This work was primarily funded by a grant from Pew Charitable Trusts with additional funding from a fellowship from the Alfred P. Sloan Foundation awarded to SMM. Funding agencies for individual tracking datasets are listed in Supporting Information. Authors declare no competing interests. All major scripts, functions, utilization distributions (core and home range) for all species and MPA shapefiles used in this study will be available online at github.com/melinda.conners/megafauna_mpas. Most of the raw tracking datasets are archived in public data repositories and available by request; see Supplementary Table S1 for database location and dataset IDs.

Marine protected areas (MPAs) are increasing in number and size around the globe in part to facilitate the conservation of marine megafauna. However, their utility for that purpose is not well established. Using a global tracking dataset from 36 species across five taxa, chosen to reflect the span of home range size in marine megafauna, we show most MPAs are too small to encompass complete home ranges of most species. Based on size alone, existing MPAs could encompass only 40% of the home ranges of the smallest ranged species and < 1% of the largest ranged species. Further, where home ranges and MPAs overlapped in real geographic space, MPAs encompassed < 8% of core areas used by all species. Despite most species’ ranges being much larger than existing MPAs, we demonstrate that benefits from MPAs are still likely to accrue by protecting critical life history stages.