's National Coded Wire Tagging and Tag Recovery Programme, with special thanks to Anne Cullen, Deirdre Cotter, and Russell Poole of the Marine Institute. Red points are where observations of post-smolts are available but are inconsistent with the model, i.e. In fact, 85 and 75% of the modelled post-smolts were within a 2-week interval of when post-smolts were observed in the surveys in 2008 and 2008/2009 combined, respectively. The distribution at sea probably depends on a combination of factors such as abiotic environmental conditions, prey availability, and stock-specific migration patterns (Hansen and Quinn, 1998; Jacobsen and Hansen, 2001; Holm et al., 2004). In the only study of the migration patterns of salmon in the Northeast Atlantic, Booker et al. Atlantic salmon are migratory. The simulations were run to the end of August. There, only 32 and 43% of the modelled distribution was within a 2-week interval centred on the time of the observations for 2008 and 2008/2009 combined, respectively. Schematic overview of the main surface currents in the Northeast Atlantic and the Nordic Seas. Pepin and Helbig (2012) and Stenevik et al. We thank the reviewers, Myron Peck, and Hans-Harald Hinrichsen for constructive comments and helpful suggestions that improved the manuscript and guest editor Peter Hutchinson for his efficient handling of the manuscript. a rheotactic behavioural response, in accord with the results from recaptured tagged fish and the published literature (Shelton et al., 1997; Booker et al., 2008). The post-smolts caught were genetically allocated to different groups at different assignment levels using the SALSEA-Merge Genetically-based Regional Assignment of Atlantic Salmon Protocol (GRAASP) database (J. Gilbey, pers. The simulations identified at least two key areas along the migration routes where the subsequent drift is particularly sensitive to horizontal perturbations, either because of variability in ocean currents or modelled parameters of post-smolt behaviour. The sensitivity of the post-smolt migratory response was modelled in relation to different swimming speeds of the post-smolts, interannual differences in windforcing, and a range of possible swimming behaviours. bars), and the exponential line fitted (black line). The model domain covers the Northeast Atlantic and the region to the north, including part of the Arctic Ocean. comm.). One model for marine migration of Atlantic salmon Salmo salar proposes that North American and southern European stocks (<62 degrees N) move directly to feeding grounds off west Greenland, then overwinter in the Labrador Sea, whereas northern European stocks (>62 degrees N) utilize the Norwegian Sea. Wild Atlantic salmon are capable of incredible bursts of speed while hunting. Individual migration routes for six tagged Atlantic salmon (tag IDs are given above panels). The distribution was also less to the north, mainly because the post-smolts were displaced farther west and were, therefore, less likely to follow the inner branch of the NwAC. The simulated migration of post-smolts in 2002 resulted in a very different distribution pattern and migration routes from those of 2008 (Figure 4b). His name means ‘the jumper’ in Latin, referring to the legendary capacity to jump over water falls that are insurmountable for most other fish species. Relative to the output for 2002 and 2008 from the model with no temperature/salinity preference, there was a distinct change in direction to the south in the Norwegian Sea (west from Møre, Norway, at 63°N) in one of the key areas described previously. These dates represented the peak post-smolt migration periods for the respective stocks. For a species experiencing global population decline, it is thus vital to better understand migration behaviour, both in the river and marine stages. (2008) and the optimum swimming speed, defined as the minimum energy expenditure per metre, for post-smolt Oncorhynchus nerka of 1.6 body length s−1 (Videler, 1993). Release and recapture locations of tagged Atlantic salmon are shown as blue and green boxes, respectively, and the defined migration route for the recaptured tagged post-smolts is indicated as a thick blue line. The minimum (dashed line) and averaged (solid line) active swimming speeds were calculated by removing the maximum and the averaged modelled current speed, respectively, from the mean migration speeds along the migration path. A black ring around a green or a red point indicates that modelled post-smolts are present. This implies that there were two different pathways, both ending in the same area, but with different environmental conditions such as light availability, prey, and predators. The swimming speed was estimated using information from 86 tagged hatchery-reared smolts of Irish origin released between 1996 and 2009 and recaptured within the same year as their release (Figure 1). For each tagged fish, the average migration speed along the path was calculated to match the time and location of each recapture. Young Atlantic salmon spend two to three years in their home river before going on a one to three year journey in the North Atlantic where they grow into an adult. Swimming speeds >1.5 body length s−1 resulted in only slightly better overlap, particularly for the southern stock. The model reproduced the hydrographic and circulation features in the southern Norwegian Sea (Vikebø et al., 2010), where the modelled annual mean volume flux of the inner branch of the Norwegian Atlantic Current (NwAC), the Norwegian Atlantic Slope Current (NwASC), equalled the values obtained by Orvik et al. The more coastal migration route in 2002 may have had consequences for the post-smolts in terms of food availability and other factors influencing behaviour and physiology and could be one possible explanation for the observed higher growth rates in 2002 relative to 2008 (Jensen et al., 2012; see also Figure 3). (in press) combined model outputs and observations for survey design purposes, and Vikebø et al. Because the post-smolts mainly migrate close to the surface, within the uppermost 1 m (Holm et al., 2004), no vertical migration was assumed and only surface currents were used to calculate the movement of each post-smolt on an hourly basis. Both mean and maximum velocities from the model were calculated in grid boxes along the path, where each grid box was 125 km wide and 25 km long. Atlantic salmon smolt are usually 2-3 years old when they begin their migration in U.S. waters, but migrating smolt are often older at higher latitudes. After Atlantic salmon smolts enter the ocean, they migrate as post-smolts to feeding areas during late spring and summer (Thorpe, 1988; Mills, 1989) and are distributed over large areas of the North Atlantic (Holm et al., 2004). Once they have reached their breeding grounds, the females dig depressions, known as 'redds', in the gravel; the eggs and sperm are released simultaneously into the water.