With over 250 species, squid (subclass Teuthoidea) is the largest group within the cephalopods. Like their relative the cuttlefish (Sepia), squid has a circle of ten arms around its mouth opening, eight of which are relatively short and equipped with suction discs over their entire length. Two of the arms have developed into tentacles which are more slender, much longer and only have suckers on the slightly broader, spoon-shaped front ends. The squid uses these to keep hold of its prey when it shoots its tentacles forwards at lightning speed during hunting. Then, with the help of the eight short arms it moves its prey towards the mouth opening. Squid vary greatly in size. Some species are just a few centimetres long and weigh only a few grams whereas others can be almost a metre in length. The biggest giant squid to be caught live was ten metres long and weighed half a tonne. Giant squid (Architeuthis) have even been sighted with a length of over 20 metres long, whereby the tentacles account for about two thirds of this length. Squid are probably the biggest invertebrate animals that ever existed on earth.
The few cephalopod species that live in European waters include the common or “European” squid Loligo vulgaris) and veined squid (Loligo forbesii). Both species are members of the Loliginidae family. They grow quickly and are sexually mature within the first year. Their distribution areas overlap partially, although L. forbesii is more often to be found in northern waters (the species penetrates as far as 59°N), and L. vulgaris prefers southern regions, particularly the Mediterranean. The distribution area in the East Atlantic ranges from the Faeroe Islands and southern Norway, through the Mediterranean as far as the Gulf of Guinea on the West African coast. Sometimes the animals go astray and are even to be found in the Baltic. In autumn, common squid migrate from the northern waters to spend the winter at greater depths off Portugal. In May and June they return to their spawning grounds, a journey which can take them as far as the North Sea. Loligo vulgaris mainly lives at depths of 40 to 150 metres but also in deeper regions as far as 500 metres.
Whilst Loligo forbesii normally reaches sizes of around 75 cm Loligo vulgaris is much smaller reaching only 40 to 50 cm in length (mantle length about 20 cm, very rarely reaching 40 cm) and weights of 1.5 kg. The males are slightly larger than females of the same age. Common squid has a round cylindrical, relatively slender body that tapers torpedo-like to the rear. At the rear end of the body there are horizontal fins on both sides that stretch over two thirds of the body length and together – viewed from above – have the shape of a rhomboid. The colour of the body ranges from dull transparent grey to reddish brown, and the back is more intensively coloured than the underside. The mantle of the squid’s body, known in the fish trade as the tube, is stabilized by a flat inner structure made of a chitinous, calciferous substance. Compared to the body the head seems relatively small. This impression is even reinforced by the unusually large eyes that are covered by a transparent membrane. Measured against the body size squid have the biggest eyes in the animal kingdom! The Loligo species are members of the group of closed-eye squid whose front eye chamber is closed except for a small opening with a corneal fold. The function of this closing device is unknown; perhaps it protects the eyes from the water pressure. Also noteworthy are the mouth parts of the squid whose shape is reminiscent of a parrot’s beak. With this sharp edged corneal formation the animals bite large pieces from their prey before they cut them into smaller pieces using their toothed tongue.
Permanent swimmers and skilful fish hunters
Squid are predators and their spectrum of feed depends on their age and the season. Juveniles mostly feed on crustaceans, polychaetes and arrow worms. Older animals mainly (and some species solely) eat fishes but sometimes even fellow squid. As “visual animals” squid normally hunt during the daytime. They locate their prey optically, grip it with their tentacles and then use their arms to draw it towards their mouths. In brightly lit coastal sections, for example near larger towns and tourist centres, squid also hunt at night. The light from hotels, restaurants and coastal boulevards attracts numerous fishes into the shallow water and with them squid that make use of this twilight to track their prey. Both commercial and sports fishermen have also recognized that strong sources of light attract squid and they use this knowledge to concentrate the squid close to their boats and within reach of their fishing gear.
