Brackish water , sometimes termed brack water , is water occurring in a natural environment that has more salinity than freshwater , but not as much as seawater . It may result from mixing seawater (salt water) and fresh water together, as in estuaries , or it may occur in brackish fossil aquifers . The word comes from the Middle Dutch root brak . Certain human activities can produce brackish water, in particular civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming . Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it can be damaging to the environment (see article on shrimp farms ).
46-578: Littorina Sea (also Litorina Sea ) is a geological brackish water stage of the Baltic Sea , which existed around 7500–4000 BP and followed the Mastogloia Sea , a transitional stage of the Ancylus Lake . This stage and form of the body of water is named after common periwinkle ( Littorina littorea ), then a prevailing mollusc in the waters, which indicates its salinity. A transgression of
92-556: A staple food source since at least 3000 BC. The fish is served numerous ways, and many regional recipes are used: eaten raw, fermented, pickled , or cured by other techniques, such as being smoked as kippers . Herring are very high in the long-chain omega-3 fatty acids EPA and DHA . They are a source of vitamin D . Water pollution influences the amount of herring that may be safely consumed. For example, large Baltic herring slightly exceeds recommended limits with respect to PCB and dioxin , although some sources point out that
138-407: A feeding method also used by adult herring on larger prey items like krill. 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. Copepods, the primary zooplankton, are
184-405: A few centimetres. If copepod concentrations reach high levels, schooling herrings adopt a method called ram feeding . In the photo below, herring ram feed on a school of copepods. They swim with their mouths wide open and their operculae fully expanded. The fish swim in a grid where the distance between them is the same as the jump length of their prey, as indicated in the animation above right. In
230-450: A herring in one locality might be called something else in another locality. Some examples: The species of Clupea belong to the larger family Clupeidae (herrings, shads , sardines , menhadens ), which comprises some 200 species that share similar features. These silvery-coloured fish have a single dorsal fin , which is soft, without spines. They have no lateral line and have a protruding lower jaw. Their size varies between subspecies:
276-437: A major item on the forage fish menu. Copepods are typically 1–2 mm ( 1 ⁄ 32 – 3 ⁄ 32 in) long, with a teardrop-shaped body. Some scientists say they form the largest animal biomass on the planet. Copepods are very alert and evasive. They have large antennae (see photo below left). When they spread their antennae, they can sense the pressure wave from an approaching fish and jump with great speed over
322-610: A natural defense against hurricane and tsunami damage in particular. The Sundarbans and Bhitarkanika Mangroves are two of the large mangrove forests in the world, both on the coast of the Bay of Bengal . Some seas and lakes are brackish. The Baltic Sea is a brackish sea adjoining the North Sea . Originally the Eridanos river system prior to the Pleistocene , since then it has been flooded by
368-471: A range of salinity regimes and is not considered a precisely defined condition. It is characteristic of many brackish surface waters that their salinity can vary considerably over space or time. Water with a salt concentration greater than 30‰ is considered saline . See the salinity table from the Misplaced Pages salinity article . Brackish water condition commonly occurs when fresh water meets seawater. In fact,
414-409: A school of herring into a tight bait ball . Different predatory species then use different techniques to pick the fish off in the bait ball. The sailfish raises its sail to make it appear much larger. Swordfish charge at high speed through the bait balls, slashing with their swords to kill or stun prey. They then turn and return to consume their "catch". Thresher sharks use their long tails to stun
460-526: A species only found in deep water in the Baltic, while pike are confined to the less saline surface waters. The Caspian Sea is the world's largest lake and contains brackish water with a salinity about one-third that of normal seawater. The Caspian is famous for its peculiar animal fauna, including one of the few non-marine seals (the Caspian seal ) and the great sturgeons , a major source of caviar . Hudson Bay
506-544: Is a brackish marginal sea of the Arctic Ocean , it remains brackish due its limited connections to the open ocean, very high levels freshwater surface runoff input from the large Hudson Bay drainage basin , and low rate of evaporation due to being completely covered in ice for over half the year. In the Black Sea the surface water is brackish with an average salinity of about 17–18 parts per thousand compared to 30 to 40 for
