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Scientists confounded by observation that fish are shrinking: 'We still don't understand'

"This is a pretty fundamental question."

"This is a pretty fundamental question."

Photo Credit: iStock

Scientists have observed a strange phenomenon in oceans worldwide: Fish are getting smaller, even in areas unaffected by overfishing. The exact reason is unknown, though researchers have a few theories.

What's happening?

According to The Washington Post, an analysis published in the journal Science found that almost 75% of marine fish across the globe have decreased in size between 1960 and 2020. 

While overfishing and rising average temperatures caused by human-induced air pollution levels are key drivers of this phenomenon, scientists still aren't sure why fish are shrinking in size in response to warmer ocean temperatures, per the Post. 

"This is a pretty fundamental question," a University of Massachusetts at Amherst conservation biologist, Lisa Komoroske, told the outlet. "But we still don't understand why."

However, since over three billion people worldwide depend on seafood such as fish for a significant portion of their calorie intake, according to the World Bank, it's crucial for scientists to understand the mechanisms behind this evolutionary response.

Why is it concerning that fish are shrinking?

As the Post explained, since billions of people rely on fish for protein, they will have to catch more fish to get the same amount of calories. Not only does this put pressure on coastal communities that count on a healthy ocean for income and food, but it also threatens fish populations already struggling because of hotter ocean temperatures, pollution, and overfishing

Komoroske told the Post this phenomenon is known among scientists as the "temperature-size rule," and it's been observed in both protected and unprotected marine areas. 

For years, the scientific consensus was that fish were shrinking because their gills couldn't handle having a larger body. Rising ocean temperatures mean they need more oxygen to survive, so having a bigger body would be an evolutionary disadvantage. 

However, a recent study led by Komoroske and her colleague, Joshua Lonthair, found that the brook trout they'd raised in warm water had gills that were an adequate size for their oxygen requirements. 

Scientists posit that the shrinking of fish could simply be a product of evolution or that another organ besides their gills is causing stunted growth. 

It's important to understand the root cause of the fish shrinking since the Post reported that it could disrupt marine ecosystems and reduce profits for fishermen. 

"It's a problem for the fishery," Art Bloom, a salmon fisherman in Alaska's Bristol Bay, told the outlet. "They don't present as well in the supermarket." 

What's being done about smaller fish?

As the Post explained, scientists are working hard to figure out what's causing fish to shrink in response to hotter ocean temperatures. In addition, commercial fishing and whaling bans around the world are helping restore balance to ocean ecosystems and give fish and other sea life a better chance of survival. 

There's also a huge movement underway toward clean energy sources such as solar and wind, which will reduce pollution and, consequently, the rising temperatures putting pressure on animals, including fish. Reducing our reliance on oil and thus the importing and exporting of that oil will also reduce the likelihood of oil spills that threaten ocean life. 

Plus, there's a silver lining to the fish shrinking. Inês Martins, an ecologist who discovered that fish are getting smaller, told the Post that many of these fish are increasing in population despite their reduced size. 

We can also help our fish friends by making the switch to an electric vehicle, installing solar panels, or even eating less meat. By reducing the amount of pollution we produce, we give all life a chance to thrive. 

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