Fish stocks are declining as the oceans heat up, placing a major food and income source at risk for millions of people around the world, according to new research published on Thursday.
The study found that the amount of Seafood that humans could sustainably harvest of a wide range of species declined 4.1 percent from 1930 to 2010, a victim of man-made climate change.
"This 4 percent decline looks small, but it's 1.4 million metric tons of fish from 1930 to 2010," said Chris Free, lead author of the study, published in the journal Science.
Scientists have warned that global warming will strain global food supplies in the coming decades. But the new findings – which separate the effects of warming water from other factors, such as overfishing – suggest that climate change is already having a serious impact on seafood.
Fish account for 17% of the protein intake of the global population and 70% for people living in some coastal and island countries. according to the UN Food and Agriculture Organization.
"Fish provide a vital source of protein for more than half the global population, and about 56 million people worldwide are supported in some way by sea fishing," said Dr. Free.
As the oceans warmed, some regions were particularly hit. In the northeastern Atlantic Ocean and the Sea of Japan, fish populations decreased by up to 35% during the study period.
"East Asian ecosystems there isWe have seen some of the biggest declines in fishing productivity, "said Dr. Free. "And this region is home to some of the largest growing human populations and highly dependent populations of seafood."
Now, a postdoctoral researcher at the University of California, Santa Barbara, Dr. Free began research while a Ph.D. student at Rutgers University.
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Marine life has been subjected to some of the most drastic effects of climate change. The oceans have absorbed 93% of the heat that is trapped by the greenhouse gases that humans pump into the atmosphere.
A study published in January, also in Science, found that ocean temperatures were rising much faster than previous estimates.
Amid these changing conditions, fish are shifting where they live, in search of their preferred temperatures. High ocean temperatures can kill both the fish themselves and the food sources on which they depend.
"Fish are like Goldilocks: they do not like very hot or very cold water," said Malin L. Pinsky, an associate professor at the School of Environmental and Biological Sciences at Rutgers University and co-author of the new study.
In about a quarter of the regions studied, fish had expanded its range. On the Atlantic coast of the United States, sustainable catches of black sea bass increased by 6% over the study period.
Another quarter of the regions saw no significant changes in fish stocks, such as the northwest Atlantic Ocean, where Atlantic herring is plentiful.
But half of the regions did not do well either. The northeastern Atlantic Ocean – home to Atlantic cod, the main source of fish and chips – has had a 34% decline in sustainable catches.
In general, more fish populations have declined than they did over the eight decades of the study.
The researchers focused on sustainable catches, using a measure developed by the United Nations that quantifies the amount of food that can be harvested repeatedly from a fish base population. "Fisheries are like a bank account and we are trying to live on in the interest," said Dr. Pinsky.
Several previous studies predicted that climate change would lead to fewer oceanic fish in the future, but the new research looked at historical data to determine that the falls had already begun.
"This will be one of those innovative studies that are cited repeatedly," said Trevor Branch, an associate professor at the University of Washington School of Aquatic and Fisheries Science who was not involved in the study. "Most of what I've seen before in terms of the impacts of climate change has been speculative in terms of: We think this is what will happen in the future. This is different. "
The researchers used a dataset of 235 fish populations located in 38 ecological regions around the globe. The detailed data told not only where the fish were, but also how they responded to environmental effects, such as changing the water temperature.
The team compared these data with records that showed how ocean temperatures changed over time, broken down by the various regions. These regional analyzes were important because some parts of the ocean warmed up faster than others.
"So we connect those to whom the populations responded positively, negatively and who did not respond at all," Dr. Pinsky said.
The data revealed some other trends. Fish populations in the cooler parts of their areas tended to outperform those in warmer areas – for those fish, the extra heat was too much. This was especially troubling to the researchers, because the data they used was less detailed in the tropics. Fish losses in these regions may have been higher than in the regions where the study was concentrated, Dr. Pinsky said.
Hot areas were even worse when they were overfished. Researchers have suggested that overfishing made fish even more vulnerable to temperature changes by impairing their ability to reproduce and damage the ecosystem.
Protecting against overfishing and improving overall fisheries management could help, the researchers said. But, in the end, they said, the solution is to slow down or stop climate change.
A separate study published in the journal Science Advances, found that limiting heating to 2.7 degrees Fahrenheit, or 1.5 degrees Celsius, above pre-industrial levels – a goal of the Paris climate deal – could result in billions of dollars in extra revenue for fisheries globally. Much of this would be in the developing world, where many people rely on fish for protein.
"We hope this underscores the importance of explaining the fact that climate change is driving changes in productivity," Dr. Free said of his research. "Fisheries managers need to come up with new, innovative ways to account for these shifts. This includes reducing catch limits in hot negative years, but may also include increasing catch limits in colder positive years. Having regulations that are adaptable to climate change will really be important in order to maximize food potential. "
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