Fish
Herring
Clupea harengus · also called herring, atlantic herring
The herring is a plain little silver fish, and it may have shaped the history of northern Europe more than any king. Salted herring fed the continent for centuries and made the fortunes of the Hanseatic League and the Dutch Republic. And in schools of billions, in the dark, the fish appear to keep in touch with one another by releasing tiny bursts of bubbles from their back ends.
Overview
The herring lives in the North Atlantic on both sides, from Biscay into the Arctic, with a Pacific herring filling the same role in the North Pacific. It is 20–35 cm long, deep blue-green above and brilliant silver on the sides, with loose scales that rub off at a touch. It sieves copepods and other plankton from the water.
Schools of billions
Herring form some of the largest animal aggregations on Earth — schools of hundreds of millions of fish, cubic kilometres in volume, that change shape in seconds as one unit.
Communication by fart
Herring release bursts of high-pitched pulsed sound by venting gas from a duct near the anus, mostly at night and more often when crowded. The pulses are at frequencies herring hear well but their predators hear poorly, and the likely purpose is to keep the school together in the dark. The discovery won an Ig Nobel Prize.
Carpets of eggs
Unlike most sea fish, herring lay sticky eggs on the seabed in dense layers, sometimes centimetres thick over a wide area.
Status
The herring is Least Concern overall, though several regional stocks have collapsed and been rebuilt — most dramatically the North Sea in the 1970s. It remains one of the most heavily fished species in the world, and a keystone forage fish for cod, tuna, seabirds, seals, and whales.
Herring: common questions
Do herring really communicate by farting?
They produce sound by venting gas from the swim bladder through a duct that opens near the anus, so in plain terms, yes, the noise comes out of the fish's rear end. The behaviour was described in a 2003 study that recorded captive herring making rapid trains of clicks, which the researchers named Fast Repetitive Tick sounds, almost entirely at night and much more often when the fish were crowded together. The work was awarded an Ig Nobel Prize, which honours research that makes people laugh and then think. The current interpretation is that the sounds are social, letting a herring keep track of its neighbours and keep the school cohesive in darkness when vision fails.
How big can a herring school get?
Enormous. Acoustic surveys have detected spawning herring schools estimated at hundreds of millions of individual fish, forming a continuous layer many kilometres across and tens of metres deep. Such a school can hold a substantial fraction of a regional herring population in a single mass. The fish within it coordinate their movements so tightly, using vision, the lateral line sense, and perhaps the FRT sounds, that the whole school turns, splits, and reforms as if it were one animal, a behaviour that helps confuse predators.
Why has the herring mattered so much to human history?
For centuries herring was one of the cheapest and most abundant sources of protein in northern Europe, and, salted or smoked, one of the few that could be stored and shipped. Controlling the herring catch and its trade was a route to wealth and influence. The medieval Hanseatic League grew rich on Baltic herring, the Dutch built much of their seventeenth-century prosperity on the North Sea fishery, and Scottish and Scandinavian coastal communities were organised around the seasonal arrival of the shoals. When stocks shifted or crashed, whole towns declined and populations moved.
What eats herring?
Almost everything larger. Herring sit near the base of the North Atlantic food web as a key forage fish, converting plankton into a rich, oily package that supports the animals above them. Cod, haddock, tuna, mackerel, and other predatory fish feed on herring, as do seals, dolphins, and porpoises, and vast numbers of seabirds such as gannets, puffins, and gulls. Baleen whales, including humpbacks and minke whales, target herring schools directly, and a humpback's dramatic lunge-feeding, bursting through the surface with its mouth open, is often a herring school being taken.