The SALSEA project identified quite a range of possible sources of salmon mortality during the long migration of young smolts to their feeding grounds. It did not aim to quantify or fully understand these. It is evident however, that since these factors can vary in time and space, such variation can be expected to account for some if not most of the variability in return rates observed back to home-water rivers. As plans for new research develop, the Atlantic Salmon Trust believes it is necessary to consider how such research can be targeted and prioritised. Previous work on marine fisheries suggests it is possible to identify an overall Strategic Framework that would provide a basis for selecting key research priorities, which could potentially help to boost the overall number of smolts reaching their feeding grounds.
AST believes that a strategic approach is vitally important, as it would place candidate mortality factors within an overall spatial and temporal framework, covering the full lives of salmon at sea. Such an approach could help to quantify the potential of each factor to influence survival (i.e. the “likely suspects”) and to link these dynamically in such a way that the cumulative effects of these factors could explain the variations in survival of different year classes of salmon.
This would be akin to an “accounting exercise” and can be used to identify the likely impact ,both individually and cumulatively, of the “likely suspects”. A key objective is to prompt specific, testable scientific hypotheses about the factors influencing salmon survival. It is also planned to learn more about how these factors influence marine survival and how best to target research so as to further refine the current estimates of the scale of mortality at each part of the marine phase of the salmon’s life cycle. A particular focus would be on identifying where and how mortality factors had changed between earlier periods of higher marine survival (60’s and 70’s) and the more recent/current low survival phase.
The AST believes that a Suspects Framework should be developed on a collaborative basis, involving Europe and north America. Work is ongoing to refine the Suspects Framework, with a view to sourcing partners for the initiative both at a national and international level.