The Pacific bluefin tuna population has declined by 96.4 percent since fishing began, according to a just-released scientific assessment.

The assessment was made by the International Scientific Committee for Tuna and Tuna-Like Species in the North Pacific Ocean (ISC), a body established in 1995 to provide scientific advice to the region's fishery management bodies. According to Amanda Nickson, director of the Pew Environment Group's global tuna conservation program, although there have been some previous efforts to determine population levels of Pacific bluefin, “there are a lot of different models for fish stock assessment, and so you're not always comparing apples to apples. So from our perspective this is the first truly comprehensive assessment that we've seen."

The ISC report is laconic in its conclusion that the biomass of Pacific bluefin “is near historically low levels and experiencing high exploitation rates," and that “extending the status quo fishing levels is unlikely to improve stock status." Nickson argues, somewhat more forcefully, that the way in which Pacific bluefin has been fished and managed amounts to an entirely predictable recipe for disaster.

“Over 90 percent of the catch is juveniles, caught in nursery and spawning areas," she explained to Discovery News. “Literally, the zero-to-three-year age class, so they're being caught on their spawning grounds before they can reproduce, with no catch limit – and gee whiz, we're at 3.6 percent of the original population. I wonder why?"

Amazingly, she says, the first catch limit for the species wasn't established until last year, and even then only in the eastern range of a species that migrates across the Pacific Ocean. It didn't take long for it to be exceeded.

“The 2012-2013 catch was not to exceed 10,000 metric tons, and specifically not to exceed 5,600 metric tons in 2012," she explained. “However, in 2012, the catch was more than 6,600 metric tons and so the fishery was shut down in August."

The ISC assessment comes just days after a Pacific bluefin was sold for a record $1.76 million at Japan's Tsukiji fish auction. And while such exorbitant prices are at least as much a function of bidders willing to take a massive loss in exchange for the publicity attached to buying the first bluefin of the season, monetary value and ecological impact are hardly unconnected.

As John Hocevar of Greenpeace explained to Discovery News after reading the ISC report: “It looks like overfishing has been happening since the 50s or 60s. When people are still willing to spend a million dollars on one of the last bluefin in the ocean, that's a recipe for extinction."

Nickson argues that, at least for a while, it is time for the fishery to be shut down.

“Our view is that the most responsible course of action is to suspend the fishery and then ensure that there are appropriate, scientifically-informed management measures in place," she explains. “The kind of things that would need to be in place in the future would be minimum size limits for catch of Pacific bluefin, and a good strong hard catch limit that covers the entire Pacific basin, along with improved management and enforcement."

Whether the countries involved in Pacific bluefin fishing – primarily Japan, South Korea, Mexico and the United States – will take those steps remains to be seen, however.

“We are waiting to see what the countries involved will do by way of taking action at this point," Nickson says.

Photograph of Pacific bluefin tuna by Richard Herrmann/