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#1732855414909552-401: Is commonly used as cooling water for power generation and in a variety of ways in the mining, oil, and gas industries. Once desalinated it can also be used for agriculture, livestock, and municipal uses. Brackish water can be treated using reverse osmosis , electrodialysis , and other filtration processes. Herring Herring are various species of forage fish , mostly belonging to
598-679: Is the Atlantic herring , which comprises over half of all herring capture. Fish called herring are also found in the Arabian Sea , Indian Ocean , and Bay of Bengal . Herring played an important role in the history of marine fisheries in Europe, and early in the 20th century, their study was fundamental to the development of fisheries science . These oily fish also have a long history as an important food fish , and are often salted , smoked , or pickled . Herring were also known as "silver darlings" in
644-422: Is very low and the fish fauna consists predominantly of freshwater species such as roach , dace , carp , perch , and pike . The Thames Estuary becomes brackish between Battersea and Gravesend , and the diversity of freshwater fish species present is smaller, primarily roach and dace; euryhaline marine species such as flounder , European seabass , mullet , and smelt become much more common. Further east,
690-686: The Atlantic herring (the type species) found in the North Atlantic, and the Pacific herring mainly found in the North Pacific. Subspecific divisions have been suggested for both the Atlantic and Pacific herrings, but their biological basis remains unclear. In addition, a number of related species, all in the Clupeidae, are commonly referred to as herrings. The table immediately below includes those members of
736-682: The Baltic herring ( Clupea harengus membras ) is small, 14 to 18 cm (about 5.5 to 7 inches); the proper Atlantic herring ( Clupea harengus harengus ) can grow to about 46 cm (18 in) and weigh up 700 g (1.5 lb); and Pacific herring grow to about 38 cm (15 in). At least one stock of Atlantic herring 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 feet) of water, while North Sea (bank) herrings spawn at down to 200 m (660 ft) in autumn. Eggs are laid on
782-469: The blue whale , is said to be the largest biomechanical event on Earth. Adult herring are harvested for their flesh and eggs, and they are often used as baitfish . The trade in herring is an important sector of many economies around the world. In Europe, the fish has been called the "silver of the sea", and its trade has been so significant to many countries that it has been regarded as the most commercially important fishery in history. Herring has been
828-406: The crab-eating frog , Fejervarya cancrivora (formerly Rana cancrivora ). Mangroves represent important nesting sites for numerous birds groups such as herons, storks, spoonbills, ibises, kingfishers, shorebirds and seabirds. Although often plagued with mosquitoes and other insects that make them unpleasant for humans, mangrove swamps are very important buffer zones between land and sea, and are
874-508: The pelagic zone . Conversely, they are a central prey item or forage fish for higher trophic levels . The reasons for this success are still enigmatic; one speculation attributes their dominance to the huge, extremely fast cruising schools they inhabit. Herring feed on phytoplankton , and as they mature, they start to consume larger organisms. They also feed on zooplankton, tiny animals found in oceanic surface waters , and small fish and fish larvae. Copepods and other tiny crustaceans are
920-423: The Øresund where the recession of sea level exposes less dry land. During the period, temperate deciduous forest crept north to cover the littoral hinterland. Brackish water Technically, brackish water contains between 0.5 and 30 grams of salt per litre—more often expressed as 0.5 to 30 parts per thousand (‰), which is a specific gravity of between 1.0004 and 1.0226. Thus, brackish covers
966-409: The Baltic approximately 4500 BP widened its ocean link, allowing it to reach a peak of salinity during the warmer Atlantic period of European climatology. At this peak, the sea bore twice the volume of water and covered 26.5% more land than it does today. As the period ended, the features of the modern coast appeared, including lagoons, spits, and dunes. Notable exceptions include steep terraces such as
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#17328554149091012-690: The Baltic, copepods of the genus Acartia can be present in large numbers. However, they are small in size with a high escape response, so herring and sprat avoid trying to catch them. These copepods also tend to dwell more in surface waters, whereas herring and sprat, especially during the day, tend to dwell in deeper waters. Predators of herring include seabirds , marine mammals such as dolphins , porpoises , whales , seals , and sea lions , predatory fish such as sharks , billfish , tuna , salmon , striped bass , cod , and halibut . Fishermen also catch and eat herring. The predators often cooperate in groups, using different techniques to panic or herd
