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Artículo de publicación ISISome 290 species of squids comprise the order Teuthida that belongs to the molluscan Class Cephalopoda. Of these, about 30-40 squid species have substantial commercial importance around the world. Squid fisheries make a rather small contribution to world landings from capture fisheries relative to that of fish, but the proportion has increased steadily over the last decade, with some signs of recent leveling off. The present overview describes all substantial squid fisheries around the globe. The main ecological and biological features of exploited stocks, and key aspects of fisheries management are presented for each commercial species of squid worldwide. The history and fishing methods used in squid fisheries are also described. Special attention has been paid to interactions between squid fisheries and marine ecosystems including the effects of fishing gear, the role of squid in ecosystem change induced by overfishing on groundfish, and ecosystem-based fishery management

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Cephalopods are voracious, versatile predators. They generally have a short life span and a single spawning event followed by death. Populations are subject to dramatic fluctuations and their impact on prey populations is equally variable. The prehensile arms and tentacles of cephalopods, coupled with a highly evolved sensory system, allow them to occupy a broad trophic niche and migrations enable populations to exploit the temporal and spatial variability of production systems and populations of prey. Shoaling is a common behavioural feature of many species which facilitates prey capture and contributes to the impact of cephalopods on prey populations. Research on cephalopod stomach contents is hampered because the beak is used to bite the prey into small pieces so hard parts, which are usually needed for identification of prey species, are often rejected causing potential bias in estimation of diet. Cephalopods may also feed unnaturally in the presence of sampling gear. Despite these problems there is a growing body of data on cephalopod predation collected using direct observations, conventional visual analysis of stomach contents and serological methods. Most species feed on small crustaceans as juveniles and shift the diet to larger fish and other cephalopods during growth. This shift is accompanied by ontogenetic changes in the allometry of the brachial crown. There is increasing evidence that myctophid fishes are an important food resource for oceanic squid. The diet and stock size of some commercially exploited squid populations is sufficiently well known to quantify the impact of a single generation on the prey community. Where there is predation on commercial stocks of fish and crustaceans, the effect of cephalopod feeding on recruitment may be significant. Cephalopods are trophic opportunists in marine food webs from polar to equatorial seas.

Two large (dorsal mantle length 42.5 and 47.5 cm), mated spent females of circum-Antarctic bathypelagic cranchiid squid Galiteuthis glacialis were caught early in March 1992 at the surface of the ice hole in the western Weddell Sea over depths 1915±1920 m by the team of the U.S.A.-Russian Ice Station Weddell-I. The structure of the reproductive system of adult females is described for the ®rst time in detail.Both were gelatinous, devoid of tentacles, with empty or almost empty stomachs. The empty spermatangia (sperm reservoirs of spermatophores) 30±35 mm in length were distributed in the mantle tissues parallel to the mantle surface and to each other in the dorso-anterior part of the mantle: 13 in one female, parallel to the body axis, and 20 in the other, parallel (13) or perpendicular (7) to the body axis. In the latter case, they represented probably two mating events. The spermatangia lay nearer to the inner than the outer mantle side and opened by a round window on the inner side; the skin with chromatophores above them remained intact. The spermatozoa had one¯agellum and rod-like heads, length 5.0±5.3 mm, width 1.2±1.5 mm. The most characteristic features are: a very simple type of blood vessel branching making each micro-gonad currant-like, not grape-like; a very compact disposition of oviducal, nidamental glands and gill, forming a united complex located on both sides of the mantle cavity; and an ovary connected by mesentery along all its length with the continuation of the stomach from the caecum to the end of the gastrogenital ligament. Only immature degenerating trophoplasmatic oocytes, length 0.9±1.4, av. 1.0±1.2 mm, were contained in ovaries; only one mature egg (length 3.3 mm, width 2.4±2.5 mm) was found in each female. The absence of oocytes <0.9 mm and 1.5±3.2 mm indicates that the maturation of oocytes proceeds rather synchronously, one large portion of eggs (some tens of thousands) matures in a short time while others degenerate. The residual fecundity is assessed to be approximately 20,000 eggs.It is hypothesized that mating occurs shortly before spawning and that mature males do not undergo gelatinous degeneration and do not lose tentacles. Spermatophores are placed on the inner side of the female's mantle with the aid of the male's tentacles and/or arms (less probably by the penis), but the exact mode of implantation is unclear. Spawning probably occurs at depths of adult habitat (approx. 500±2500 m), may be multiportional but short; the exhausted female loses neutral buoyancy, rises to the surface and dies. Rising to the surface after spawning is a common feature of females of many meso-and bathypelagic squids undergoing gelatinous degeneration during maturation (Onychoteuthidae, Gonatidae, Histioteuthidae, Cranchiidae, etc.) and may explain the common occurrence of large deep-water squids in the stomachs of seabirds, including those incapable of diving, and marine mammals.