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In June 2015, Dwayne "The Rock" Johnson startled the fitness world when news of his daily diet plan went viral. As it turned out, it included an absurd amount of cod.
It started after he shared his diet and exercise regimen with Muscle and Fitness magazine, which published a detailed breakdown of each of his seven meals.
Four of those meals contained cod. When FiveThirtyEight ran the numbers, they came up with over 2 pounds of cod per day (the recommended serving for a normal human is about a quarter-pound) and a yearly total of 821 pounds per year.
This means The Rock — at least at one point (more on this in a moment) — consumed more than twice the daily recommended safe amount of mercury.
But that's not the only issue: Cod stocks are in deep trouble.
An October 2015 study in the journal Science found that the once-plentiful cod fishery in the Gulf of Maine, the coastal body of water that stretches from the north shore of Massachusetts up to the Canadian Maritimes, is headed for collapse.
The culprit? Climate change.
Andrew Pershing, the study's lead author and the chief science officer of the Gulf of Maine Research Institute, told Business Insider that warming sea-surface temperatures negatively affect cod populations, but the actual reasons aren't totally clear yet.
The Gulf of Maine is at serious risk because it's warming so rapidly — 99.9% faster than the rest of the world's oceans, according to the study.
The level of warming and the speed at which it's happening is unprecedented, even for a highly variable part of the ocean like the Gulf of Maine, according to scientists.
"We're moving in to this new reality where we're seeing ecosystems pushed way beyond our historical reference points," said Pershing.
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A big reason behind the collapse, the study found, is that when the government sets cod quotas for commercial fishing operations, they don't account for environmental factors — specifically, warming sea surface temperatures. This has proved disastrous for bodies of water that are changing as rapidly as the Gulf of Maine.
Typically, managers of fisheries set quotas based on population.
"Basically the assumption is that fishing is the main driver on the population," Pershing said. "You look at the stock, and if it's down, you pull the quotas down. If you're no longer catching as many fish, that should allow the population to rebound."
According to Pershing's study, this assumption breaks down if the environment moves quickly away from average conditions.
Previously, sea-surface temperature was not thought to have a major effect on cod populations. When the Gulf of Maine started warming quickly, scientists began to see the effects.
"Temperature just hadn't been recognized as a major driver of cod populations before," said Pershing. "It's one of those Catch-22s where you see the effect of temperature only because we've had such a big effect in the last 10 years."
On the graph below, you can see how warming sea-surface temperatures correlate with declines in cod-spawning stock over the last 35 years:
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This knowledge is surprisingly new. Fisheries' quotas, determined by regulators through careful estimations, simply don't take rising temperature into account.
So while the Gulf of Maine is warming and becoming increasingly inhospitable to cod, they are still being fished at the same rate. And now, this has resulted in rampant overfishing.
"What I'm really trying to highlight with this work," says Pershing, "is that we need to account for environmental change in our models."
Still, while the effect the warming oceans are having on cod populations is clear, the actual mechanism driving this warming is less clear.
Getty Images"In the paper, we lay out some hypotheses, but we really don't know what's driving it yet," said Pershing. "That's really something I hope people will start to look at in the future."
But the study isn't all bad news. Some other fish species, for example, could be unaffected by the change or even affected in the opposite direction, said Pershing.
"The conditions that are good for haddock are bad for cod," Pershing said. "So the boom we're seeing now in haddock could be related to the same mechanisms."
Fishermen and regulators alike will be forced to adapt to a new normal in the Gulf of Maine.
As for "The Rock" Johnson's thoughts on eating cod? Here's what he told Tech Insider via Twitter:
https://twitter.com/mims/statuses/700750350442168321
@DaveMosher @techinsider well the theory is that it's an extremely lean fish with very little fats and great source of protein. I hate it. ????
No word yet on what proteinaceous substitute he's switched to, but if Johnson is still looking for alternatives, he might want to try hake or domestically farmed tilapia.
They're both more sustainable than cod is right now, according to the Marine Conservation Society, and the Natural Resources Defense council says they have the "least" amount of mercury compared to other fish.
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