A Tail as Old as Time

While I’m certainly more of a science geek than a history buff, I remember sitting in World History in 10th grade learning about early explorers, the Enlightenment, and the dawn of the Industrial Revolution and wishing I could have witnessed those events – or at least heard stories from those who lived through those historic times. Imagine if we had that kind of access to our world’s oceans?

Well, we do! Kind of…we just need to figure out how to communicate with sharks.

Greenland shark
Greenland shark (Source: bbc.com)

Scientists recently discovered that Greenland sharks live for centuries. Yes, you heard that correctly…centuries.

In fact, one of the sharks studied was estimated to be nearly 400 years old! That makes her nearly 4 times older than the oldest human (Jeanne Louise Calment clenched that title at 122 years old) and knocked off the bowhead whale, which have been known to live for more than 200 years, as the oldest vertebrate species.

Side note: Much to my surprise, however, Greenland sharks don’t hold the record for longest-living animal. That award goes to Ming, an Icelandic clam, known as the ocean quahog. On individual lived to be 507 years old before scientists killed it in the name of research. Yikes…Wouldn’t want to be the person who did that.

greenlandshark2
Greenland shark (Source: abc.net.au)

Greenland sharks are found in the cold waters of the North Atlantic and have been observed to depths of more than 1800 meters – that’s more than a mile below the surface! Like many other shark species, they are considered apex predators, meaning they are the top carnivores of their ecosystem, eating other species of fish.

These sharks can grow to be 4-5 meters long at maturity, but it takes them a longgggg time to get there since they grow less than a single centimeter per year. Females typically outgrow males and don’t reach sexual maturity until they’re anywhere between 125-175 years old.

Because these sharks are extremely slow growing and don’t begin reproducing until they’re more than 100 years old, scientists are concerned about their conservation. Greenland sharks have been recorded as bycatch (non-targeted catch) in arctic and subarctic commercial fisheries, and these sharks have also been subjected  recent commercial exploitation.

And this is a big deal because removing even just a few of these slow-growing sharks from the ecosystem can have major impacts on the population and ecosystem.

So how exactly do you figure out how old a shark is??

otolith-placement
Diagram of otolith placement in a generic bony fish. (Source: noaa.gov)

When aging fish, scientists examine a small bone found within a fish’s ear called an otolith. Otoliths are found directly behind the brain of bony fish and are typically the size of a dime. As the fish grows, the otolith also grows and rings form on the otolith, similar to the growth rings you’d see on a tree trunk. Using the growth rings observed on the otolith, scientists are able to estimate the age of a fish.

ringpic
Similar growth ring patterns seen in an otolith (left) and tree trunk (right). (Source: noaa.gov; usda.gov)

Sharks, on the other hand, have no bones – their skeleton is made of cartilage. Instead, scientists examine the lens of the eye use carbon dating. Researchers used the eye lens nuclei from 28 female Greenland sharks and determined that the oldest shark was estimated to be 392 ± 120 years old and was more than 5 meters in length!

Mind. Blown.

And unlike the sad tale of Ming, the ocean quahog, these sharks survived their encounter curious researchers!


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