One of the most important fisheries in the world is provided by the true herrings, which belong to the bony fish family Clupeidae. This family contains a wide variety of fishes with distinctive habits. Although most of the species are marine, a few are anadromous—that is, they spend their lives in the sea and enter rivers to spawn. Other species remain permanently in freshwater.
Herrings are small, silvery fish with a deeply forked tail. They rarely grow over 11 lb (5 kg) in weight. Herrings have a ridge of scales on the belly midline, which is sharp-edged, and they have no visible lateral line.
Herrings contribute greatly to the economy of some countries—wars have even been fought for rights to important fishing grounds, which are widely distributed, except for extremely cold parts of the Arctic and Antarctic Oceans.
Since herrings tend to migrate in enormous schools, they can be caught readily be commercial fishers. They are also key parts of the diet of some species of whales, seals, gulls, and predatory fish. Herrings eat plankton that they strain from the water with their gill rakers, trapping these organisms as water passes across their gills.
The Atlantic herring (Clupea harengus) may be the most plentiful pelagic (or open-ocean) fish, and is found on both sides of the North Atlantic Ocean. Due to intensive overfishing, however, the population of herrings has been markedly reduced.
Spawning times vary but most often occurs in the fall and occasionally in the spring or summer. Each female may deposit 25,000-40,000 eggs, which are heavy and sink to the bottom. On the way down a thick covering of mucus causes the eggs to stick to anything they encounter. It takes up to two weeks for the eggs to hatch, the time depends on such variables as depth and temperature. There is no parental care. In the first year the young may reach a size of 5 in (13 cm), reaching 10 in (25 cm) after two years. In their third year they may have acquired enough fat to be harvested as a source of oil. Herrings become sexually mature in their fourth year.
The term sardine is generally applied to small herrings. It also is applied to such forms as the Pacific sardine (Sardinops sagax). The sprat or brisling (C. sprattus) from the European side of the Atlantic is considerably smaller than the Atlantic herring.
The Atlantic menhaden or mossbunker (Brevoortia tyrannus) is the most numerous of all fish in the mid-Atlantic waters of North America. It has a stubby shape and generally weighs under a pound. Due to its heavy oil content it is not palatable, but makes an excellent fertilizer, fishmeal, and oil. Traveling in massive schools near the surface, these fish can cause a swirling motion of the water. Schools of menhaden may be located by the presence of flocks of seabirds feeding on them.
The American shad (Alosa sapidissima) is considered to be the largest herring, since it has an average weight of 3 lb (1.5 kg) and can reach 12 lb (6 kg). It is found in the Atlantic Ocean from the St. Lawrence River south to Florida. Toward the end of the nineteenth century, shad were introduced into the Pacific Ocean and this species now ranges from Alaska to California. The shad is an anadromous fish, in that it spends its adult life in the ocean but swims up the rivers to spawn.
When spawning, the sexes separate with the males entering the river first, followed by the females, known as roe shad. Each female carries a tremendous number of eggs, estimated at 30,000 on average, although larger females can carry several times that number. As with the other herrings, the eggs are dropped at random since they are sticky and heavy, readily sinking to the bottom but tending to adhere to objects. The young shad remain in the streams until strong enough to enter the sea. Males are sexually mature at about their fifth year, at which time they return to spawn. Females may take a bit longer to mature and reenter the rivers to spawn. Shad are caught as they are traveling upstream when they are energetic. They are caught commercially as well as for sport, and they are highly prized for human consumption, especially the roe.
The alewife (Alosa pseudoharengus) is a close relative of the American shad but is smaller in size. Ocean-moving alewives are anadromous. Some populations in the eastern United States are landlocked and are found in great abundance in the Great Lakes. Tons of alewives die during some summers, resulting in an intolerable, smelly nuisance on beaches. Alewives are caught commercially in seines and nets, and are used for fishmeal and fertilizer.
Dickson Hoese, H., and R.H. Moore. Fishes of the Gulf of Mexico, Texas, Louisiana, and Adjacent Waters. College Station and London: Texas A&M; University Press, 1977.
Whiteman, Kate. World Encyclopedia of Fish & Shellfish. New York: Lorenz Books, 2000.