Will Bluefin Tuna Be Allowed to Recover?
The Atlantic bluefin tuna are a prized sport fish, a fast-swimming predator of other fish, and a source of high priced sushi in Japan. A mature bluefin can reach seven to eight feet in length and a weight of several hundred pounds. Such a fish is worth many thousands of dollars in the sushi trade. For the last ten years the bluefin population in the West Atlantic has been about 10 percent of its historic or natural level due to overfishing. The international commission that sets catch quotas on the fishery has set a quota of about 2,000 tons of bluefin per year in the West Atlantic during this time. The quota has slowed the decline of the population but has not allowed it to rebuild.
We spoke with Dr. Elizabeth Babcock of the Wildlife Conservation Society about her work to help recover the populations of this extraordinary top predator of the seas.
ER: Dr. Babcock, what is your training?
BB: I got my Ph.D. in fisheries biology from the University of Washington School of Fisheries in Seattle in 1998. After that I got a job at the Wildlife Conservation Society in New York. WCS was founded a hundred years ago as the New York Zoological Society and it does fieldwork all over the world, working with a wide variety of species; for the last five years we’ve been interested in fisheries issues. My job is primarily to work with fisheries stock assessment; that is, the scientific information that is used to advise management of fisheries. I work on bluefin tuna, swordfish and sharks, and I’m starting to work on white marlin.
ER: Why are you interested in those fish?
BB: One reason, of course, is that they are so big and charismatic, but all of these species that we work on are seriously depleted. These are all species that are highly migratory and are fished both within the territorial waters of various countries and also in international waters, which means that it’s problematic to manage them. Historically most of them have been overfished. All of those species I mentioned — bluefin tuna, white marlin, swordfish, and quite a few shark species in the Atlantic — are all overfished.
ER: What is the market for bluefin?
BB: The current fishery is mainly focused on the sushi market. Bluefin tuna are one of the more valuable species in Japan because bluefin tuna, also called toro or fatty tuna, is one of the most expensive and popular dishes in sushi restaurants. That market in Japan is what drives the modern fishery. It’s mainly a long-line fishery, though there is some purse seining.
ER: Where do you work?
BB: I work with the Western Atlantic population of bluefin tuna. We assume that there are two populations on the North Atlantic, one in the Western Atlantic and one in the Eastern Atlantic; the Western Atlantic population is about one-tenth the size of the Eastern Atlantic population. Over the last two years new tagging data indicates that there’s more migration between these two populations than had been assumed in the past. Historically they’ve been managed as if they were two completely separate populations and two completely separate fisheries, but it looks like the migration rates are fairly high. It’s even possible that fish move between the western spawning area in the Gulf of Mexico and the eastern spawning area in the Mediterranean Sea.
ER: The Mediterranean is highly polluted.
BB: It is. Bluefin tuna spawn in the Mediterranean, and the fishery there has been pretty much out of control for the last ten years. There’s theoretically a total catch quota imposed on the eastern fishery, but it’s exceeded every year. Some countries don’t even report their catches, so we don’t have a good idea of what the total catch is in the Mediterranean and in the Eastern Atlantic. That population is certainly declining, and there is a real need for more management and enforcement in the eastern fishery.
ER: Who is responsible for managing bluefin?
BB: I should focus on the western stock, which is the one that I’ve worked on the most. Both the Eastern and Western Atlantic stocks are managed by the International Commission for the Conservation of Atlantic Tuna (ICCAT), which is an international management body that was formed by a treaty among the nations that fish for tuna in the Atlantic.
The ICCAT Commission, which is a political body, makes the decisions about what the total catch quotas can be for each species that they manage, including Eastern and Western Atlantic bluefin. That decision is made on the basis of the scientific report that’s produced by the ICCAT Standing Committee on Research and Statistics, which has working groups on each species that do the stock assessment.
The part where I participate is at these working group meetings that do the stock assessments. The stock assessment meetings have been generally every two years, so there was one in 2000 and there will be one this year in July.
