Sustainable skipjack: managing fisheries and reducing food loss

Skipjack tuna is enjoyed worldwide. But perhaps nowhere does this fish play a more fundamental culinary role than Japan, where fresh skipjack––called katsuo in Japanese and popularly referred to as “bonito” in English––is commonly eaten as sushi or seared and seasoned with garlic, onions, and soy sauce to make katsuo no tataki, a dish served in many izakaya restaurants.

But the lion’s share of Japan’s skipjack tuna catch is processed and shaved into flakes called katsuo kezuri-bushi, packed with mouth-watering umami, that are central to Japanese cuisine, or washoku. These are typically sprinkled over boiled vegetables and tofu, or simmered in hot water with dried kombu kelp to make dashi, a traditional soup stock with many uses, from boiling foods to making sauces, not to mention a key ingredient in miso soup, an essential of any Japanese meal.

As the number of fishing trawlers in the world’s oceans has increased, so has the catch of skipjack tuna. Between 1950 and 2016, the catch of skipjack in the western and central Pacific increased over tenfold.

Though the fish are relatively abundant and reproduce rapidly, overfishing is a global concern. Although Ajinomoto Co. is not directly involved in skipjack fishing, we source it for our flagship product, HONDASHI^®, a granulated form of dashi.

These days, consumers want to know where their food comes from and whether it’s sustainably and ethically sourced. Every fish, too, has a story of how it got from the ocean to your table. Sustainable fishing is about protecting marine ecosystems and ensuring that those who earn their living from fishing can continue to do so far into the future.

In simple terms, this means not catching more of any given fish than the population can sustain and remain productive and healthy. It extends to minimizing environmental impacts, adapting to changing environmental circumstances, and complying will all laws and regulations.

To conserve the skipjack, we need to understand it better. Information on its breeding habits, migration, and growth is vital to fishery management. But for a fish that’s always on the move, that’s a tall order.

Since 2009, the Ajinomoto Group has partnered with the National Research Institute of Far Seas Fisheries to tag about 10,000 skipjack a year off the Pacific Coast of Japan to track migration routes. We’ve learned they migrate northward from subtropical waters via four distinct routes, and they spend the daytime in the deep ocean, moving to shallower waters at night. Much has been revealed about their diet, as well.

We’re also very conscious of preventing food loss. In making our HONDASHI^® Japanese soup stock—a process that involves gutting and deboning the freshly caught fish, then simmering and wood-smoking the fillets for several hours—we ensure no part of the skipjack goes to waste. Co-products of the process, including the head, bones, and internal organs, are used to make tuna extract, fish sauce and seasonings, calcium-enriched products, and fertilizer. Even the charred wood leftover from smoking is used to enrich crops.

But the Ajinomoto Group is just one piece of the puzzle. Skipjack tuna occupy a vast swath of the world’s oceans. With careful management, future generations will also be able to savor this precious global food resource, be it on a plate or in a steaming bowl of soup.