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A blood-chilling tale of survival

by
01 September 2016, at 1:00am

Dr David Williams returns from New York, having witnessed an astonishing sight in Central Park, where terrapins thrive with freezing blood.

IF MY CALCULATIONS ARE RIGHT, this little offering is the 25th in the series of Perambulations – thanks for keeping on reading! And it’s our 25th wedding anniversary too, so we splashed out a bit and took our three teenage sons across to New York for a week.

I’m writing this on the flight back, one delayed somewhat because as night fell and we taxied to the runway a host of turtles (well we would call them terrapins I guess) was found wandering across the tarmac and it took quite a while to remove them to a place of refuge and clear our path for take-off.

I have heard of flocks of birds causing problems at airports, but not colonies of chelonia. A quick Google of “turtle” and “JFK airport” yields the answer – these diamond-backed terrapins (Malaclemys terrapin if you want to be specific) aren’t wandering at all – they are migrating to their nesting sites with the tarmac runways getting in the way.

It’s our transportation technology which is at fault, not the reptiles. But put a 500-tonne jumbo jet up against a bale of a hundred of these little creatures (and yes, before you ask, that is the correct collective noun for turtles!) and one might expect the aircraft to win but for the concern regarding these endangered reptiles, hence our wait on the runway.

This was not our first encounter with chelonia on our holiday. On a walk through Central Park, we stumbled across (only metaphorically you understand) a turtle pond.

In fact at this time of summer the pond exhibits a rich green ooze of algal bloom – and Algal Bloom Advisory Notices warn against swimming in or drinking the water. But this doesn’t stop a number of Pseudemys scripta elegans, the red-eared slider, poking their heads up out of the emerald water.

The Central Park website tells us that in the 1980s they were released by nearby residents. That of course is only half the story. Those of us involved in care for captive reptiles at that time will remember the craze for Mutant Ninja turtles morphed into a passion for real terrapins, bought as tiny youngsters and then discarded when they grew bigger and bolder.

I well remember seeing these when I worked at the Beaumont Animals’ Hospital at the RVC in the early 1990s next door to the Regent’s Park canal where they were happily breeding. Another quick Google search brings up an article on “Tiny terrapin that threatens wildlife”. Reading further on, we learn that “conservationists warn [that] terrapins eat ducklings, frogs and sh in the wild. A matchbox-sized creature found in London’s Regent’s Canal suggests they have been breeding over summer in the particularly humid conditions”.

There are two problems with that piece of internet mis-information. For one the piece is from 2013 and the second is that it originates from the Daily Mail! Had they asked around, they would have discovered that the terrapins had been living in the canal for well over 10 years – the ones I saw there, often with mild to moderate vitamin A deficiency, were small dinner plate-sized animals back in the early 90s.

I can understand how these reptiles survive in the benign climate of central London, but New York oscillates from well below freezing to up in the 90s. The winter of 2015 saw the Hudson river freeze over and you have to wonder how the poikilothermic terrapins managed.

I guess the answer is that as ice oats, if you can sink to the bottom as terrapins do, and hold your breath until the ice thaws, then there isn’t a problem! But can we really believe they can manage that?

As a matter of fact Holden, in J. D. Salinger’s The Catcher in the Rye back in 1951, has the same question about where the ducks on Central Park’s Lagoon (a much bigger stretch of water than the turtle pond) go in the winter.

Horowitz, his cab driver, points out that fish “don’t go nowhere – they stays right where they are”. Salinger has the conversation continuing with Holden pointing out: “They can’t just ignore the ice. They can’t just ignore it.”

“Who’s ignoring it? Nobody’s ignoring it!” Horwitz said. He got so damn excited and all, I was afraid he was going to drive the cab right into a lamppost or something.

“They live right in the goddam ice. It’s their nature, for Chrissake. They get frozen right in one position for the whole winter.”

Well Horwitz had it right to a degree. We now know that antifreeze proteins and glycoproteins keep sh and some terrapin species from freezing or slow both freezing and thawing, allowing survival in these incredibly harsh environments.

Quite apart from freeze damage, how do these animals cope with the ischaemic challenges of having their blood freeze? The topic is the subject of whole books – take Cerebral ischaemic tolerance: from animal models to clinical relevance for example, but in reality what concerns me is how we mess this all up so much of the time.

Those Central Park terrapins seem to do amazingly well in a slimy green pool that would fail any animal welfare inspection were it a captive enclosure. They survive incredible changes in temperature where every spring, reptile vets see animals which have not fared anything like as well in captive environments where the temperatures should be controlled much more carefully than the vagaries of the external environment. Should we be keeping these animals in captivity in the first place?

Which takes me back to our happy time in Central Park. Only in America... only in America would you find an owner taking his two pet turtles out on a leash. But of course at 90 degrees they are having the time of their lives. Or am I right?

Can we know if these animals, still essentially wild creatures, can lead a good life when kept on a leash and not allowed the freedom to explore their environment which their free compatriots “enjoy”? Or is sure food and ready protection a price worth paying for limits to your behaviour? I guess we will never really know!