Increases in the generation of electricity using marine renewable energy (MRE) are planned globally, with Wales potentially playing a key role in the MRE industry, including hosting the world’s first deployment of a utility scale tidal kite off the coast of Anglesey by Minesto UK Ltd. Assessment and understanding of the environmental impacts of MRE devices and developments are urgently needed, but remain challenging due to diverse development locations, device designs and the complexities of studying top predators, which are a focus of many impact assessments.We present findings from the SEACAMS2 project focused on Minesto’s Holyhead Deep development off North Wales, where multi-disciplinary instrument moorings have been used assess potential overlap of small pelagic fish with planned operational devices and the driving process for any overlap. Predictable variation in depths reached by fish schools during vertical migrations were observed, with clear links to physical processes found, and so potential overlap with a tidal kite could be calculated.By understanding overlap in space and time between MRE devices and prey species of top predators such as small pelagic fish, uncertainty of impacts can be reduced. Current work to understand fish behaviour with an actively deployed MRE kite and other sub-sea structures will also be introduced.