1058-479: The North Sea but still receives so much freshwater from the adjacent lands that the water is brackish. As seawater is denser, the water in the Baltic is stratified, with seawater at the bottom and freshwater at the top. Limited mixing occurs because of the lack of tides and storms, with the result that the fish fauna at the surface is freshwater in composition while that lower down is more marine. Cod are an example of
1104-554: The United Kingdom. A number of different species, most belonging to the family Clupeidae , are commonly referred to as herrings. The origins of the term "herring" is somewhat unclear, though it may derive from the same source as the Old High German heri meaning a "host, multitude", in reference to the large schools they form. The type genus of the herring family Clupeidae is Clupea . Clupea contains only two species:
1150-409: The air. Some whales lunge feed on bait balls. Lunge feeding is an extreme feeding method, where the whale accelerates from below the bait ball to a high velocity and then opens its mouth to a large gape angle. This generates the water pressure required to expand its mouth and engulf and filter a huge amount of water and fish. Lunge feeding by rorquals , a family of huge baleen whales that includes
1196-599: The almost endless stream of herring allows a herring to eventually snap up the copepod. A single juvenile herring could never catch a large copepod. Other pelagic prey eaten by herring includes fish eggs, larval snails , diatoms by herring larvae below 20 mm ( 13 ⁄ 16 in), tintinnids by larvae below 45 mm ( 1 + 3 ⁄ 4 in), molluscan larvae, menhaden larvae, krill , mysids , smaller fishes, pteropods , annelids , Calanus spp., Centropagidae , and Meganyctiphanes norvegica . Herrings, along with Atlantic cod and sprat , are
1242-477: The animation, juvenile herring hunt the copepods in this synchronised way. The copepods sense with their antennae the pressure wave of an approaching herring and react with a fast escape jump. The length of the jump is fairly constant. The fish align themselves in a grid with this characteristic jump length. A copepod can dart about 80 times before it tires. After a jump, it takes it 60 milliseconds to spread its antennae again, and this time delay becomes its undoing, as
1288-477: The cancer-reducing effect of omega-3 fatty acids is statistically stronger than the carcinogenic effect of PCBs and dioxins. The contaminant levels depend on the age of the fish which can be inferred from their size. Baltic herrings larger than 17 cm (6.7 in) may be eaten twice a month, while herrings smaller than 17 cm can be eaten freely. Mercury in fish also influences the amount of fish that women who are pregnant or planning to be pregnant within
1334-435: The egg layers are too thick they suffer from oxygen depletion and often die, entangled in a maze of mucus . 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 exposed eggs. The individual eggs are 1 to 1.4 mm ( 3 ⁄ 64 to 1 ⁄ 16 in) in diameter, depending on
1380-474: The eyes are well pigmented. The rest of the body is nearly transparent, virtually invisible under water and in natural lighting conditions. The dorsal fin forms at 15 to 17 mm ( 19 ⁄ 32 to 21 ⁄ 32 in), the anal fin at about 30 mm ( 1 + 3 ⁄ 16 in)—the ventral fins are visible and the tail becomes well forked at 30 to 35 mm ( 1 + 3 ⁄ 8 in)— at about 40 mm ( 1 + 9 ⁄ 16 in),
1426-485: The family Clupeidae referred to by FishBase as herrings which have been assessed by the International Union for Conservation of Nature . Also, a number of other species are called herrings, which may be related to clupeids or just share some characteristics of herrings (such as the lake herring , which is a salmonid ). Just which of these species are called herrings can vary with locality, so what might be called
Littorina Sea - Misplaced Pages Continue
1472-530: The family of Clupeidae . Herring often move in large schools around fishing banks and near the coast, found particularly in shallow, temperate waters of the North Pacific and North Atlantic Oceans , including the Baltic Sea , as well as off the west coast of South America. Three species of Clupea (the type genus of the herring family Clupeidae) are recognised, and comprise about 90% of all herrings captured in fisheries. The most abundant of these species
1518-554: The larva begins to look like a herring. Herring 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; however, distinguishing clupeoids one from another in their early stages requires critical examination, especially telling herring from sprats . At one year, they are about 10 cm (4 in) long, and they first spawn at three years. Herrings consume copepods , arrow worms , pelagic amphipods , mysids , and krill in
1564-412: The most common zooplankton eaten by herring. During daylight, herring stay in the safety of deep water, feeding at the surface only at night when the chance of being seen by predators is less. They swim along with their mouths open, filtering the plankton from the water as it passes through their gills. Young herring mostly hunt copepods individually, by means of "particulate feeding" or "raptorial feeding",
1610-463: The most extensive brackish water habitats worldwide are estuaries , where a river meets the sea. The River Thames flowing through London is a classic river estuary. The town of Teddington a few miles west of London marks the boundary between the tidal and non-tidal parts of the Thames, although it is still considered a freshwater river about as far east as Battersea insofar as the average salinity
