Opinion - Tuna-tarianism

‘Tunatarianism: the practice of subsisting on a diet composed on any digestible food except products containing tuna.’

Let’s be clear, I just made that up – nothing like that officially exists and I’m pretty sure I’m the only ‘tunatarian’ out there. Now, before you press send on the hate mail, I do not want to convert anyone nor do I want to talk about my principles. I simply get a lot of questions which is why I’m going to try to explain the science behind my decision not to eat tuna – whatever you do with it, you decide.

The huge debate about tuna, played out world-wide in the press, revolves largely around only one species: the Northern Bluefin Tuna (Thunnus thynnus). Hunted to the brink of extinction with populations worldwide plummeting to about 10 percent of their normal numbers, it is not hard to see why the focus lies here. It is a charismatic fish too, as far as fish go, measuring up to 4.5m and fetching up to US$300.000 per fish(!) on the Japanese market.

Frozen tuna on their way to the Japanese market. Photo EPA

The term tuna, however, encompasses much more than just this one species. As far as we know there are over 48 species of tuna, widely but sparsely distributed throughout the oceans of the world. Over 99% of the yearly commercial catch consists of only seven species: Skipjack (Katsuwonus pelamis – 60%), Yellowfin (Thunnus albacares – 24%), Bigeye (Thunnus obesus – 10%), Albacore (Thunnus alalunga – 5%) and three species of Bluefin (Thunnus thynnus, Thunnus orientalis and Thunnus macoyii - 1%). These are the species I’ll talk about in the rest of the article.

What you find in your sushi and as a steak in supermarkets and restaurants usually comes from the larger species (yellowfin, bigeye and bluefin). The stuff in the tins is mostly comprised of Skipjack, one of the smallest tuna species fished commercially and at the moment also one of the most stable population-wise. A note of concern however, the pressure on its population is immense and still rising fast.

The reasons for my tuna-tarianism are three-fold: the fact that all tuna species are apex predators and have an enormous impact on the overall marine ecosystem, the flawed manners of harvesting them and the seemingly impossible task of negotiating capturing pressure by farming. I will explain these in more detail.

Ecological impact

In general, the impact of any nation’s fisheries is described in terms of the raw tonnage of fish it catches. This gives a skewed picture of the real impact on marine life. The problem is found in the food chains of the ocean. The impact of every fish on the overall ecosystem is different.

Very roughly, the aquatic food chain can be broken down in four layers. The base is formed by water plants and small plankton that derive their energy from the sun (called photo-autotrophs – photo = light and auto = self, meaning literally feeding itself on light). The layer above feeds on them, called herbivores (plant-eaters). Then we come to the carnivores (meat-eaters) that feed on the herbivores. Last, and on top of the pyramid, we find the apex predators, the ones that feed on the carnivores.

Illustration by National Geographic, food chain data from FishBase.

As a rule animals get larger as they move up in the food chain. There are also less of them, they breed slower, become older and are less resilient against hunting. And they depend on the lower layers in the food chain to survive. Tuna eat enormous amounts of fish, including mid-level predators like mackerel, which in turn feed on fish like anchovies, which prey on microscopic plankton. A large tuna must eat the equivalent of its body weight every ten days to stay alive, so a single 500kg tuna might need to eat as many as 15.000 smaller fish in a year. Such food chains are found throughout the world's ocean ecosystems, each with its own apex animal. Any large fish—a Pacific swordfish, an Atlantic mako shark, an Alaska king salmon, a Chilean sea bass—is likely to depend on several levels of a food chain.

In the terrestrial ecosystems, the apex predators are widely known – lions, tigers, wolves. In the ocean they are not as well received. Sharks, killer whales, swordfish, tuna - they are feared, little researched and mostly just food. If, for sake of comparison, the giant bluefin lived on land, its size (4.5m), speed (70km/h), and epic migrations (entire pacific several times over) would ensure its legendary status, with tourists flocking to photograph it in national parks. But because it lives in the sea, its majesty lies largely beyond comprehension.

All tuna species are apex predators, also the smaller ones. These don’t quit need the same number of fish to sustain themselves as the large species do, but the principle is the same. In terms of impact on the overall ecosystem, a pound of tuna on average represents roughly a hundred times more impact than a pound of sardines.

To me, the commercial exploitation of an apex predator on the scale we do now, is illogical, not natural and obviously unsustainable. We’re eating too much above our food chain level.

Fishing methods

In the current situation, rich nations tend to favour and buy large apex predators like tuna instead of smaller fish lower in the food chain. As a result, fisheries have explored every corner of the worlds ocean with increasing efficient fishing methods.

Pole and line

Pole and line fishing of tuna on a 'commercial' scale

The least invasive technique to catch a tuna is called pole and line fishing - you know, the thing dads do with their sons. A report in 2009 estimated about 11% of the world’s tuna production is caught this way. It is a very selective technique with not much chance of any by-catch (considering most fisherman can tell the difference between a dolphin and a tuna), it has a small ecological impact and doesn’t generally occur too far from shore. It is a labour intensive technique and very likely cannot supply the current demand from the developed nations.

