Snoek, Barracouta
Thyrsites atun (Euphrasén, 1791), known as the snoek in South Africa and as the barracouta in Australasia, is a long, thin species of snake mackerel found in the seas of the Southern Hemisphere, and a popular food fish in South Africa, particularly along the west and southwest coast. Despite its Australasian name, it is not closely related to the barracuda.
In South Africa it was originally called the "zeesnoek" (Sea Snoek) by Dutch colonists who arrived in the Cape in 1652. It is said to have reminded them of the freshwater pike (or snoek) found in the Netherlands.
In Australia it lives in western and southern Australian waters especially Western Australia, Victoria and Tasmania, where it is called the barracouta.
In New Zealand, it is more common in the colder waters around the South Island. It is also called barracouta in this region.
Off Chile and Argentina it is called the sierra).
The fish can reach a length of 200 centimetres (79 in) SL though most do not exceed 75 centimetres (30 in) SL. The maximum recorded weight for this species is 6 kilograms (13 lb). It is very important to commercial fisheries and is also a popular game fish. It is currently the only known member of its genus.
T. atun has 19 to 21 dorsal spines and about 113 dorsal rays, 1 anal spine and 10 to 13 anal rays, 35 vertebrae. The body is elongate and compressed, with a single lateral line on the upper body then curving ventrally. Body colour is blue-black on top with a paler belly, first dorsal fin is black. Contains an anticoagulant in its bite.
Thyrsites atun is widely distributed in the colder waters in the Southern Hemisphere. In the southwest Atlantic, it is known from Uruguay, Argentina and Tierra del Fuego. In the eastern Atlantic, from Tristan da Cunha and South Africa. In the western Indian Ocean, from South Africa and the St. Paul and Amsterdam islands. In the eastern Indian Ocean, Tasmania and the southern coast of continental Australia. In the southwest Pacific, from New Zealand and the southern coast of Australia. In the southeast Pacific, from southern Peru, Chile, and Tierra del Fuego.
On the African coast it is found from Moçâmedes in northern Angola, along the coast of Namibia and the coast of the Northern Cape and Western Cape provinces of South Africa as far east as Algoa Bay, but mostly between the Kunene River and Cape Agulhas.
Although it is distributed circumglobally, Thyrsites atun lives in coastal waters, and regional populations may consist of discrete stocks. Off New Zealand, three stocks are recognised. Off Australia, the population may made up from three to five stocks, and it is thought that the southern African population may comprise a northern and a southern stock, with some mixing, mostly from north to south.
Understanding
T. atun is found near continental shelves or around oceanic islands, and feeds on small fish like anchovy and pilchard, crustaceans, cephalopods and other invertebrates.
This species will form schools near the bottom or midwater; sometimes even near the surface at night. It prefers sea water temperature between 13 and 18 °C (55 and 64 °F).Thyrsites atun are reputed to attack anything that moves near them in the water.
In the South African population 50% sexual maturity occurs at 3 years at a fork length of about 73 cm.
Spawning occurs during winter and spring, (May to November with a peak from June to October) along the continental shelf break of the western Agulhas bank and the South African west coast, at a depth of between 150 and 400 m. The eggs and larvae are transported by currents to the primary nursery area north of Cape Columbine and the secondary nursery area east of Danger Point, where the juveniles remain until maturity.T. atun eggs hatch about 50 hours after fertilization, and the larvae initially eat phytoplankton, first feeding at 3.5 mm, about 3 to 4 days after hatching. When they reach about 8 mm long, they start eating the larvae of other fishes, which are most abundant during spring and summer in this region.After the first year of growth they reach between 33 and 44cm length.
The main prey species of the South African population are the Clupeoid fishes sardines, Sardinops sagax and anchovies, Engraulis japonicus, on which it is a major predator in the southern Benguela ecosystem. It consequently affects the zooplankton populations further down the food chain.
Juveniles smaller than 24 cm mostly feed on lanternfish (Lampanyctodes hectoris), euphausids (Euphausia lucens), and amphipods (Themisto gaudichaudii). Between 25 and 49 cm, lanternfish, T. gaudichaudii, anchovies, and sardines. Subadults from 50 to 74 cm, anchovy, euphausids, and sardines. Adults larger than 75 cm, sardines and anchovies. Offshore, snoek eat almost exclusively teleosts of both pelagic and demerssal species, including sardines, roundherring and hake (Merluccius spp). Larger adults eat more hake, sardine and horse-mackerel (Trachurus trachurus). A large number of other species, including a range of invertebrates, have been identified as less frequent prey from analysis of stomach contents.
