N° 385October 2011

Jumbo squid, the ogre invading the Pacific

Scientific news Actualidad cientifica

Actualité scientifique

Since 2000, the jumbo or Humboldt squid has been experiencing a remarkable population explosion in the waters off Peru. A cephalopod*, which can reach 4 metres in length and weighs 50 kg, it has invaded the cold waters of the South-East Pacific, both in the open ocean and nearer the coasts.

A flourishing floreciente The proliferation of the pota, as Peruvian fishermen commonly call it, is a boon for them, who have seen hake stocks collapse because of overfishing. In 2004, the government took steps to control excessive catches, including the introduction of policies to fix quotas and cut down the fleet. The fishing operators hence turned to the jumbo squid. Today, a potero –a small timber trawler– can land up to 5 tonnes per day, which are sold to processing businesses which turn them into meal for animal feed, frozen fritters or surimi paste, destined for export. The Peruvian fishermen have become the second producers in the world after the Chinese, mainly for squid and anchovy.

Not a fussy predatorWhy is there such a proliferation of this squid, known scientifically as Dosidicus gigas, off the Peruvian coast? IRD scientists and their partners1

recently described the feeding strategy of this voracious predator, hitherto not well known in Peru. The jumbo squid proves to be highly adaptable, extremely generalist in its diet. It therefore preys on anything that comes its way, including shrimps, lantern fish, hake and anchovy. In most marine species, the larger the size of an animal, the greater its role in the food chain and the larger the prey it goes after. The investigations showed that this is not always the case in this squid. Indeed some of the largest individuals can feed solely on small shrimps.Furthermore, it has a very broad predation range, from the surface down to more than 2000 m depth. However, it prowls more especially in the oxygen minimum zones2, some tens of metres below the surface down to 800 metres, where shrimps and

The jumbo squid, Dosidicus gigas, is proliferating in the South-East Pacific thanks to its high degree of adaptability to environmental changes and to its versatile feeding strategies.

The jumbo squid can grow up to 4 metres in length from the end of its tentacles to its tail. Known scientifically as Dosidicus gigas, it is a voracious predator in the oceans. It feeds on anything that comes its way, a wide range including shrimps, hake, anchovy or even its own kind. This cephalopod* has been proliferating in the waters off Peru, in spite of a decrease in its prey, especially hake owing to overfishing. A Franco-Peruvian research team1 took advantage of an innovatory method to produce the first description of the squid’s remarkable feeding strategy, in the journal PlosOne. These scientists explain the boom of the pota, as the Peruvian fishermen call it, both in biological and economic terms.Up to now the jumbo squid has not only managed to resist excessive exploitation of fishery resources. It has drawn benefit from this trend. Tuna, sea bream, jack mackerel, also less abundant owing to extension of the oxygen minimum zones2 which force them further out from the coasts, are giving way to the squid, enabling it to forage nearer the land. A windfall for Peru, which has become the world’s second largest exporter, after China, thanks to squid and anchovy fishing.

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some mesopelagic fish3 shelter from other preda-tors. Contrary to its prey, rendered lethargic from the deficit in oxygen, the squid remains active under such conditions.

A highly innovatory methodThe great adaptability of these squid was esta-blished through analysis of the chemical composi-tion of the gladius, an internal chitinous shell equiva-lent to the cuttlefish bone. Gladius tissue is inert, developing by accretion4 as the animal grows. This method of chronological analysis is very recent and yields a record of the nature of the food the squid has eaten at successive points of its life. First the carbon isotopic composition5 of samples was used to deduce the origin –near the coast, further offs-hore, etc.– of what each individual has taken in at different times of its existence. The migrations the cephalopod has undertaken were traced in this way. The pota was found to accomplish several extensive migrations during its 12 to 18 month life-span. The second investigation identified the nitrogen isotopic composition of the gladius which defines the indivi-dual’s position in the food chain. Stomach content analysis performed on around 40 potas gave infor-mation on the more recent foraging strategies they had practised.

