Bluefin tuna is one of the most delicious and desirable fish on the planet, which is why the species' population is dwindling. Japan is responsible for 80% of the world’s total bluefin consumption, and with these dish depleting in the wild surrounding the island nation, Japan has already turned to other sources for their sushi, sashimi, and more.

Mexico’s port of Ensenada is a huge base for tuna ranching, where tons of boats capture young Pacific bluefin tuna migrating between western and eastern Pacific waters. Most of these fish are destined for Japan, and since the late 1990s, roughly 30% of Japan's sashimi-grade bluefin tuna has been sourced from Mexican tuna ranches.

It's complicated to determine whether tuna ranching is sustainable or not. Measures are taken to reduce environmental impact on local fish populations and water quality, but ranching relies on the capture of juvenile fish too young to reproduce, meaning that none of these fish will reach maturity and lay eggs to replenish the species' population.

While some ranchers point out that the Pacific bluefin's population is experiencing a rebound, all three bluefin species — Atlantic, Pacific, and southern — remain on the Seafood Watch Red List of seafood to avoid. Protecting bluefin tuna populations will require both international cooperation and time to let the species recover.