Can bluefin tuna farms work?

Scrawled on the white board hung behind the bar at Noshi Sushi in Los Angeles, the word "otoro" (fatty tuna) beckons seafood lovers. For the connoisseur, this is the main attraction, the filet mignon of sushi.

Atop a small mound of rice, a heavily marbled slice of fish sits precariously — so oily that it's on the verge of falling apart. With one bite, the exquisite cut of bluefin will melt into oblivion.

Bluefin tuna may not be a household name, but its taste and texture are famous — and increasingly infamous — among sushi aficionados across the world. Hailed as the finest cut of tuna sashimi, the oily, fatty belly of the bluefin has also found its way onto many do-not-eat lists among consumers and environmentalists because the fish's numbers have plummeted in recent years.

PHOTOS: Bluefin tuna farms

With the advent of commercial fishing operations and a skyrocketing global appetite for sushi, the Atlantic bluefin has suffered from rampant overfishing. According to the International Commission for the Conservation of Atlantic Tunas (ICAAT), its numbers are now 70% below their 1970 levels.

As some sushi fans scramble to find sustainable yet equally decadent alternatives to the bluefin, commercial fishing operations are looking for ways to minimize the effect on wild stocks.

Today, a glimmer of hope for guilt-free bluefin tuna lies south of the border. Umami, an Icelandic seafood conglomerate, purchased a Mexican aquaculture operation in late 2010 and is ranching what it calls "sustainable" Pacific bluefin. It's one of several bluefin ranches that have cropped up in waters across the world.

Though 90% of bluefin is consumed in Japan, sushi's popularity has exploded in the U.S. in the last 20 years, and with it came high demand for the fatty underbelly of the bluefin. But with diminishing numbers of wild-caught fish available, sushi chefs are turning to ranched tuna to fulfill the demand.

Kenshi Yamada, sushi chef and owner of Noshi Sushi, began serving the Baja-farmed bluefin six months ago. "The farmed fish tastes a little different, but most people can't tell the difference in taste. It has a little more fat than the wild fish," he says.

Umami sees the market opportunity but faces the challenge of meeting the demand in a way that will please the connoisseur and environmentalist alike.

"It's really hard to have sustainable and bluefin sort of in the same sentence. It's always a bit of an oxymoron," says Peter Bridson, aquaculture research manager at the Monterey Bay Aquarium, an oceanic research and conservation institution.

The bluefin's migratory nature, as well as relatively slow sexual maturity, compounds the problem with fishing it sustainably. The Pacific bluefin spawns in the waters between the Philippines and southern Japan, then migrates more than 6,000 miles to Baja. The Pacific bluefin is closely related to the Atlantic bluefin and for years was considered to be the same subspecies.

"The tuna come over to Mexico when they're 1 to 2 years old, and then when they're 5 to 6 years old they start migrating back over toward the other side of the Pacific to reproduce," Bridson says. "So every tuna that's caught in Mexico — whether it's eaten directly or whether it's stuck into the ranch — is not going to be able to reproduce."

The Obama administration in May declined to protect the Atlantic bluefin tuna under the Endangered Species Act. The National Oceanic and Atmospheric Administration instead classifies it as a species under concern while it awaits updated data outlining the effect of more-stringent fisheries management under ICAAT.

In 2010, the administration backed a proposed ban on the international trade of the Atlantic bluefin tuna at the Convention on International Trade in Endangered Species. The proposal ultimately failed to get the necessary two-thirds vote of represented nations, due in large part to staunch opposition to the ban by Japan, a huge consumer of bluefin.

Though the Atlantic species is under the greatest threat, concerns also loom over the Pacific bluefin, which Umami catches in its pens.

"There has never been an instance of a fish caught to extinction," says Karl Petur Jonsson, an Umami spokesman. "It's not like the American buffalo. The fish are down there."

But, in fact, fisheries have collapsed before. Notably, the cod population off Newfoundland served as a subsistence food source for centuries but was wiped out in the 1990s by industrial fishing fleets. Moratoriums were introduced in an effort to allow stocks to replenish naturally — but the cod have yet to return in anything like their previous numbers.

Umami-owned Baja Aquafarms operates two concessions off northern Baja California — 21 pens tucked behind the Coronado Islands — and an additional 11 pens 70 miles south, off craggy Salsipuedes. Each of these 100-foot-deep floating feedlots holds roughly 60 tons of the prized fish.

Starting every year in the late spring, a fleet of boats, aided by spotter planes, catches and hauls fish back here for systematic fattening and eventual slaughter.

Unlike meat sources such as beef, pork or even salmon, which are bred and farmed, even ranched tuna must be considered a "wild" animal source. Bluefin tuna, which average 600 pounds at maturity, are notoriously difficult to breed in captivity, and thus, ranches such as Baja Aquafarms must catch wild tuna, only to fatten them up to increase the yield of meat. But because the fishermen are taking from an already depleted population of fish, the sustainability of such practices is questionable.

Still, Umami, which reported sales of $42 million in the fiscal third quarter ending March 31, with a profit of $10 million, says its operations have lessened its environmental footprint.

"Our operations are fundamentally different from other operations in the way that we farm the fish longer," Jonsson says. "The amount of fish we have to catch from the ocean is less, and the overall utilization of natural resources is better."

He points out that ranches once would feed an individual bluefin only for a few months, but they are now fed for up to three years to weights of close to 300 pounds — minimizing the number of individual fish that need to be caught while maximizing each fish's yield of flesh.

Javier Vivanco has managed the daily operations at Baja Aquafarms for a decade. He pulls up to the young adult pens to give the tuna their second feeding of the day. The bluefin boil up to the surface clockwise while a legion of sea lions bark and dive for scraps.

"We're not using pellets of artificial feed. We're using real food — the natural feed source of the bluefin," Jonsson says as he motors out of the San Diego harbor.

Fresh, locally caught sardines are shoveled into the pens daily by the boatload. Jonsson touts Umami's feed conversion ratio — the weight of feed mass converted into body mass — as 17 to 1, meaning it takes 17 pounds of sardines to make a single pound of bluefin flesh in these waters off Baja.

By comparison, according to Monterey Bay's Bridson, farmed salmon require 3 to 4 pounds of feed per pound of weight gain. "The bluefin is very energy intensive," he says. "It's more like a Ferrari than a Toyota Prius in that respect. It's a really difficult species to ever grow sustainably."

But Jonsson is quick to note that in the wild, bluefin take nearly twice the toll on bait fish, eating 30 pounds for every pound of growth.

While Umami highlights its measures of sustainability, it is working on developing a "closed-loop cycle," the process of spawning bluefin in captivity and raising them to market maturity. But this is a project in its infancy. To date, only Kinki University in Japan, a pioneer in aquaculture, has been able to successfully hatch bluefin eggs in a lab, raise the fish — known as kindai — and sell the mature fish commercially. With three generations of fish spawned in captivity, Kinki no longer needs to take fish from the sea.

Although the closed-loop cycle for bluefin may represent the last best hope for saving the species, even this is not a long-term solution, according to Monterey Bay's Bridson. "The best way to be eating bluefin is to reduce our consumption down to what we can catch from a very well-managed, sustainable fishery, and it's probably not a species that should ever really be farmed or ranched."

food@latimes.com

A documentary on the state of the bluefin tuna is scheduled to air at 7 and 10 p.m. July 21 on Current TV.

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