A new study warns that overfishing has shrunk marlin, swordfish, and tuna populations by 90 percent since 1950. Given the crisis, why does a can of tuna still cost under a buck?
Because the species that end up in your tuna casserole aren't the ones being severely depleted. The Dalhousie University report focuses on bluefin tuna, particularly the southern bluefin, considered a great delicacy by sashimi connoisseurs. Southern bluefin tuna can exceed 400 pounds, though the average weight per catch is closer to 20; that catch weight has declined over the years as commercial vessels glean younger and younger fish from the oceans. The species does not reach reproductive maturity until the age of 8 (bluefin may live to 40), so overfishing has seriously curtailed the replenishment of fishing stocks. (The northern bluefin tuna, which can exceed 1,000 pounds, is also in danger, though a bit less so than its tastier cousin.)
As visitors to Tokyo's Tsukiji fish market can attest, a choice southern bluefin can fetch upward of $40,000—a price that makes it an uneconomical choice for, say, Starkist's Chunk Light tuna. That's why big-time canners instead prefer smaller, less flavorful species. Albacore, the so-called chicken of the sea, is what you'll get if the tin says "white meat." Also popular are skipjack and yellowfin. The former is considered the world's most widely consumed tuna species, and cans full of these species are often marked "light tuna." All of these tuna variants mature relatively quickly, with reproduction starting at the one-year mark for skipjack. That means the aggressive commercial harvest has had less severe consequences for these early bloomers. The casserole-grade species are also much smaller, with the average skipjack weighing in at 7 pounds. Smaller fish tend to be more numerous since they require less nourishment to survive and reproduce.
That's not to imply that overfishing hasn't affected fish prices for normal consumers. Once considered a cheap protein source for the world's poor, much fresh fish is now too expensive for all but affluent diners. A recent study by the WorldFish Center estimated that, in a worst-case scenario, prices for tilapia, carp, and other low-grade fish could jump by 70 percent, in real terms, by 2020. On the canned front, albacore, skipjack, and yellowfin stocks are generally considered "fully exploited," meaning that a marked increase in annual catches could, eventually, put an end to your supermarket's two-for-a-dollar deals.
Bonus Explainer: Another side effect of overfishing is the gastronomical interest in species previously disdained. Restaurant habitués will note the appearance of mahi-mahi on menus over the past decade; previously, the species was deemed a "rat of the sea"—too low-brow to be served in polite company.
Explainer thanks Ransom Myers and Boris Worm of DalhousieUniversity.