Now, a new study has borne out those observations on a huge scale, documenting body size declines in fish across the entire state of Alaska in four different species of salmon: chinook, sockeye, silver and chum.

Alaska is “the last largely pristine North American salmon-producing region”, the authors write. Yet the size of the Yukon region chinooks – the largest of the four salmon species – has diminished the most, by 10% compared with those caught before 1990.