Effects of Climate on Salmonid Productivity: A Global Meta-Analysis Across Freshwater Ecosystems.

Gallagher, Brian K.¹*, Sarah Geargeoura², Dylan J. Fraser¹, ¹Concordia University, Montreal, QC, Canada, ²Environment and Climate Change Canada, Gatineau, QC, Canada

Salmonids are of immense socio-economic importance in much of the world, but are threatened by climate change. We conducted a systematic review and meta-analysis to identify key patterns shaping the effects of climate on salmonid productivity, ultimately collecting 1,321 effect sizes from 156 studies. Patterns in climate effects were complex, and were driven by spatial (latitude, elevation), temporal (time-period, age-class), and biological (range, habitat type, anadromy) variation within and among study populations. These trends were often (but not always) consistent with predictions based on salmonid thermal tolerances. Namely, warming and decreased precipitation tended to reduce productivity when high temperatures challenged upper thermal limits, while opposite patterns were common when cold temperatures limited productivity. Overall, climate impacts on salmonids were highly variable, implying that future declines in some areas may be counterbalanced by gains in others. In particular, we suggest that future warming should (1) increase salmonid productivity at high latitudes and elevations (especially > 60° and > 1,500m), (2) reduce productivity in populations experiencing hotter and dryer growing season conditions, (3) favor non-native over native salmonids, and (4) impact lentic habitats less negatively than lotic ones. These patterns should help conservation and management organizations identify populations most vulnerable to climate change, which can then be prioritized for protective measures. Our framework enables broad inferences about future productivity that can inform decision making under climate change for salmonids and other taxa, but more widespread, standardized, and hypothesis-driven research is needed to expand current knowledge.