Probably the world's most abundant food fish throughout history has been fished and eaten since before history began. Man has been fattened on herring for something like 2,500 years. But only in the last 25 he has begun to know anything much about it.
Before then, the herring had been put down as a migratory fish because its great shoals appeared a the surface first in the north and then successively farther south. They progressed off the British Iales at so regular a cadence that in the days before instant communication between ship and shore, the girls who cleaned and packed the catches traveled southward along the coast at a rate parallel with the fleets. They were confident that at each stop they would rendezvous with the boats that landed their fish and put out for the more.
Nobody questioned the obvious deduction that the herring were swimming from north to south or in the spring from south to north. But they weren't. Herring are not migratory fish. They are homebodies grouped into great families, each with its own feeding and spawning ground. They do not leave them.
The explanation is that herring are coldwater fish. They demand a temperature of 43 to 59 degrees Farenheit. When surface temperature rise above that level, the fish take refuge in the cooler depths. Autumn arrives, bringing lower temperatures first, of course, to the north. The herring there rise to the surface, impelled also by the fading light which makes it difficult to find their prey in deep waters. And as the cold wave travels south, the herring of each sector rise likewise, one family after another. It looks like horizontal migration. But it isn't.
The French seemed to have sensed this because in their language hareng franc or hareng foncier means herring which stays in the same place. This implies that there are others which do not. But as these terms entered the language long before ichthologists pierced the secrets of the herring, we may assume that no herring are migratory unless discover proof to the contrary.
Herring are grouped into families not only by territories but also by age. A single school will be made up of fish born in the same year, at least until all have reached full growth when they are about one foot long. This is because they are shoaling fish that lived until the present era of overfishing in tremendous schools "a half dozen miles long and wide," writes Dale Brown in "The Cooking of Scandinavia."
In schooling fish, the distance between one individual and its neighbors right and left is regulated by the fish's lateral line which runs along its flanks from head to tail. Only recently has it been discovered that the lateral line acts as a sort of radar, enabling fish to swim in bands and maintain uniform spacing without bumping into each other. This varies with each species in accordance with its size. It is by development of this organ that some fish are able to deliver electric shocks.
Nature has worked out two patterns for schooling fish. Some species swim abreast, their heads on an even line. Others swim with each fish's head opposite the middle of the bodies of the fish to right and left. Herring belong to the second type. The distance between individuals is such that each fish can swim forward at the same rate as the others but has no room to turn around. Obviously all the fish in such a school must be of the same size or the whole society would be thrown out of kilter. Herring run a one-party state.
The compact school of fish that results from the herring's swimming habits is a boon for fishermen who can scoop up great quantities of fish in a single netting, less easy to do with fish capable of scattering in all directions. The uniformity of size imposed by the schooling habit has also had its effect on history and gastronomy. Because all herring taken at the same time from the same fishing grounds were of the same size, herring in medievel times provided a more reliable monetary standard than coins. This was at a time when every large city struck its own. Coins had different shapes, sizes and metallic content. The bewildering variations were further complicated by the happy habit of shaving some of the metal off the edges of gold or silver pieces. This is why some old coins bear imbossed inscriptions on their edges to foil this debasement.
Prices expressed in terms of so many herring were automatically translatable in terms of the currencies of both sides in monetary transactions. When payments were figured in terms of herring, the fish themselves did not actually change hands. The herring was simply the unit of account. Gifts and legacies were valued at their worth in herring. Gifts and legacies were valued at their worth in herring. And when Count Matthew of Burgundy leased land from the monastery of St. Josse, the yearly rent was set down as 10,000 herrings, although it is highly unlikely that he paid it in this currency. The church likewise accepted its tithes expressed in terms of herring.