Into the blue: Inferring marine distribution of Canadian and Irish Atlantic salmon (Salmo salar L.) in the North Atlantic Ocean from tissue concentrations of bioaccumulated cesium-137

Atlantic salmon returning from marine migrations to eastern Canada and western Ireland during 2002/2003 were analyzed for tissue concentrations of bioaccumulated cesium-137 (137Cs). Canadian and Irish salmon demonstrated concentrations (0.20 +/- 0.14 Bq kg-1 and 0.19 +/- 0.09 Bq kg-1, respectively) suggesting similar oceanic feeding distributions. Canadian aquaculture escapees had similar mean tissue concentrations (0.28 +/- 0.22 Bq kg-1 wet wt) suggesting migration with wild salmon, however significantly higher concentrations in 1SW escapees (0.43 +/- 0.25 Bq kg-1 wet wt) may alternatively suggest feeding on freshwater prey within original estuaries. High concentrations of wild Canadian 1SW salmon indicated trans-Atlantic migration. Estimates of Canadian and Irish salmon feeding east of the Faroes (∼8°W) were 15.6% and 10.0%, respectively. I propose most anadromous North Atlantic salmon utilize the North Atlantic Gyre for marine migration and should be classified as one trans-Atlantic straddling stock.