Image: Kim Birnie-Gauvin ©
Species description and status: Atlantic salmon (Salmo salar) is native to the temperate and subarctic regions of the North Atlantic Ocean. In many areas, it is one of the most economically and culturally valuable fish species - and it is exploited in commercial, subsistence and recreational fisheries. Atlantic salmon have a diverse array of life-histories, but most forms are anadromous with a juvenile phase in fresh water, followed by a long migration to the ocean for feeding and growth, and a return migration to fresh water to spawn. Salmon reproduce in rivers on both sides of the North Atlantic Ocean, and their oceanic feeding areas cover large areas (Figure 1).
Long-distance migrations between freshwater and ocean habitats expose Atlantic salmon to multiple threats, and a number of human factors have contributed to the species general decline during the last decades. Atlantic salmon have been lost from many rivers, and during the past decades, substantial reductions in population sizes have been observed for numerous populations.
Figure 1. Assumed geographical marine distribution of the Atlantic salmon in the North Atlantic Ocean and the associated countries that hold natural spawning populations of Atlantic salmon (from Thorstad et al. 2011).
Knowledge gaps: Human impacts in rivers and coastal areas affect many Atlantic salmon populations. In large parts of the distribution range, aquaculture activities in the coastal areas affect Atlantic salmon populations negatively, and to some extent so do other coastal, human activities. Many local and regional impact factors are well studied, whereas some are less well known.
On a broad scale, changes in marine ecosystems are considered prominent contributors to the recent declines. For European populations, it is perceived that declines are associated with shifts in marine food web structure that reduce salmon growth at sea. However, this is not well understood, and it is difficult to investigate because of great uncertainty over how Atlantic salmon use the ocean and how they distribute themselves at sea as a function of inter-year differences in environmental conditions, the animals age and experience, and the time of the year.
Knowledge on the relative importance of the different human impacts is vital for prioritizing management measures. It is necessary to disentangle impacts occurring in rivers, coastal areas and the ocean – and ecosystem driven population declines – from these impacts. Much more information on the coastal migration and large-scale ocean distribution and migration routes of Atlantic salmon is required. This has been recognized as a priority by the North Atlantic Salmon Conservation Organization (NASCO). For more information, visit: http://www.nasco.int/sas/pdf/archive/other_reports/SALSEA_TrackBrochure.pdf.
Regions of interest: North Atlantic Ocean, including the Baltic Sea.
Telemetry tools: Acoustic transmitters and receivers in coastal areas and offshore sites where marine receiver lines can be deployed. PIT-tags for recording sea survival. Pop-up satellite archival tags (PSAT) and data storage tags (DST).
Benefits: Using the ETN to further characterize Atlantic salmon movements and behaviour throughout coastal and ocean areas in the North Atlantic would greatly enhance our ability to manage this culturally and economically important species. To study a widely migrating species that crosses many national jurisdictions like the Atlantic salmon, with many hundreds of genetic stocks, joint research efforts, sharing of infrastructure and international collaboration are needed.
Contacts: Kim Aarestrup and Eva B. Thorstad
Reference : Thorstad, E.B., Whoriskey, F.G., Rikardsen, A.H. & Aarestrup, K. 2011. Aquatic nomads: the life and migrations of the Atlantic salmon. In: Aas, Ø., Einum, S., Klemetsen, A. & Skurdal, J. (eds.) Atlantic Salmon Ecology, Chapter 1, pp. 1-32. Wiley-Blackwell.