Richard Hamblyn

Salmon – the name, it’s thought, derives from the Latin salire, ‘to leap’ – has always been a fish apart, marked by its unusual capacity to migrate between the distinct worlds of salt and fresh water. According to William Camden’s Britannia (1586), the salmon leaps of Pembrokeshire were Britain’s first tourist attractions, at which scores of people would gather to ‘stand and wonder at the strength and sleight by which they see the Salmon get out of the Sea into the said River’. People still crowd the banks of the Teifi to watch the returning salmon launch themselves at the cascading waters in brute determination to reach their ancestral spawning grounds upstream.

The largest migration of life on earth departs every night from the twilight zone, the kilometre-deep middle layer of open ocean in which the majority of living creatures can be found. As darkness falls, millions of tons of animals, ranging in size from the smallest arrow worms to the largest cetaceans, swim their way up to the photic zone to feed in relative safety, braving shallower waters...