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Many salmon populations in both the Pacific and Atlantic Oceans have experienced sharply decreasing returns and high ocean mortality in the past two decades, with some populations facing extirpation if current marine survival trends continue. Our inability to monitor the movements of marine fish or to directly measure their survival precludes experimental tests of theories concerning the factors regulating fish populations, and thus limits scientific advance in many aspects of fisheries management and conservation. Here we report a large-scale synthesis of survival and movement rates of free-ranging juvenile salmon across four species, 13 river watersheds, and 44 release groups of salmon smolts (>3,500 fish tagged in total) in rivers and coastal ocean waters, including an assessment of where mortality predominantly occurs during the juvenile migration. Of particular importance, our data indicate that, over the size range of smolts tagged, (i) smolt survival was not strongly related to size at release, (ii) tag burden did not appear to strongly reduce the survival of smaller animals, and (iii) for at least some populations, substantial mortality occurred much later in the migration and more distant from the river of origin than generally expected. Our findings thus have implications for determining where effort should be invested to improve the accuracy of salmon forecasting, to understand the mechanisms driving salmon declines, and to predict the impact of climate change on salmon stocks.

Item Type:	Refereed Article
Keywords:	acoustic arrays Pacific Ocean Shelf Tracking mark-recapture
Research Division:	Agricultural, Veterinary and Food Sciences
Research Group:	Fisheries sciences
Research Field:	Aquaculture and fisheries stock assessment
Objective Division:	Environmental Management
Objective Group:	Coastal and estuarine systems and management
Objective Field:	Coastal or estuarine biodiversity
UTAS Author:	Semmens, JM (Professor Jayson Semmens)
ID Code:	72021
Year Published:	2011
Web of Science® Times Cited:	87
Deposited By:	Sustainable Marine Research Collaboration
Deposited On:	2011-08-18
Last Modified:	2012-06-15
Downloads:	465 View Download Statistics