For the Western Atlantic the bluefin population is at about 20 percent of the level that it should be. The current goal of the management is to rebuild to a population level that will allow the greatest catch to be taken every year without depleting the population. Currently the stock is at about 20 percent of that level.
Both the US law and international law require rebuilding to at least that level. The current population is at 20 percent of that level, maybe about 10 percent of what it was historically before the fishery developed. It is quite depleted, even in terms of conservation biology and not fisheries, it’s at a low level.
Bluefin isn’t even the worst of the ICCAT species. The white marlin and blue marlin are both severely depleted and still declining. At least bluefin tuna has stabilized a little bit. It hasn’t declined all that much since the early nineties.
ER: What does the commission do to protect the fishery?
BB: ICCAT has been setting quotas at around 2000 to 2500 metric tons for Western Atlantic bluefin since the mid-eighties. That level of catch is low enough to stop the population from declining any further, but it’s not allowing the population to rebuild to a higher level.
This 2500 metric tons is allocated amongst all of the nations that fish for Western Atlantic bluefin tuna, which is mainly the US, Canada and Japan. Each of those countries has such a small quota that they can only take bluefin tuna as by-catch and they end up discarding quite a few bluefin tuna because they’ve exceeded their quota.
ER: So they’re caught and then thrown back?
BB: Yes. That’s exactly right. Fishermen are not allowed to keep bluefin if they’ve already caught more than their limit, so they throw them back even though they’re already dead. In bluefin tuna science everything is subject to debate. There are a lot of uncertainties, and one of the uncertainties is how many fish are discarded dead every year. The reports in logbooks in the US fishery have been lower than the numbers estimated from observer data.
ER: The quota is an incentive to waste fish.
BB: That’s right, and that’s typical in fisheries. The more restrictive the management has to be, the more discarding there is, particularly when there are limits on how many fish can be landed in a particular trip.
I've seen video from long-line vessels where they have a trip limit of one or two bluefin and they want to catch the biggest fish that they can, so they keep everything they catch and then on their way in throw them all away except for the biggest one. That happens because the quotas are set low because the stock is so depleted; if it could rebuild to a higher level there could be a lot fewer restrictions on the fishery.
ER: The juvenile tuna are probably not living long enough to reproduce.
BB: That’s right. The average age in the catch is fairly low. The fish start to be susceptible to the fishery at age one. They grow quickly when they’re young, so even the one year olds are caught in the purse seine fisheries. Certainly the mortality on the juvenile fish is quite high. That’s one of the main problems.
ER: Is there any place where they’re not fished?
BB: There used to be. The reason that the two stocks in the Western and Eastern Atlantic have been managed separately for so long is that historically there wasn’t much of a fishery in the Central Atlantic.
Twenty years ago ICCAT arbitrarily drew a line at 45 degrees west and assumed that everything west of that was the western stock and everything east of that was the eastern stock. That worked for years because there was no fishing in the Central Atlantic, but then fisheries started expanding out into the Central Atlantic. The central Atlantic catches are mainly counted as eastern Atlantic fish because they’re east of the line, but they’re targeting fish that might not have been susceptible to a fishery before that central Atlantic fishery developed.
There pretty much isn’t any place in the North Atlantic that doesn’t have at least some long-lining effort. There are a few closures in the territorial waters of various countries; there’s a closure in the Gulf of Mexico to protect juvenile bluefin tuna in US waters, but in the high seas there aren’t any closures and I don’t know if there ever will be for bluefin tuna. ICCAT is looking at the idea of having closures in the high seas for protecting juvenile swordfish, and that certainly could be done also for bluefin tuna. It’s a good idea.
ER: How good is the catch data?
BB: One advantage with bluefin tuna compared to some of the other highly migratory species is that most of the catch of bluefin, at least the large bluefin, goes into the Japanese market, which means that you can use data from the Japanese market to determine what the total catch was. So we have at least some understanding of how high the illegal and unreported fishery catches are. That’s not the case for some other species where there’s a lot of fishing on the high seas and we have no idea where the catch goes.
