They have only one breeding season, the timing dictated by the moon and its influence on the tides. Catching Capelin Five thousand kilometres away, off the coast of Newfoundland, are fish called capelin, who also have only one breeding season. In these cold waters the breeding season is later, from the end of May onwards. For three months the fish come inshore in huge dense shoals. Capelin are an essential food supply to many other marine animals.
Cod follow the shoals inshore, eating adults and young.
Whales and seals also partake. But sea birds in particular rely on them at the beginning of their breeding season. The decline of the Atlantic puffin, in the 1970s and 80s, was attributed to over-fishing of the capelin. These separate but connected events, repeated every year under the dark sea, reveal a tantalising glimpse into a world far removed from everyday experience - a world where the lives of animals are rules by the phases of the moon.