Bluefin tuna: the mark of a great traveler!

THE MTR ROYAN PROJECT

What is the Mission Thon Rouge ?
Created in 2025, the Mission Thon Rouge (MTR) is an association dedicated to organizing fish tagging campaigns for scientific research.
Initiated by the Pays Royannais Sport Fishermen's Association (PSPR), the Royan Town Hall, the local SNSM (Sea Rescue), and the MTR association, this project is based on a unique synergy between scientists, recreational fishermen, and institutions. The objective is simple yet ambitious: to provide concrete assistance to IFREMER (French Research Institute for Exploitation of the Sea) in its study of Atlantic bluefin tuna populations.

Mission Area: From Cordouan to Arcachon Although the association is based in Royan, our tagging campaigns cover a strategic maritime sector ranging from the Cordouan Lighthouse to the northern Arcachon Bay, extending up to 30 nautical miles offshore. This area represents a vital migratory corridor for bluefin tuna during the summer season.

Operational area - MTR

The Bluefin Tuna: A Little-Known Great Traveler
The Northern bluefin tuna (Thunnus thynnus) is an iconic species, fished for over 7,000 years. It is an essential "apex predator" for the balance of marine ecosystems.

• A marine athlete: It can weigh over 600 kg (up to 900 kg) and measure up to 4 meters.
  
• An untiring migrator: During its 40-year lifespan, it travels thousands of nautical miles to feed in cold waters and reproduce in warm waters.
  
• Complex management: Its constant movement between the Atlantic and the Mediterranean makes its protection difficult without precise knowledge of its trajectories.
  

Our main missions consist of:

• Collecting DNA samples (determining sex and age).
• Studying complex migratory routes of the bluefin tuna.
• Analyzing the climatic impact on large pelagic populations.

No-Kill Commitment: All tuna are tagged and released in less than 2 minutes to guarantee their well-being and survival.

Biologging & Argos Tags

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:

Illustration of satellite tracking via ARGOS tag

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.

POP-UP Tag

Records temperature, light, and depth for approximately 1 year.

Satellite Transmission

Surfaces to transmit data via satellite.

Goniometry

MTR is certified to locate and recover tags at sea (value €12,500).

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.

Tuna tagging - MTR

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:

Tuna tracking via ARGOS tag

• 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).