The Herring: An Important for a marine food chain: For now the conveyor is still operational, and the relatively warm waters in the northward-flowing Gulf Stream, North Atlantic Drift and Norway Current moderate the climate of northwest Europe.
The Herring: An Important for a marine food chain
On the Arctic coast of Norway, it means the water is open at latitudes that would otherwise be frozen over, and this has given rise to another series of extraordinary events.
A key species here is the herring. They live in large, fast-moving shoals and were once so numerous that they were (and still are) popular targets for commercial fisheries. As a consequence, many stocks were overfished.
By the early 1970s, herring populations in the northeast Atlantic, for example, took a hammering, with a collapse of the North Sea fishing industry in the British Isles.
Off Iceland and the Faeroes, the herring disappeared almost entirely, leaving only a small stock of spring-spawning herring off the Norwegian coast, and these fish, which usually overwintered in deep water, mysteriously moved inshore in winter.
Here, Norway could impose an exclusive economic zone, protecting the surviving stock. Fishing came to a halt, and the herring were rescued from irreversible depletion. These days, the herring are back in the Norwegian fjords in abundance and, at Andfjorden, their shoals attract a smart and immensely powerful predator – the true killer whale or orca.
Herring are easier to catch when tightly packed together, so a pod of orcas works as a team to corral the fish. They isolate a shoal and drive it to the surface, blowing bubbles and showing their white undersides to provoke the fish’s schooling reaction to danger.
The whale’s behaviour is known as ‘carousel feeding’, because the whales swim constantly around the periphery of the shoal, calling as they go.
During the day, the herring are in deep waters, 150 to 300 metres down, so it can take up to three hours to drive them up and trap them against the surface, whereas in the early morning the herring are in shallower water and easier to herd. And, when the fish are tight together, the orcas debilitate their prey by slapping the herring with their powerful tails.