A Motley Crew

Modern technology is becoming increasingly valuable to scientists for observing animals in the wild. Recently, drones (also known as unmanned aerial vehicles or UAVs) have become especially useful because they can be used to monitor species which live in environments which are challenging to access, like offshore marine environments. Many studies, across the world, are now employing drones to capture footage of sharks for scientific research and we are learning so many new things as a result! In fact, drones are allowing us to witness sharks and rays mixing in ways we have never seen before...

Drone footage has capture golden cownose rays and whale sharks feeding very close to each other in Mexico (Frixione et al, 2020).

Come Fly With Me

The development of drones has undoubtedly revolutionized how scientists can collect data in challenging or inhospitable environments. Every year drones become increasingly more valuable, as the technology rapidly advances; we are now able to capture much clearer footage thanks to improving video technology and are able to record much higher resolution video for a longer period of time thanks to increasing storage (Frixione et al, 2020). To learn more, check out Attack of the Drones.

Drones have become very useful for scientists studying sharks and rays, as they can collect data on a wide range of different marine animals (Butcher et al 2019)

As drones make it possible to observe animals in the wild without disturbing them too much, we are able to watch as they perform their natural behaviours (Frixione et al, 2020).

For instance, a research team who have been deploying drones to observe "elasmobranchs" (sharks, skates and rays) in the Bahía de La Paz (the Bay of La Paz) in Mexico, have make surprising discoveries about the "movement ecology" of sharks and rays in the region (Frixione et al, 2020).

Footage captured in July has shown that whale sharks (Rhincodon typus) come into the area much earlier than we previously thought. Also, what was especially interesting, was that the video showed whale sharks feeding alongside cow nose rays (Rhinoptera steindachneri). When two different species share the same space and/or resources like this, it is known as "co-occurance"). There were no records of these two species sharing the same foraging sites before it was captured on this drone footage (Frixione et al, 2020).

Drones have captured footage of whale sharks feeding in the Bay of La Paz (Frixione et al, 2020)

Dinner Bell

The scientists working in Mexico hypothesised that this dinner-date between susrprising species occurring usually early in the year, might have been caused by a natural phenomenon known as an "upwelling". Upwellings are caused by winds that drive water away from the coast and draw deep, nutrient-rich water up to the surface. This makes the area very "productive", as a plethora of nutrients are drawn up from below. These nutrients feed more phytoplankton and can lead to "plankton blooms" (Frixione et al, 2020).

Whale sharks are filter-feeders; eating only tiny zooplankton (Image Credit: Arturo de Frias Marques / WikimediaCommons)

Whale sharks and cownose rays both eat microscopic organisms, so they can often be found feeding in nutrient-rich waters around upwellings. Therefore, it seemed that both species probably moved into the area off the coast of Mexico to target seasonally abundant plankton, but that they arrived at the party early that year because persistent southerly winds created unseasonably rich upwellings in the bay. Once there, as they were not a threat to each other, they feasted peacefully side-by-side (Frixione et al, 2020).

An Angel from Above

These findings are very important because populations of both of these species are declining in the wild; whale sharks are classified as Endangered and golden cownose rays as Near Threatened on the IUCN Red List of Threatened Species (IUCN; Frixione et al, 2020).

If we are to protect endangered species, it is very important to understand where and when they migrate, and where their critical habitats are. Both of these species are protected by both Mexican and International law, and in the study area, targeted shark fisheries are being replaced by ecotourism companies. This means that these fish are now being valued as a living resource, rather than as a commodity to be extracted and consumed. So hopefully these animals can find some relative safety when feeding together in these waters in the future... And maybe we'll even be lucky enough to witness some more of it with drones.

Golden cownose rays (Image Credit: Atomische / WikimediaCommons)

References

Butcher PA, Piddocke TP, Colefax AP, Hoade B,Victor M. Peddemors VM, Lauren Borg L & Brian R. Cullis BR (2019). Beach safety: can drones provide a platform for sighting sharks? Wildlife Research, 46, 701–712. Access online.

Frixione MG, García MdJG & Gauger MFW (2020). Drone imaging of elasmobranchs: Whale sharks and golden cownose rays co-occurrence in a zooplankton hot-spot in southwestern Sea of Cortez. Food Webs, 24, e00155. Access online.

IUCN (2020). The International Union for the Conservation of Nature Red List of Threatened Species. Access online.

By Sophie A. Maycock for SharkSpeak