AQUACULTURE DEVELOPMENT, FRESHWATER HABITAT QUALITY AND THE ATLANTIC MULTIDECADAL OSCILLATION (AMO) AS DRIVERS OF ATLANTIC SALMON (Salmo salar) POPULATION TRENDS

摘要

Declining stock levels of Atlantic salmon Salmo salar, have been recorded in Ireland and northeast Atlantic since the 1970s. The drift net fishery was closed in Ireland in 2006. Controlling harvest based on an individual river conservation limit was implemented in 2007. From 2007 to 2011 fishing for salmon has been limited to single stock fisheries in bays and estuaries. To examine if conservation measures put in place have halted this decline the trends in stock abundance have been examined. The level of Lepeophtheirus salmonis on returning wild salmon was assessed (Jackson et al. 2013a) as was the impact of sea lice on migrating Atlantic salmon smolts at eight locations in Ireland with an analysis of lice-induced marine mortality (Jackson et al. 2013b). Levels of sea lice were high on returning adult wild fish. The results suggest that while sea lice-induced mortality on outwardly migrating smolts can be significant in up to 40% of cases, it is a minor and irregular component of marine mortalityin the stocks studied, and is unlikely to be a significant factor influencing conservation status of salmon stocks. Factors governing survival such as wild-farmed interactions, freshwater habitat and Atlantic Multidecadal Oscillation (AMO) were assessedand their impacts discussed.