Tuna has been getting a lot of attention lately, but for all the wrong reasons. In January, a popular front-page article in the New York Times found frighteningly high levels of mercury in tuna from Manhattan sushi restaurants. The consumer’s response? It still tastes good (and it’s not like we’re eating thermometers). New Yorkers were wise to detect an element of sensationalist scaremongering in the Times article, but now there’s a genuine, urgent reason to avoid that succulent sushi: Tuna is facing regional extinction. Thanks to worldwide demand for “the chicken of the sea,” tuna populations have been plummeting despite efforts at sustainable fishing.
Although the situation is alarming, we are not at a total loss—we’ve been through this before, said a panel of scientists at “Last Best Chance for Tuna: Learning from the Cod Collapse.” In the early 1990s, the once plentiful Canadian cod stock collapsed, prompting the government to issue a moratorium on cod fishing and to reopen the hunt on the harp seal—cod’s major predator. But despite these efforts, the cod population continues to exist in a state of dire and possibly irreversible depletion.
There are diverse lessons to be learned from the cod collapse, says the panel. By analyzing our mistakes with cod conservation, they recommended urgent actions to revive the tuna population. According to Stanford University’s Barbara Block, cod showed us that proper fish management requires an improved understanding of their basic biology and population structure. For her research, she fits Atlantic bluefin tuna with data-logging satellite tags, mapping their migration patterns and collecting physiological data.
For a long time, researchers believed that Atlantic tuna existed in two populations which have suffered different fates. The western Atlantic population, which are spawned in the Gulf of Mexico, has been afflicted by a 90% drop in population since the 1970s, while the European population of the Mediterranean, though declining, has not fallen to the same level of devastation. Block found that these populations are genetically distinct, signaling important biodiversity, and that although they spawn on opposite sides of the ocean, they mix together when foraging in the middle of the north Atlantic.
Block’s results challenge the way the International Commission for the Conservation of Atlantic Tunas set catch quotas for managing the tuna populations. The mixing of these populations makes the highly threatened west Atlantic population seems healthier than it really is because it’s “subsidized” by the European population. This prompts quotas that are beyond what the population can actually sustain, which means that fishing in both the Mediterranean and the mid-Atlantic foraging grounds—which has skyrocketed to meet rising consumer demands— has been directly contributing to the devastation of the Gulf of Mexico stock.
Block’s data also showed that the fish of the western Atlantic stock are late bloomers—they spawn at the age of 12, four years later than had been assumed. Juvenile bycatch thus poses a serious threat, and may alone push the Gulf of Mexico population past the brink of collapse.