Also, it still relies on live bait. A study published this month suggests that if the Pacific Islands were to provide all the tuna they currently provide, but only through pole and line fishing, catching all the bait fish required would seriously deplete stocks of those species such as anchovy.

Purse-seine

By far the most common technique used today, taking about 62% of the world production, is a method called purse-seines. A seine is a common fishing net, weighed down at the bottom and held vertical in the water by floats at the top. The purse-seine has an extra feature. It has rings at the bottom with a rope through them. When the rope is pulled it draws the rings together, closing the net at the bottom, like an old-fashion purse. It is a widely used technique, catching fish species that school.

The obvious problem is their indiscriminate nature, catching everything within the reach of the net. Taking into account that schools of tuna are often visually located by dolphin activity, the by-catch of these is considerable.

Bluefin tuna caught in Norway with purse seine method. Photo: Edvin Bakkevik & Arne Saltskar

This problem has sparked the use of another device, called a FAD, a Fish Aggregating Device, to help find tuna without relying on dolphins. The principle is based on a quirky behaviour most fish display: their fascination with floating objects. Simply: stick anything large in the open ocean - a buoy, a big log, a raft, whatever – and many marine species will be attracted to it and start living around it. The reasons for this behaviour are not exactly clear and vary per species. But fisheries have used it to their advantage, deploying sophisticated objects equipped with sonar and GPS into the ocean, sweeping up the catch whenever it tells them the time is right. The problem is that most tuna species around these objects are mingled, not discriminating large species from small, targeted species. They are also generally mixed with a variety of shark species, many of which are (highly) endangered.

Longline

The third method used widely, catching about 14% of the world’s tuna production, is longline fishing. As the name suggests is uses long lines, with lots of side-lines containing hooks to catch fish. Lines are often several kilometres long, containing generally over 2500 hooks. The method became controversial because of its considerable by-catch of sea-turtles, albatrosses and other seabirds.

My point is that at the moment it is impossible to tell where your fish comes from and how or when it was caught. Most of the time you don’t even know exactly what species of fish you are eating – only something under the common denominator ‘tuna’. To me, that is not nearly good enough.

Farming

Many nations, meanwhile, are trying to compensate for the world's growing seafood deficit by farming or ranching high-level predators such as salmon and tuna. Atlantic bluefin are already ranched in great numbers — taken from the wild and fattened in net pens with wild forage fish like herring and sardines. Taking in consideration the amount of lower-level species these apex species need, outlined earlier in this article, this promotes a new problem altogether.

Some countries are even trying to raise them completely in captivity, successfully creating (or at least claiming to) third generation farmed tuna. How much of this is true and how stable this is remains unclear. Remember we’re not talking sheep here, this is like farming lions in a 10x20m cage, feeding them with wild-caught mountain goats. Apex predators have never ticked the box of being great staple foods, being too wild to tame, too large to hold in small farms and feeding on meat, not plant-material. I wonder why it would be so different in this case?

If Atlantic bluefin is not farmed, it will most likely become an even more scarce luxury item. Global fishing moratoriums on the species have been proposed (and then rejected by the many nations that catch or buy bluefin, notoriously Japan). But other options being discussed include drastically reducing fishing quotas in the next few years and closing spawning grounds in the Mediterranean and the Gulf of Mexico to fishing entirely.

Perhaps, in the end, this is what the Atlantic bluefin tuna might really need. Not human intervention to make them spawn in captivity. But rather human restraint, to allow them to spawn in the wild, in peace.

Other options

In my opinion, tuna is emblematic of a lot wrong with today’s global fisheries and especially consumer ignorance: wild-caught, apex species driven, negligent stock management and consumer’s indifference to the fate of the species they eat.

Not all is bad of course. The skipjack tuna populations remain resilient even though there is extreme fishing pressure on them. Large companies are looking into better fishing methods and developing countries are starting to get a word in. Just a few weeks ago in a speech in New Zealand, Professor Ray Hilborn of the University of Washington said that when it came to the vast majority of tuna species, there were as many tuna in our oceans as there were 60 years ago – which is true. Remember that of the 48 species, only seven are commercially harvested, the other 41 species remain largely untouched and healthy.

Consuming fish is extermely healthy for a human being and it is a great part of a balanced diet. But our approach of consistently and automatically reach for the large apex predators like salmon and tuna is not balanced at all.

Today there are many alternatives available that are worth considering, like eating lower on the marine food chain thus reducing the overall impact on marine ecosystems. For example, buying farmed tilapia instead of farmed salmon, because tilapia are largely herbivorous and eat less fish meal when farmed; choosing trap-caught black cod over long-lined Chilean sea bass, because fewer unwanted fish are killed in the process of the harvest; and avoiding eating apex predators like tuna altogether, because harvesting them in commercial numbers is simply unsustainable.

There you have it, my reasons for being a tunatarian.