Setting the Record Straight on Bluefin Tuna

Last week, I received a comment on a recent blog accusing me of posting a “factually flawed” and “extremely misleading” report of a new study by the International Union for the Conservation of Nature (IUCN) on the dangers facing global bluefin tuna populations.  The commenter cherry picked facts to create a misleading and overly rosy depiction of the current status of bluefin tuna around the world.  Below, I rebut his specific assertions and inferences to set the record straight.

According to the Science paper’s summary of the IUCN report:

"All three bluefin tuna species (southern bluefin, Thunnus maccoyii; Atlantic bluefin, T. thynnus; and Pacific bluefin, T. orientalis) are highly valued, long-lived, and large-bodied marine fishes, with geographically restricted spawning sites, as well as relatively short spawning periods of 1 or 2 months, all of which make them susceptible to collapse under continued excessive fishing pressure.  Southern bluefin has already essentially crashed (its current adult biomass is about 5% of its estimated virgin biomass), a trend that is similar to the western Atlantic bluefin, whose population was greatly reduced in the 1970s, with little sign that the population is rebuilding."

The commenter asserts that “nobody understands” how IUCN came to these conclusions.  Well, the fisheries scientists who conducted the report, as well as the experts who carry out the regular stock assessments on which it’s based, appear to have a clear understanding of what drove these conclusions.  As to the commenter’s specific assertions regarding bluefin, here are some specific responses:

First, he claims that Atlantic bluefin tuna is at 57% of its “virgin” biomass and that it will rebuild to its “virgin” status within 10 years.  While it’s true that the most recent 2010 ICCAT Stock Assessment estimates a current spawning stock biomass of 57% of levels in the late 1950s for the Eastern/Mediterranean stock of Atlantic bluefin (the Western Atlantic stock is managed and assessed separately, but more on that in a moment), this actually equates to 35% of a reasonably healthy population level (i.e., the level required to achieve so-called maximum sustainable yield, the largest catch that can be taken for a species on an ongoing basis) and to an even lower proportion of the unfished, “virgin” population.  Moreover, accounting for high catches in recent years, much of the decline has been in just the last decade.  According to ICCAT, the stock is overfished (hence the need for a rebuilding plan) and still undergoing overfishing, meaning the rate of catch is higher than the level needed to achieve maximum sustainable yield.

The rebuilding plan predicts a 60% chance of rebuilding the stock to a reasonably healthy level by 2022 if catch is restrained to 13,500 metric tons per year, well below recent reported catch levels.  The commenter asserts that “the stock is readily rebuilding” merely because a plan has been adopted.  Yet, the reduction in catch levels necessary for achieving the plan’s rebuilding goals are well below recent catch levels, and those reported catch numbers are themselves considered highly underestimated due to pervasive illegal, unreported, and unregulated fishing.  According to ICCAT:

“Information available has demonstrated that catches of bluefin tuna from the East Atlantic and Mediterranean were seriously under-reported between the mid-1990s through 2007.  The Committee views this lack of compliance with TAC and underreporting of the catch as having undermined conservation of the stock.”

The average reported catch from 2000-2009 was just under 31,000 metric tons and that excludes illegal, unreported, and unregulated catch, so it will be a major challenge to restrain all sources of fishing mortality – both legal and illegal – below the new rebuilding quota of 13,500 tons.  While we hope that the commenter’s optimistic outlook on rebuilding comes true, it’s hard to imagine absent much improved compliance and enforcement given the amount of illegal harvesting that has, and seems likely, to continue.

The Western Atlantic bluefin stock is even more depleted.  According to NOAA Fisheries Service, Western Atlantic bluefin is both overfished and subject to overfishing.  The IUCN study shows a 72% decline in spawning stock biomass over the past four decades, based on ICCAT 2010 data.  In addition, last year’s Deepwater Horizon oil disaster, which overlapped temporally and spatially with some bluefin spawning, may have significant impact on population levels in the years to come.

The most recent stock assessment for Southern bluefin reports current spawning stock biomass at about 5% of “virgin” biomass.  In response, catch levels for 2010 and 2011 were cut to 9,449 metric tons, which is about 65% below the average catch from 1994 to 2009.  However, simply lowering the allowable catch absent stronger protections against IUU fishing will not magically prevent overharvest of this extremely depleted fish population, especially given the powerful economic incentives to skirt the law (see my colleague’s blog on the impact of bluefin prices on the species’ survival).

Pacific bluefin is currently estimated at between 40-60% of “historically observed biomass,” according to IUCN’s latest report.  NOAA Fisheries lists the species as currently subject to overfishing.  The latest stock assessment projects that recent catch levels, if continued, could diminish the stock to 25% of historic biomass or less within a generation.

These are the facts.  (Although the comment's author did not divulge this, the comment was posted by a public relations executive for Atlantis Group, a multinational seafood supply company that specializes in bluefin, according to LinkedIn.)

Let’s stop wasting time with an artificial debate and start discussing solutions. 

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