(Saving Seafood) June 25, 2013 — On June 26, the International Commission for the Conservation of Atlantic Tunas (ICCAT) will convene in Montreal to discuss the stock assessment for Atlantic bluefin tuna. In advance of the meeting, a debate has arisen among marine scientists, environmental groups, and industry stakeholders over the appropriate level of allowable bluefin harvest. This debate revolves around several unresolved scientific questions about the nature of the bluefin stock. How those questions are addressed at the Montreal meeting will impact how the international bluefin quota is set.
Bluefin: Low vs. High Recruitment
One of the more pressing unresolved issues in bluefin management is the most appropriate way to estimate "recruitment," the number of bluefin that are born into the population. Based on the level of recruitment, fisheries managers predict the future growth of the stock and what level of catch will enable it to reach a biomass that can produce the maximum sustainable yield. If the stock is not found to be at its projected biomass and recruitment targets, it is considered overfished.
Currently, there are two hypotheses about the trajectory of bluefin recruitment: a "high recruitment" and a "low recruitment" scenario. According to the "high recruitment" hypothesis, annual reproductive success is a function of the number of spawning females in the population at any given time; the more spawners there are the more offspring are predicted to grow and become adults. Under a "high recruitment" scenario, the bluefin population is predicted to be able to reach levels far higher than currently observed. If the "high recruitment" hypothesis is correct, bluefin should be able to reach levels not seen since before the 1970s. If they are not seen at those levels, the result is assumed to be due to overfishing. Managers would then set lower catch limits that are restrictive until that level is again reached.
The "low recruitment" hypothesis holds that bluefin reproductive success in any given year is more a function of the prevailing environmental and ecological conditions affecting such diverse factors as spawning behavior and the survival of bluefin eggs and larvae. Adult female bluefin tuna can produce huge numbers of eggs, but how many actually survive to become adults themselves is determined by natural conditions. Such conditions are currently believed to favor relatively lower recruitment and a smaller achievable biomass. Under this scenario, the stock levels currently being observed are at just about the levels the low recruitment hypothesis predicts. It therefore does not make sense to restrict the catch further in an effort to achieve a higher biomass, because natural factors prevent the stock from ever reaching those targets. The low recruitment scenario hypothesizes that natural environmental and climatic changes — not overfishing — are the reasons for the smaller stock sizes since the 1970s, and catch levels and expectations should be managed accordingly.
Under a high recruitment scenario, bluefin would currently be considered overfished, and catch levels would need to be reduced to zero for many years in order to reach the higher biomass target. But under a low recruitment scenario, bluefin is not considered overfished, and the quota could be safely raised from the current 1,750 metric tons to as much as 2,600 metric tons.
10 Members of Congress Call for an Increase in Bluefin Quota
A bipartisan group of three Senators and seven Representatives — all of them active in US fisheries policy — wrote to Russell Smith, NOAA's Deputy Assistant Secretary for International Fisheries, who will serve as head of the U.S. Delegation at the ICCAT meeting in Montreal, where managers will decide between the highly debated "low" and "high" recruitment scenarios.
The lawmakers noted ICCAT's "progressive reduction" in Atlantic bluefin tuna Total Allowable Catch (TAC) over the past decade, remarking "the U.S. allocation of this stock may be insufficient to sustain our traditional and valuable U.S. fisheries in any given year."
The Senators and Representatives stated that they are aware of the scientific debate, noting, "Much of this debate centers on the choice managers must make between the so-called 'low' and 'high' recruitment scenarios which relate to the relationship between the estimated size of the spawning stock and annual levels of reproduction. The upcoming ICCAT inter-sessional meeting in Montreal, Canada presents a substantial opportunity for the U.S. and other ICCAT nations to collectively resolve the 'high-low' recruitment issue and make progress on other critical scientific and management issues."
"Specifically, we ask you to pursue all possible means to secure an increase in the TAC for the western Atlantic bluefin tuna stock within the range of ICCAT scientific advice," wrote the lawmakers.
The positions taken by the U.S. Government at ICCAT in recent years have been a point of contention for industry members, who feel they have been betrayed by NOAA's international policies and negotiating positions.
"I'm grateful to the Members of Congress and the Senate who have been longstanding supporters of the pelagic longline fishery and all U.S. bluefin tuna fisheries. Unfortunately, in recent years, positions advanced by U.S. negotiators at ICCAT have ignored the interests of our American fishermen,'" stated Ernie Panacek, President of the Blue Water Fishermen's Association. He continued, "As a result, valuable U.S. fisheries, including bluefin tuna and swordfish, are being strangled by our own government. The Magnuson-Stevens Act mandates that our domestic fisheries management balance the dual objectives of resource sustainability and fishery viability. That same perspective needs to be reflected in our international fishery management efforts."
Pew Asks ICCAT for "Precautionary Management"
On June 12, The Pew Charitable Trusts' Director of Global Tuna Conservation, Amanda Nickson, sent a letter to ICCAT members asking that they take "precautionary" measures when deciding the global TAC for the stock at their Montreal meeting.
Ms. Nickson's letter was prompted by Pew's concern that some ICCAT member governments were allegedly requesting a total catch increase based on future stock projections. Along with the letter, Pew presented a "factsheet", a "White Paper" outlining the history and science surrounding the debate, and a five-minute video.
"Best Available Science" vs. "Unsupported Hypothesis"?
