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Estuarine survival and migratory behaviour of Atlantic salmon Salmo salar smolts

Authors

  • E. A. Halfyard,

    Corresponding author
    1. Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS, B3H4J1 Canada
    2. Ocean Tracking Network, c/o Dalhousie University, 1355 Oxford Street, Halifax, NS, B3H4JI Canada
      Tel.: +1 902 494 2357; email: eahalfyard@dal.ca
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  • A. J. F. Gibson,

    1. Fisheries and Oceans Canada, 1 Challenger Drive, Dartmouth, NS, B2Y2A2 Canada
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  • D. E. Ruzzante,

    1. Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS, B3H4J1 Canada
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  • M. J. W. Stokesbury,

    1. Ocean Tracking Network, c/o Dalhousie University, 1355 Oxford Street, Halifax, NS, B3H4JI Canada
    2. Department of Biology, Acadia University, 33 Westwood Avenue, Wolfville, NS, B4P2R6 Canada
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  • F. G. Whoriskey

    1. Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS, B3H4J1 Canada
    2. Ocean Tracking Network, c/o Dalhousie University, 1355 Oxford Street, Halifax, NS, B3H4JI Canada
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Tel.: +1 902 494 2357; email: eahalfyard@dal.ca

Abstract

To estimate mortality rates, assess the spatio-temporal dynamics of natural mortality and examine migratory behaviour during the fresh to saltwater transition, 185 wild Atlantic salmon Salmo salar smolts were implanted with coded acoustic transmitters. Seaward migration of tagged S. salar from four river systems in an area of Nova Scotia, Canada known as the Southern Upland was monitored using fixed receivers and active telemetry over 3 years. Cumulative survival through the river, inner estuary, outer estuary and bay habitats averaged 59·6% (range = 39·4–73·5%). When standardized to distance travelled, survival rates followed two patterns: (1) constant rates of survival independent of habitat or (2) low survival most frequently associated with inner estuary habitats. In rivers where survival was independent of habitat, residency periods were also independent of habitat, post-smolts exhibited few upstream movements, took a more direct route to the ocean and reached the ocean rapidly. Alternatively, in rivers where survival was habitat specific, residency was also habitat specific with overall increased residency, more frequent upstream movements and delayed arrival to the open ocean. The sudden disappearance of most (75–100%) smolts and post-smolts assumed dead during the course of this study warrants further examination into the role of avian predators as a mortality vector.

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