...For over twenty years the IATTC has been aware of ecosystem issues, and has moved towards EAFM in many of its management decisions (e.g., SAC-10 INF-B; JuanJorda et al. 2018). Within the framework of the Strategic Science Plan (SSP), the IATTC staff is conducting novel and innovative ecological research aimed at obtaining the data and developing the tools required to implement EAFM in the tuna fisheries of the EPO. Current and planned ecosystem-related activities by the staff is summarized in the SSP (IATTC-93-06a) and the Staff Activities and Research report (SAC-1301). Determining the ecological sustainability of EPO tuna fisheries is a significant challenge, given the wide range of species with differing life histories with which those fisheries interact. While relatively good information is available for catches of tunas and billfishes across the entire fishery, this is not the case for most non-target (i.e. “bycatch”) species, especially those that are discarded at sea or have low economic value (see section 2 and IATTC Special Report 25). Furthermore, environmental processes that operate on a variety of time and spatial scales (e.g., El Niño-Southern Oscillation, Pacific Decadal Oscillation, ocean warming, anoxia and acidification) can influence the abundance and horizontal and vertical distribution of species to different degrees, which in turn affects their potential to interact with tuna fisheries. Biological reference points, based on estimates of fishing mortality, spawning stock biomass, recruitment, and other biological parameters, have been used for traditional single-species management of target species, but the reliable catch and/or biological data required for determining such reference points, or alternative performance measures, are unavailable for most bycatch species. Similarly, given the complexity of marine ecosystems, there is no single indicator that can holistically represent their structure and internal dynamics and thus be used to monitor and detect the impacts of fishing and the environment. The staff has presented an Ecosystem Considerations report since 2003, but in recent years this report has continued to evolve in content, structure, and purpose. Its primary purpose is to complement the annual report on the fishery (SAC-13-03) with information on non-target species and on the effect of the fishery on the ecosystem, and to describe how ecosystem research can contribute to management advice and the decision-making process. It also describes some important recent advances in research related to assessing ecological impacts of fishing and the environment on the EPO ecosystem and its associated species.