12 Conserving Tuna: The Most Commercially Valuable Fish on Earth
12 Conserving Tuna: The Most Commercially Valuable Fish on Earth
Learning Objectives
- Describe the adaptive significance of biological characteristics of tuna.
- Describe how migratory patterns complicate tuna conservation.
- Summarize major historical changes in tuna fishing.
- Recognize and name the most common commercial tuna species of the world.
- Describe key elements of supply chains for industrial tuna fishing.
- Understand how national sovereignty influences international fisheries management.
- Relate current trends to future sustainability of tuna fisheries.
12.1 What’s Special about Tuna?
Tuna are highly adapted for life in the open ocean. Their streamlined bodies, built for speed and endurance, make long-distance migrations possible. In fact, the name “tuna” comes from the Greek thunnos, derived from the verb thuo, which means “to dart” or “to rush.” One cannot help but be mesmerized when watching tuna swimming—an experience hard to come by. Only a few public aquariums have exhibits large enough for the largest tuna. Divers swim with Bluefin Tuna in floating cages in Australia and Malta. Carl Safina, one writer who swims with tuna, described the Bluefin Tuna as “half a ton of laminated muscle rocketing through the sea as fast as you drive your automobile” (Ellis 2008).
Tuna regulate their core body temperature with specialized circulation near their swimming muscles, a condition known as heterothermy. Bluefin Tuna can elevate their core body temperature up to 20°C above surrounding ocean temperature to enhance swimming efficiency. The swimming mode of tuna involves high-frequency tail beats (1–2 Hz) with a stiff tail fin and extra-long tendons that connect the large muscles directly to the tail fin. Other metabolic adaptations lead to capacities exceeding those of other fish, such as an increased heart size, large gill surface area, high blood oxygen–carrying capacity, and elevated hematocrit. When speed is required, the tuna switches into high-speed mode: large dorsal and ventral fins retract into cavities, while the pectoral fins are pressed flat against the body. Consequently, tuna are among the fastest-swimming fish.
Heterothermy also allows tuna to migrate into cold waters to follow abundant prey fish. Bluefin Tuna swim in both subtropical oceans and cold seas. Tuna are also known for remarkable daytime vertical migrations to find abundant prey in deeper and colder waters. They migrate from spawning grounds to feeding grounds that may be separated by over 5,000 miles. Therefore, the tuna cross country borders, which makes drawing boundaries around populations nearly impossible. Arrival of tuna near coastal regions is predictable, and communities hold celebrations, festivals, and fishing tournaments when they arrive. Managing tuna is hard because they travel between many different jurisdictions.
The larger tuna species have long been targets of game fish enthusiasts, such as authors Ernest Hemingway and Zane Grey. Ernest Hemingw