Underwater ultrasonography confirms pregnancy and identifies developmental stages in free-swimming oceanic manta rays (Mobula birostris).

This study provides the first in situ confirmation and developmental characterization of pregnancy in free-swimming oceanic manta rays (Mobula birostris) using underwater contactless ultrasonography in Revillagigedo National Park, Mexico. Foetal morphology enabled characterization of developmental stages, including one middle-stage and two late-stage pregnancies. External distension was absent in the middle-stage case but detectable in late-stage pregnancies, though not always evident in video imagery. These findings demonstrate that underwater ultrasonography is a feasible, non-invasive approach to improve pregnancy detection and refine reproductive parameters in wild manta ray populations.