Environmental change influences the life history of salmonSalmo salarin the North Atlantic Ocean

Abstract

Annual mean total length (LT) of wild one-sea-winter (1SW) Atlantic salmon Salmo salar of the Norwegian River Imsa decreased from 63 to 54 cm with a corresponding decrease in condition factor (K) for cohorts migrating to sea from 1976 to 2010. The reduction in LT is associated with a 40% decline in mean individual mass, from 2 to 1·2 kg. Hatchery fish reared from parental fish of the same population exhibited similar changes from 1981 onwards. The decrease in LT correlated negatively with near-surface temperatures in the eastern Norwegian Sea, thought to be the main feeding area of the present stock. Furthermore, S. salar exhibited significant variations in the proportion of cohorts attaining maturity after only one winter in the ocean. The proportion of S. salar spawning as 1SW fish was lower both in the 1970s and after 2000 than in the 1980s and 1990s associated with a gradual decline in post-smolt growth and smaller amounts of reserve energy in the fish. In wild S. salar, there was a positive association between post-smolt growth and the sea survival back to the River Imsa for spawning. In addition, among smolt year-classes, there were significant positive correlations between wild and hatchery S. salar in LT, K and age at maturity. The present changes may be caused by ecosystem changes following the collapse and rebuilding of the pelagic fish abundance in the North Atlantic Ocean, a gradual decrease in zooplankton abundance and climate change with increasing surface temperature in the Norwegian Sea. Thus, the observed variation in the life-history traits of S. salar appears primarily associated with major changes in the pelagic food web in the ocean.

Maternal inheritance influences homing and growth of hybrid offspring between wild and farmed Atlantic salmon

“…The latter may explain why Atlantic salmon size increases in rivers with a mean water flow of ≤30 m 3 s −1 (Schaffer & Elson 1975, Jonsson et al 1991. Size differences between adults of the present test groups were, however, small, and well within the size of salmon regularly entering the River Imsa (Jonsson et al 2016). However, one may speculate that AquaGen salmon, originating from populations of multi-sea-winter salmon, may be genetically adapted to spawn in rivers larger than the River Imsa, and thus actively avoid entering this small river on their return.…”

“…These low recapture rates decrease the power of the results, and may be partly influenced by the handling and tagging of the smolts (Hansen & Jonsson 1988). More importantly, however, Atlantic salmon mortality at sea is high and has increased since the mid-to late 1980s (Chaput 2012, Jonsson et al 2016. Furthermore, hatchery smolts (used in the present experiment) have lower sea survival and stray more than wild conspecifics (Jonsson et al 2003, Jonsson & Jonsson 2006, Araki et al 2008, Westley et al 2013.…”

Environmental influences on life history strategies in partially anadromous brown trout (Salmo trutta, Salmonidae)

“…The duration and timing of marine migrations are likely governed by tradeoffs between mortality risk and growth opportunities in different habitats, and the most beneficial strategy may vary among individuals and populations. Possibly, the fitness of different aged smolts is also similar as indicated from calculations of survival and fecundity of female Atlantic salmon (Jonsson, Jonsson, & Albretsen, 2016). Possibly, the fitness of different aged smolts is also similar as indicated from calculations of survival and fecundity of female Atlantic salmon (Jonsson, Jonsson, & Albretsen, 2016).…”

Evidence for long‐term change in length, mass and migration phenology of anadromous spawners in French Atlantic salmon Salmo salar

“…Concomitantly, Atlantic salmon Salmo salar L. 1758 populations have suffered a tremendous decline in abundance across their distribution range (Jonsson & Jonsson, ; Chaput, ; ICES, ), together with marked changes in life‐history traits and population structure. In particular, a decline in the proportion of late maturing fish has been reported for many European and North American stocks (Baglinière et al ., ; Otero et al ., ; ICES, ; Jonsson et al ., ). Those changes have been accompanied by a decline in length and mass of fish and a variation in age at maturity (Aprahamian et al ., ; Bacon et al ., ; Jonsson et al ., ) together with a delay in adult migration timing (Valiente et al ., ; Todd et al ., ).…”

“…For instance, higher proportions of 1 sea‐winter (1SW) fish in the late 20th century and more multi‐sea‐winter (MSW) fish in this century have been reported by Jonsson et al . (). Such changes are expected to affect population growth rate, raising concerns about the viability of this species of high economic value.…”