It has a somewhat peculiar appearance with a large bump on its forehead and up along its back. But who cares about looks when you get the job done? The humpback salmon breeds in a much shorter time than regular Pacific salmon when it swims upstream to spawn. It produces a lot of offspring, which is why Russians and Norwegians have introduced them.

»Such is often the case with invasive species. They arise because enterprising people want access to more resources«, explains Peter Rask Møller, associate professor and curator at the Natural History Museum of Denmark.