The environmental association Vita Nativa (based in Olhão) suggested that I might like to tell you all about the ‘Turtle Problem’ and how an invasive alien species has become one of the main threats to biodiversity, not just in Portugal, but around the world.

How did this happen?

Well, who remembers the Teenage Mutant Ninja Turtles? It’s probably been a while since you watched the animated TV show, so let me just refresh you a little on their origin story. They were bought by a boy at a pet shop, but on his way home he tripped, fell and sent the young turtles tumbling deep down into the New York City sewage system. Now, you may have thought that, being so far from their natural habitat, that would have been that, so to speak, for those tenacious teenage terrapins.

However, if you remember the show at all you will know that Leonardo, Michelangelo, Donatello and Raphael (all named after Italian Renaissance artists) actually went on (after a little bath in radioactive sewage and mentoring from Splinter, their rat sensei) to kick everybody’s butt they came up against.

Well, ironically, this story became a sort of self-fulfilling prophecy.

Fans of the show (that ran from 1987 to 1996) went out to buy their very own exotic ninja turtles. The top picks were sub-species of the pond slider (Trachemys scripta) or ‘Tartaruga-da-Flórida’ in Portuguese (as they are native to the Eastern United States and Northeastern Mexico).

The most popular was the red-eared slider (Trachemys scripta elegans) that has a little splash of red on its ‘turtleneck’. But there’s also the yellow-bellied slider (Trachemys scripta scripta) that has a yellow belly and stripes.

Both these species were very easy to produce in captivity in large numbers and between 1989 and 1994 an estimated 26 million of these species were sold all over the world, with a large percentage going to Europe - with Portugal being one of the main destinations for this ‘turtle-mania’.

Now, this is where what happened differs slightly from the TV show.

Although a few of these stealthy little ninjas may have indeed escaped down the sewer on the way home, the vast majority were released. You see, turtles live an awfully long time. Up to 60 years in some cases.

And so, what was a cheap little impulse buy to make the Ninja Turtle fans of the household happy, soon starts to grow (to about the size of a dinner plate) and thus requires large and expensive tanks to accommodate. This, and the fact they can also be a little snappy, noisy and are still around long after the kids have gotten over their Ninja Turtle phase, means it’s hardly surprising that people would eventually decide to set them free and let them ‘take their chances’ in various rivers, streams, parks and public gardens.

However, what they didn’t know is that their chances are actually pretty good. Being from Florida, they are used to having things like alligators to contend with (I’m guessing), and so, like the Ninja Turtles that got them into this mess, they turn out to be some pretty serious badasses.

They are highly adaptable omnivores and aren’t fussy to sample any and every local delicacy on offer. This includes many kinds of plants and animals, including insects, amphibians, reptiles, small mammals and even birds.

This sudden, new and fierce competition has left the local turtle species rather ‘shell-shocked’. In Portugal, we have two types of native turtles. The Mediterranean (or Spanish) pond turtle (Mauremys leprosa), which is the largest freshwater turtle in Europe. And, the European pond turtle (Emys orbicularis) which, unfortunately, is becoming increasingly rare. The destruction of wetlands, people catching them and the fact that they are late to the dating game (and there’s high infant mortality) all mean that they were having a tough time of it anyway, even before these illegal aliens landed and started eating all their food and, being a lot less stand-offish when it comes to that sort of thing, snagging all the best nesting sites.

Indeed, these new kids on the block reproduce a lot faster and so the population levels soon become uncontrollable, jeopardising the survival of not just the native turtles but many other species and, because everything is interconnected, the entire ecosystem. I didn’t even mention how they can contribute to the spread of diseases and parasites that can not only affect the native turtle populations and other aquatic biodiversity, but also, us humans (Salmonella).

So, what to do?

Well, a good start is that it’s now illegal to sell pond sliders here in Portugal. However, it’s still possible to find various other exotic species in pet shops. Vita Nativa says that you can probably find the false map turtle (Graptemys pseudogeographica), as well as various subspecies of the river cooter (Pseudemys concinna).

Now, although these aren’t nearly as abundant and dispersed throughout the local ecosystems, they are from the same sort of area and have their ninja cousins Floridian fighting spirit and, as such, could have the same detrimental impact on the native biodiversity in any place they are introduced.

So, Vita Nativa urges that if you are thinking about buying or adopting a turtle you realise it’s a big commitment. It seems to me that a turtle really isn’t just for Christmas, it’s for life. They also stress that if for any reason you want to get rid of them, then you should contact the ICNF (Instituto da Conservação da Natureza e das Florestas) and they will come and take it to a new home (but in captivity).

So, not releasing any more is one part of the solution, the other, is to try and catch some. I saw on Facebook that back in December Vita Nativa had gotten their waders on and waded into the freezing water at the Parque da Paz in Almada to set up traps to catch the stealthy illegal ninjas that have taken over the place. This, they say, will hopefully help the Mediterranean pond turtle return to their rightful place as ‘Lord of the Lake’ once more.