The Thalassa is a seventy-five-metre ship, delivered in 1996, whose principal activities involve population ecology and assessing species fished in the Channel, the Bay of Biscay and the North Sea. For this work, she is fitted out with fishery echo sounders and trawling systems. She is also a multipurpose vessel designed to undertake research cruises relating to physical oceanography. Following her refit in 2017, the Thalassa can now undertake geoscientific cruises and deploy the HROV Ariane. She can accommodate up to twenty-five scientists and technicians, and operates mainly in the Atlantic and the Mediterranean.