Squid are permanent swimmers that follow their prey – mostly fishes – in orderly swarm formations. They move both horizontally and vertically coordinated in the water. A group can suddenly and synchronously change its direction of movement without getting confused. The wing-like side fins are mainly used for guidance and rarely for propulsion. At the front of the mantle cavity lies the siphon, a trunk-like lengthening at the exit of the mantle cavity. It is muscular, very mobile and can be moved in any direction, and the squid uses it for locomotion via precise jet propulsion. In this form of locomotion, water is sucked into the mantle cavity and expelled out of the siphon in a fast, strong jet. The direction of the siphon can be changed to suit the direction of travel. This jet propulsion is extremely effective. From a stationary start the animals can reach very high speeds and even shoot several metres high out of the water like a rocket. When fleeing from predators squid often “fly” 30 or 40 metres over the water’s surface.
Rapid growth, short life, early death
The life cycle of the common squid can be aptly described with the formula “short life, early death”“. Exactly how old squid can become is controversial but cephalopod experts name the maximum lifetime of males at one and a half years, and females are apparently hardly older than one year when they die. The majority of L. vulgaris squid already die after the first spawning without their gonads being able to regenerate and mature again. This extremely short lifespan forces common squid to a hasty life and explains why the animals are almost continuously searching for prey. When the squid larvae hatch from the egg after a good three weeks in 20°C warm water they are only just under one centimetre in size but very well developed and already similar to the adult squid. Drifting with the currents they first have to survive a planktonic phase which lasts approximately two months. Already during this period the baby squid eat incessantly and grow accordingly fast. Their growth is heavily dependent on temperature which can lead to huge differences in size and growth between individual regions in their area of distribution. Common squid off Portugal grow about 0.8 mm per day in the first 240 days of their lives. After that the daily growth rate of male squid even increases to 1.7 mm. In the colder North Sea vulgaris squid, which hatch in June, measure about 12 cm after six months, and after ten months between 17 and 21 cm.
With this growth rate the animals are sexually mature after ten months, in warmer waters sometimes even two or three months earlier. There are no species-typical spawning times and the individual populations reproduce at very different times over the course of the year within the whole distribution area: in the Mediterranean off the Catalan coast mostly in March and April, in Greek waters from November to April, and in the Central Adria throughout the year, but mainly from January to May. Squid that are ready to spawn are caught off Portugal from October to February and between April and June, in the North Sea the main spawning season begins in April and often lasts until into August.
Environmental factors influence population size
Large swarms of squid gather in the spawning grounds to mate. To synchronize the final maturation, the partners exchange optical signal stimuli. The female stimulates the male by making the rear portion of its body shell transparent and presenting its mature genitals. Aroused males take on an intensely red hue, lie down next to the females and clasp them with their tentacles. With the fourth left arm, which serves as a copulatory organ (hectocotylus), the male then pushes a sperm packet, called a "spermatophore", into the oviduct of the female. Fertilization takes place a little later during egg-laying which is often watched over by the male. Large males produce several hundred spermatophores which they try to distribute among as many females as possible. Individual males survive the mating process and can spawn a second time. Fertility varies – depending on the size of the females – between 30,000 and 70,000 eggs. Common squid usually lay several dozen eggs that are held in elongated, sausage-shaped looking gelatinous tubes. These are attached by their sticky base onto suitable substrates, mostly stones or aquatic plants, sometimes simply on the sandy ocean floor. When after a few weeks the females have expelled all their eggs the exhausted animals die.
All common squid – not only the juveniles – are very sensitive to abrupt changes in their living conditions, and particularly to changes in temperature. The water temperature influences both hatching and survival rates of the young squid and also their swimming activity, regional distribution and the lifespan of older animals. In warm southern waters common squid mostly live several months longer than in the relatively colder north. The dependence of common squid on external environmental conditions causes stock fluctuations, and population sizes can vary greatly from year to year within the distribution area.
This is also reflected in the cephalopod fishery where landings vary considerably when viewed regionally. Approximately 4 million tonnes of cephalopods (squid, cuttlefish and octopus) are currently caught worldwide per year. Species of the Loliginidae family account for about 500,000 t of this total. The economic importance of this group is accordingly great, especially in those countries where squid is particularly common on the menu. It is impossible to say exactly how many common squid are caught, however. The available data allows only rough estimates because Loligo vulgaris, forbesii and the other squid species that are fished in European waters are rarely separated and recorded by species. Added to this difficulty is the fact that squid are caught mainly as bycatch in other fisheries and rarely targeted specifically. This also explains why demersal trawls account for the largest share of the European squid fishery. 90% of squid are caught with this gear off the Catalan coast, the remaining 10 per cent goes to purse seine and artisanal fishing methods such as hand fishing, pelagic longlines and pots. In the Gulf of Cadiz up to 99% of the squid landed are caught using bottom trawls.
