| Atlantic herring | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Clupeiformes |
| Family: | Clupeidae |
| Subfamily: | Clupeinae |
| Genus: | Clupea |
| Species: | C. harengus |
| Binomial name | |
| Clupea harengus Linnaeus, 1758 |
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Atlantic herring (Clupea harengus) is a fish in the family Clupeidae. It is one of the most abundant fish species on earth. Herring can be found on both sides of the Atlantic Ocean, congregating in large schools. They can grow up to 45 centimetres (18 in) in length and weigh more than 0.5 kilograms (1.1 lb). They feed on copepods, krill and small fish, while their natural predators are seals, whales, cod and other larger fish.
The Atlantic herring fishery has long been an important part of the economy of New England and the Canadian Maritime provinces. This is because the fish congregate relatively near to the coast in massive schools, notably in the cold waters of the semi-enclosed Gulf of Maine and Gulf of St. Lawrence. North Atlantic herring schools have been measured up to 4 cubic kilometres (0.96 cu mi) in size, containing an estimated 4 billion fish.
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The small-sized herring in the inner parts of the Baltic Sea, which is also less fatty than the true Atlantic herring, is considered a distinct subspecies (Clupea harengus membras) ("Baltic herring"), despite the lack of a distinctive genome.
Atlantic herring have a fusiform body. Gill rakers in their mouths filter incoming water, trapping any zooplankton and phytoplankton.
Atlantic herring are in general fragile. They have large and delicate gill surfaces, and contact with foreign matter can strip away their large scales.
They have retreated from many estuaries worldwide due to excess water pollution although in some estuaries that have been cleaned up, herring have returned. The presence of their larvae indicates cleaner and more–oxygenated waters.
Atlantic herring can be found on both sides of the ocean. They range across North Atlantic waters such as the Gulf of Maine, the Gulf of St Lawrence, the Bay of Fundy, the Labrador Sea, the Davis Straits, the Beaufort Sea, the Denmark Straits, the Norwegian Sea, the North Sea, the English Channel, the Celtic Sea, the Irish Sea, the Bay of Biscay and Sea of the Hebrides.[1] Although Atlantic herring are found in the northern waters surrounding the Arctic, they are not considered to be an Arctic species.
Herring-like fish are the most important fish group on the planet. They are also the most populous fish.[2] They are the dominant converter of zooplankton into fish, consuming copepods, arrow worms chaetognatha, pelagic amphipods hyperiidae, mysids and krill in the pelagic zone. Conversely, they are a central prey item or forage fish for higher trophic levels. The reasons for this success is still enigmatic; one speculation attributes their dominance to the huge, extremely fast cruising schools they inhabit.
Orca, cod, dolphins, porpoises, sharks, Rockfish, seabird, Whale, squid, Sea Lion, Seal, tuna, Salmon, and fishermen.
Herring are pelagic–prey includes copepods, amphipods, larvalsnails, diatoms by larvae below 20 millimetres (0.79 in), peridinians, molluscan larvae, fish eggs, euphausids, mysids, small fishes, menhadenlarvae, pteropods, annelids, tintinnids by larvae below 45 millimetres (1.8 in), Haplosphaera, Calanus, Pseudocalanus, Acartia, Hyperia, Centropagidae, Temora, Meganyctiphanes norvegica.
Young herring capture copepods predominantly individually ("particulate feeding" or "raptorial feeding"),[3] a feeding method also used by adult herring on large prey items like euphausids.
If prey concentrations reach very high levels, as in microlayers, at fronts or directly below the surface, herring become filter feeders, driving several meters forward with wide open mouth and far expanded opercula, then closing and cleaning the gill rakers for a few milliseconds.
At least one herring stock spawns in every month of the year. Each spawns at a different time and place (spring, summer, autumn and winter herrings). Greenland populations spawn in 0–5 metres (0–16 ft). North Sea (bank) herrings spawn at up to 200 metres (660 ft) in autumn. Eggs are laid on the sea bed, on rock, stones, gravel, sand or beds of algae. "...the fish were darting rapidly about, and those who have opportunity to see the fish spawning in more shallow water ... state that both males and females are in constant motion, rubbing against one another and upon the bottom, apparently by pressure aiding in the discharge of the eggs and milt" (Moore at Cross Island, Maine).
