Maguro

gn: justify;”>Tuna is the crown jewel of the sushi bar. Lean scarlet slices of maguro are a mainstay of the industry and one of the most popular sushi selections in the United States. Unfortunately, our ever-growing demand for tuna is beginning to have deleterious effects on the oceans.

The tuna is an impressive animal. It is a schooling fish of the open sea that can migrate thousands of miles through the oceans. Tuna are apex predators, voracious consumers of other fish and sea life. Some species, like the bluefin, can reach tremendous proportions: A mature bluefin tuna can outweigh a pony.

There are five species of tuna commonly found at the sushi bar. This section deals with yellowfin and bigeye, the two species commonly sold as maguro. The third species, bluefin, is discussed in the section on toro. The fourth species, albacore, is very popular in the industry and generally sold as shiromaguro. The fifth species is skipjack tuna; see the section on katsuo (bonito) for more information.

Yellowfin tuna (Thunnus albacares) is the backbone of the high-end tuna industry. It is generally caught with longlines (long ropes baited with hooks in series) or with gill nets, and often hails from the southern and western reaches of the Pacific. Although known as kihada in Japanese, it will be listed as maguro on U.S. sushi menus.

Yellowfin is found in the Pacific, Indian, and Atlantic oceans, and these distinct populations are under different amounts of pressure. The stock in the Atlantic is the healthiest and best understood, and it is not currently being overfished. The Pacific and Indian Ocean stocks, however, are being heavily exploited and populations are dwindling.

Bigeye tuna (Thunnus obesus) makes up a large portion of the sushi-grade product in the United States. Chances are that if your maguro isn’t yellowfin, it’s bigeye. Bigeye is known as mebachi in Japanese but is almost never advertised as such.

Bigeye stocks around the world are suffering under heavy fishing pressure. This species is generally caught in the tropical Pacific, and populations in this area are in the most trouble. In the eastern Pacific, for example, immature and juvenile bigeye comprise over fifty percent of the total catch.

An issue common to both bigeye and yellowfin tuna is the gear utilized to catch them. Longlines, purse seines, and trolled hand lines are all used to land these fish, and each has a different impact on the ecosystem.

Hand lines are relatively precise in terms of targeting the species. Longlines, however, tend to have high levels of bycatch (unintended species and juveniles that are caught and discarded), thus indiscriminately killing turtles, sharks, seabirds, juvenile tuna, and other animals. Purse seines—a large net pulled around a school of fish, the ends joined into a circle, and then closed at the bottom—are generally better than longlines, but they too can be highly destructive. If boats using purse seines employ buoys and floats (known as fish aggregation devices or FADs) to concentrate schools of tuna, the bycatch problem is exacerbated and the level of damage increases.

Compared to bluefin, neither yellowfin nor bigeye are major mercury concerns. That being said, these are still long-lived fish at the top of the food chain. Due to their formidable appetites, they have the capacity to concentrate significant levels of mercury in their bodies. Small children and pregnant women may want to exercise additional caution.

The state of affairs is quite complex, but here are the basics:

U.S. Pacific and Atlantic troll- or pole-caught yellowfin are your best choices when ordering maguro. Populations are stable, they are not being overfished, and the use of hand lines has reduced bycatch to low levels.

U.S. Pacific and Atlantic longlined yellowfin is caught from strong tuna populations, but these fisheries can have high levels of bycatch.

Imported and U.S. Gulf of Mexico troll- or pole-caught yellowfin has low bycatch but draws from depleted populations. Some of these fisheries also have very little management in place.

Purse-seined yellowfin (except from the Indian Ocean, South America, and the Philippines) is a questionable compromise when considering stock strength (moderate), bycatch (moderate), and management (varying). It is better than some alternatives, but not great.

Purse-seined yellowfin from the Indian Ocean, South America, or the Philippines is an unacceptable option, with high levels of bycatch, lax management, and shaky stock strength.

Imported and U.S. Gulf of Mexico longlined yellowfin fleets target weak stocks and have an unacceptable level of bycatch. This is the worst of the yellowfin options.

Bigeye is slightly simpler:

Troll-caught U.S. Pacific and Hawaii bigeye is a strong choice due to effective management, low bycatch, and rebounding populations.

Troll-caught imported bigeye is a surprisingly sound choice, as these fisheries tend to operate with low bycatch levels, and bigeye stocks have shown reassuring trends in recent years.

Longlined bigeye from the U.S. Pacific and Hawaii incurs a higher level of bycatch than would be ideal, but management and stocks are strong.

All U.S. Atlantic bigeye is a source of concern due to weak stocks.

Imported longlined bigeye should be avoided. The fishery tends to incur high levels of bycatch and to put heavy pressure on stocks.

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