Séminaire CEFE : Investigating the drivers of Atlantic salmon populations decline across the Atlantic basin

Séminaire CEFE

Mardi 21 mai 2019 – 15h00

Grande salle de réunion du CEFE | 1e étage, aile C

Sans titre

Maxime Olmos

Agrocampus Ouest, Rennes

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My research is motivated by the desire to understand the functioning of wild animal populations in order to improve the scientific basis for conservation (and management) of these populations. A major challenge in understanding the response of populations to global change is to separate out the effects of local drivers acting independently on specific populations, from the effects of global drivers that impact multiple populations and synchronize their dynamics. This presentation investigates the drivers of the widespread decline of Atlantic salmon (Salmo salar) populations in the North Atlantic Ocean over the last four decades. We developed a hierarchical Bayesian life cycle model to quantify the trends and the spatial covariation of key life history traits characterizing the marine phase of the life cycle for multiple populations across the North Atlantic basin. The model is based on a collective analysis of the dynamics of 24 stock units (SUs) from North America, Northern and Southern Europe in a single hierarchical model over the period 1971–2014. We found strong coherence in the temporal variations of life history traits across SUs. The results provide evidence of a decline in the marine survival together with an increase in the proportion of fish that mature after the 1st winter at sea, common to all SUs. We also found that this synchronous decline in marine survival is likely a response of populations to temporal variations of environmental conditions encountered by salmon in the common feeding areas. Finally, our findings support the hypothesis of a response of salmon to large scale bottom-up environmentally driven changes in the North Atlantic. We also demonstrate that the new model brought major contributions to improve the scientific basis of Atlantic salmon stock assessment in the North Atlantic.

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