Diversity of rays and sharks in drop of water

Studying elusive and rare animals is often a challenge. This is especially true in large marine systems, and even more if the visibility is poor or in remote areas. Fortunately, due advanced research tools we can now determine the presence of illusive animals, like rays and sharks, a little bit easier.

Globally more and more studies are focusing on sharks and rays, but unfortunately some regions lack behind. One of these regions is West Africa, where sharks and rays are thought to play an important role in large intertidal ecosystems.

The team has collected a 2L water sample and filters this using a fine mesh filter and a portable vacuum pump. This method proved to be so successful that we will continue this project during our next expedition to the Bijagos Archipelago.

For us, working on shark and ray ecology within the Bijagos Archipelago, the unknown status of these animals is a tricky problem. How do you study the ecology of a group of species when you do not know which species are actually part of that group? Well, that is exactly what we try to study using a relatively new technique called “environmental DNA”.

Environmental DNA uses the principle that all living organisms leave DNA behind in their direct surroundings, through feeding, skin shedding, injuries, mating, etc. So basically for aquatic and marine environments, this means we can filter this DNA using a portable setup and very fine meshed filters. That is exactly what we did on 80 sample locations around Fermosa, Bubaque, Bruce and Orango during our last expedition. Later in the lab we extract the DNA from these filters, clean the DNA, amplify it and send it out to a sequencing lab.

The first results of this study are very promising, showing a high abundance of a small whip ray species (Fontitrygon margaritella), which accounts for 75% of all detected elasmobranch DNA. Other detected species include Lusitanian cownose rays (Rhinoptera marginata), blackchin guitarfishes (Glaucostegus cemiculus), scalloped hammerhead sharks (Sphyrna lewini), nurse sharks (Ginglymostoma cirratum) and milk sharks (Rhizoprionodon acutus). We will continue this research during our next expedition and we are thankful to the World Wildlife Fund to support the continuation of this study!

Published by Guido Leurs

Marine predator ecology, specialized in shark and ray research.

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