Greenland sharks can live for hundreds of years, but scientists have never understood why. Now, researchers may have finally discovered the secret to the animals' startling longevity: their never-changing metabolism. The surprising finding goes against scientists' previous assumptions and could have major implications for how these animals adapt to climate change.
Greenland sharks (Somniosus microcephalus) have an average lifespan of at least 250 years but can potentially reach over 500 years old, likely making them the longest-living vertebrates in the world.
These sharks dwell in the Arctic and North Atlantic Ocean at depths of up to 8,684 feet (2,647 meters).
The exact reasons for their long lifespans have been hard to pin down. Researchers have long assumed that their longevity was related to their super-cold environments — they can survive in waters as cold as 29 degrees Fahrenheit (minus 1.8 degrees Celsius) — and minimal movements, according to a statement about the latest findings.
But the new research, which was presented at the Society of Experimental Biology Conference held in Prague from July 2 to July 5, suggests the sharks' longevity could be related to their metabolic activity, which does not seem to change over time like it does in other animals.
"This is important for us as it shows the sharks don't show traditional signs of aging," study lead author Ewan Camplisson, a doctoral student at the University of Manchester, told Live Science in an email.
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Metabolism is the chemical process in which enzymes break down nutrients into energy and the processes that use this energy to build and repair tissues. In most animals, the rate of metabolism decreases over time. This leads to reduced energy production, slower repair and regeneration of cells, as well as a reduced ability to remove cellular waste products that can cause further cell damage.
To measure the sharks' metabolism in the new study, the researchers took tissue samples from the muscle of 23 Greenland sharks that were caught on the south coast of Disko Island in central Greenland.
The team then measured the activity of five different enzymes in the samples to work out their metabolic rate and their response to different environmental temperatures.
The researchers then calculated the age of each shark by measuring their body length — a 2016 study created a model to estimate the age of Greenland sharks from their total body length which was used here. They found that the sampled sharks ranged from 60 to 200 years old.
Surprisingly, when the researchers compared the sharks' enzyme activity, they found that there was no change across the different ages.
"In most animals, you would anticipate seeing some enzymes have reduced activity over time as they degrade and become less efficient," Camplisson said. But this is not the case with Greenland sharks.
The stable metabolism across Greenland sharks' ages suggests they don't degenerate like other animals do, which is likely the reason for their long lifespans.
Tests also showed all enzymes had "significantly higher" activity at warmer temperatures — a finding that was expected, as enzymes tend to have higher activity at increased temperatures.
"We wanted to investigate if the Greenland shark's enzymes were specifically adapted to work more effectively in cold conditions, but we did not see this trend," Camplisson said. "The higher activity in warmer conditions would suggest that if these sharks were forced into a warmer environment, then their metabolism would increase significantly which would likely alter their lifestyle."
This finding is particularly relevant, as global sea surface temperatures are expected to increase by 2.1 F to 5.8 F (1.2C and 3.2C) by 2100 due to global warming. And the Arctic's average temperature has already risen three times faster than the global temperature, according to the World Wide Fund for Nature.
Camplisson hopes to test more hallmarks of aging and investigate the sharks' metabolism further to better understand how to protect them as global warming impacts their environment.
