Increasing Regional Temperatures Associated with Delays in Atlantic Salmon Sea-Run Timing at the Southern Edge of the European Distribution

Populations of Atlantic salmon Salmo salar at the edge of the species' distribution are the most vulnerable to environmental changes. Those inhabiting southern European rivers are expected to be particularly affected by global warming. However, they are exploited as a very valuable resource for the region, attracting tourism and generating substantial income. In the central part of northern Spain (Asturias), there is a long tradition of sport fisheries (angling). The first salmon caught in a river each year is called the campanu. Analysis of a 50-year time series demonstrates that the run timing of the Asturian Atlantic salmon has changed over this period, as inferred from significant delays in the date of capture of the campanu. Average campanu weight has experienced a parallel significant decrease but age has not changed, indicating diminution of salmon condition. These changes are statistically associated with an increase in regional temperature, there being a minor effect of the global climate North Atlantic Oscillation index. Negative effects of high temperatures on salmon run and feeding, together with long migratory routes, may explain these results.