Moving out of the box: using GPS telemetry to redefine space use and habitat selection of European pond turtles (Emys orbicularis) in Mediterranean wetlands

Abstract

The European pond turtle (Emys orbicularis) is a redlisted freshwater turtle species and a protected species in France. It is relying strongly on immerged habitats for most of its active life cycle, but depends also on land habitats for egg deposition. As most wetland species, it is undergoing severe pressures due to the reduction and degradation of its habitats. In the Mediterranean, rises in salinity levels are a particular threat to the species’ populations.

In this study, using multi-sensor animal-borne tags, I have investigated the space use and habitat selection of the European pond turtles in Mediterranean wetland ecosystems. I have been able to highlight methods for egg-laying site detection as well as robust methods for home-range estimation and habitat selection when handling autocorrelated GPS data.

The equipped European pond turtles layed their eggs in very delimited perimeters, and we found that they can lay eggs both in semi-natural habitats and in human cultures. Their space use and home range size seemed to be very dependant of the hydrographical context. Home range size was also much smaller during the autumn and seemed to be larger for males than for females. More generally, the pond turtles avoided the regions with highest salinity of the study sites, with what seemed to be a tolerance threshold to salinity for salinity levels above 4 to 6 g/l.

Even though these results are still preliminary, they could provide key guidelines to decision makers in terms of methods to monitor European pond turtles and indicators to monitor the quality of their habitats.

Popular Abstract

Turtles don’t like salt!

About coastal turtles…

The European turtle Emys orbicularis is a freshwater turtle found in ponds and wetlands throughout Europe, and is a protected species in France. It is a species that spends most of its active time in water, mostly ponds and canals, where it eats or through which it moves for most travels. European pond turtles even bask “in” water, on dead trees found in the ponds and canals they live in! Dry land is very seldom used by them, mostly for egg-laying. But this also means that they rely very strongly on wetland habitats, which are threatened in many ways. In the Mediterranean, one rising threat is the salinization of coastal wetlands. Indeed, as sea levels are rising due to climate change, all coastal ecosystems become saltier and saltier, and at a very fast rate. This can be a big problem for plants and animals that have evolved and adapted to specific conditions. And this is why it is key to study how a protected species, the European pond turtle, reacts to different salinity levels.

Towards a new alliance: tagging turtles with GPS

How to investigate turtle movement? Today we have an amazing tool: animal-borne tags! They are small devices that we can glue to the animals, in which there is a GPS logger and an accelerometer (just like in your smartphone). A small solar panel allows the tag to recharge its batteries, and a small antenna sends the data directly to our computer by satellite network. These little devices allow us to get much more precise data about where the turtles are and how much they move. This way, we can almost study the turtles from their own point of view!

Where are my eggs?

With these new tags, we have been able to develop a new method to uncover where the turtles lay their eggs. When we combined the recordings of the GPS, and the accelerometer, we could look at where the turtles moved a lot during the night. We obtained clusters of points: egg-laying sites. These were mainly in light vegetation in the protected area where we study the turtles, but some also layed eggs in agricultural fields. Understanding and monitoring this behaviour can be very important, and shows that it is important to discuss with people working in agriculture if we want to protect the species the best that we can.

Big home or small home, water will tell!

We also looked at the size of the home range of the turtles: the area that they use for most of their activities. It seemed that the home range of the turtles was much bigger when the overall area of ponds and canals it could swim through was larger. This is expected as we know that they use water bodies to move around, and that they spend a lot of time basking in the sun on dead trees in the middle of ponds or canals. One of the males we equipped even travelled to a different wetland, using of course, mainly canals to get there!

Salt, a rising issue on the coast

However, even if the amount of space the turtles use seemed linked to the size of the water bodies they live in, where they move was linked to something else. They preferred to go towards areas with mixes of vegetation types, and mixes of vegetation and large water bodies. And most of all they seemed to avoid the saltiest regions of the wetlands. Furthermore, when the salinity rose too much one summer, they all either moved away to less saltier ponds or started to estivate: sleeping under the mud for the hottest and driest months of the summer. We found that European pond turtles did not tolerate when the salinity in the water was higher than 4 to 6g/L. We think that this information could be important for decision makers in monitoring and conserving coastal wetlands along the Mediterranean.

Advisors: Olivier Scher, Conservatoire d’espaces naturels d’Occitanie, and Aurélie Coulon, CESCO et CEFE, French national history museum.

• author: Uzan, Yakov
• supervisor: Olivier Scher; Aurelie Coulon; Susanne Åkesson
• organization: Degree Projects in Biology
• course: BIOM02 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9185137
• date added to LUP: 2025-02-13 13:08:39
• date last changed: 2025-02-13 13:08:39