It is possible to control the bluefin tuna fishery with a quota, at least in the West. In the Eastern Atlantic they’ve had less luck in keeping the catches down.
ER: Is that because of lax governmental control?
BB: That, and it involves more countries. In the West it’s pretty much the US, Canada, and Japan; in the East it’s all of Europe and North Africa, plus the high seas fleets. It’s a much more complex fishery involving many nations that have less of a history of controlling the behavior of their fishing fleets.
ER: That puts American fisheries management in a good light for once.
BB: ICCAT is one context in fisheries management where the US and Canada are often the good guys.
ER: What is the plan for bluefin?
BB: ICCAT has a rebuilding plan for bluefin tuna, which means that they are setting total allowable catch quotas that should allow the population to rebuild. It’s a twenty-year rebuilding plan that started in 1998, so theoretically the commission believes that the population will have rebuilt by the year 2018.
The population dynamics models that are used with these stock assessments often produce ambiguous results. At the 1998 assessment there were two different scenarios about the relationship between spawning stock biomass and recruitment of young fish. Those two different scenarios — and no one has any idea which of them was more realistic — ended up giving different results about what the prospects of rebuilding were.
Under one scenario the population would decline and under one it would increase. But then in the year 2000, in the next assessment with the same two scenarios, they were both optimistic. Both predicted that the current quota would allow the population to rebuild in twenty years. That’s in a way, a fluke of the fitting methodology and the data.
We have no idea what’s going to happen at the assessment this year. There’s a lot of political pressure from the fishing industry to raise the quota because there’s some indication that the population might be rebuilding a little bit.
ER: So they want to hammer the fishery again.
BB: Right. Every time the current year’s biomass is a little bit higher than the last year’s the fishermen want to take some of those fish. The idea of keeping the quota low so that the population can rebuild faster is not a popular one politically. Pretty much only the conservation organizations take that point of view, although US law does require rebuilding overfished populations.
ER: What law is that?
BB: The Magnuson-Stevens Fishery Conservation and Management Act says that populations that are overfished must be rebuilt in ten years if that’s possible, and if it’s not possible to rebuild in ten years they have to be rebuilt in the number of years it would take to rebuild if the fishery was closed, plus one mean generation time of the fish population.
The law is specific that populations need to be rebuilt rapidly. Of course, this is ICCAT and ICCAT doesn’t have that ten-year rule.
ER: I understand they are a top predator.
BB: Yes they are, although they’re hunted themselves. They’re the prey of some of the fast pelagic sharks. Mako sharks hunt bluefin tuna.
Shark biologists enjoy telling people that mako sharks can out-swim a bluefin tuna. There’s a quote about mako sharks in Hemingway’s The Old Man and the Sea that I always liked. It said about mako sharks, They were built to out-swim the fastest swimmers in the sea.
ER: Do you have any evidence of them shifting prey species or changing their hunting patterns?
BB: There are quite a few biological studies being done of one sort or another, a lot of work on tagging and on the reproductive biology. For the most part, though, studies that have been done on bluefin tuna have been looking for the information needed for the science that informs management. There hasn’t been all that much diet and food web research because that’s not the information that’s used in stock assessment, or historically that information hasn’t been used in stock assessment.
There is a trend in fisheries toward considering more ecosystem processes in management. To do that sort of thing you need to do more diet studies.
I would say in general the state of knowledge about biology for bluefin is better than many of the other highly migratory species. For this work I’ve been doing on white marlin, I was shocked to discover that no one’s even aged them. One of the first things you need to know is how many fish of what ages are being caught in the fishery and what age they mature so you know whether you are fishing on the immature part of the stock. It’s not known at all for white marlin, even though they’ve been fished for decades. At least we have good catch at age data for bluefin.
ER: Why do we know so little about their biology?
