When I tell Westerners that one of the ocean’s most majestic predators is at risk of extinction due to its status as a luxury food item in Asia, most of them roll their eyes and tell me that they’ve already heard about the ecological havoc wrought by shark fin soup. Sharks, however, are not the only top predator being overfished for high-end cuisine. Human appetites currently threaten all three species of bluefin tuna, and the overfishing may be even harder to stop, because sushi, sashimi, and sesame encrusted fusion filets have achieved levels of worldwide popularity that shark fin soup has never approached.
High global demand for bluefin tuna has led to an industry of tuna farming, but perhaps the better term for these operations would be “loophole piracy”. Tuna farmers behave like the witch in “Hansel and Gretel” by catching large numbers of small fish, confining them to net pens, and feeding them until they grow large enough to be killed and eaten. The reason for this ghoulish behavior is that catch limits on bluefin tuna are set by tonnes of fish, not by numbers of individuals, and by catching large numbers of smaller, lighter fish to fatten in pens, tuna farmers can sell more total tonnes of tuna than the quotas would otherwise allow. This process results in a lot of money, but in no baby tuna, because bluefin destined for farms are caught before they are old enough to breed and although they eventually grow larger, it seems that they would rather die virgins than attempt to mate in net pens. While defenders of fish farming claim that it reduces the need to fish wild species, tuna farming depends on a continued supply of new young wild fish and magnifies the effects of overfishing.
Those who would defend tuna farming point out that laboratories have succeeded in spawning bluefin tuna under artificial conditions, but the process is too expensive to be attractive to commercial tuna farmers (Kawasaki 1-Sep-2014), who continue to use the “Hansel and Gretel” method. Even if closed-loop tuna breeding does become widespread, it will do nothing to solve the problem of tuna-farming being an inherent drain on human food supplies and marine ecosystems. Tuna are one of the few fish that warm their blood metabolically and also, like sharks, must swim constantly in order to breathe. This leads to extremely high energy demands and producing 1kg of bluefin tuna requires 10-20kg of feed (Ottolenghi 2008). Furthermore, as tuna are exclusively carnivorous, all of this feed is generally fish and squid that could have otherwise been used to feed humans or to help sustain seabird and marine mammal populations.
The final defense of tuna farming is that it increases the supply of a highly preferred food item available to rich and middle class consumers around the world. While this is probably true, squandering fish protein to create luxury products in a world where 6 million children die of protein malnutrition each year (Otten et al. 2006) is morally indefensible. Tuna farming is a shameful example of our current economic system prioritizing “profits over people”.
While I won’t deny that raw bloody tuna is delicious, I understand that my taste preferences don’t justify overfishing and food injustice. While farmed tuna is a luxury that some of us can afford financially, the moral cost is much too high.
Kawasaki. 1-Sep-2014. “Nissui closes life-cycle bluefin tuna farming”. undercurrentnews. http://www.undercurrentnews.com/2014/09/01/nissui-closes-life-cycle-bluefin-tuna-farming/
Otten JJ, Hellwig JP, Meyers LD eds. 2006. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. Institute of Medicine of the National Academies. National Academies Press. Washington, DC. USA.DRIEssentialGuideNutReq
Ottolenghi, F. 2008. Capture-based aquaculture of bluefin tuna. In A. Lovatelli and P.F. Holthus (eds). Capture-based aquaculture. Global overview. FAO Fisheries Technical Paper. No. 508. Rome, FAO. pp. 169–182 tunafeed
 Bluefin has become popular with Americans in spite of a historic cultural aversion to both raw fish and food that bleeds. We still retain an aggravating tendency to overcook steak though.
 Unfortunately I was unable to find a more current figure for protein malnutrition, because it doesn’t seem to be quantified all that often.