Understanding to what extent human activities have altered marine biodiversity is an increasingly urgent societal challenge and of considerable scientific and policy concern.Our ignorance of the pressures upon and fate of marine biodiversity is, in part, because there are few synoptic global indicators to measure changes in marine biodiversity. Moreover, it has proven challenging to effectively incorporate ecosystem considerations into fisheries management decisions and advice. The main objectives of the OceanTuneIn project are (1) to develop new indicators for measuring biodiversity change in oceanic marine ecosystems using tunas and billfishes as sentinels of ocean health, and (2) to develop management guidelines to determine how these indicators can be effectively used for improving management and conservation of oceanic ecosystems. These objectives will be achieved through six main tasks: (1) Developing indicators of pressure, and ecological state for measuring biodiversity change; (2) Testing the performance of candidate indicators to identify reference points against which ecosystems can be assessed; (3) Developing management guidance in the performance and interpretation of candidate indicators to aid decision-makers in their potential use; (4) Training the Fellow in quantitative state-of-the-art methods; (5) Fostering collaborations with the tuna Regional Fisheries Management Organizations and (6) Raising societal awareness through effective communication of benefits of healthy oceans for the well being of humanity. The new knowledge, tools, training, and collaborations generated in this project have the potential to enhance Europe’s capacity to meet strategic national and international policy commitments in light of the European Commission Marine Strategy Framework Directive and the 2020 Convention on Biological Diversity Aichi Targets.