The Pew "factsheet" titled "The Best Available Science on Western Atlantic Bluefin Tuna ," divides the current scientific debate over bluefin into "best available science," which Pew says should be accepted, and "unsupported" hypotheses, which should be rejected. Of these issues, Pew considers the low recruitment scenario as not being supported by the "best available science," stating, "there is no evidence of an environmental change that would have caused a permanent reduction in recruitment." They also dismiss as "unproven" a hypothesis that bluefin mature earlier than age 9, as currently accepted by ICCAT.
But Pew's conclusions on what is the "best available science" and their labeling of other alternatives as "unsupported hypotheses" have been called into question by prominent fisheries scientists. A response to Pew's materials, written by Dr. Steve Cadrin, of the University of Massachusetts School for Marine Science and Technology, and President of the American Institute of Fishery Research Biologists; Dr. Molly Lutcavage and Ben Galuardi, of the University of Massachusetts Large Pelagics Research Center; and Dr. Walt Golet, of the University of Maine, calls Pew's "factsheet" an "irresponsible distortion of the information available to justify reductions in fishing."
In their response, the scientists point out that "Atlantic bluefin tuna stock assessments are highly uncertain, primarily because of the highly migratory nature of tuna as well as the diverse, expansive and international fisheries for tuna," and that "many aspects of Atlantic bluefin tuna biology are not known definitively, and alternative hypotheses should be considered by scientists and fisheries managers."
They conclude that the "the Pew factsheet is a subjective selection of information, lacks scientific credibility and appears to be agenda driven." Highlights of their argument are presented below.
The Relationship Between Stock Size and Recruitment
Pew dismisses the low recruitment hypothesis as "unsupported," but this is not a view backed by ICCAT. The Commission has instead concluded that there is not enough evidence to definitively prove that either recruitment model is correct. As a result, ICCAT presents stock managers with projections based on both scenarios in their reports. As the response to the Pew "factsheet" notes, the last Bluefin Tuna Stock Assessment Session in 2012 stated: "this year, the Group maintained the two alternative spawner-recruit hypotheses explored in several prior assessments: the two-line (low recruitment potential hypothesis) and the Beverton and Holt spawner-recruit formulation (high recruitment potential hypothesis)."
Far from being unsupported, there are several pieces of evidence backing the low recruitment model. The range of the species has contracted, with bluefin no longer appearing in some areas, such as off the coasts of Norway and Brazil, where they were once prevalent. Temperature shifts associated with the North Atlantic Oscillation (NAO) have also been observed since 1970, which, along with other climatic and environmental variability in the marine ecosystem, may have influenced the growth of the bluefin population.
The Age of Bluefin Maturity
Pew also errs in its account of bluefin maturity, the age at which the fish are able to begin reproducing. Like recruitment, not much is known conclusively about the age of bluefin maturity, and there are several possibilities considered to be plausible by ICCAT, which concluded in 2012, "there remains considerable uncertainty about the maturation of western bluefin tuna." Pew supports the idea that bluefin from the western Atlantic stock begin reproducing around age 9, a theory drawn from samples taken from tuna spawning grounds in the Gulf of Mexico, while claiming that the hypothesis that bluefin mature earlier, possibly around age 5, is "unproven." However, there is substantial evidence supporting this claim.
A 2009 study, "New Results on Maturity Status of Western Atlantic Bluefin Tuna, Thunnus Thynnus," dissected the reproductive organs of a wide sample of bluefin in order to determine when they reach maturity. Among the samples tested, bluefin were found to reach maturity as early as age 5. This indicates that bluefin from the western Atlantic stock may reach maturity much earlier than is currently assumed and, perhaps more logically, at about the same age as their close cousins which spawn in the Mediterranean. According to Dr. Cadrin, the methods used to determine maturity in this study are "much more scientifically credible than the current approach used to estimate maturity, the size frequency of fish in the Gulf of Mexico."
Intentional Misrepresentation?
In their response, Dr. Cadrin and his colleagues noted that Pew cited a "document (Rosenberg et al. 2012) that analyzed stock-recruitment estimates from the 2010 stock assessment to conclude that the information available supports the high recruitment hypothesis. However, when one of the co-authors of the Rosenberg et al. report updated the analysis with stock-recruitment estimates from the 2012 stock assessment, the revised results had nearly equal support for both the high recruitment and low recruitment hypotheses."
"The primary author of the PEW white paper … was an observer at the 2012 stock assessment meeting, and was aware of the revised analysis, but failed to report that important finding in either the factsheet or the white paper. The omission of the most recent results from the analysis reveals a subjective selection of information in the PEW white paper and factsheet."
Who decides? ICCAT or Pew?
What can be considered "the best available science" on bluefin tuna is highly disputed. There is much about the stock that is either unknown or poorly understood. Pew's attempts to dismiss theories that are accepted as valid by the scientific community have also come under fire from industry. "Once again the Pew Charitable Trusts, with this blatantly distorted advocacy paper, shows it intends to buy its way into meddling in the management responsibilities and conservation programs of the competent authorities such as ICCAT," said Rich Ruais, Executive Director of the American Bluefin Tuna Association.
Ruais added that the US "adheres to and utilizes 'the best available science'," and that "it would be irresponsible to base any U.S. policy on the Pew driven bluefin tuna analysis outside of the ICCAT scientific process. The ICCAT Standing Committee on Research and Statistics [SCRS] is the authority and the source for the 'best available science' for shared Atlantic highly migratory fish."
Read the letter from 10 Members of Congress to Russell Smith, Deputy Assistant Secretary for International Fisheries and US Delegate to ICCAT
Read the letter from the Pew Charitable Trusts to ICCAT
Read the Pew document, "The Best Available Science on Western Atlantic Bluefin Tuna"
Read "Response to PEW factsheet on 'The Best Available Science on Western Atlantic Bluefin Tuna'"