Every year, salmon migrate from the Pacific Ocean or the Atlantic Ocean to the rivers where they are born. Changes in migratory pathways have been suggested as a factor affecting the survival of North American post-smolts (Friedland et al., 1999), and they may also affect the survival of European post-smolts. The Atlantic salmon (Salmo salar) has for ages been the icon for migrating fish as well a symbol of vitality. 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. Less is known about the swimming behaviour of post-smolts, but new technologies such … Modelling the migration of post-smolt Atlantic salmon (Salmo salar) in the Northeast Atlantic. The locations of the released particles were west of Ireland and southwest of Norway, to represent both a southern and a northern European salmon stock, respectively (Figure 1). An estimated migration speed of 20 cm s−1 (Booker et al., 2008) was used for the post-smolts to swim from the release point to the nearest location in the defined path. There have been few attempts to model the migration trajectories and temporal distribution of post-smolts, probably because of the lack of knowledge of the behavioural processes that affect migration. The difference in the timing of modelled and observed smolt occurrence was usually less than a few days, but at some locations north of 72°N in 2009, the modelled distribution was delayed by 1 month (KAM, pers. Less is known about the swimming behaviour of post-smolts, but new technologies such as data storage tags and acoustic tracking, are being used to increase the understanding of the behaviour of salmon at sea (Reddin et al., 2004; Rikardsen et al., 2007; Hedger et al., 2008; Martin et al., 2009). We caught the wild smolts in a smolt trap and selected the largest individuals from the run. 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. Atlantic salmon return to their native river, and even the same stretch of the river from which they were born, with amazing accuracy. The sensitivity analysis indicated that faster swimming speed gave better overlap between modelled and observed distributions. 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. As the migration of post-smolts is the sum of drift with the ocean currents and active swimming, both components were included in the particle-tracking model. Some particles moved into the North Sea, and several of these continued northwards into the Norwegian Sea after a period. – ICES Journal of Marine Science, 69: 1616–1624. Additionally, the particle-tracking model has a built-in behavioural module that was modified for individual post-smolt growth and active swimming behaviour. Their migration is a 4,000-kilometer (2,000 nautical miles) round-trip voyage. Oxford University Press is a department of the University of Oxford. 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. In this study, the migration of salmon post-smolts during their first 4 months at sea in the Northeast Atlantic was investigated using a high-resolution numerical ocean model driven by atmospheric hindcast data. There was a considerable difference in the model output using swimming speeds of 1.0 and 1.5 body length s−1, but swimming speeds >1.5 body length s−1 only improved the model results slightly. This might be caused by the relatively high-resolution ocean current fields, in space (4 km) and time (daily), used in the particle-tracking model resolving mesoscale variability in the currents, and hence causing a delay in the northward transport. 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. Each colour represents a different month at sea, beginning in May. (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). Hence, the body length was estimated in the model to increase by 0.6% per day. Despite their speed and strength, Atlantic salmon face many natural and man-made threats. The main reason for this is the avoidance of the coastal water over the Norwegian shelf and farther offshore. As we do not know in detail the response of post-smolts to horizontal gradients in temperature and salinity, the post-smolts in the model were guided by a filtered hydrographic signal represented by climatological monthly mean temperatures and salinities. That’s the best year since 2011. Post-smolts originating in southern European rivers move north with the currents (Shelton et al., 1997), possibly to minimize energy expenditure and maximize growth during migration (Hansen et al., 1993). For full access to this pdf, sign in to an existing account, or purchase an annual subscription. The simulated migration of post-smolts in 2002 resulted in a very different distribution pattern and migration routes from those of 2008 (Figure 4b). comm.). In addition, the minimum distance between the modelled distribution locations and the captured post-smolt location for each post-smolt, on the date of capture, was calculated, and averaged for all observations in each experiment. Despite being born in rivers, most Atlantic salmon migrate to the sea to feed and grow. Information on the migration and distribution of Atlantic salmon during their first months at sea is available from the systematic sampling of post-smolts at sea (Holst et al., 1993, 2000; Holm et al., 2000). It is also possible that the southern stock group included post-smolts that originate from regions other than the west of Ireland. It was also co-sponsored by the Atlantic Salmon Trust and the Total Foundation, who we thank for financial support. Our results also indicate that salinity may be important in post-smolt orientation in the open sea. 