Squid, cuttlefish and octopus populations are exploding around the world. These fast-growing creatures with great adaptive capacity are perfectly equipped to cope with the disruptions induced by the most pronounced effects of climate change and overfishing. This is revealed in work that my colleagues and I recently published in the journal Current Biology.
Aeople have severely depleted, and in many cases depleted, the resources for sustainable fisheries to meet the food needs of an increasingly dense world population. From a food chain perspective, we tend to catch the largest predators first. and then the other species. The fishermen targeted sharks, tuna and whales, and then medium-sized fish such as cod, hake and halibut, which generally live a long time and grow slowly.
The vacant space left by overfished fish can be occupied by other species, especially rapidly proliferating animals, headed by cephalopods. Squid, cuttlefish and octopus move in a "fast lane": their growth is short and their lifespan lasts, usually one or two years. They lay many eggs, and these eggs have high mortality rates. relatively low Female octopus females patiently watch over the development of their offspring while squid embryos are protected by a protective mucous membrane. These characteristics allow cephalopods to adapt quickly to changes in their environment; this is what has happened in recent decades.
These species remain mysterious and are notoriously difficult to count. To get a fair and comprehensive picture of their abundance, we looked at "catch rates" - the number of individuals caught per boat - over the past 60 years. We used a large data set of 35 different species (52 % squid, 31 % octopus and 17 % cuttlefish) from the major ocean areas. Most were target species for fishers, while others were unwanted or bycatch species. Data from the fisheries were used as well as data from specific research studies.
In all of our work, we have uncovered a real and statistically significant increase in cephalopod populations. Deep-sea squid and cuttlefish that are rather static in their existence are thriving, as are squid that move over the seabed and those that travel thousands of kilometres from their breeding grounds to the sites where they find their food. At a time when marine biodiversity is clearly threatenedcephalopods seem to be experiencing a new kind of blooming.
Climate change and the population boom
The "giant squid" is one of the most blatant examples of this phenomenon. Also known as the "Humboldt squid", it usually weighs between 1 and 2 kilos and has a life cycle of one year. It is found in the warm waters of the eastern Pacific Ocean where it has enabled the emergence of small-scale fishing in Mexico, Chile and the United States. in Peru.
However, a warm El Niño event followed by a cold La Niña season delays their maturation and allows them to live for an additional year: their life cycle then reaches two years. During this second year, they continue to grow rapidly and eventually reach much larger sizes than normal. In fact, these climatic phenomena have led to the emergence of large groups of animals with extended life cycles. They can thus weigh between 25 and 40 kiloswhich is 10 times their normal size.
Following the 1997-2000 El Niño/La-Niña episodes, these squid began to move up the up and down the Pacific coast towards northern California; they reached Alaska, which has led to the current development of the world's most important cephalopod fisheries. Annual catches range from 600,000 to one million tonnesThis is now a very important source of income for communities in these areas of the Pacific.
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But since the life cycle of these giant squid is affected by ambient water temperature over the course of a year or two, another strong El Niño event could end the existence of these animals, with new populations returning to the average size of the species. This is what recently happened in the Gulf of California in Mexico, putting local fisheries in great difficulty; and this could also happen in Peru and Chile, regions where a powerful El Niño episode has occurred in recent months.
The explosion in the number of squid, cuttlefish and octopus will have interesting consequences, both for their own ecosystems and for human communities. On the one hand, this phenomenon could benefit sharks and other large fish that depend on these species for food, and on the other hand, it could also be beneficial to some fishermen.
However, cephalopod populations are much less stable than fish with longer life cycles. These populations generally go through successive phases of expansion and recession, their biomass varying greatly from one year to the next; this makes any forecasting about them very delicate. Income from their fishery is therefore dependent on these changes; the economic and species conservation risks are also often compounded by the lack of cooperative communication between the various players in the fishing industry.
At a time when fisheries are becoming increasingly interested in cephalopods, it is becoming crucial to manage these resources well to prevent them from suffering the same fate as many fish species whose stocks have dramatically declined.
Alexander ArkhipkinHonorary Research Fellow, School of Biological Sciences, University of Aberdeen
Header image: © Morten Brekkevold, Flickr
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