Contemporary ocean warming and freshwater conditions are related to later sea age at maturity in Atlantic salmon spawning in Norwegian rivers
Villar, Jaime Otero; Jensen, Arne Johan; Stenseth, Nils Christian; Storvik, Geir Olve; Vøllestad, Leif Asbjørn; L'Abée Lund, Henning
Journal article, Peer reviewed
Published version
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http://hdl.handle.net/11250/2449879Utgivelsesdato
2012Metadata
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Sammendrag
Atlantic salmon populations are reported to be declining throughout its range,
raising major management concerns. Variation in adult fish abundance may be
due to variation in survival, growth, and timing of life history decisions. Given
the complex life history, utilizing highly divergent habitats, the reasons for
declines may be multiple and difficult to disentangle. Using recreational angling
data of two sea age groups, one-sea-winter (1SW) and two-sea-winter (2SW)
fish originated from the same smolt year class, we show that sea age at maturity
of the returns has increased in 59 Norwegian rivers over the cohorts 1991–
2005. By means of linear mixed-effects models we found that the proportion of
1SW fish spawning in Norway has decreased concomitant with the increasing
sea surface temperature experienced by the fish in autumn during their first
year at sea. Furthermore, the decrease in the proportion of 1SW fish was influenced
by freshwater conditions as measured by water discharge during summer
months 1 year ahead of seaward migration. These results suggest that part of
the variability in age at maturity can be explained by the large-scale changes
occurring in the north-eastern Atlantic pelagic food web affecting postsmolt
growth, and by differences in river conditions influencing presmolt growth rate
and later upstream migration.