Studying small rays with big drones

How do you study the feeding ecology of small benthic whiprays in a turbid intertidal ecosystem? With some eyes in the sky we can get a great deal of information of these small animals.

The Bijagos Archipelago contains vast intertidal areas or so-called “intertidal mudflats”, which are an important foraging area for the thousands of migratory shorebirds that visit the area every boreal winter. Every day these birds have two low tide cycles during which the potential food sources (i.e. bivalves, worms and crustaceans) are exposed and accessible for the birds. However, six hours later during the high tide cycle, these same prey species are accessible to another predatory guild: rays and sharks.

A clear imprint of a whipray species on a sandy intertidal flat.

While walking over the intertidal areas during low tide, we observed a large number of characteristic ray imprints, indicating possible foraging behavior of these small whipray species (Fontitrygon margarita and Fontitrygon margaritella). On some mudflats these so-called ” ray pits” were found in high densities, whereas in other areas these densities were low or ray pits were absent.

To get a better understanding on which areas of these mudflats these small rays utilize, we got some help from above.

One of the drones operated by The Fieldwork Company to map the intertidal areas of the Bijagos Archipelago.

With drones like these, the Fieldwork Company can map entire mudflats. After an expedition, these aerial photographs are stitched together and a digital neural network is trained to automatically recognize ray pits in each photograph.

During our next expedition (October – December 2019) we will continue to work with The Fieldwork Company in the Bijagos to continue with this important part of our study.

Aerial view of an intertidal mudflat with ray pits in the Bijagos.

Published by Guido Leurs

Marine predator ecology, specialized in shark and ray research.

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