Talk Evaluation of the use and effectiveness of underpasses implemented on the new highspeed railroad SEA between Tours and Bordeaux to maintain optimal permeability for semi aquatic mammals

As part of the construction of the 302 km new high-speed rail-road between Tours and Bordeaux, the highest level of mitigation measures to ensure continuous connectivity and permeability for semi aquatic mammals was implemented, particularly for the critically endangered European mink Mustela lutreola and the vulnerable Otter Lutra lutra. 173 crossing and bridges under the line were equipped for semi aquatic mammals, on every stream, from little ditches to main watercourses. Various types of passageways were built depending of the hydraulic facility: natural banks, 1 to 3 levels of staged concrete walkways on one side only or on both sides, culverts.

A 5-year monitoring is ongoing to evaluate the use and effectiveness of these different types of underpasses for micro to medium sized mammals, using complementary methods: (1) monitoring of otter spraints places on the passageways and upstream to the infrastructure (2) ink footprint traps, placed on every passageway, even in the riverbed, targeting all mammal species, (3) hair-trap tubes targeting small mammals and (4) faeces-trap tubes targeting shrews, hair and faeces species being identified by genetic typing, (5) camera traps, to study the behaviour of the animals.

In 2015, 45 first underpasses dispatched along the rail-road were monitored during 3 sessions of about 30 days. Survey of 253 potential otter spraints places revealed that in the south of the study area where the species is common, all types of underpasses were used efficiently, since habitats situated upstream were substantial and attractive. 3662 passages of 16 free-ranging mammal species or species-group were recorded in all the 33 underpasses monitored by footprint traps. 483 passages of small carnivores were recorded in 31 underpasses, with a significant preference for the highest available level of walkways by the common genet, stone and pine martens, and weasels, whereas otters preferred the river bed, and passages of polecats were insufficient to conclude. Genetic analyses of hairs and faeces revealed the presence of 10 free-ranging small mammal species in the surroundings of the 23 underpasses monitored with hair- and faeces-trap tubes, among which 6 were detected on the passageways, including the aquatic shrew Neomys fodiens.

These preliminary results are promising, but the 5-year survey of in total 159 underpasses will be essential to correctly evaluate and compare, according to the local environmental parameters and the type of underpasses, the crossing of the different species through the infrastructure, especially as the habituation of the species and the ongoing reconstruction of plant-covered accesses are two undeniable components for the frequent use of the underpasses by the fauna.

effectiveness; high-speed rail-road; mitigation measures; monitoring; new transport infrastructure; semi aquatic mammals; passageways; underpasses; use.