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Eating Tuna

posted by Veronique Koch on 09 November 2012

Since we produced Fish Meat it has been clear to us that tuna, particularly Atlantic bluefin tuna, are not the best choice for farmed seafood. The feed conversion ratio is simply too high, meaning that it takes a lot of fish to feed the tuna that are being raised. Moreover, Atlantic bluefin tuna are an endangered species and in order to farm them young tuna are taken out of the wild and kept in pens, meaning less fish will be available to spawn in the wild to produce the next generations. You can learn more about it in THIS video.


But there is strong evidence that eating fish is highly recommended for human health, since fish contains a high concentration of omega-3 fatty acids and is an excellent source of lean protein. This made us wonder: if you had to eat tuna, if you really can’t resist the temptation, which tuna would be best to eat?


There are actually two things to consider when selecting your tuna, which are their overfished status and their high levels of contaminants. Let’s start with the overfishing.


Which tuna choice is the least harmful to the environment?


According to the Monterey Bay Aquarium’s Seafood Watch program, most types of tuna are to be avoided:


“Tuna are fast-growing fish that reproduce at an early age and produce plentiful offspring – traits that can help them withstand heavy fishing. However, as one of the top three seafoods in the U.S., tuna is in very high demand and many populations are in decline.”

Tuna is the second most popular seafood after shrimp in the U.S., but, like all large predatory fishes,  tuna have declined by 90% globally.


But if you must eat tuna, we recommend investigating how your tuna was caught. There are several ways to catch tuna: purse seines (large nets towed out by boat to surround a school of tuna), longlines (long fishing lines with hooks at regular intervals to catch whatever is passing by), trolling (dragging a fishing line through the water) and even pole-and-line fishing. The first two methods are problematic because they bring in a lot of what is called bycatch, or non-targeted fish or other animals (like dolphins).


This is why the Seafood Watch program recommends choosing troll or pole-and-line caught tuna. The idea is that these fishing methods are much more selective, reducing bycatch. Indeed, even “dolphin safe” tuna, caught using purse seines that give dolphins a chance to escape the net, cause a lot of undue stress to the animals, interrupting their regular feeding and migration patterns.


In terms of species, yellowfin tuna and skipjack are the preferred choices since those fisheries are relatively healthy. These are both found in chunk light tuna. They are both caught mostly using purse seine nets, with some troll or pole-and-line fishing as well.


Which tuna choice is the least harmful to me?


The other problem with eating tuna is that it has been found to contain high levels of many contaminants, especially mercury (which is particularly harmful to the nervous system). Mercury can be naturally occurring or can come from industrial pollution, and once it gets into the air it finds its way into rivers and streams, becoming methylmercury. The process in which contaminants get into tuna and other fish is known as bioaccumulation. One World One Ocean did a great infographic of bioaccumulation here.


Pollutants, such as anthropogenic mercury, are released into the water, where they are absorbed by micro organisms, which are then consumed by small macro organisms, and so on up the food chain until they reach top predators such as the tuna. Tuna eat a lot, which accounts for the high levels of contaminants built up in their bodies.


The Environmental Working Group has created a tuna calculator to help you estimate how much tuna you can safely eat based on your gender and weight (this calculator assumes you do not eat any other seafood). The FDA recommends that pregnant women (who offload their mercury load to their unborn children) and children under 5 consume no tuna at all. The nervous systems, brains, hearts, kidneys and lungs of young children are susceptible to the harmful effects of mercury


However, Dr. Dariush Mozaffarian, assistant professor of medicine and epidemiology at Harvard Medical School and the Harvard School of Public Health says that the benefits of eating heart-healthy omega-3 rich tuna outweighs the risks, and stresses that the limits set by the EPA are conservative by a factor of ten.


So does the choice really come down to damaging your nervous system or risk a heart attack? No. Different kinds of fish have different levels of contaminants, and one can choose wisely. Eating lower on the food chain means that you are eating fish that have bioaccumulated far less contaminants. Examples of these are tilapia or catfish. But if you insist on eating tuna, you have options there, too.


Canned tuna, for example, generally comes in two varieties: albacore and chunk light. Albacore comes in more solid pieces, and is sourced from albacore tuna. These are very large fish, and so they contain high amounts of contaminants. Chunk light is a far more popular choice, possibly because it is generally cheaper. Luckily so, because chunk light tuna is made out of a smaller species of tuna, like the skipjack or yellowfin.



Your best candidates


Going by the criteria above, we went in search of commercially available tuna that would be the least damaging to the environment and your health. Once again, we don’t endorse eating tuna. You’re much better off eating lower in the food chain. But some companies have found a less harmful way of harvesting tuna.


Here is what we found:




Several companies sell troll-caught albacore tuna that is lower in mercury because they catch smaller fish that have not consumed enough fish to be toxic. EcoFish sells canned albacore troll-caught by small family boats in the Pacific Northwest. They are also independently tested for contaminant levels by Seafood Safe.


Skipjack and yellowfin


Skipjack and yellowfin tuna are lower in mercury because they are a smaller species, and companies like Wild Planet Foods sell pole-and-line caught light tuna to ensure they are sustainably caught, as well.




But if you’d really like to eat canned fish, why not try wild salmon? Canned salmon is usually mostly sockeye or pink from Alaska. They are low in contaminants (including the PCBs found in farmed salmon) and are fished sustainably.

One thought on “Eating Tuna

  1. I found out a lot I did not know about different types of tuna in the market, and what would be best. Now have to see how this works out in a grocery store. PS Salmon is not tuna, and doesn’t make a decent sandwich; and I wouldn’t be caught dead buying a can of salmon, as it is squishy-yucky.

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