Cheat­ing death

With great age comes great re­spect, as the fa­mous say­ing goes. If that’s the case, these an­cient an­i­mals com­mand a great deal of ad­mi­ra­tion! What’s the se­cret to long life, and is it re­ally pos­si­ble to live for­ever?

World of Animals - - What’s Inside... - Words Adam Mill­ward

These su­per se­niors re­ally have got time on their side

The shark that lives for cen­turies

Like most things that dwell in the depths of the ocean, Green­land sharks have long been a mystery. Na­tive to the icy wa­ters of the north­ern At­lantic and Arc­tic, they favour the bathy­pelagic, or ‘mid­night’, zone where no nat­u­ral light pen­e­trates and pres­sure lev­els reach 800 times that at the sur­face.

Green­land sharks aren’t ever go­ing to be hot favourites to win a beauty contest. They can ri­val great whites in size, with larger spec­i­mens ex­ceed­ing seven me­tres (23 feet), but they lack the stream­lined body of their fa­mous cousins. Their fins are stunted, their skin is mot­tled brown-grey and they of­ten have par­a­sites dan­gling from their eye­balls. But looks aren’t a con­cern for these fish – they’re play­ing the long game.

There’s been a sus­pi­cion that they are long-lived since the 1950s, when a lucky sci­en­tist caught the same in­di­vid­ual twice and de­ter­mined its

growth rate was less than a cen­time­tre per year.

This the­ory was borne out by a pa­per pub­lished in 2016 that ra­dio­car­bon-dated crys­tals in their eyes. The largest and old­est shark ex­am­ined was aged at 392 years old – give or take 120 years. Tak­ing the up­per­most end of that es­ti­mate range, this means the shark could have the­o­ret­i­cally been born as long ago as 1504 – when Henry VII was king! This makes them the long­est-lived ver­te­brates on Earth.

One ex­pla­na­tion for their record-break­ing longevity is their cold habi­tat, with low tem­per­a­tures of­ten as­so­ci­ated with slow me­tab­o­lism and devel­op­ment. It’s es­ti­mated these sharks don’t even reach sex­ual ma­tu­rity un­til 150 years old! An­other con­tribut­ing fac­tor may be their slow heart rates, which is about one beat per 12 sec­onds ver­sus one beat per sec­ond in a rest­ing hu­man adult.

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