Scientists aged Spinetail Devil Rays (Mobula mobular) and Bentfin Devil Rays (Mobula thurstoni) that were caught in small-scale fisheries in Indonesia, Kenya, and Pakistan using growth rings visible in sections of their vertebrae, much like aging a tree. Using length-at-age data, somatic and population growth (r_max) was then estimated, addressing key data gaps in the life history of these endangered species.

The results show that fishing levels were greater than population growth suggesting that devil rays in the Indian Ocean are being caught at unsustainable levels, putting them at high risk of further population decline. In addition, the team warn that the species’ low population growth, due to slow growth, few offspring and long reproductive cycles, makes them highly vulnerable to overfishing.

Guiding sustainable fishing practices

Published in the journal Marine Biology, the findings have the potential to inform crucial conservation efforts and guide sustainable fishing practices in the Indian Ocean.

The study found that Indian Ocean the Spinetail Devil Ray grows more slowly and is therefore less resilient to fishing pressure than populations of the same species in other parts of the world, suggesting that their life history may vary in different parts of the species range.

The results also show that most Bentfin Devil Rays sampled in Indonesia were juveniles raising concerns that the fishery is removing young individuals before they reproduce, which could lead to rapid population declines.

Senior author, Per Berggren, Professor of Marine Megafauna Conservation, School of Natural and Environmental Sciences, Newcastle University, said: “With fishing rates exceeding sustainable limits, we need urgent management and conservation efforts to prevent further population declines and species extinctions.”

First author, Dr Ellen Barrowclift, said “Devil rays have amongst the lowest population growth rates of all sharks and rays but are high value catch in many small-scale fisheries. Urgent management interventions are needed to address unsustainable fishing in order to halt decline and allow these iconic, endangered species to recover.”

The study provides critical data that can guide conservation efforts and sustainable fisheries policies. Without immediate action, the continued overfishing of devil rays in the Indian Ocean could push these already endangered species closer to extinction.

Reference

Barrowclift, E., Temple, A.J., Pardo, S.A. et al. Age, growth, and intrinsic sensitivity of Endangered Spinetail Devil Ray (Mobula mobular) and Bentfin Devil Ray (M. thurstoni) in the Indian Ocean. Mar Biol 172, 24 (2025). https://doi.org/10.1007/s00227-024-04564-6