The Working Group on Fisheries Acoustic Science and Technology (WGFAST) met in Nantes, France, on 29 May 2015. Verena Trenkel, France, served as Chair. There were 43 participants who discussed the report from the linked Working Group on Target Classification (WGTC), the needs created by the increasing use of wideband acoustics and resulting potential future activities for WGFAST, the contribution to the South Pacific regional management organization (SPRFMO) initiative on calibrating echosounders on fishing vessels, the organization of an ICES training course on how to run an acoustic survey and other initiatives. The working group meeting followed the ICES Symposium on “Marine Ecosystem Acoustics – observing the ocean interior across scales in support of integrated management”, which attracted 214 participants from 31 countries. During the symposium 94 talks including three key note talks and 87 posters were presented on i) recent developments in acoustic sensor and platform technologies, ii) acoustic characterization of aquatic organisms, ecosystem structure, and ecosystem processes and iii) the contribution of acoustics to integrated ecosystem assessments and management. The presentations were followed by lively debates.