The ray-finned saltwater fish known as the bonito is also called, by some fishermen I know, the tiger tuna—a nickname that refers to its taxonomy (bonito and tuna are in the same family) and to its iridescent blue-green stripes. Early one morning in late December, the sky was overcast on the waters off the coast of Dana Point, in Southern California’s Orange County, and still the scales of a thrashing six-pound bonito, reeled in by the chef Junya Yamasaki, shimmered brilliantly. Yamasaki, who is fifty years old, tall, and slender, with long black hair that he wears in a bun, detached the fish from the line. Then, with practiced ease, he used one hand to hold it by its gills and the other to drive a small metal stake between its eyes and directly into its brain—a technique known in Japan as ike jime. The bonito’s body twitched until Yamasaki slid a thin metal wire down the column of its spinal cord, a second step called shinkei jime, which arrests its nervous system.

The method is considered significantly more humane than the standard alternatives for killing a fish (thwacking it on the head, letting it suffocate), and is analogous to halal and kosher butchery, which both require that animals be slaughtered with a swift, decisive cut to the throat. It also results in fish that tastes better and stays fresh significantly longer. “The process brings out the best characteristic of every species,” Yamasaki told me—a firm silkiness for white fish, a clean acidity for tuna. It works in part by stemming the flood of stress hormones and other chemicals that a fish’s body begins to release upon capture, staving off rigor mortis and the stink of decay. Conner Mitchell, a restaurateur and a commercial fisherman, and the captain of the Jamaica Day—the small pilothouse boat we were fishing on—was impressed the first time he saw Yamasaki do it. “I’m looking at a fish that would have been stiff, now as flexible as tissue paper,” Mitchell said.

In Japan, you can assume that the fish at any good restaurant met its end by way of ike and shinkei jime; in the U.S., the same is true at restaurants offering catch imported from Tokyo’s famed Toyosu Market. Among the fishermen of Southern California, the practice can largely be traced to Yamasaki, whose evangelism has quietly transformed the local seafood supply. On the deck of the Jamaica Day, Mitchell and an array of other energetic restaurant-industry dudes in their thirties—all of whom learned the technique under Yamasaki’s tutelage—set up rods, checked the boat’s radar, and gleefully spotted clusters of birds diving in the distance, which signalled that schools of bonito swam beneath them. Whenever a line began to jerk, the group exploded in a joyful chorus. Then the men took turns reeling the fish in, and putting them out of their misery.

Twice, I reeled in a bonito myself—a process that I found surprisingly intimate, just me and an invisible squirming weight at the other end of the line. Both times, I struggled as I turned the crank, heart pounding, almost certain that I wouldn’t succeed, until I caught sight of a silver flash at the water’s surface. Then Danny Miller or Cole Moser—a chef and a bartender, respectively—would pull it on board. As Miller gutted one particularly beautiful specimen, tossing its organs into the spray before slipping it into a slurry of ice and salt water, he pointed out that, because of the ike and shinkei jime, the fish had retained its vibrant color. If it had died slowly, it would have already gone dull and gray.

A full week later, when I unwrapped the bonito fillets that Yamasaki had sent me home with, I was amazed to find the skin undiminished, the flesh a rosy pink. I’d grown used to being disappointed by fish from the supermarket, its flavor so often muddy or bitter, with the occasional bracing whiff of ammonia. The bonito smelled barely of the ocean, clean and faintly salty. Following Yamasaki’s instructions, I seasoned each fillet generously before flash-searing it on a ferociously hot cast-iron pan, then sliced it into thick chunks to dip into soy sauce. The flesh was sweet, a little tart, and supple, like a piece of ripe fruit.

Several times in the past few months, when I’ve called Yamasaki on the phone—we met last year, at the Hollywood Farmers’ Market—I’ve reached him in the middle of a long drive. About once a week, he hops into his crimson 1997 Jeep and travels several hours from Los Angeles to forage for mushrooms or to dive for shellfish, at locations that he prefers not to disclose, accompanied by his dogs, Artichoke and Chanterelle. Chanterelle, a large and spirited three-year-old Belgian Malinois mix, has a challenging temperament; on the boat, Yamasaki pulled up a pant leg to reveal a big, gnarly scab where she’d bitten his calf. “I think one of the reasons she’s crazy is because, during the tuna season, I give her all the trimmings,” he joked—at least one of his fishing buddies has gotten mercury poisoning. “I’m a zero-waste chef, you know?”

