Fish stock assessment is traditionally a time-consuming, expensive, and invasive task, as sampling entails hiring a research ship, catching some fish and counting them. To make it less resource-intensive, and more fish-friendly, a group of German researchers have designed and built a high-tech underwater fish observatory - or UFO as they've called it.
The observatory comprises a rugged subsea lander bristling with multiple sensors that measures and classifies fish as they pass through its vicinity. It uses a combination of both acoustic and optical technology, in the form of high-resolution sonar and extremely light-sensitive stereoscopic underwater cameras that were originally conceived for military applications. The sonar triggers the cameras for more detailed analysis, when fish are detected in visible range. Other sensors onboard the lander include ones for measuring turbidity, current, conductivity and pressure as well as a receiver for detecting 'tagged' fish.
The UFO is purely observational and therefore non-invasive. It is significantly less cost and labour-intensive than conventional sampling methods. Moreover, because it is permanently fixed on the seabed, it can carry out long-term observations, allowing researchers to glean insights into behavioural characteristics.
Transmitting the information gathered from multiple sensor streams back to the surface calls for some reliable connectivity, which was supplied as a package by the specialist underwater technology firm MacArtney. The sensors are interfaced by SubConn connectors and cable assemblies hooked up to a Nexus Mk C multiplexer, which is, in turn, linked to topside via a modified TrustLink chamber termination and a 500m armoured fibre-optic signal and power cable. Beyond providing signal and data infrastructure between sensors, topside and seabed, the MacArtney kit also allows operators to trigger a pop-up recovery buoy to be deployed after the operational phase.
The lander was installed last year 300m away from FINO3, a fixed research platform in the North Sea located 80km west of Sylt at the northernmost tip of Germany. Operated by the University of Applied Sciences, Kiel, the platform is used to carry out research and technology projects on behalf of various universities and companies.
The UFO was installed by divers. Afterwards, the cable was laid to the FINO3 platform and the topside end of the cable was inserted into the platform tower and connected to a junction box. An initial operational test proved successful and the first live camera images of a school of fish were beamed up shortly after.
The landmark project was undertaken by Hamburg-based Thünen Institute of Sea Fisheries, the Computer Science and Electrical Engineering Dept at the University of Applied Sciences in Kiel and MBT GmbH.