Estimating non‐US longline fishing impacts on Hawai‘i pelagic false killer whales in a transboundary assessment area

Abstract Effective management of marine megafauna requires accurate assessments of anthropogenic impacts, yet accounting for non‐US fishing mortality remains a challenge when evaluating the Hawai‘i pelagic false killer whale ( Pseudorca crassidens , FKW) population. This study addresses spatial disparities in FKW bycatch estimates by integrating high‐resolution datasets, particularly Global Fishing Watch (GFW), with publicly available Regional Fishery Management Organization effort data to estimate non‐US fishing impacts within the newly expanded FKW assessment area. By leveraging fine‐scale GFW vessel activity data, we apportioned non‐US longline fishing effort to the assessment area and estimated annual FKW bycatch using interaction rates from United States and regional fisheries observer programs. Results indicate that from 2012 to 2023, non‐US fleets accounted for approximately 9% of total longline effort and contributed to an estimated mean of 1.3–4.7 FKW interactions per year, depending on the interaction rate applied. Our approach highlights the potential to allocate officially reported fishery information to a much finer spatial scale so it aligns with management needs. By incorporating GFW data, our approach enhances the accuracy of FKW bycatch estimates. Future applications of GFW and similar datasets could improve spatially explicit assessments of transboundary fisheries impacts, reducing uncertainties in protected species management and facilitating data‐driven policy decisions.