title: Basin-scale phenology and effects of climate variability on global timing of initial seaward migration of Atlantic salmon (Salmo salar).
abstract: Migrations between different habitats are key events in the lives of many organisms. Such movements involve annually recurring travel over long distances usually triggered by seasonal changes in the environment. Often, the migration is associated with travel to or from reproduction areas to regions of growth. Young anadromous Atlantic salmon (Salmo salar) emigrate from freshwater nursery areas during spring and early summer to feed and grow in the North Atlantic Ocean. The transition from the freshwater ('parr') stage to the migratory stage where they descend streams and enter salt water ('smolt') is characterized by morphological, physiological and behavioural changes where the timing of this parr-smolt transition is cued by photoperiod and water temperature. Environmental conditions in the freshwater habitat control the downstream migration and contribute to within- and among-river variation in migratory timing. Moreover, the timing of the freshwater emigration has likely evolved to meet environmental conditions in the ocean as these affect growth and survival of the post-smolts. Using generalized additive mixed-effects modelling, we analysed spatio-temporal variations in the dates of downstream smolt migration in 67 rivers throughout the North Atlantic during the last five decades and found that migrations were earlier in populations in the east than the west. After accounting for this spatial effect, the initiation of the downstream migration among rivers was positively associated with freshwater temperatures, up to about 10 °C and levelling off at higher values, and with sea-surface temperatures. Earlier migration occurred when river discharge levels were low but increasing. On average, the initiation of the smolt seaward migration has occurred 2.5 days earlier per decade throughout the basin of the North Atlantic. This shift in phenology matches changes in air, river, and ocean temperatures, suggesting that Atlantic salmon emigration is responding to the current global climate changes.
authors: Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, Oslo, N-0316, Norway.
authors: Jaime
authors: J
authors: Otero
authors: Jan Henning
authors: JH
authors: L'Abée-Lund
authors: Ted
authors: T
authors: Castro-Santos
authors: Kjell
authors: K
authors: Leonardsson
authors: Geir O
authors: GO
authors: Storvik
authors: Bror
authors: B
authors: Jonsson
authors: Brian
authors: B
authors: Dempson
authors: Ian C
authors: IC
authors: Russell
authors: Arne J
authors: AJ
authors: Jensen
authors: Jean-Luc
authors: JL
authors: Baglinière
authors: Mélanie
authors: M
authors: Dionne
authors: John D
authors: JD
authors: Armstrong
authors: Atso
authors: A
authors: Romakkaniemi
authors: Benjamin H
authors: BH
authors: Letcher
authors: John F
authors: JF
authors: Kocik
authors: Jaakko
authors: J
authors: Erkinaro
authors: Russell
authors: R
authors: Poole
authors: Ger
authors: G
authors: Rogan
authors: Hans
authors: H
authors: Lundqvist
authors: Julian C
authors: JC
authors: Maclean
authors: Erkki
authors: E
authors: Jokikokko
authors: Jo Vegar
authors: JV
authors: Arnekleiv
authors: Richard J
authors: RJ
authors: Kennedy
authors: Eero
authors: E
authors: Niemelä
authors: Pablo
authors: P
authors: Caballero
authors: Paul A
authors: PA
authors: Music
authors: Thorolfur
authors: T
authors: Antonsson
authors: Sigurdur
authors: S
authors: Gudjonsson
authors: Alexey E
authors: AE
authors: Veselov
authors: Anders
authors: A
authors: Lamberg
authors: Steve
authors: S
authors: Groom
authors: Benjamin H
authors: BH
authors: Taylor
authors: Malcolm
authors: M
authors: Taberner
authors: Mary
authors: M
authors: Dillane
authors: Fridthjofur
authors: F
authors: Arnason
authors: Gregg
authors: G
authors: Horton
authors: Nils A
authors: NA
authors: Hvidsten
authors: Ingi R
authors: IR
authors: Jonsson
authors: Nina
authors: N
authors: Jonsson
authors: Simon
authors: S
authors: McKelvey
authors: Tor F
authors: TF
authors: Naesje
authors: Oystein
authors: O
authors: Skaala
authors: Gordon W
authors: GW
authors: Smith
authors: Harald
authors: H
authors: Saegrov
authors: Nils C
authors: NC
authors: Stenseth
authors: Leif Asbjørn
authors: LA
authors: Vøllestad
mesh_terms: D025041:Animal Migration; D000818:Animals; D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D057231:Climate Change; D009792:Oceans and Seas; D045483:Rivers; D020317:Salmo salar / Q000502:physiology*; D013696:Temperature; D013997:Time Factors
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: Atlantic salmon; North Atlantic; freshwater conditions; phenology; sea surface temperature; smolt emigration