Species and origin specific susceptibility to bird predation among juvenile salmonids

• Main Author: Torbjörn
• Format: Article in Journal/Newspaper
• Language: English
• Published: Zenodo 2023
• Subjects: Atlantic salmon; Salmo salar
• Online Access: https://doi.org/10.5281/zenodo.7549782

This repository includes all code and data for reproducing the analyses in Säterberg et al. (2023) "Species and origin specific susceptibility to bird predation among juvenile salmonids". 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 PIT tagged hatchery-reared and wild juveniles of Atlantic salmon and Sea trout (25769 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, 90 % credibility interval [CRI] = 0.14-0.53), followed by wild trout (0.19, 90% CRI = 0.08-0.37), hatchery-reared salmon (0.13, 90% CRI = 0.07-0.23) and wild salmon (0.08, 90% CRI = 0.04-0.14), in subsequent order. This order in predation probability was consistent across all studied tag- and release-years, suggesting that the opportunistically foraging of cormorants affects the overall survival of juvenile salmonids, but that the inherent predation risk between different salmonid types differs systematically.