How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small Drones

This study demonstrates that small, commercially available drones combined with aerial photogrammetry provide a highly accurate, non-invasive method to measure body size and assess sex and maturity of reef manta rays (Mobula alfredi) in Raja Ampat. Measurements of disc width, disc length, and cranial width from 86 individuals showed strong linear relationships and low measurement error, enabling reliable estimation of size-at-maturity and clear sexual dimorphism, with females significantly larger than males. By eliminating the need for in-water interaction, this approach minimizes disturbance to a vulnerable species while delivering robust demographic data essential for identifying nursery areas, monitoring population structure, and evaluating the effectiveness of long-term protection and tourism management within Marine Protected Areas.

Authors:

Edy Setyawan, Ben C. Stevenson, Muhamad Izuan, Rochelle Constantine, Mark V. Erdmann

Publisher:

Drones

Keywords:

aerial photogrammetry, marine megafauna, unmanned aerial vehicle, sexual dimorphism, size at maturity

Group Species:

Elasmobranch

Species:

Reef manta ray

Scale:

Raja Ampat

Year:

2022