NIOZ (Royal Netherlands Institute for Sea Research) is conducting a European open procurement procedure for the supply, configuration, and delivery of a subsea acoustic fish detection system as part of the rifHerstel XL project. The system will enable autonomous, long-term monitoring of fish presence, species composition, and biomass in the vicinity of artificial reef structures in Dutch coastal waters. The system must support a minimum uninterrupted deployment duration of six months at an operational water depth of approximately 40 metres, and shall include at least one split-beam wideband transducer for target detection and tracking. Supply of one (1) subsea acoustic fish detection system, including subsea frame, transducer(s), and data acquisition unit, with an estimated contract value of EUR 800,000 excluding VAT.