15 different species of water turtles live in Germany’s rivers, streams and lakes – but only one of them is part of the local fauna: the European pond turtle. The remaining 14 turtle species were introduced and entered our natural environment primarily through abandoned pets, as a study reveals. It is fitting that non-native water turtles are particularly common in cities and regions close to cities.
For a long time there was only one native water turtle in Central Europe: the European pond turtle (Emys orbicularis). This turtle, up to 20 centimeters long and usually colored dark brown, lives in the quiet, flat shores of lakes, ponds, river oxbows and other still bodies of water. It prefers muddy, nutrient-rich waters that are overgrown with aquatic plants. However, this once common turtle species has become rare and is considered potentially endangered and even threatened with extinction in Germany. The few remaining populations have partly developed from abandoned animals.
14 alien species of turtles
But now the pond turtle has some company: Numerous species of water turtles live in German waters that were not originally native here. Biologists led by Hedi Schloddarick from the Technical University of Berlin have now examined in more detail which and how many of these are. “The focus of our study was three questions: How great is the diversity of non-native water turtle species? How are these species distributed in Germany? And to what extent is their distribution related to human factors?” explains Schloddarick. To do this, the team evaluated 1,770 turtle records that came from scientific publications and citizen science projects.
The result: In the lakes, rivers, ponds and streams of Germany there are 15 species of water turtles, including the European pond turtle – 14 of which are not originally native here. They were imported through the pet trade and abandoned by pet owners. “By far the most common species occurring in Germany is the North American letter-eared turtle Trachemys scripta, with 1,237 records – it accounts for around 70 percent of all observations,” reports senior author Johannes Penner from the Museum für Naturkunde Berlin. This aquatic turtle is originally from the Mississippi region of the USA and is popular as a pet.
Animal trade and abandoned specimens
As early as the 1950s, a subspecies of this species, the red-eared slider turtle (Trachemys scripta elegans), was so popular that it was sold millions of times and was one of the most frequently traded reptile species worldwide. However, it soon became clear that this North American water turtle could quickly become an invasive species if introduced into other regions. In 1997, the European Union therefore banned the import of this subspecies. However, because demand remained high, other subspecies of Trachemys scripta and hybrids were introduced to Europe and traded instead.
As a result, the different variants and subspecies of the North American letter-eared turtle are now also widespread in Germany. According to the new survey, it is also one of the three introduced species that can now reproduce in our country and are therefore considered established. The other two aquatic turtle species are the common slider (Pseudemys concinna) and the false map turtle (Graptemys pseudogeographica). “The wide distribution of these species can probably be explained by their great popularity as pets. They are considered to be relatively easy to care for, look attractive and were available cheaply for a long time,” says Schloddarick.
Most common in metropolitan and peri-urban areas
The geographical distribution of the 14 species of water turtles not native to our area supports the assumption that most of them entered the wild through release. The team found that the diversity and number of turtles are particularly high in cities and peri-urban areas. The main focus is on the metropolitan areas in western Germany, but also in and near Hamburg, Heidelberg, Freiburg, Stuttgart and Munich. In East Germany, on the other hand, there is only a larger distribution center in the Berlin area and some evidence near Leipzig.
“The pattern confirms a close connection between the distribution of animals and human presence. It strongly suggests that human activities – particularly the abandonment of pets – play a crucial role,” says Schloddarick. According to biologists, measures to prevent the further spread of these non-native turtle species are urgently needed. Because even if only a few of these species are currently considered potentially invasive, this could change in the near future: “However, due to climate change, more species could reproduce successfully in the future, possibly spread and cause greater impacts on native ecosystems,” explains the biologist.
What can you do?
For some aquatic turtle species that are already established in our country, import bans and trade restrictions may no longer be enough: “In 2016, Trachemys scripta was added to the ‘EU list of unwanted species’,” says Penner. Nevertheless, this turtle has continued to spread. In the already artificial environments of metropolitan areas, the spread of alien turtles is less of a problem. “But in natural areas that border habitats of endangered species, such as those of the European pond turtle, quick action is crucial,” the researchers write. There it is necessary to monitor the stocks more closely and regulate them if necessary.
“In addition, turtle observations can be reported via iNaturalist and the “Turtles of Germany” project there,” explains co-author Frederic Griesbaum from the Museum für Naturkunde Berlin. “The more people take part, the better it will be possible to understand the distribution and spread of non-native turtle species in Germany and to develop targeted protective measures for animals and ecosystems.”
Source: Senckenberg Society for Natural Research; Specialist article: NeoBiota, doi: 10.3897/neobiota.107.178668