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World fishing: the fish of discord

What impact has ocean warming already had in recent decades on the distribution of fish stocks?

Fish are ectothermic organisms: their internal temperature depends on the temperature of the water. If this changes, it will first have a physiological impact on them: the warmer the water, the faster the fish populations will mature and tend to become smaller. And if their prey don’t grow as fast as they do, some populations risk collapsing.

Then there is the spatial or biogeographical impact. The fish have three choices. Either they can’t do anything and they will suffer from climate change and see their numbers shrink until they collapse. Either they descend through the water column in search of a more optimal environment but that means dealing with more pressure and less oxygen. Either they will gain higher latitudes. This is a phenomenon that we began to observe concretely from the 1980s and which has since accelerated. On the eastern and western coasts of Canada, we are beginning to see tropical species such as sunfish. In Europe, cod is another emblematic example: its distribution center, which was in the North Sea, is beginning to move to the Norwegian Sea.

How fast do these migrations take place?

Fish are estimated to move poleward at the rate of 30 km to over 100 km per decade on average, depending on the ecology of the species. But these migrations will mechanically create traffic effects with traffic jams that will generate enormous competition between species. On the European side, all the coastal species, for example, will pass through the Norwegian coasts and on the American side, through the Bering and Labrador Straits. Moreover, in the southern hemisphere, all coastal species will find themselves stuck in Patagonia or South Africa, because the lands of the Antarctic continent are far too far away for them to reach. As for the species that will reach the poles, they will still have to face six months of night per year. Will they be able to adapt to it?

Your study looked at the impact of these migrations on fish stocks shared between two or more countries. What are its conclusions?

More than 30% of the world’s fish stocks are transboundary, either with the high seas or between several countries. According to our projections, 23% of these shared stocks will change their natural distribution by 2030, whatever the climate change scenario, which will affect 78% of the Exclusive Economic Zones (EEZs are maritime areas located between territorial waters and international waters, over which States have an exclusive right to exploit resources, editor’s note). And these distribution changes will increase exponentially by 2100, when they will affect 45% of stocks, and affect 81% of countries in the world.

However, we are not talking about species representing small economic stakes, but cod, swordfish, yellowfin tuna or Atlantic bluefin tuna. The latter are negotiated for hundreds of thousands of euros per individual, with a record in millions of dollars in 2019. In terms of global income, cross-border fishing represented 76 billion dollars (nearly 70 billion euros, editor’s note) between 2005 and 2010.

Who will be the states that will benefit from this new mapping of fisheries resources, and who will be the big losers?

The more the countries are located towards the north, the more they will be winners and the more they are towards the Tropics, the more they will be losers. This is the great paradox of global warming: the countries of the North, which are the biggest emitters of CO2, suffer the least from global warming and vice versa. In the northern hemisphere, the whole band of temperate countries before the pole – in particular Norway, Russia, Canada and the United States – will benefit from these changes. In the southern hemisphere, Argentina, New Zealand and South Africa will benefit from this new windfall for a time. But the mid-latitude of some of them is not so important: first they will gain fish stocks, then these will collapse, as the fish continue to migrate, as in New Zealand.

The countries of the Tropics will be the big losers, such as Mexico, Ecuador, the Mediterranean countries and the Horn of Africa. By 2030, the EEZ of French Guiana could lose between 43 and 54% of its transboundary stocks, that of the Maldives, 47 to 61% of them and Brazil about 70%. The situation is likely to be particularly catastrophic in the Philippines, Indonesia and Micronesia, where fishing is the main resource.

However, there is one dimension that our study does not take into account: the ability of people to adapt to new species of fish that may arrive and have never been exploited before. Not to mention the ability of species to adapt to these new environments. Our work concerns 9,000 species, yet there are more than 19,000 in the world, half of them being not or very little exploited.


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