- Third photo-identification campaign for whale sharks in Djibouti.
- Four beacons have been set by the Megaptera association and the National Sea Center of Boulogne-sur-Mer (Pas-de-Calais) Nausicaa.
- Previous campaigns have helped lift part of the veil on this mysterious fish.
Everyone knows what a whale shark is. Paradoxically, scientists have very little information on the lifestyle of this impressive animal which can reach almost 15 meters long in adulthood. It is to fill this gap that, since 2016, the association Megaptera and the National Sea Center of Boulogne-sur-Mer (Pas-de-Calais) Nausicaa have been carrying out photo-identification campaigns of these giant fish offshore from Djibouti, Africa.
Ludwig Coulier, a biologist at Nausicaa, returned on Saturday from a week-long mission to the Horn of Africa in the Gulf of Tadjourah. It is the third such trip he has made in the past four years. At 45, surrounded by members of the Megaptera association and local staff, he participated in the installation of four beacons on “young” whale sharks. "These are fish that regularly rise to the surface for food, so we can approach them fairly easily in apnea without specific equipment," he explains. However, the task is not easy since it is still carried out between 3 and 4 meters deep and the beacon must be placed on the dorsal fin of the shark.
"We have never seen very young whale sharks"
The transmitters used this time have a range of 300 days and will provide information on the water temperature and the movements of the identified individuals. “We know that between November and February, there is a concentration of juvenile whale sharks, that is to say, 10 to 15 years old. What we want to understand is why they come here during this period and why from one year to the next we never see the same individuals again, ”continues the biologist.
There are many unknowns around this giant of the seas which begin to be lifted thanks to the previous missions. “We don't really know where and how they reproduce and we have never seen very young whale sharks. The 2017 campaign allowed us to follow a shark from the Gulf of Tadjourah to Madagascar where we find a large and older population. The assumption is that the conditions for reproduction are met there ”, according to Ludwig Coulier.
A species "particularly sensitive to plastic microparticles"
Successive missions have also resulted in less exciting findings. “40% of sharks are threatened with extinction, including the whale shark. There is fishing for the fins, but also pollution of the marine environment. The whale shark filters water for food, so it is particularly sensitive to plastic microparticles, ”says the scientist.
Fifteen years ago, when Ludwig Coulier went to Djibouti, he could observe up to thirty different whale sharks. Last week, he saw only eight. “We don't know if there is a real decline in the population or if they are going less and less to this area. There are still a lot of unknown parameters that we may discover thanks to the last campaign. "
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