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. However, the different growth rate of post-smolts in the 2 years was controlled by food availability rather than sea temperature (Jensen et al., 2012). The migration distance is the distance along the defined migration path (Figure 1) between the release and recapture locations. The area of overlap between observed (2008/2009) and modelled (2008) distributions of post-smolts for (b) the southern and (c) the northern stock. The swimming speeds of all post-smolts were estimated for different distances travelled and averaged over three different intervals: 0–500, 500–1000, and 1000–2000 km. As it is not clear currently what levels of temporal and spatial variation in temperature or salinity affect the behaviour of post-smolts, we chose to use the monthly mean climatology of temperature and salinity (Engedahl et al., 1998). 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. The results from this study suggest that any climate-driven change in windforcing patterns would affect the migration routes of post-smolts. A swimming speed of 0 body length s−1 corresponds to passive drift with the currents. (a) Locations of trawl stations in 2008 (black dots) and 2009 (squares). For example, the model missed or delayed the migration timing of several post-smolts in the northern Norwegian Sea. Based on data collected between 2003 and 2007, catches of Scottish salmon account for 60% and Search for other works by this author on: Marine Scotland Science, Freshwater Laboratory, School of Biological, Earth and Environmental Sciences, Modelling the transport of cod larvae from the Lofoten area, Modelling the trajectories of migrating Atlantic salmon (, Canadian Journal of Fisheries and Aquatic Sciences, Production of monthly mean climatological archives for the Nordic Seas, The North Atlantic Oscillation, surface current velocities, and SST changes in the Subpolar North Atlantic. 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). At the release point, the body length was set to 16 cm (Kennedy and Crozier, 2010). Averaged active swimming speeds for migrating post-smolts (body length s−1) with error bars within different ranges of migration distance. 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. Migration routes changed in two key areas between the 2 years. Travelling upstream from November to February, Atlantic salmon can be spotted jumping over weirs and waterfalls to get to the gravelly headwaters where they breed. Atlantic salmon returning to freshwater have an incredible ‘homing instinct’ that guides them back to the … In the only study of the migration patterns of salmon in the Northeast Atlantic, Booker et al. Although there was a good agreement between the modelled and observed spatio-temporal distributions of post-smolts, there were some differences. Post-smolts have a preference for waters of higher salinity and will move offshore to the outer branch of the current rather than migrating north with the stronger inner branch. Some have been known to eat salmon eggs. The comparison with observed distributions was made for both 2008 only and 2008/2009 combined. For instance, there have been no (or few) surveys to the south and west of the Faroes, but the model suggests that in some years, this area is a potential migration route, though minor in terms of post-smolt numbers. Redd (nest) surveys at Rocky Brook and Clearwater tributaries of the Southwest Miramichi had among the highest numbers for the past 20 years. Characterization of Full-Length vasa, dnd, and ly75 cDNAs in Atlantic Salmon. The Atlantic salmon is an anadromous species, that is, it spawns in freshwater streams, the adults return to sea and the young remain in fresh water for 2 or 3 years. At each location with a trawl station, with or without the presence of post-smolts, the modelled distribution was checked for particles within a radius of 25 km of that location and ±1 week in time. The Fish and Wildlife Service still continues to monitor and assess Atlantic salmon resources in the Connecticut River. Mork, K. A., Gilbey, J., Hansen, L. P., Jensen, A. J., Jacobsen, J. In freshwater, predators like mergansers, striped bass, and river otters can take their toll, while industrial pollution, dams, and clear-cutting alter their environment. The effect of salinity on post-smolt swimming behaviour has received less attention than temperature. The simulations were performed for 2008, a year with SALSEA-Merge marine surveys, and 2002. PM was partly supported by the Beaufort Marine Research Award in Fish Population Genetics funded by the Irish Government under the Sea Change Programme. Within each year and location, the particles were released over a 3-week period, with a Gaussian distribution, centred on 1 May for the Irish stock (Kennedy and Crozier, 2010) and 15 May for the Norwegian stock (Hvidsten et al., 1998). 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. North American Atlantic salmon migrate in the spring from the rivers where they were born. Information on the migration and distribution of Atlantic salmon during their first months at sea is available from the systematic sampling of post-smolts at sea (Holst et al., 1993, 2000; Holm et al., 2000). Observed lengths of 2-year-old post-smolt Atlantic salmon captured in the Northeast Atlantic by surface trawling in 2008 and 2009 (black dots with s.d. Capable of diving over 900 metres (3,000 feet), wild Atlantic salmon consume deep sea creatures and small fish that school closer to the surface. Moreover, the model missed the post-smolts caught west of Ireland. While at sea, salmon remain in coastal areas or travel 2,500 km across the Labrador Sea to Greenland. (2008) modelled the trajectories of 15 fish emanating from the west of Ireland, using random, current-directed, and temperature-directed swimming. 