The Éric Tabarly bridge in Nantes is a 210m long cable-stayed road bridge crossing the Loire River, that was inaugurated in 2011. It is composed of a 27 m wide steel deck divided into two spans by a 57 m high steel pylon, being the main span 143m long. In the context of the European Research Project DESDEMONA (DEtection of Steel DEfects by Enhanced MONitoring and Automated procedure for self-inspection and maintenance), the bridge has been equipped with a dynamic monitoring system, constituted of 16 uniaxial accelerometers installed both on the deck and on the Pylon, with accelerations being recorded with a sampling rate of 100 Hz. This paper describes the dynamic monitoring system installed in the bridge and the results achieved during the first months of operation, including the characterization of vibration levels (maximum and effective values) as well as the automatic identification of the bridge modal properties. Finally, the effects of operational and environmental conditions on modal properties are studied.