Although the inadequate data basis does not allow a detailed assessment of the proportion and the importance of Loligo vulgaris for European squid fishing it is still possible to derive general trends from the FAO statistics which record the total annual landed volumes. According to these data, a total of 24,781 t squid were fished by all European countries together in 2013, a significant decline compared to previous years: at the turn of the millennium annual landed volumes were still steady at around 100,000 t. Such a sharp drop in catches can hardly be explained by environmental fluctuations in population size which are quite typical of the common squid. The continuity of the decline rather gives reason to suspect that the stocks are overexploited, and thus overfished. This suspicion is supported by the International Council for the Exploration of the Sea (ICES). An ICES report from 2011 confirmed that squid landings in the first decade of the new millennium fluctuated between 12,464 and 3,143 with the lowest values being registered in 2009 and 2010. A similar trend can also be observed in veined squid (Loligo forbesii), whose stock has been declining in the southern regions of its distribution range since 1990. However, some scientists doubt this decline seeing it rather as a consequence of global climate change, because in the same period the abundance of this squid species had risen significantly off Scotland. It is possible that the cold tolerant forbesii squids are withdrawing from more southern areas because the water there is too warm for them. The population of common squid (L. vulgaris) off Morocco, Mauritania, Senegal and Gambia was already classified by ICES as overfished in 2007.
Indispensable in Mediterranean cuisine
More exact appraisal and evaluation are difficult because there are no regular stock assessments and thus no fisheries management for common squid and other squid species. Although plans for monitoring the stocks were made time and again, so far nothing has come of them. The few national attempts to regulate the squid fisheries are ineffective throughout Europe, and in many places illegal and obviously excessive fishing is still common. Most coastal states even refrain completely from regulating the squid fishery in any way or imposing restrictions. In the UK – apart from requirements for mesh sizes in the cod-end of the nets – there are no limiting rules for the targeted squid fishery. Spain stipulates a minimum landing size for squid, sets guidelines for the fishing gear and permitted fishing times. Portugal is making modest efforts to set up a kind of stock control for common squid. But that’s it, because most other European countries show little interest in fisheries management for squid. Perhaps this is because the expense, considering the size of the resource, appears unreasonably high, but probably also because the species are not very important and are subject to strong natural fluctuations, leading to doubts that the stocks could be stabilized by fisheries management strategies anyway. For off West Africa, where ICES classified the population as overfished in 2007, there are very extensive measures to regulate the cephalopod fishery, for example, provisions on net mesh sizes, seasonal area closures to protect spawning, closed fishing zones, limited entry for fisheries, as well as individual transferable quotas (ITQ).
Nevertheless, regulatory and protective measures would seem to make sense wherever squid and other cephalopods are popular components of the human diet. In Europe, these areas include especially the Mediterranean countries from Spain to Greece. In the Adriatic region 1,000 to 1,500 t common squid are caught each year, plus a number of other cephalopod species. While squid is rarely consumed in Central and Northern Europe (and then almost exclusively in the form of those fried rings that are cut from the tubes of the animals and after over-long preparation usually have a rubbery, chewy consistency) the range of uses for squid in Mediterranean cuisine is much broader. On the menu appear not only the tubes, but – and almost more frequently – the tentacles and even the ink that is used for pasta and special sauces. Whether filled or on its own in tomato stock, as seafood salad, cooked, marinated, fried, stewed or grilled squid and cuttlefish can be prepared in many ways. Their meat is rich in protein, low in fat with not even 90 kcal / 100 grams. In addition, almost all of the squid can be used: only the beak and internal skeleton are not suitable for consumption. Probably the most common mistake in the preparation of squid is that it is cooked too long. A witty aphorism that applies well to the preparation of squid: "I’ve been boiling this egg for over half an hour and it’s still not soft". Squid should never be overcooked to ensure that it maintains its optimum "bite".