Illex argentinus, Argentine shortfin squid

Illex argentinus, a close relative of the other North Atlantic Illex species, concentrates on the Patagonian shelf edge and spreads over the shelf from Southern Brazil to the Falkland Islands. It supports one of the world’s largest squid fisheries. The fishery mostly exploits the winter spawning, south Patagonian stock, which is more abundant, grows to a larger body size and extends further south than the summer spawners. Spawning takes place in the northern part of the range and the eggs hatch into a typical ommastrephid rhynchoteuthon paralarva. I. argentinus is short-lived and semelparous living approximately one year, at the end of which the squid die after spawning. Growth is rapid and the largest individuals - females from the South Patagonian, winter spawning stock - reach a mean mantle length of 330 mm (maximum of 400 mm ML) when fully grown. Large scale migrations between the spawning grounds and the feeding grounds, and back again, over the one year life cycle are accompanied by diel vertical migrations. Immature and maturing squid occur 3 - 20 m off the bottom during the day but at night they ascend to 5 - 20 m over the shelf and to 20 - 200 m beyond the shelf break. Mature squid of the South Patagonian Stock migrate northward along the continental slope to the spawning grounds in May – July remaining close to the sea bed (500 - 900 m) at night and ascend to 200-300 m above the bottom during the day. The paralarvae are thought to feed using their proboscis, on body mucus enriched with microorganisms and other food particles that stick to it. Juveniles and adults are opportunistic predators feeding on fishes, crustaceans, and cephalopods including smaller conspecifics. The diet generally reflects the plankton and nekton available. Small quid 50% of annual food intake and is also consumed by hoki, red cod, dogfish, and various species of penguin, albatross, some petrels and several seals and dolphins. In the vicinity of the Falkland Islands the southern Patagonian stock has few important predators because squid have grown to a relatively large size before they arrive there. I. argentinus is host to 21 known species of parasite, mostly the larval stages of helminths and trematodes. The fishery is pursued by trawlers but mostly by jiggers which attract the squid with powerful lights that can be seen in visible band satellite imagery. The largest annual catch to date was 1.153 tonnes taken in 1999. There are substantial variations in recruitment and stock size driven by environmental variability.

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