ARTICLE Predicting climate change effects on subarctic–Arctic populations of Atlantic salmon (Salmo salar) Richard D. Hedger, Line E. Sundt-Hansen, Torbjørn Forseth, Ola Ugedal, Ola H. Diserud, Ånund S. Kvambekk, and Anders G. Finstad Abstract: We predict an increase in parr recruitment and smolt production of Atlantic salmon (Salmo salar) populations along a climate gradient from the subarctic to the Arctic in western and northern Norway in response to future climate change. Firstly, we predicted local stream temperature and discharge from downscaled data obtained from Global Climate Models. Then, we developed a spatially explicit individual-based model (IBM) parameterized for the freshwater stage, with combinations of three different postsmolt survival probabilities reflecting different marine survival regimes. The IBM was run for three locations: southern Norway (59°N), western Norway (62°N), and northern Norway (70°N). Increased temperatures under the future climate regimes resulted in faster parr growth, earlier smolting, and elevated smolt production in the western and northern locations, in turn leading to increased egg deposition and elevated recruitment into parr. In the southern location, density- dependent mortality of parr resulting from low summer wetted-areas reduced predicted future smolt production in comparison to the other locations. It can be inferred, therefore, that climate change may have both positive and negative effects on anadromous fish abundance within the subarctic–Arctic according to geographical region. Résumé : Nous prédisons une augmentation du recrutement de tacons et de la production de saumoneaux des populations de saumons atlantiques (Salmo salar) le long d'un gradient climatique allant de la région subarctique a ` la région arctique dans l'ouest et le nord de la Norvège, en réponse aux changements climatiques futurs. Nous avons d'abord prédit la température et les débits de cours d'eau locaux a ` partir de données obtenues de modèles climatiques planétaires transposées a ` l'échelle locale. Nous avons ensuite élaboré un modèle basé sur l'individu (IBM) spatialement explicit paramétré pour le stade en eau douce, avec des combinaisons de trois probabilités de survie post-saumoneau différentes reflétant différents régimes de survie en mer. L'IBM a été exécuté pour trois endroits, a ` savoir le sud de la Norvège (59°N), l'ouest de la Norvège (62°N) et le nord de la Norvège (70°N). Les températures plus élevées des régimes climatiques futurs se traduisaient par une croissance plus rapide des tacons, une smoltification plus précoce et une production accrue de saumoneaux dans les régions ouest et nord, dont découlaient une ponte et un recrutement de tacons accrus. Dans la région sud, la mortalité dépendant de la densité des tacons découlant de la réduction des surfaces mouillées estivales faisait en sorte de réduire la production de saumoneaux future prévue par rapport aux autres régions. Il est donc possible de conclure que les changements climatiques pourraient avoir des effets tant positifs que négatifs sur l'abondance de poissons anadromes dans les régions subarctiques–arctiques, selon l'emplacement géographique. [Traduit par la Rédaction] Introduction Anadromous salmonids are culturally and economically impor- tant species throughout the Northern Hemisphere. However, population abundances of Atlantic salmon (Salmo salar) are at his- torically unprecedented low levels in some rivers, and future cli- mate change is expected to have a potentially strong influence on population abundance (Todd et al. 2008; Jonsson and Jonsson 2009, 2011). Present and future climate effects on these fishes are therefore a major concern for both conservation and resource management. In particular, temperate populations in both Eu- rope and North America have received considerable attention (Reist et al. 2006; Bates et al. 2008; Jonsson and Jonsson 2009). Species with complex life cycles where habitat requirements change through ontogeny are particularly susceptible to climate change owing to the multiple climate-related drivers at each life stage (see Graham and Harrod 2009 and examples within). This is particularly relevant for anadromous salmonids, where the com- plexity of their life cycle means that the fish will be affected by multiple climate-related drivers at each life stage in both fresh- water and marine environments (ACIA 2006). For example, McDaniels et al. (2010) lists over 10 processes that potentially affect sockeye salmon (Oncorhynchus nerka) in Canada, and Walsh and Kilsby (2007) list over 20 processes that potentially affect Atlantic salmon in both freshwater and marine environments in the UK. Other potential drivers may also exist. Geographical differences in climate effects may mean that different stages of the life history may be affected differently among populations. Within rivers, changes in temperature and discharge regime have been pre- dicted to affect salmon abundance by reducing suitable habitat or increasing mortality during key stages (Battin et al. 2007; Walsh and Kilsby 2007). Jonsson and Jonsson (2009) suggest that climate change could cause earlier migration within the season, younger age-at-smolting and sexual maturation, and increased disease sus- ceptibility and mortality. The potential effects of increased ma- rine temperatures on marine growth and survival of salmonids is less understood. Higher marine survival rates have been found in warmer years (Friedland 1998; Kallio-Nyberg et al. 2004; Rikardsen et al. 2008), although the relationship may be specific according to natal river (Friedland et al. 2005). Climate change may act upon fishes directly via climate-induced changes in environmental pro- Received 3 May 2012. Accepted 21 October 2012. Paper handled by Associate Editor Michael Bradford. R.D. Hedger, L.E. Sundt-Hansen, T.F. Forseth, O. Ugedal, O.H. Diserud, and A.G. Finstad. Norwegian Institute for Nature Research, Trondheim, NO-7485, Norway. Å.S. Kvambekk. The Norwegian Water Resources and Energy Directorate (NVE), P.O. Box 5091, Majorstua, NO-0301, Oslo, Norway. Corresponding author: Richard D. Hedger (e-mail: richard.hedger@nina.no). Pagination not final/Pagination non finale 1 Can. J. Fish. Aquat. Sci. 70: 1–10 (2013) dx.doi.org/10.1139/cjfas-2012-0205 Published at www.nrcresearchpress.com/cjfas on xx February 2013. Can. J. Fish. Aquat. Sci. 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