Stock photo: Shortly afterwards, there was a fish stuck in the rubber octopus. Photographer: Erlend Astad Lorentzen

Researchers Investigate Stress and Quality in Pole-Caught Bluefin Tuna

The WelTuna project is meticulously tracking the condition of Bluefin tuna from the moment they are hooked until they reach the plate, aiming to establish best practices for animal welfare and meat quality in this new fishery.

Documenting Welfare and Quality in a New Fishery

Researchers from the Norwegian Institute of Marine Research (HI), led by project manager Michael Breen, are focusing on the potential of pole-and-line fishing to supply a high-quality Bluefin tuna to the lucrative restaurant market. This method offers a unique opportunity to document a fishery from its inception.

• Project Scope: The WelTuna project comprehensively documents everything, including the fishing process, the tuna's behavior during the haul, the meat's chemistry both before and after culling, and the culling method itself. The goal is to maximize fish welfare and produce the highest possible meat quality.

• The Challenge: Bluefin tuna are large but also delicate; proper and rapid processing is crucial both during and after capture to prevent damage to the meat, according to Michael Breen.

Researchers Martin Wiech, Neil Anders and Michael Breen compare the fillet sample with the newly developed "manual" from Nofima. Photographer: Pauline Paolantonacci / Institute of Marine Research

Deep Dives and Low Stress Levels Observed

Angling is typically conducted from fast, small boats where fishermen troll with rubber squid. Upon biting the hook, a large fish, sometimes up to 300-kilograms, immediately dives, often plunging over a hundred meters.

• Tuna Behavior: Michael Breen notes that over half of the observed Bluefin tuna have quickly returned to the school after diving, exhibiting the same behavior and speed as the other fish, seemingly little affected by the hooking.

• Stress Monitoring: Observations are made using a camera and accelerometer attached to the hook. Initial findings suggest that the fish may not have an elevated stress level during this part of the haul, although more data is needed for a definitive conclusion on stress levels.

• Rapid Hauling: Anglers minimize the haul-in time by following the fish with the boat and only beginning to pull hard when directly above the tuna. Some land the fish in less than 30 minutes in total, reports Michael Breen.

Lysverket chefs Thibault and Julio cut up the fish. Photographer: Pauline Paolantonacci / Institute of Marine Research

Combating 'Burnt Tuna Syndrome' and High Quality Results

A major concern in Bluefin tuna handling is "overheating" when the fish is stressed or poorly managed. This phenomenon, known as yake and mure in Japanese and often called "burnt tuna syndrome," ruins the meat. The mechanisms are complex, possibly involving temperature, lactic acid, and stress hormones.

• Killing Methods: Quick killing is vital. Researchers are investigating culling methods suitable for small boats, such as the Japanese ikejime technique.

• Initial Findings: Despite rumors that burnt tuna syndrome would be prevalent in pole-and-line caught Bluefin tuna, the WelTuna project's initial results indicate the opposite, suggesting this method creates good conditions for achieving restaurant-quality fish.

  

  Lysverket manager Christopher Haatuft continues to cut down on bluefin tuna at Nordhordland fish. (Photo: Pauline Paolantonacci / HI)

• Michelin Endorsement: The first Bluefin tuna caught this year for the project was served at the Michelin restaurant Lysverket in Bergen. Star chef Christopher Haatuft called it "perhaps the best bluefin tuna we have ever tasted," attributing the quality to the short intake time (around 20 minutes), rapid euthanasia, and subsequent treatment.

• Future Outlook: The 2025 fishing season has been slow, but the research team is focused on gathering more samples and more data for the following year.

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