Growth variation of Atlantic salmon Salmo salar at sea affects their population-specific reproductive potential

P Jacobson,A Gårdmark,R Whitlock,M Huss,J Östergren,K Leonardsson

doi:10.3354/meps13734

Abstract

Understanding the processes shaping the dynamics of anadromous fish populations is essential for their management and conservation. Yet, little is known about how variation in performance at sea affects their population dynamics. Here we show that variation in body growth at sea contributes to explaining variation in the reproductive potential for 2 Atlantic salmon Salmo salar populations, but to a varying extent. To this end, we assembled data collected during 50 yr for 2 Baltic salmon populations of hatchery origin, including annually released smolts, survival at sea estimates, size-specific growth at sea, annual length distributions of returning adult females and their reproductive potential. The regression models fitted to explain the reproductive potential of our 2 study populations improved when growth at sea was included as an explanatory variable, in addition to smolt year class abundance and estimates of their survival at sea. This link between body growth at sea and population-level reproductive potential suggests that growth at sea can be important to consider when resolving variation in recovery and dynamics among salmon populations sharing the same sea.

Highlights

The dynamics of fish populations are governed by the loss and production of biomass, both of which are determined by the success of individuals to survive, grow, mature and spawn
The mean length at age increased with sea age but varied among smolt year classes for both Dalälven and Umeälven (Fig. S7)
We combined long-term data sets of smolt year class abundance, survival and growth at sea, returning adult female length distributions and size-specific individual fecundity data for 2 salmon populations sharing the same sea and demonstrate that body growth at sea contributes to explaining variation in the reproductive potential of 2 Baltic Sea salmon populations

Summary

Introduction

The dynamics of fish populations are governed by the loss and production of biomass, both of which are determined by the success of individuals to survive, grow, mature and spawn. Growth and fecundity depend on body size and, will vary among differently sized individuals within fish populations (Lorenzen 1996, Persson & de Roos 2013, Hixon et al 2014). Accounting for these sizedependencies is paramount for understanding the dynamics of fish populations (Persson et al.2007, van Leeuwen et al 2008, Ohlberger et al 2011). Assessing variation in performance at sea, such as survival and growth, using observational data and testing how such variation affects population dynamics is challenging, especially for species that migrate across habitats and have a wide distribution. For the iconic anadromous Atlantic salmon Salmo salar, we have limited knowledge about how variation in performance at sea affects their population dynamics (ICES 2010, Aas et al 2011, Soto et al 2018, Susdorf et al 2018).

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Discussion

Conclusion