They say you are what you eat and our Associate Director, Josh Stewart, has been putting this to the test! Working in collaboration with a group of research institutes and conservation organisations (see below), he has been investigating the feeding ecology of five mobulid species (manta and mobula rays) that are landed at sites in the Philippines, Sri Lanka and Peru. Understanding what drives feeding and competition among this vulnerable group of species can help us develop strategies to prevent bycatch. ⠀
The team discovered that species shared a greater dietary overlap in low-productivity areas like the Philippines, and a lower overlap in the highest-productivity regions like Peru. It burns a huge amount of energy for these filter-feeding rays to drive themselves through the water once they open their mouth, so they need to ensure that the pay-off in food in worth it. It could be that in areas where prey densities are lower, competing species end up feeding on the same food as they are all seeking out prey available in high enough densities to be energetically profitable. Conversely, in high productivity regions where there is plenty of available prey, different sized mobulids can take advantage of their unique traits (deep divers, thermal tolerance, etc) to feed on their preferred foods, rather than being constrained to one high-density prey item. This helps to explain why multiple species of mobula and manta are captured in the same nets in some regions, like the Philippines, whereas the different species are landed in different locations and times of year in other regions, like Peru.
To find out more read the newly published paper: Trophic overlap in mobuld rays: insights from stable isotope analysis
This work was led by @joshstwrt
in collaboration with the @MantaTrust
, The Semmens Lab at @scripps_ocean
, and @marinemegafauna