Thermal habitat of adult Atlantic salmon Salmo salar in a warming ocean

Abstract

The year-round thermal habitat at sea for adult Atlantic salmon Salmo salar (n = 49) from northern Norway was investigated using archival tags over a 10 year study period. During their ocean feeding migration, the fish spent 90% of the time in waters with temperatures from 1.6-8.4 C. Daily mean temperatures ranged from −0.5 to 12.9 C, with daily temperature variation up to 9.6 C. Fish experienced the coldest water during winter (November-March) and the greatest thermal range during the first summer at sea (July-August). Trends in sea-surface temperatures influenced the thermal habitat of salmon during late summer and autumn (August-October), with fish experiencing warmer temperatures in warmer years. This pattern was absent during winter (November-March), when daily mean temperatures ranged from 3.4-5.0 C, in both colder and warmer years. The observations of a constant thermal habitat during winter in both warmer and colder years, may suggest that the ocean distribution of salmon is flexible and that individual migration routes could shift as a response to spatiotemporal alterations of favourable prey fields and ocean temperatures. K E Y W O R D S archival telemetry, Atlantic salmon, data-storage tags, North Atlantic Ocean, Salmo salar, temperature

Redefining the oceanic distribution of Atlantic salmon

“…Salmon from southern populations used more southern ocean areas, and hence stayed in warmer water, than salmon from the northern populations. We cannot rule out that salmon from different populations have different temperature preferences due to different thermal selection regimes in their home rivers, but similar to a previous study 29 , we suggest that the differences in thermal habitat among populations utilising different areas at sea are mainly driven by availability of prey fields. There is generally little support for the hypothesis that variation in salmonid growth rates reflects thermal adaptations to their home stream 39 .…”

“…The study was carried out over several years, with not all sites having tagging undertaken in the same years. There is a possibility that geographic area use and overlap among populations may vary among years, according to variation in environmental conditions among years 29 . However, data from multiple years for some populations suggest consistent population specific migration routes and area use among years, indicating that the principal patterns are stable over time for particular salmon populations.…”

“…The development of electronic tracking technologies has opened new possibilities to collect detailed spatially unbiased information on fish migrations and individual behaviour over large ocean areas 21 , 22 . For Atlantic salmon, the use of archival tags has expanded our knowledge of where they feed in the ocean 12 , 23 – 26 and provided detailed data on individuals’ depth and temperature use 27 – 29 . However, archival tags have typically been used in studies of single populations, or in limited geographical areas, and included a low number of individuals.…”

Redistribution of salmon populations in the northeast Pacific ocean in response to climate

“…We show that the weighted mean SST varied among stocks by 2.7°C, suggesting there is not a fundamental, physiologically driven SST that universally predicts Chinook salmon abundance and occurrence. Tagging data from a single stock of Atlantic salmon also suggest flexibility in their thermal habitat use (Strøm et al, 2020). Conducting a species‐level analysis that ignores stock‐specific differences in distribution (e.g., Abdul‐Aziz et al., 2011; Cheung & Frölicher, 2020) would yield errant projections of future distribution.…”

The Decline and Impending Collapse of the Atlantic Salmon (Salmo salar) Population in the North Atlantic Ocean: A Review of Possible Causes

“…As a result, we now have a rather detailed knowledge of the feeding (Lear 1972;Hansen and Pethon 1985;Dixon et al 2017Dixon et al , 2019, migratory behavior (Dadswell et al 2010;Jensen et al 2014;Strøm et al 2018;Almodóvar et al 2020) and genetic characteristics (Bradbury et al 2016b(Bradbury et al , 2021Gilbey et al 2017) of salmon while at sea in the North Atlantic Subpolar Gyre (NASpG), the cold water complex of currents that spans the North Atlantic from Labrador to Norway north of the Gulf Stream (Figure 1; Hátún et al 2009;Dadswell et al 2010). With the advent of acoustic and data storage tags our knowledge of marine habitat usage by S. salar continues to expand (Jákupsstovu 1988;Guðjónsson et al 2015;Strøm et al 2020). In summary, the use of high-seas habitat for growth by anadromous Atlantic salmon was probably an advantageous evolutionary step for the species (Spares et al 2015).…”