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By Marlene Cimons
As ocean temperatures climb, many species of fish—tuna among them—likely will shrink, decreasing in size by as much as 30 percent, according to a new study published in the journal Global Change Biology.
The study confirms the authors' previous research, which showed that fish won't be able to get enough oxygen to grow if ocean waters keep heating up. Fish, as cold-blooded animals, cannot regulate their own body temperatures. When ocean waters become warmer, a fish's metabolism accelerates, and it needs more oxygen to sustain its body functions. Fish breathe through gills, organs that extract dissolved oxygen from the water and excrete carbon dioxide.
The problem is that the gills' surface area does not grow at the same pace as the rest of the fish's body—and warm water contains less oxygen than cooler water. If a fish like cod grows 100 precent larger, its gills might only grow by 80 percent or less, according to the study.
Tuna, which are fast-moving and need more oxygen may shrink by as much as 30 percent, researchers said. By contrast, brown trout, which are not as active as tuna, will only decrease in body size by about 18 percent with each degree Celsius of warming.
"There is a point where the gills cannot supply enough oxygen for a larger body, so the fish just stops growing larger," said William Cheung, director of science for the Nippon Foundation—University of British Columbia Nereus Program and a co-author of the study.
Warmer waters hold less oxygen, causing fish to shrink. Global Change Biology
Daniel Pauly, the study's lead author and a principal investigator with Sea Around Us, a University of British Columbia research initiative, agreed. He emphasized that "fish are constrained by their gills in the amount of oxygen they can extract from the water. This constraint manifests itself especially in big fish. With increasing temperatures, fish require more oxygen but get less."
The researchers first posited their principle about warming waters and fish size, which they call "gill oxygen-limitation theory," or GOLT, in a 2013 paper published in Nature Climate Change. Their conclusions were challenged by three researchers from Norway and France who claimed their models were based on "erroneous assumptions."
Cheung and Pauly responded to the criticism "by restating both the principle upon which the 2013 study was built, and by re-computing the effect of warming on shrinkage in more detailed fashion, which increased the shrinkage," Pauly said.
With a drop in maximum body size, potential fisheries production will decrease "and that will directly affect the fishing industry," Cheung said. This could result in a loss of potential catch amounting to about 3.4 million metric tons for each degree Celsius of atmospheric warming, he said.
"Some parts of the world, such as in the tropics, are going to see even larger decreases," he said. "This will have substantial impacts on the availability of fishes for people." Scientists said that fish are already shrinking.
"We are already seeing the effects and shrinking of fishes due to warming," Cheung said. "For example, colleagues in the UK analyzed long-term data of fish body size in the North Sea and found that fish stocks such as haddock and sole had decreased in maximum body size in the last few decades, and such shrinkage of size was significantly related to ocean warming in that region, even after correcting for the effects of fishing."
Moreover, oxygen-starved fish may truly end up breathless. Pauly noted that oxygen deprivation is already killing fish in the U.S. and around the world. Though, he added, "Oxygen scarcity doesn't necessarily kill fish. If it is mild, it will only reduce their growth. This is the reason why fish farmers aerate their ponds on very warm days, when the fish therein are literally gasping."
Oxygen scarcity will affect a multitude of sea creatures, not just smaller fish, but also larger species further up the food chain. "They are affected by global warming because their prey are," Pauly said.
"Basically, big fish eats small fish," Cheung said. "So, changes in body size may alter food web interactions and structure, affecting ecosystem functions and services."
Reposted with permission from our media associate Nexus Media.
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In a big victory for animals, Prada has announced that it's ending its use of fur! It joins Coach, Jean Paul Gaultier, Giorgio Armani, Versace, Ralph Lauren, Vivienne Westwood, Michael Kors, Donna Karan and many others PETA has pushed toward a ban.
This is a victory more than a decade in the making. PETA and our international affiliates have crashed Prada's catwalks with anti-fur signs, held eye-catching demonstrations all around the world, and sent the company loads of information about the fur industry. In 2018, actor and animal rights advocate Pamela Anderson sent a letter on PETA's behalf urging Miuccia Prada to commit to leaving fur out of all future collections, and the iconic designer has finally listened.
If people in three European countries want to fight the climate crisis, they need to chill out more.
"The rapid pace of labour-saving technology brings into focus the possibility of a shorter working week for all, if deployed properly," Autonomy Director Will Stronge said, The Guardian reported. "However, while automation shows that less work is technically possible, the urgent pressures on the environment and on our available carbon budget show that reducing the working week is in fact necessary."
The report found that if the economies of Germany, Sweden and the UK maintain their current levels of carbon intensity and productivity, they would need to switch to a six, 12 and nine hour work week respectively if they wanted keep the rise in global temperatures to the below two degrees Celsius promised by the Paris agreement, The Independent reported.
The study based its conclusions on data from the UN and the OECD (Organisation for Economic Co-operation and Development) on greenhouse gas emissions per industry in all three countries.
The report comes as the group Momentum called on the UK's Labour Party to endorse a four-day work week.
"We welcome this attempt by Autonomy to grapple with the very real changes society will need to make in order to live within the limits of the planet," Emma Williams of the Four Day Week campaign said in a statement reported by The Independent. "In addition to improved well-being, enhanced gender equality and increased productivity, addressing climate change is another compelling reason we should all be working less."
Supporters of the idea linked it to calls in the U.S. and Europe for a Green New Deal that would decarbonize the economy while promoting equality and well-being.
"This new paper from Autonomy is a thought experiment that should give policymakers, activists and campaigners more ballast to make the case that a Green New Deal is absolutely necessary," Common Wealth think tank Director Mat Lawrence told The Independent. "The link between working time and GHG (greenhouse gas) emissions has been proved by a number of studies. Using OECD data and relating it to our carbon budget, Autonomy have taken the step to show what that link means in terms of our working weeks."
Stronge also linked his report to calls for a Green New Deal.
"Becoming a green, sustainable society will require a number of strategies – a shorter working week being just one of them," he said, according to The Guardian. "This paper and the other nascent research in the field should give us plenty of food for thought when we consider how urgent a Green New Deal is and what it should look like."
- Reduced Work Hours as a Means of Slowing Climate Change ›
- How working less could solve all our problems. Really. | ›
- Needed: A shorter work week – People's World ›