The SUMMER project will explore recent findings that suggest that the mesopelagic zone of oceans contains 90 % of the planet’s fish biomass. Even if a fraction of this is correct, the exploitation potential in fishmeal production, nutraceuticals and pharmaceuticals is enormous. However, as the role of mesopelagic fish is not understood in terms of the ecosystem, it is first necessary to establish tools to accurately estimate their biomass and the interspecies impact at that level. Using eDNA, acoustics and gut analysis among other tools, SUMMER will also investigate the environmental repercussions of such exploitation. The resulting outcome will provide a better idea of the mesopelagic commercial potential and its impact on ecosystem balances.