As a kid, Yamasaki, who grew up near Osaka, went fishing with his father. It was only when he became a chef—a career he stumbled into while putting himself through art school, in Paris—that he taught himself ike and shinkei jime, which are associated with the Akashi Strait, a famous fishery not far from his home town. As the executive chef at Koya, an udon bar in London, Yamasaki cooked live eels, whose bodies could remain jumpy and unwieldy even once their heads had been chopped off. After learning how to paralyze the spinal cord on an eel, he found handling other fish to be easy. “Ask a vet—it’s much more difficult to do an operation on a Chihuahua than a Doberman,” he told me.

In 2018, Yamasaki moved to L.A. to open a Japanese restaurant, which evolved from a pandemic-era food truck to an idiosyncratic izakaya, called Yess, in the Arts District. (After his current lease ends later this month, he will open a cheekily named pop-up, Fuck Yess, while he looks for a new location.) From the start, he knew that he wanted to serve seafood, and that he wanted to commit to using local ingredients, as he’d done at Koya. Between London and L.A., he spent a few months at a Zen temple back in Japan, where practitioners grew their own vegetables and rice. “They pursue this as kind of a mission to learn about life,” he told me. He was dismayed that the best seafood he could access in L.A. was imported from Japan: “It’s fresher than the fish, ironically, from Santa Barbara, which takes a couple of days, sometimes a week.” He researched species native to California’s waters—opaleye, calico bass, moray eel—only to discover that most weren’t even sold commercially. “And then I found this YouTube video of somebody spearfishing, and I said, ‘Oh, my God, this is what you have to do,’ ” he told me.

Many of this era’s chefs claim to be obsessed with seasonality and local sourcing; for Yamasaki, it’s a life style, an all-encompassing pursuit. After taking swimming lessons, he learned to spearfish, and to free dive, so that he could gather fish, sea urchin, and lobster by hand. Without a commercial license, he wouldn’t be able to sell what he caught; he realized that if he wanted a steady supply of the best possible fish for Yess, he’d need some local fishermen to take up ike and shinkei jime. Most of his cold e-mails and Instagram D.M.s went unanswered. Finally, Eric Hodge, an auto mechanic in Ojai who’d been fishing commercially for a few years, agreed to take him out on the water for a demonstration. Hodge was amused that Yamasaki was prone to seasickness. “I think he threw up all day,” Hodge said, of their first fishing trip. But, after tasting what they’d caught and butchered, he was convinced that Yamasaki was on to something.

Yamasaki told Hodge that if they created a market for the product, and got other chefs and fishermen excited about the technique, Hodge could triple his revenue. (Hodge overshot this almost immediately.) Soon afterward, Yamasaki met Mitchell, who supplies seafood for his own restaurant, Dudley Market Venice. “What we learned, especially from Junya, was way more about the philosophy of why you’re doing it,” Mitchell said. “It’s not just ‘Run the wire down the fish.’ It’s about the fact that you’re trying to care this much from the second you take this fish’s life.” Within a few years, ike and shinkei jime became the gold standard for locally caught seafood in L.A. Among the prestigious restaurants to which Hodge sold his catch was Providence, in Hollywood, one of only two restaurants in the city to earn three Michelin stars.

In El Segundo, just north of Manhattan Beach, the founders of a startup called Seremoni have designed and manufactured a machine, the Poseidon, that performs an automated version of ike jime, with the goal of making high-quality fish more accessible. The company installs Poseidons, each about the size of a phone booth, on the boat decks of local fishermen, then purchases the catch at a premium. Each fish is slipped into a tubular opening of the machine, as if going in for an MRI, and then an A.I.-powered sensor determines where on its head to insert a mechanical spike. Restaurants, including Eleven Madison Park and Le Bernardin, in New York, have started serving what the company calls “Seremoni-grade” fish. Yamasaki himself serves the brand’s black cod.

Though I admire the ingenuity and idealism behind Seremoni, it was easy to see, on the Jamaica Day, what would be lost by delegating any part of the process to a robot. As we motored offshore in the morning, the brisk wind lashing our faces, we spotted a pair of sea lions dozing on the surface of the water; later, dolphins arced around us in every direction. Several times, at dusk, after the group had agreed to pack it in, a flash on the radar or a fresh flock of birds inspired Mitchell to whip the boat around and chase one more catch. When I remarked that the addictive thrill of deep-sea fishing seemed not unlike that of gambling, Mitchell laughed and said, “I think just as many people have lost their wives doing it.” As the sun set, he grew reflective. “The thing I’ll never get over is how there are so few people out here, and we all know each other,” he told me. “It’s the greatest place to be alone in L.A. I hope the TikTok kids never figure it out.” ♦