Using the FLOWBEC seabed frame to understand underwater interactions between diving seabirds, prey, hydrodynamics and tidal and wave energy structures

The NERC/Defra collaboration FLOWBEC-4D is investigating the environmental and ecological effects of installing and operating arrays of wave and tidal energy devices. The FLOWBEC seabed platform combines a number of instruments to record information at a range of physical and multi-trophic levels at a resolution of several measurements per second, for a duration of 2 weeks to capture an entire spring-neap tidal cycle. An upward-facing multifrequency echosounder is synchronised with an upward-facing multibeam sonar aligned with the tidal flow. An ADV is used for local current measurements and a fluorometer is used to measure chlorophyll (as a proxy for plankton) and turbidity. The platform is self-contained, facilitating rapid deployment and recovery in high-energy sites. Five 2-week deployments have been completed at wave and tidal energy sites at EMEC in Orkney (UK), both in the presence and absence of renewable energy structures. Using multifrequency target identification and multibeam target tracking, the depth preference and interactions of birds, fish schools and marine mammals with renewable energy structures can be tracked. Seabird and mammal dive profiles, predator-prey interactions and the effect of hydrodynamic processes during foraging events throughout the water column can also be analysed. These datasets offer insights into how fish, seabirds and marine mammals successfully forage within dynamic marine habitats and also whether individuals face collision risks with tidal stream turbines. Measurements from the subsea platform are complemented by 3D hydrodynamic model data, concurrent shore-based marine X-band radar and shore-based seabird observations. This range of concurrent fine-scale information across physical and trophic levels will improve our understanding of how the fine-scale physical influence of currents, waves and turbulence at tidal and wave energy sites affect the behaviour of marine wildlife, and how tidal and wave energy devices might alter the behaviour of such wildlife. These results can be used to guide marine spatial planning, device design, licensing and operation, as these individual devices are scaled up to arrays and new sites are considered.