A Motley Crew
Updated: Apr 27, 2021
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. Also, 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. 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!
For instance, a research team in Mexico have been deploying drones to observe "elasmobranchs" (sharks, skates and rays) in the Bahía de La Paz (the Bay of La Paz). They flew a quad-copter drone (with four helicopters atop four arms and a camera to take video footage) near Mogote Beach in late July, in order to investigate what species they could see swimming in shallow water. Mobula rays (Mobula spp.), cownose rays (Rhinoptera spp.) and whale sharks (Rhincodon typus) are seasonally abundant in this region (Frixione et al, 2020).
Yet, despite being an elasmobranch-rich area, the researchers were surprised by what they saw on their footage...
Firstly, they were delighted to see whale shark sightings at an unusual time of the year. Normally, whale shark abundance begins to rise in the bay from late August or September, as they move into the area to feed, but this footage was captured in July (Frixione et al, 2020).
Also, what was especially interesting, was that the video showed whale sharks feeding alongside cow nose rays (Rhinoptera steindachneri) (this is known as "co-occurance"). There were no previous records of these two species sharing the same foraging sites (Frixione et al, 2020).
The researchers hypothesised that the unusual dinner-date, usually early in the year, might have been caused by "upwellings". An upwelling is caused by winds driving water away from the coast and drawing deep, nutrient-rich water up to the surface. This makes the area very "productive", as the enhanced nutrients feed more phytoplankton and creates "plankton blooms". Whale sharks and cownose rays both feed on plankton. Therefore, it seemed that both species probably moved into the area 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 (Frixione et al, 2020).
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, 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.
References
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.
IUCN (2020). The International Union for the Conservation of Nature Red List of Threatened Species. Access online.
By Sophie A. Maycock for SharkSpeak.