Awesome, unexpected and unforgettable: a sudden bolt of silver as a tuna jumped clear of the sea. Nobody else saw it, and I (Angus Atkinson) almost thought I was hallucinating. But since I first saw one from a boat just off the south Devon coast ten years ago, Atlantic bluefin tuna have steadily increased in the southwest UK. Last year I even saw them from the shore, and tuna now supports a local fishery. Tuna is not the only species to make a rapid change in the southwest UK about a decade ago.