Fish populations are dwindling as the oceans warm, threatening an essential source of food and income for millions of people around the world, according to a new study released Thursday.
The study found that the amount of Seafood that humans could sustainably harvest from a wide range of species decreased by 4.1% from 1930 to 2010, a victim of climate change caused by humans.
"This 4% drop seems small, but it was 1.4 million tonnes of fish from 1930 to 2010," said Chris Free, lead author of the study, which appears in the journal Science.
Scientists have warned that global warming will put pressure on global food supplies in the coming decades. But new discoveries – separating the effects of water warming from other factors, such as overfishing – suggest that climate change is already having a serious impact on seafood.
Fish represents 17% of the protein intake of the world's population and not less than 70% among the inhabitants of some coastal and island countries. according to the United Nations Organization for Food and Agriculture.
"Fish is a vital source of protein for more than half of the world's population. Some 56 million people around the world benefit in one way or another from sea fishing, "said Dr. Free.
With the warming of the oceans, some regions have been particularly affected. In the north-east Atlantic Ocean and the Sea of Japan, fish populations have declined to 35% on the duration of the study.
"Ecosystems in East Asia HaWe have seen one of the biggest declines in fisheries productivity, "said Mr. Free. "And this area is home to some of the largest growing human populations and populations heavily dependent on seafood."
A postdoctoral researcher at the University of California at Santa Barbara, Mr. Free began research while holding a Ph.D. student at Rutgers University.
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Marine life has suffered some of the most dramatic effects of climate change. The oceans have absorbed 93% of the heat captured by greenhouse gases that humans pump into the atmosphere.
A study published in January, also in Science, revealed that ocean temperature was increasing much faster than previous estimates.
In the midst of these changing conditions, fish move where they live, in search of their favorite temperatures. High ocean temperatures can kill the fish themselves and the food sources they depend on.
"The fish look like Goldilocks: they do not like their water too hot or too cold," said Malin L. Pinsky, associate professor at the Faculty of Environmental Sciences and Biology at the University of Michigan. Rutgers University and co-author of the new study.
In about a quarter of the regions studied, the fish had expanded their range. Off the Atlantic coast of the United States, sustainable black bass catches increased by 6% over the study period.
Another quarter of the regions did not observe any significant changes in fish populations, as the northwest of the Atlantic Ocean, where Atlantic herring is abundant.
But half of the regions did not have the same results. The Northeast Atlantic, home to Atlantic cod, the mainstay of fish and chips, recorded a 34% decline in sustainable catches.
Overall, the number of fish declined during the eight decades studied.
Researchers focused on sustainable catches, using a measure developed by the UN that quantifies the amount of food that can be harvested repeatedly from a base population of fish. "Fishing is like a bank account and we try to live with interest," said Dr. Pinsky.
Several previous studies had predicted that climate change would reduce the number of marine fish in the future, but new research looked at historical data to determine that declines had already begun.
"This is one of those innovative studies that will be cited over and over again," said Trevor Branch, associate professor at the School of Aquatic and Fisheries Sciences at the University of Washington, who did not participate in the study. study. "Most of what I've seen before in terms of the impact of climate change has been speculative:" We think that's what will happen in the future. "It's different."
The researchers used a dataset of 235 fish populations in 38 ecological regions of the world. The detailed data told them not only where the fish were, but also how they reacted to environmental effects such as changes in water temperature.
The team compared these data with records showing that ocean temperature has changed over time, broken down by region. These regional analyzes were important because some parts of the ocean warmed up faster than others.
"We then matched the populations to which the populations responded positively, negatively and not at all," said Dr. Pinsky.
The data revealed other trends. Fish populations in the coldest parts of their range tend to perform better than those in warmer areas – for these fish, the extra heat was too much. This was particularly troubling for researchers because the data they used was less detailed in the tropics. Fish losses in these areas may have been higher than in the areas studied, Dr. Pinsky said.
The hot areas had even more trouble being overexploited. The researchers suggested that overfishing makes fish even more vulnerable to temperature changes by impairing its reproductive capacity and damaging the ecosystem.
Guarding against overfishing and improving overall fisheries management can help, the researchers said. But ultimately, they said, the solution lies in slowing or stopping climate change.
A separate study, published Wednesday in the journal Science Advances, it was found that limit warming to 2.7 degrees Fahrenheit, or 1.5 degrees Celsius, compared to pre-industrial levels – a goal of the Paris agreement on climate – could generate billions of dollars in additional income for fishing around the world. Much of this would be in developing countries, where many people rely on fish protein.
"We hope this highlights the importance of taking into account that climate change is leading to productivity changes," Dr. Free said of his research. "Fisheries managers need to find new and innovative ways to account for these changes. This includes reducing catch limits in warm and negative years, but may also include increasing catch limits in colder positive years. Having a climate change-adapted regulation will really be important to maximize the food potential. "
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