Species- and origin-specific susceptibility to bird predation among juvenile salmonids

Torbjörn Säterberg*, Philip Jacobson, Maria Ovegård, Johan Östergren, Jörgen Rask , Niels Jepsen, Ann-Britt Florin

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

Juvenile salmonids often experience high mortality rates during migration and bird predation is a common source of mortality. Research suggests that hatchery-reared salmonids are more prone to predation than wild salmonids, and that Atlantic salmon (Salmo salar) experience lower predation than Sea trout (Salmo trutta), yet telemetry studies have displayed equivocal results. Here, using a large data set on passive integrated transponder (PIT) tagged hatchery-reared and wild juveniles of Atlantic salmon and Sea trout (25,769 individuals) we investigate predation probability by piscivorous birds (mainly Great Cormorants Phalarocorax carbo) on salmonids originating from River Dalälven in Sweden. Bird colonies and roosting sites were scanned annually (2019–2021), and the temporal dynamics of bird predation on salmonids released in 2017–2021 was assessed. Hatchery-reared trout was clearly most susceptible to cormorant predation (0.31, 90CRI] = 0.14–0.53), followed by wild trout (0.19, 90.08–0.37), hatchery-reared salmon (0.13, 90.07–0.23), and wild salmon (0.08, 90.04–0.14), in subsequent order. This order in predation probability was consistent across all studied tag- and release-years, suggesting that the opportunistic foraging of cormorants affects the overall survival of juvenile salmonids, but that the inherent predation risk between different salmonid types differs systematically.
Original languageEnglish
Article numbere4724
JournalEcosphere
Volume14
Issue number12
Number of pages14
ISSN2150-8925
DOIs
Publication statusPublished - 2023

Keywords

  • Atlantic salmon
  • Avian predation
  • Great Cormorant
  • Phalarocorax carbo
  • PIT tag
  • Salmo salar
  • Salmo trutta
  • Sea trout

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