Whale sharks, big friendly giants of the ocean
Whale sharks are about the opposite of your archetypal shark. These gentle giants, the biggest fish in Earth’s oceans, are living on a steady diet of plankton (with the addition of small crustacean, fish and squids). There’s still a lot we don’t know about this wildlife marine species, though. Understanding their movement patterns by tracking them using Argos PTTs helps to ensure that they are effectively protected.
Whale sharks (Rhincodon typus) are at serious risk of extinction, since they have been killed for their liver oil, for their fins and also accidentally hit by boats or caught in nets. They have been classified as “endangered”, with a decline of more than fifty percent of the population globally.
Whale sharks are moving often, and far. This makes it difficult to tell if a decline in sightings in one country is meaningful. Most of the countries or regions for which we have long-term sightings records show a decline, which is the basis of their globally Endangered conservation status. However, in some places at some periods, such as Thailand in 2017, there were a lot of whale shark sightings; but we can’t tell if this is a sign of recovery, or just a shift in population. Moreover, we don’t know where the newborns and most of the adults are, since most sightings, done in feeding grounds, are of juvenile males. These need to be worked out to understand if this population is in recovery or continuing to decline.
Whale sharks are living in warm waters (above 20°C) all around the globe – in Philippines, Madagascar, Tanzania & Mozambique, Gulf of Mexico, Galapagos… The Philippines hosts the third largest known population. Dedicated research by LAMAVE (Large Marine Vertebrates Research Institute Philippines) and citizen science has identified over 600 individuals in the Sulu and Bohol Seas, yet the proximity of this population to fisheries in the South China Sea is a concern. In light of this, understanding the movements of whale sharks in the Philippines is vital to identify conservation priorities for the species.
Argos tags allow to track the sharks over large geographical distances, and also get information on temperature preferences and diving behavior. Seventeen juvenile whale sharks were tagged in the April 2015-April 2016 period by researchers from LAMAVE, Marine Megafauna Foundation (MMF) and Tubbataha Management Office (TMO) in three different locations in the Philippines. Tags were tethered to each whale shark by a 1.8-meter line, to ensure the tags break the surface more frequently. Transmission occurs when the wet/dry sensor of the tag is triggered. Thus the team was able to follow the movements of those juvenile whale sharks in near real-time. Tracking lasted from 6 to 126 days.
All whale sharks stayed within the Philippines over the tracking period, showing the importance of the archipelago for the species. LAMAVE continues to study whale sharks in five key areas in the Philippines, working with local and national governments as well as collaborating organisations to develop conservation strategies for this species. More whale sharks are tagged even now (July 2018) by the same team.
Featured photo: An Argos-tagged juvenile whale shark swims through the waters of Panaon Island, Southern Leyte (Credits LAMAVE).
Gonzalo Araujo, Christoph A. Rohner, Jessica Labaja, Segundo J. Conales, Sally J. Snow, Ryan Murray, Simon J. Pierce, Alessandro Ponzo. Satellite tracking of juvenile whale sharks in the Sulu and Bohol Seas, Philippines. PeerJ, 2018; 6: e5231 DOI: 10.7717/peerj.5231
Large Marine Vertebrates Research Institute Philippines (LAMAVE) www.lamave.org
Argos user stories about a similar campaign in Mozambique area https://www.clsamerica.com/mmfmozambique