Pota benefiting from overfishingWith its short life cycle of less than 18 months, a rapid metabolism and an extremely diverse diet, the

jumbo squid not only avoids harm from the region’s excessive fishing pressure –adapting to what is available– but reaps the benefits. For one thing, in ten years the numbers of tuna, sea bream and jack mackerel, which prey on the cephalopod’s juvenile stages, have plummeted off Peru owing to over-fishing. But more particularly, the squid gains from another phenomenon, which exerts a strong limit on marine life. This is the expansion of the oxygen minimum zones over the past 50 years induced by climate change. This extension has pushed the large predators further out towards the open ocean, clearing the way for the jumbo squid to forage in coastal waters.The local population is benefiting from this miracle fishing resource. However, a shadow looms over the pota-industry based economy built up over ten years. Isn’t this squid in its turn in danger of beco-ming a victim of overfishing? The animal has gained much from the intense exploitation of other major predators, and appears highly resistant to heavy fishing pressure thanks to its short life and reproduc-tion cycles that allow rapid stock renewal. However, its boom in population is closely linked to environ-mental conditions. At present these are favourable. But, in the context of the ongoing global climate change, will this be true in the future?

Copy editor – Gaëlle Courcoux - DIC, IRDTranslation – Nicholas FLAY

The industry based on pota fishing has brought an economic boom in the North-East region of Peru. The squid are turned into meal for animals (processing plant in background), fritters or surimi for export over the whole world.

Contacts

Anne LORRAIN,researcher at the IRD

Tel.: +33 (0)2 98 22 40 71 anne.lorrain@ird.fr

UMR 195 Laboratoire des Sciences de l’Environnement Marin - LEMAR (IRD / CNRS / Université de Bretagne occidentale)

AddressIRD Brest BP 7029 280 Plouzané

Arnaud BERTRAND,director of research at the IRD

Tel.: +33 (0)4 99 57 32 25arnaud.bertrand@ird.fr

UMR 212 écosystèmes marins exploités – EME (IRD / Ifremer / Université de Montpellier II)

AddressCentre de recherche halieutique méditerranéenne et tropicaleRue Jean Monnet - BP17134203 Sète Cedex

References

Lorrain Anne, Arguelles J., Alegre A., Bertrand Arnaud, Munaron J. M., Richard P., Cherel Y. Sequential Isotopic Signature Along Gladius Highlights Contrasted Individual Foraging Strategies of Jumbo Squid (Dosidicus gigas). PLos One, 2011, 6 (7), p. e22194.

Key words Jumbo squid, fisheries, food chain, Peru

CoordinationGaëlle CourcouxInformation and Culture Department Tel: +33 (0)4 91 99 94 90Fax: +33 (0)4 91 99 92 28fichesactu@ird.fr

Press officeCristelle DUOSTel: +33 (0)4 91 99 94 87presse@ird.fr

Indigo,IRD photo libraryDaina RECHNERTel: +33 (0)4 91 99 94 81indigo@ird.frView the IRD photos concerning this article, copyright free for the press, on:www.indigo.ird.fr

Graphic design and layoutLaurent CORSINI

1. These investigations were conducted by researchers from the IRD, IMARPE (Instituto del Mar, Peru) and the CNRS (Centre d’Etude Biologiques de Chizé et La Rochelle).

2. Layers of oceanic water, several hundred metres thick, where oxygen concentration is at its lowest. See FAS n°345 - Ecouter l’océan pour une meilleure gestion des pêches.

3. Living in the mesopelagic zone situated between 200 and 1 000 metres depth and generally migrating towards the surface at night.

4. Development of tissue by accumulation of material.

5. The isotopic composition of an element is the ratio between stable isotopes of that element (for example 13C/12C o 15N/14N).

FOR FURTHER INFORMATION

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The tentacles of octopus, cuttlefish or squid are really the animal’s foot, divided into arms equipped with suckers… and attached above their head! Belonging to the Mollusca, they make up the class Cephalopoda, from the Greek kephalê, head, and podos, foot.

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