Technology Serving the Ocean: Biologging To solve the mystery of these migrations, scientists use biologging, a technique that involves equipping animals with smart electronic tags.

The ARGOS Satellite System
The tags used, called Argos tags, are true onboard computers:

1. Recording: For approximately one year, the tag records depth, water temperature, and light levels.
2. Automatic release: At a programmed date, the tag detaches from the fish and floats to the surface.
3. Transmission: Once floating, it transmits its data to Argos satellites.
4. Analysis: An algorithm then reconstructs the precise underwater trajectory of the tuna.

Participatory and Responsible Science
The strength of the Mission Thon Rouge lies in the involvement of expert recreational fishermen.

• Fishing protocol: Only rod and reel fishing is used, as it is considered the safest for the survival of the fish.
• Capture and Release ("Catch & Release"): The goal is not capture, but tagging. The fish is brought alongside, equipped with its tag, and sampled for DNA in less than 2 minutes before being released.
• Animal welfare: Rigorous protocols validated by ICCAT (International Commission for the Conservation of Atlantic Tunas) guarantee maximum survival of individuals.

Concrete Results for the Future
In 2025, the tagging days in Royan were a total success: 20 tuna were tagged and released in just two days. These data allow for:

• Mapping migratory routes with unprecedented precision (some tags revealed journeys of over 12,000 nautical miles).
• Understanding the impact of climate change on species distribution.
• Sustainably managing fisheries by integrating these discoveries into international scientific advice (ICCAT).