1656-629: The most important commercial species to humans in the Baltic Sea. The analysis of the stomach contents of these fish indicate Atlantic cod is the top predator, preying on the herring and sprat. Sprat are competitive with herring for the same food resources. This is evident in the two species' vertical migration in the Baltic Sea, where they compete for the limited zooplankton available and necessary for their survival. Sprat are highly selective in their diet and eat only zooplankton, while herring are more eclectic, adjusting their diet as they grow in size. In
1702-537: The oceans. The deep, anoxic water of the Black Sea originates from warm, salty water of the Mediterranean . Lake Texoma , a reservoir on the border between the U.S. states of Texas and Oklahoma , is a rare example of a brackish lake that is neither part of an endorheic basin nor a direct arm of the ocean, though its salinity is considerably lower than that of the other bodies of water mentioned here. The reservoir
1748-431: The pens the farmed fish are kept in. Another important brackish water habitat is the mangrove swamp or mangal . Many, though not all, mangrove swamps fringe estuaries and lagoons where the salinity changes with each tide. Among the most specialised residents of mangrove forests are mudskippers , fish that forage for food on land, and archer fish , perch-like fish that "spit" at insects and other small animals living in
1794-500: The river. This type of ecological succession from freshwater to marine ecosystem is typical of river estuaries. River estuaries form important staging points during the migration of anadromous and catadromous fish species, such as salmon , shad and eels , giving them time to form social groups and to adjust to the changes in salinity. Salmon are anadromous, meaning they live in the sea but ascend rivers to spawn; eels are catadromous, living in rivers and streams, but returning to
1840-412: The salinity increases and the freshwater fish species are completely replaced by euryhaline marine ones, until the river reaches Gravesend, at which point conditions become fully marine and the fish fauna resembles that of the adjacent North Sea and includes both euryhaline and stenohaline marine species. A similar pattern of replacement can be observed with the aquatic plants and invertebrates living in
1886-471: The sea bed, on rock, stones, gravel, sand or beds of algae . Females may deposit from 20,000 to 40,000 eggs, according to age and size, averaging about 30,000. In sexually mature herring, 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, seaweed, or stones, by means of their mucous coating, or to any other objects on which they chance to settle. If
Littorina Sea - Misplaced Pages Continue
1932-720: The sea to breed. Besides the species that migrate through estuaries, there are many other fish that use them as "nursery grounds" for spawning or as places young fish can feed and grow before moving elsewhere. Herring and plaice are two commercially important species that use the Thames Estuary for this purpose. Estuaries are also commonly used as fishing grounds and as places for fish farming or ranching. For example, Atlantic salmon farms are often located in estuaries, although this has caused controversy, because in doing so, fish farmers expose migrating wild fish to large numbers of external parasites such as sea lice that escape from
1978-441: The shoaling fish. These sharks compact their prey school by swimming around them and splashing the water with their tails, often in pairs or small groups. They then strike them sharply with the upper lobe of their tails to stun them. Spinner sharks charge vertically through the school, spinning on their axes with their mouths open and snapping all around. The sharks' momentum at the end of these spiraling runs often carries them into
2024-457: 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), or 11 days at 10 °C (50 °F). Eggs die at temperatures above 19 °C (66 °F). The larvae are 5 to 6 mm ( 3 ⁄ 16 to 1 ⁄ 4 in) long at hatching, with a small yolk sac that is absorbed by the time the larvae reach 10 mm ( 13 ⁄ 32 in). Only
2070-420: The trees, knocking them into the water where they can be eaten. Like estuaries, mangrove swamps are extremely important breeding grounds for many fish, with species such as snappers , halfbeaks , and tarpon spawning or maturing among them. Besides fish, numerous other animals use mangroves, including such species as the saltwater crocodile , American crocodile , proboscis monkey , diamondback terrapin , and
2116-510: Was created by the damming of the Red River of the South , which (along with several of its tributaries) receives large amounts of salt from natural seepage from buried deposits in the upstream region. The salinity is high enough that striped bass , a fish normally found only in salt water, has self-sustaining populations in the lake. Brackish water is being used by humans in many different sectors. It
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