More than just sushi fish: The secrets of the bluefin tuna revealed

It is enormous in size, crosses oceans, and dives to a depth of more than a kilometer. However, its fate is fragile. The Atlantic bluefin tuna, one of the most impressive and iconic creatures in the marine system, is much more than just a luxury fish for sushi; it is a super-predator that tells the story of the sea.

We spoke with Dr. Eyal Bigal, a postdoctoral researcher leading studies at Stanford University and the Morris Kahn Marine Research Station at the University of Haifa. His research, presented at the 54th Annual Conference on Science and Environment and partially funded by the Israel Ministry of Energy, focuses on tagging and tracking these giant fish to better understand their life cycles and ensure their international protection.

What is the bluefin tuna?

"The bluefin tuna is a bony fish, one of the largest in the world," Dr. Bigal explains. "It lives for over 30 years, reaches a weight of over 650 kg, and a length of more than three meters. Ecologically, it is a 'super-predator' at the top of the food chain. Its role is vital because it regulates the populations of the species it preys upon. The state of these super-predators serves as an indicator of the sea's overall health."

Bluefin tuna swim enormous distances, crossing the Atlantic and the Mediterranean. There are two main populations: the West Atlantic population, which breeds in the Gulf of Mexico, and the East Atlantic population, which includes those found near Israel. While populations faced severe depletion in the 1960s due to industrial fishing, they are now recovering thanks to international conservation efforts.

Managing a shared resource

Management is carried out by the International Commission for the Conservation of Atlantic Tunas (ICCAT). The organization collects scientific data and distributes fishing quotas to member countries. Israel is currently in the process of joining ICCAT. "This is problematic because it is not a local species, but fish that swim half the world. It is vital to treat them as a shared resource," Dr. Bigal notes.

Unique adaptations and history

Bluefin tuna possess remarkable physiological adaptations:

1. A unique heat exchange system in their blood vessels allows them to maintain an internal temperature higher than the environment, enabling them to survive in very cold water.

2. Fat-rich muscle tissue provides energy for long-distance migrations.

3. A hydraulic mechanism controls the dorsal fin, ensuring maximum hunting efficiency.

Historically, the fish has been valued for 2,500 years. Archaeological findings in the eastern Mediterranean include tuna bones, ancient salting factories, and even coins featuring the fish. Aristotle himself wrote about the bluefin tuna, highlighting its cultural and economic importance.

Research and environmental impact

In Israel, the primary fishing method is "longline fishing," involving a 15 km line with hooks. Unfortunately, this is a non-selective method, often catching sharks, swordfish, and juvenile tuna as bycatch.

To study migration, Dr. Bigal's team uses satellite tagging. A lemon-sized computer is attached to the fish, recording temperature, depth, and light intensity. Once the device detaches, it floats to the surface and transmits data via satellite.

"We recently discovered a new breeding area along the US coast, which breaks old models," says Dr. Bigal. "Furthermore, we see tuna returning to areas where they had disappeared at the end of the last century."

Climate change also poses a threat, as warming waters force tuna to seek cooler habitats in northern latitudes, potentially rendering current breeding grounds less suitable.

What can the public do? "The most important thing is to know what we are eating," Dr. Bigal concludes. "We must ensure that selective fishing methods are used and support long-term ecological research to maintain the stability of our marine systems."

The article was prepared by Zavit — the news agency of the Israel Society of Ecology and Environmental Sciences.