Natural hybridization between Atlantic salmon, salmo-salar, and brown trout, salmo-trutta, in northern Spain

Hybrids between Atlantic salmon and brown trout were detected in two of four watersheds studied in northern Spain. The proportions of hybrids in samples of 'salmon’ranged from 0 to 7–7% but they were not significantly heterogeneous among locations, resulting in a mean hybridization rate of 2–3%. This is the highest rate of natural hybridization so far reported and is significantly greater than rates observed elsewhere in Europe.