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The Atlantic Salmon Trust publishes important Blue Book on Likely Suspect Framework

In 2017 the Atlantic Salmon Trust launched the Missing Salmon Project against a backdrop of continued declines in salmon runs across the North Atlantic. The aim of the project is to understand where and how the salmon are dying so that management measures can be put in place to reverse this decline. Without such a coordinated effort it is likely that salmon will become an endangered species in our lifetime.

The first part of the Missing Salmon Project was to bring together experts from around the Atlantic and Pacific to start the process of building a framework where the suspects responsible for killing the salmon could be identified. This was started at a major international workshop held in Edinburgh in November 2017 and was the first preparatory event for the forthcoming International Year of the Salmon in 2019.

Work will now proceed to identify the suspects responsible for the loss of salmon and then we aim to identify which ones we can manage to help recover fish stocks. It is an ambitious project as we need to look at what is happening to the fish across the whole of their home range in rivers and across the Atlantic.


Additional Information: key conclusions from the AST Likely Suspects Framework Blue Book:

  • The AST Likely Suspects Framework places candidate mortality factors (“likely suspects”) within an overall framework covering the freshwater migration and marine phases of the salmon’s life cycle. Key geographical areas and periods where mortality factors are known or thought to operate are characterised as ecosystem “domains”.
  • Domains can be identified at various locations, ranging from freshwater to overwintering feeding areas, and are associated with different mortality factors.
  • The overall objective is to identify the various mortality factors involved and quantify the potential for each factor to influence survival. In an approach more akin to financial accounting than mathematical modelling, the cumulative effect of these factors is made to account for the observed overall variation in survival of various life stages from smolt to adult. This can be used to identify the likely impact, both individually and cumulatively, of the “likely suspects”.
  • There will be domains where mortality factors impact many stocks, while others where only a few stocks or even a single stock are impacted.  In visualising this, it may be useful to think of salmon from a given stock on their migratory journey passing through successive mortality domains, where they are joined by salmon from other stocks, and so on.
  • It is important to concentrate on the big numbers and on places/periods where any mortality impacts are likely to affect a large number of stocks (this knowledge is important from a management perspective). Major areas of interest are not necessarily at oceanic scale – e.g. hotspots where smolts get slowed down and get preyed upon.
  • In the local context a sensible management strategy would be to maximise output of smolts and to maximise their chances of success at the critical freshwater/marine interface and during the early marine period.
  • Another aspect to be considered when looking at domains is that space/time axes in freshwater and estuaries can be very discreet; hotspots where fish get slowed down and get preyed upon.
  • Domains in freshwater may be very discreet, for example spots where say predation is high or migration is held up, whereas oceanic domains may be on a very wide scale.
  • Lessons from the Pacific are that marine survival is a very dynamic process and factors that cause significant losses to some stocks in some years, may be less significant or absent in other years.
  • Climate change impacts on salmon populations are likely to be spread over several parts of the life cycle, with responses to changes in river growth, growth at sea and hence overall year class survival having cumulative and confounding effects on population persistence.
  • Freshwater practices affect the contribution of the juvenile salmon to the ocean and managers need to understand ocean systems to make sense of the impact of freshwater decisions.
  • Declining survivals for Atlantic Salmon are similar to those of many wild populations of Coho, Sockeye, Chinook, and even-year returning pink salmon and steelhead in the southern portion of their range of the eastern North Pacific, as well as Masu salmon in the western North Pacific.
  • Freshwater factors influence subsequent survival at sea; these can be population-specific or broader in impact.
  • In the marine, there are local, regional and basin scale drivers at work, these operate cumulatively as salmon pass through various ecosystem domains and in some cases operate synergistically.
  • Climate change is a likely driver of major significance, with effects being felt at very broad scales and in different ways; for example there are trends for general ocean warming, but also there is potential for short term or single year anomalous “big” events having high impact.
  • Climate change has impacts in freshwater as well as at sea, therefore mechanisms of change are complex and multi factorial.
  • Climate change may have a hemispherical impact on salmon species.
  • Some mortality factors become critical in years of bad oceanic conditions, but matter less in good years.
  • Size selective mortality of salmon is high during years of low ocean production. In bad years the small salmon get eaten.
  • The workshop noted that a further benefit envisaged for the likely suspects concept, is that the framework being developed would be a valuable (web-based) tool to help managers and stakeholders visualise and understand the impact of the various mortality factors impacting smolt, post-smolt and salmon stocks.
  • There is a clear need to routinely integrate non-salmon scientists into the salmon scientists   Progress on salmon mortality at sea will depend on a multidisciplinary approach, so oceanographers, predator and competitor experts will also have to become involved.
  • Steps should be taken through ICES, NASCO and the EU to promote the Atlantic salmon as a pelagic species and a key indicator of marine ecosystem health.


Useful Links:

Atlantic Salmon Trust –

Missing Salmon Project –



International Year of the Salmon –

International Council for the Exploration of the Seas –

About the Atlantic Salmon Trust

The role of the Atlantic Salmon Trust is to demonstrate how salmon and sea trout can be conserved and managed to enable their value to society to be realised sustainably.

The Trust’s work concentrates on improving our knowledge of these fish, their habitats and their complex and fascinating life histories, as well as the threats to their survival. Until relatively recently this knowledge was confined mainly to the freshwater aspects of their life cycle, but the AST is also focusing on the migration and marine phase of their life.

For further details about the Atlantic Salmon Trust, please contact   tel. 0131 221 6552 or email


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