SMOLTrack I : Understanding and comparing early mortality of European salmon populations at sea
Over recent decades, the abundance of wild Atlantic salmon has been in decline throughout its migratory range despite the significant management measures put in place both domestically and at an international level. There is evidence that the initial mortality, immediately after smolts enter salt water, is very high and that this ‘point mortality’ may explain most of the variation seen in return rates of salmon. Estuarine and near-shore mortalities may also be occurring in the part of the marine life cycle where management intervention is feasible.
This project determined the mortality of salmon smolts and post-smolts during their migration through the lower parts of rivers, estuaries / fjords and near-shore areas through case studies using telemetry in rivers in five countries: Denmark, England, Ireland, Northern Ireland and Spain. Mortality of kelts migrating on the same route was also investigated in Denmark.
In combination with other published results, the research has provided crucial input on marine mortality to existing models used for assessment purposes and has tested if the measured initial mortality can explain observed variation in return rates. The findings may inform future management and conservation of (some) Atlantic salmon stocks.
The SMOLTrack I project was initiated in January 2017. Salmon were tagged with acoustic transmitters and their subsequent migration followed via acoustic listening stations. This provided novel data on lower-river and estuarine / coastal behaviour and mortality, as well as to evaluate the method’s applicability in a broader context. In addition to the scientific aims, the project intended to bring together a group of experts to provide advice on best practices and to produce a Standard Operating Procedure for this type of study.