Atlantic herring

Atlantic herring (Clupea harengus) is a herring in the family Clupeidae. It is one of the most abundant fish species in the world. Atlantic herrings 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 up to 1.1 kilograms (2.4 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 Atlantic 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. 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. Although Atlantic herring are found in the northern waters surrounding the Arctic, they are not considered to be an Arctic species. 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. The Baltic herring has a specific name in many local languages (Swedish strömming, Finnish silakka, Estonian räim, silk, Livonian siļk, Russian салака, Polish śledź bałtycki, sałaka, Latvian reņģes, Lithuanian strimelė) and is popularly and in cuisine considered distinct from herring. For example, the Swedish dish surströmming is made from Baltic herring. Herrings reach sexual maturity when they are 3 to 5 years old. The life expectancy once mature is 12 to 16 years. Atlantic herring may have different spawning components within a single stock which spawn during different seasons. They spawn in estuaries, coastal waters or in offshore banks. Fertilization is external like with most other fish, the female releases between 20,000 and 40,000 eggs and the males simultaneously release masses of milt so that they mix freely in the sea. Once fertilized the 1 to 1.4 mm diameter eggs sinks to the sea bed where its sticky surface adheres to gravel or weed and will mature in 1-3 weeks, in 14-19 °C water it takes 6-8 days, in 7,5 °C it takes 17 days. It will only mature if its temperature stays below 19 °C. The hatched larvae are 3 to 4 mm long and transparent except for the eyes which have some pigmentation.