Electronic tagging is a long standing activity on Bluefin tuna. Recurring operations take place in the Gulf of Lions, where young tunas are tagged to understand their spatial dynamics in relationship to the environment. In particular, this allows to better understand and interpret the data recorded during the aerial surveys. If we don't see many tunas during the aerial survey, does it mean there are not many tunas in the sea or does it mean they moved somewhere else ? Tagging from spawning grounds is an activity that started more recently and an important part of the POPSTAR, FISHNCHIP and PROMPT projects.
Electronic tagging consists in deploying on tunas a bunch of sensors enclosed in a casing, which typically record light, pressure and temperature. The so-called electronic tags (or Spats) are able to detach themselves after a defined time period thanks to a release system. They then transmit their data through satellite communication. This allows to collect data with recapturing the animal, a generally difficult task... The data are then used by geolocation algorithms to reconstruct the track of the fish.
The deployment of such tags is a particular operation. It has to be made quickly on a particular location on the animal, here the second dorsal fin. The fish needs to be kept in good condition to ensure its survival. Its eyes are covered by a wet cloth to calm it and a flow of water is provided to keep it oxygenated.