BB: With the highly migratory species for the most part if there is any biological data it’s done by piggybacking on commercial and recreational fishing operations. There’s little data that’s independent of the fisheries, with the exception of some of the tagging information.
ER: What is the relation of bluefin tuna to a can of tuna in the supermarket?
BB: Bluefin tuna is found in cold water, as far north as Newfoundland in the Western Atlantic. The tunas that you get in canned tuna are mainly the tropical tunas. In the Atlantic it’s bigeye, skipjack, albacore, and yellowfin tuna. These are all productive species that live in tropical waters, mainly in upwelling zones. They’re prolific, they can support large fisheries, and they’re mainly caught with purse seines. There’s a big fishery in the eastern tropical Atlantic. There’s another big fishery in the eastern tropical Pacific targeting tropical tunas, and that’s where most of the canned tuna comes from.
ER: What about the prospects for this summer’s ICCAT meetings.
BB: There are a couple issues that we are expecting to address at the meeting this summer. First of all, I mentioned earlier that the 2000 assessment was optimistic. The reason for that was that the population dynamics model that we were using estimated that there were good year classes in 1995 and 1996, some of the highest recruitments that had been seen in the entire time series. That would be good news if it were true, but the numbers of fish in the young age classes are not well estimated by the model because they haven’t been in the fishery for long.
Probably the biggest issue we need to resolve this year is whether those two high recruitments happened or whether it was a fluke in the model fit. If we did get two high recruitments in 1995 and 96, then the signs are encouraging and it should rebuild faster than we expected. If we didn’t get those high recruitments, if with two more years of data we estimate much lower numbers in those years, then the situation might be worse than it looked two years ago. That’s one big issue.
The other big issue is that the working group has decided to try to address this question of migration. So all of the national scientists from the various participating countries have been asked to present their catch data split up by regions so that we can separate out the Central Atlantic.
ER: What effect would that have?
BB: We don’t know what the effect of this new modeling approach will be. We’ve had the assumption that there was an Eastern and a Western Atlantic stock for as long as ICCAT has been managing these species, and it could be that if we move the boundary line or split out a Central Atlantic region that the outputs from the population dynamics models might be quite different, so that might require a higher or a lower quota in the east or the west. We don’t know what the results of that are going to be.
I guess I should say one final word about the political implications of all of this. If the stock assessment this year shows that the population seems to be rebuilding there will definitely be political pressure to raise the quota, but all the environmental groups that work on bluefin of course will be opposing that and trying to rebuild the stock more quickly.
The current total allowable catch is 2500 metric tons, which is about what it’s been for the last twenty years. It seems that if a quota around 2,000 or 2,500 metric tons could rebuild this population it would have done so.
ER: What is the structure of the management committees that make these decisions? Who votes on that?
BB: There are two parts of ICCAT. There’s the scientific process, which is all these working group meetings. The Standing Committee on Research and Statistics meets in September and produces a document that summarizes the information on all the species, and that process is not particularly political. Some scientists who are funded by the industry or by conservation organizations go to these meetings and participate, but it’s a scientific process.
Then the politics starts at the Commission meeting, which is in November every year. Each member nation sends representatives to the Commission that are political appointees. There are three representatives from the US, one of them is from the U.S. government, one is a commercial fisherman, and one is a sport fisherman.
Each nation has its agenda going into ICCAT. Mainly they want to keep their own quotas higher. There’s a lot of horse-trading that goes on because each country has different species that they care about.
Then at the Commission meeting it’s all one big negotiation to see what the end result will be. According to the ICCAT charter they have to reach a consensus, which means that basically any country that wants to dissent from a consensus can prevent a management action from being taken. It’s a painful political process.
But I don’t actually participate in the Commission meetings. The scientific process is much more promising from a conservation point of view. We have been working to get the ICCAT working groups to use methods like decision analysis to deal with all the uncertainty about bluefin tuna biology and fisheries. Over the years, the assessments are becoming more sophisticated, and our ability to predict the consequences of management actions is improving. And the management does depend on the science as well as the political process.