Females may deposit from 20,000 up to 40,000 eggs, according to age and size, averaging about 30,000. In sexually mature herrings, the genital organs grow before spawning, reaching about one-fifth of its total weight.
The eggs sink to the bottom, where they stick in layers or clumps to gravel, seaweeds or stones, by means of their coating mucus, or to any other objects on which they chance to settle.
If the egg layers are too thick they suffer from oxygen depletion and often die, entangled in a maze of fucus. They need substantial water microturbulence, generally provided by wave action or coastal currents. Survival is highest in crevices and behind solid structures, because predators feast on openly disposed eggs. The individual eggs are 1 to 1.4 millimetres (0.039 to 0.055 in) in diameter, depending on the size of the parent fish and also on the local race. Incubation time is about 40 days at 3 °C (37 °F), 15 days at 7 °C (45 °F), 11 days at 10 °C (50 °F). Eggs die at temperatures above 19 °C (66 °F).
The larvae are 5 to 6 millimetres (0.20 to 0.24 in) long at hatching, with a small yolk sac that is absorbed by the time the larva reaches 10 millimetres (0.39 in) is reached. Only the eyes are well pigmented (a camera works only with a black housing). The rest of the body nearly transparent, virtually invisible under water and natural luminance conditions.
The dorsal fin forms at 15 to 17 millimetres (0.59 to 0.67 in), the anal fin at about 30 millimetres (1.2 in)—the ventral fins are visible and the tail becomes well forked at 30 to 35 millimetres (1.4 in)—at about 40 millimetres (1.6 in) the larva begins to look like a herring.
The larvae are very slender and can easily be distinguished from all other young fish of their range by the location of the vent, which lies close to the base of the tail. But distinguishing clupeoids one from another in their early stages, requires critical examination, especially telling herring from sprats.
At one year they are about 10 centimetres (3.9 in) long, first spawning at 3 years.
Atlantic herring can school in huge numbers. Radakov estimated herring schools in the North Atlantic can occupy up to 4.8 cubic kilometres with fish densities between 0.5 and 1.0 fish/cubic metre. That's several billion fish in one school.[4]
Herring are amongst the most spectacular schoolers ("obligate schoolers" under older terminology). They aggregate in groups that consist of thousands to hundreds of thousands or even millions of individuals. The schools traverse the open oceans.
Schools have a very precise spatial arrangement that allows the school to maintain a relatively constant cruising speed. Schools from an individual stock generally travel in a triangular pattern between their spawning grounds, e.g. Southern Norway, their feeding grounds (Iceland) and their nursery grounds (Northern Norway). Such wide triangular journeys are probably important because herring cannibalize their own offspring. A herring school can react very quickly to evade predators; they have excellent hearing. Around SCUBA divers and remotely operated vehicles they can form a vacuole ("fountain effect"). The phenomenon of schooling is far from understood, especially the implications on swimming and feeding-energetics. Many hypotheses have been put forward to explain the function of schooling, such as predator confusion, reduced risk of being found, better orientation, and synchronized hunting. However, schooling has disadvantages such as: oxygen- and food-depletion and excretion buildup in the breathing media. The school-array probably gives advantages in energy saving although this is a highly controversial and much debated field.
Schools of herring can on calm days sometimes be detected at the surface from more than a mile away by the little waves they form, or from a few meters at night when they trigger bioluminescence in surrounding plankton ("firing"). All underwater recordings show herring constantly cruising reaching speeds up to 108 centimetres (43 in) per second, and much higher escape speeds.
The Atlantic herring fishery is managed by multiple organizations that work together on the rules and regulations applying to herring. As of 2010 the species was not threatened by overfishing.[5]
Because of their feeding habits, cruising desire, collective behavior and fragility they survive in very few aquaria worldwide despite their abundance in the ocean. Even the best facilities leave them slim and slow compared to healthy wild schools.