No, crocodiles are not immortal

Is it true that crocodiles don't age? That if they were left alone by hunters, disease and natural disasters, they would never die? An article published recently by Vice would have you believe so, but crocodile experts say the claim is, well, a crock.

The Vice article claims the saltwater crocodile – the largest croc species in the world – is the "poster child" of agelessness, and that the big reptile has no recognised lifespan limit. On top of that, it states that crocs don't show signs of wearing down with age, but simply grow bigger and bigger until they're killed, or die of stress in captivity. Crocs' endless lifespans, the article suggests, are linked to their ability to survive extreme oxygen deprivation.

These are impressive claims, and they certainly sparked interest online. The only problem? According to croc experts, none of them is true.

And crocodilian researchers were quick to express their displeasure on social media.

In dodgy science reporting, crocodile are apparently immortal? No, they're not. They don't even grow indefinitely. https://t.co/QJDHZGM71Y — Adam Britton (@adambritton) October 11, 2016

For starters, it's a myth that crocs and gators never stop growing. "No, crocodiles don't grow indefinitely, prevented from exceeding the size of a small moon only because they get killed first by a competitor!" croc researcher Adam Britton told me.

Studies on several species have shown that once a crocodile has reached its adult size, its growth slows down, eventually reaching a point where the animal is effectively not getting any bigger. "The largest crocs are the ones that grow the fastest when they are young," said Britton.

What's more, crocs do feel the effects of old age. Another crocodilian expert, Adam Rosenblatt, told me that while the ageing process in these animals is still not fully understood, the evidence we do have "all points to the conclusion that crocodilians are not immortal and are subjected to natural ageing and death processes". In the wild, an older, weaker croc is more likely to face starvation or competition, but even in captivity, the animals inevitably die. As they age, gators and crocs lose strength and overall body condition just like us humans. They tend to lose their teeth, some develop cataracts, and females produce fewer eggs.

As gators and crocs get old, they lose strength and overall body condition just like us humans. Image: raunov, Flickr

And yet, the Vice article quotes physicist Michio Kaku in saying that the 70-year croc lifespan often cited in textbooks comes down to "zookeepers dying at 70", which is fairly silly. Britton points out that zoos keep long-running records of animal growth – and death. "No matter how well you feed them, keep them free from disease and look after them, they will eventually die."

As for the crocs' "well-documented" ability to survive with little oxygen … it also doesn't exist. Saltwater crocodiles, the article claims, can survive without oxygen underwater for two hours, surface for a quick breath, and then quickly dive again. In fact, most croc dives are nowhere near this impressive. According to the Crocodilian Biology Database, the majority last only between ten and 30 minutes – and Britton adds that the animals need plenty of recovery time to catch their breath after a long dive.

So where did this two-hour idea come from? Britton points to one rather grim-sounding study. "There was a single study done in the early 70s that showed crocodiles drowned if chained underwater for around two hours. Seriously, someone did this." Yikes!



Crocodiles may not be out of the ordinary when it comes to growing old, but there are animals that do exhibit what's called "negligible senescence", or a lack of normal ageing. You'll find a classic example of this in turtles, which seem to age unusually slowly, an attribute that possibly allows them to live so long. One famously old tortoise named Jonathan is thought to be approaching 200 years of age!

That's not to say all crocs die young. The age record might belong to a three-metre (9ft) crocodile that lived in captivity in Russia for over a hundred years before dying two decades ago. You may also have heard of Cassius, who is supposedly going on 115 years old, though some experts question estimates of his age.

So, no, crocodiles do not hold the secrets of immortality, nor do they "just keep getting bigger". It may be tempting to think of these big reptiles as totally alien to us humans, but the truth is they live a lot like you do: they grow up quickly, reach full size, gradually get older and weaker, and eventually die (after what was hopefully a long – but not endless – life).



__



Top header image: Matt Francey, Flickr



