Red Eared Slider - The Threat To Endangered Spanish Turtles

Feb 19, 2012
Peter Ashby

Red Eared Slider - Nightryder84

Research shows that the irresponsible and immoral trade in the American Red Eared Slider for the pet market is threatening the native turtles of Spain.

Despite internationally-binding legislation and increasing public awareness, the trade in exotic species is strewn with examples of how matters can get out of hand when profit takes precedence over welfare and conservation.

For example, following the success of the animated film, Finding Nemo, a craze for owning ones´ very own "Nemo" led to the over-collection of uncounted clown fish from tropical reefs. It is impossible to say how many of these wild caught fish died through stress and injury.

The Red Eared Slider - Victim Of Commerce

Similarly, the Ninja Turtle phenomenon helped to boost the popularity of fresh water turtle hatchlings as pets, in particular those of the American Red Eared Slider (Trachemys scripta elegans), a species that has been factory farmed and exported all over the world in its millions.

Often retailing at the equivalent of a few dollars, their ridiculously low price means that even today, these reptiles are frequently regarded as nothing more than living toys. Housed under appalling conditions and suffering from malnutrition and stress, many are dead within a matter of weeks.

Others outgrow their housing, becoming large, powerful animals with sharp claws and a painful bite. Once the appeal of infancy wears off, they are frequently abandoned in streams and ponds where if the conditions are right, they establish themselves as unwelcome additions to the local fauna.

Alien Versus Autoctonous

Although the importation of red eared sliders was banned by the European Union in 1997, these hatchlings can still be located in European pet shops and the species has become widespread in many countries due to its ability to adapt. In Spain, it is present in wetlands throughout the country, from coastal regions to the central plateau of Castilla La Mancha.

Spain´s two native freshwater turtle species are the European pond turtle (Emys orbicularis) and the Spanish turtle, (Mauremys leprosa). The Spanish turtle is the more widespread, but both species are seriously threatened by habitat loss.

The loss of healthy wetlands is not the only factor threatening these European turtles. Recent research undertaken in Spain has showed that the invading red eared slider is outcompeting the native species in several distinct ways.

Red Eared Slider - A Resilient Species

In comparison with the Spanish species, the red eared slider is more tolerant of water contamination and human disturbance. It also reaches sexual maturity earlier, reproduces more prolifically, and can remain active at lower temperatures.

The red eared slider is also more aggressive. Under controlled, aquarium conditions, Spanish researchers found that Spanish turtles could detect the chemical secretions of the red eared slider and tended to avoid areas used by the American species.

In direct competition for food, the red eared slider was observed to be more aggressive and was therefore able to consume more, at the expense of the Spanish turtles.

A Place In The Sun

Basking in the sun is critical for freshwater turtles in order to maintain their body temperature at the levels needed to hunt, reproduce and metabolize efficiently. In order to do this, they need access to suitable logs, banks and other locations.

The Spanish researchers found that with regards to this behaviour, the slider also has the upper hand. This species only needs to bask until its body attains a temperature of approximately 27º C before returning to the water. On the other hand, the Spanish turtles need to remain in the sun until they have warmed themselves to 32º C.

The American turtle has a more rounded shell than the European species, giving it a smaller surface-volume ratio and the ability to maintain a more stable internal temperature. This ability to retain heat better, means that the slider can spend more time searching for food, and is better equipped to digest what it eats at lower ambient temperatures.

These thermo-regulatory advantages, coupled with the sliders´ ability to oust its competitors from the best basking sites, can negatively influence the metabolism of the native species and their ability to reproduce.

Defence Strategies

When threatened by potential predators, all three species withdraw into their shells. The carapace of the slider, being more rounded than that of the European species, makes it more difficult for predatory species to gain a purchase on the shell. Also, sliders remain hidden inside their shells for longer, while the Spanish turtles emerge sooner and run for water.

This means that in the presence of increased disturbance - for example, human activity - the European species repeatedly dive for shelter, further limiting the time they are able to spend maintaining a healthy body temperature. Yet again, this is to the advantage of the slider.

Ultimate Responsibility

This worrying situation is by no means unique to Spain, and has a wider negative impact on endangered amphibians, fish and entire fragile wetland ecosystems. Nor is it easily resolved, because removal of the red eared slider, once established, is costly and time consuming.

Nor is the problem limited to one species. Following the importation ban, the trade in other turtles has increased and some of these, including the map turtle (Graptemys pseudogeographica) are now established in Spanish waterways.

The ultimate responsibility for this situation lies not just within the pet trade, but in the behaviour of would-be pet owners who give little thought to the welfare and environmental consequences of their actions.

Those who truly care about freshwater turtles should completely boycott the trade in these species, lending their support instead to the many rescue societies dedicated to caring for its reptilian victims, and the conservation organisations seeking to limit the damage of such man-made catastrophies.