There are Greenland sharks older than the United States.
This deep sea species has an expected lifespan of at least 270 years. Some may live longer than 500 years. And biologists have identified an important reason for their impressive longevity. The sharks, an Arctic species dwelling thousands of feet underwater, do not age like other animals: Their metabolisms should slow as they grow older, resulting in cellular changes. But the researchers' analysis of differently aged Greenlands sharks show their metabolisms don't diminish. They are a biological curiosity.
"Every detail about this animal is fascinating and the more I find out about them, the further I am motivated to continue my work," Ewan Camplisson, a biologist pursuing a PhD at the University of Manchester, told Mashable.
Camplisson presented this new research at the Society for Experimental Biology Annual Conference in July.
The sharks don't just grow profoundly old. They're also the only shark species capable of living in the frigid Arctic year-round. And that's not all. "They are one of the slowest swimming fish when accounting for size, the females only become sexually reproductive at approximately 150 years old, they have tiny brains yet can seemingly hunt and navigate vast distances, the majority of the population live most of their lives with parasites in their eyes and their flesh is so full of toxins such as TMAO and urea that they are poisonous to eat for humans," Camplisson marveled.
Scientists have suspected the sharks' extremely slow movement and life in the cold may contribute to the species' unusual age — and these are likely important factors. But Camplisson noticed that other Arctic fish species, such as the northern wolffish, also dwell in cold waters, are predatory, and move relatively little. But this fish only lives for some 20 years. Another deep sea species, the dominant sixgill shark, is predatory, slow-moving, lives in the cold deep sea (but found in oceans around the world), yet lives for 80 years — not centuries.
"Therefore we thought that there must be other factors also involved in the Greenland sharks' longevity," Camplisson said.
So Camplisson and his team investigated the sharks' metabolism. They used preserved Greenland shark red muscle, from 23 sharks of different ages, to observe how metabolic enzymes would react when activated. The sharks ranged in age from around 60 to 200 years. As illustrated above, the muscle samples were suspended in a liquid that reacted to the enzyme's changes; the more activity, the more shift in color. A machine called a spectrophotometer, which assesses changes in light intensity, measured these changes. And as described earlier, sharks of all ages didn't show signs of any metabolic slowdown.
It's clear these Arctic sharks live a long time. But it's unclear why. It's possible that gradually growing and maturing for over a century simply sets them up for adult success.
"My best guess would be that the deep waters of the Arctic can be a challenging environment to live in, where an animal such as the Greenland shark may not have consistent access to plenty of food and they may not frequently be in contact with other Greenland sharks," Camplisson explained, noting they swim slowly in a vast ocean environment. And, crucially, they have few predators. There's not much to stop them from thriving in the depths. "Therefore, as a species with low natural mortality rates, their optimal life strategy would be one of a slow growth and building reserves of energy, so that when they do interact with the opposite sex they are in a suitable condition to reproduce," he said.
Wielding such intriguing research results, Camplisson intends to further analyze these sharks' tissues, and their anti-aging metabolisms. It won't just satisfy deep sea biological curiosity.
"I believe that if we can work out how the Greenland shark lives so long and how they seem to be so resilient to age related diseases (such as cardiac disease), we may be able to improve the quality of life within the elderly human population," he said.