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. The model indicated that the ocean conditions in 2008 could result in some post-smolts from the southern stock migrating into Icelandic waters, a finding that has been confirmed by genetic assignment to southern European rivers of post-smolts caught by Icelandic pelagic fishing boats in the same year (J. Gilbey, pers. Their migration is a 4,000-kilometer (2,000 nautical miles) round-trip voyage. 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. In 2002, the northward migration route predominantly followed the inner branch of the NwAC (Figure 1), whereas in 2008, the migration route in the Norwegian Sea followed the outer (offshore) branch of the NwAC. updated NAO index time-series from Hurrell, 1995). Based on the locations of the recaptured post-smolts, the most likely migration path, associated with the main current, was defined (Figure 1). The term anadromous refers to this type of migratory behavior. 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. The other area was in the southern Norwegian Sea, where the direction of particle movement was either along the inner or outer branch of the NwAC. In recent years, studies have shown that in the open ocean environment, salmon use the magnetic field of the Earth to guide their migration. The sensitivity of the model output to different swimming speeds showed that faster swimming speeds gave better overlap between the observed and modelled distributions for both stocks (Table 1). During this time, they hunt both in the substrate and in the current. Migration Behavior. 2.0 Atlantic Salmon (Salmo salar) The Atlantic salmon is widely distributed in Scotland (Fig. Schematic overview of the main surface currents in the Northeast Atlantic and the Nordic Seas. Hence, the use of a swimming speed of >1.5 body length s−1 would make the overlap between the modelled and observed distributions less sensitive to, for example, uncertainties or perturbations in the swimming speeds or in the speeds of ocean currents. bars), and the exponential line fitted (black line). In addition, the avoidance of the continental shelf might be more favourable because the predation pressure on post-smolts is probably higher over the continental shelf where predatory fish and birds are more abundant. Broad scale patterns of migration are identified for adult Atlantic salmon, although the resolution of available data is unlikely to be sufficient to inform site specific risk assessment. comm.). 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). Swimming speeds >2.0 body length s−1, particularly for the southern stock, did not improve the model results. Atlantic salmon are in the 1% of fish species worldwide that move between freshwater and saltwater environments. Atlantic salmon returns: 2020 turned out to be a remarkably good year in most Atlantic salmon rivers, but not all.The Penobscot in Maine had 1,601 return. comm.). By excluding the mean and the maximum modelled velocity, averaged over the same route as the tagged fish, from the migration speed, the respective mean and minimum active swimming speeds of each post-smolt could be calculated. The numbers in parenthesis in the overlap (%) and distance (km) columns show the combined 2008/2009 data for comparison with 2008 data. Red points are where observations of post-smolts are available but are inconsistent with the model, i.e. For differences >1°C/psu, the added speed was 0.5 body length s−1. Hatchery-reared salmon smolts are generally stocked during daylight hours, however, the natural migration of smolts tends to occur at night. 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. obs.). The modelled distribution is only presented if it is within a radius of 25 km of the observed location and with less than 1-week difference in time. 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. 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. This is particularly important in the southern Norwegian Sea, where a thin coastal layer with relatively freshwater, originating from the NCC, is present during spring and summer. The two locations of released particles (black dots) in the model are also shown. Simulated migration routes can be used to optimize the planning of marine surveys and salmon management through predictions of abundances. Atlantic salmon are one of nature’s greatest navigators. Observed data for 2-year-old post-smolts collected in 2002 are also shown as open circles. Individual migration routes for six tagged Atlantic salmon (tag IDs are given above panels). Migration of Atlantic salmon in The Tuloma River The Atlantic salmon (Salmo salar L.) – it is a valuable fish and is fished industrially, as well as favourite for recreational and sports fishing. (2010). Atlantic salmon are a cold water migratory species that require different habitats for each life stage. Atlantic Salmon are anadromous, living in the sea and entering rivers to spawn, although several lakes contain landlocked (ouananiche) salmon. If calculated, the journey made by salmon can reach more than 1,000 kilometers. Unlike Pacific salmon, Atlantic salmon can spawn multiple times in their life. 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). The main migration direction was northwards, but several alternative migration routes were evident before the particles eventually entered the Norwegian Sea; clockwise around the Faroes, through the Faroe–Shetland Channel, and a minor route towards Iceland. 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