Biotic and abiotic determinants of the ascent behaviour of adult Atlantic salmon transiting passable waterfalls

• Published in: River Research and Applications
• Main Authors: Lennox, R.J. (Robert J.), Thorstad, E.B. (Eva B.), Diserud, O.H. (Ola H.), Økland, F. (Finn), Cooke, S.J. (Steven), Aasestad, I. (Ingar), Forseth, T. (Torbjørn)
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: biotelemetry; exploitation; migration; Salmonidae; straying; waterfall; Atlantic salmon
• Online Access: https://ir.library.carleton.ca/pub/21757; https://doi.org/10.1002/rra.3329

The spawning migration of Atlantic salmon has been characterized by tracking salmon carrying electronic tags as they ascend rivers, but still little is known about how natural obstacles such as waterfalls influence migratory behaviour and how such behaviours are mediated by various biotic (e.g., fish size) and abiotic (e.g., discharge, water temperature, and barometric pressure) factors. The Norwegian river Numedalslågen is interrupted by natural waterfalls ranging in height from 2 to 6 m. We tagged 113 Atlantic salmon with radio transmitters in the estuary and used stationary radio telemetry stations to track fish. Ninety-one salmon were recorded in Numedalslågen, 39 of which remained in the river for spawning. Large salmon moved farther and faster upriver but also delayed longer and had lower daily probability to pass the second waterfall. Delay below and passage probability at the final, largest waterfall was affected by water discharge, wherein passage occurred when discharge was declining. Barometric pressure also i