Illegal fishing is a concern within marine protected areas (MPA) worldwide, particularly for threatened species such as manta and devil rays (mobulids). However, due to the lack of taxonomic knowledge of enforcement personnel, illegal fishing catch records relating to mobulids can be limited. Here, an examination of illegal catch photographs from local enforcement authorities of the Chagos Archipelago’s vast no-take MPA revealed approximately 79 individual mobulids from just seven vessels, equating to an estimated 20 tonnes. This is likely a vast underestimation due to the limited detection of illegal fishing activity and species-specific reporting. If catches of this magnitude are commonplace within the MPA, they are likely having a detrimental effect on local mobulid populations. Accurate and consistent catch data recording and reporting are crucial to fulfil mobulid conservation responsibilities, as is comprehensive research on the movement ecology and habitat use dynamics of all mobulid species in the region.