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Marine Ecology Progress Series

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MEPS 601:203-213 (2018)  -  DOI:

Ocean warming cannot explain synchronous declines in North American Atlantic salmon populations

David X. Soto1,2,*, Clive N. Trueman3, Kurt M. Samways1, Michael J. Dadswell4, Richard A. Cunjak1

1Canadian Rivers Institute and Department of Biology, University of New Brunswick, Fredericton, NB E3B 5A3, Canada
2Department of Earth and Environmental Sciences, KU Leuven, 3001 Leuven, Belgium
3Ocean and Earth Science, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH, UK
4Biology Department, Acadia University, Wolfville, NS B4P 2R6, Canada
*Corresponding author:

ABSTRACT: Atlantic salmon Salmo salar populations have suffered global, synchronous declines over the past decades. These declines are coincident with improvements in river habitats and reductions in high seas fisheries, implying higher rates of natural marine mortality that have been widely linked to increasing ocean temperatures in the North Atlantic. The mechanisms linking temperature to marine mortality in Atlantic salmon, however, are unclear. During the period 1980-2010, populations of S. salar returning to the St. John River, New Brunswick, Canada, after spending either 1 or multiple winters at sea have shown similar patterns of decline, coincident with recent ocean warming in the North Atlantic Ocean. Here we used stable isotope data from historic scale collections to investigate the relationship between foraging location, experienced ocean temperature and population trends for S. salar returning to the St. John River. We show that salmon spending either 1 or multiple winters at sea before returning to the St. John River consistently fed in different regions of the North Atlantic and experienced different ocean warming trends. However, both cohorts show synchronous progressive population declines over the study period. We therefore suggest that ocean warming cannot be the principal cause of increased marine mortality for salmon returning to the St. John River. Both cohorts experience similar conditions during the initial post-smolt period, and increased post-smolt mortality could underpin population declines. Our results support concentrating management and conservation efforts to reduce mortality in the post-smolt phase of salmon lifecycles.

KEY WORDS: Ocean warming · Ocean migration · Salmo salar · Sea surface temperature · Stable isotopes · Archived scale tissue

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Cite this article as: Soto DX, Trueman CN, Samways KM, Dadswell MJ, Cunjak RA (2018) Ocean warming cannot explain synchronous declines in North American Atlantic salmon populations. Mar Ecol Prog Ser 601:203-213.

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