Tuna: It’s What’s for Dinner

(Continued from the June 2017 issue)

Tuna prey mostly on smaller, often schooling, fish. The particular species depends on what is locally available at the time, but common species include herring, menhaden, hake, cod, whiting, mackerel, anchovies, sardines, smaller tuna, and also squid and crustaceans. Young tuna (and the smaller species of tuna) are preyed upon by seabirds, wahoo, sharks, billfish, and larger tuna. Because of their size and momentum, large tuna have few predators, only the largest and fastest hunters, such as toothed whales, pelagic sharks, large blue and black marlin, and of course, us. Since they have high endurance and speed, they can travel long distances every day to find food. This helps them adapt in areas where there isn’t nearly as much food as they are used to. They don’t always share, either. Schools of northern bluefin will take over a territory that other fish have been feeding from, and as a group, take the upper hand. Other fish are left with two choices: seek shelter or flee. Even though they move in as a group, skipjack break ranks when food appears and pursue the prey as individuals. Tuna will sometimes gorge themselves to the point of barely being able to move, which must present quite a problem considering the amount of swimming they have to do just to take in enough oxygen to live. Though tuna normally travel in small schools of similarly sized fish, the very large tuna, over 500 pounds, are often solitary and can be very aggressive.

Some species of tuna aren’t picky about who, or what, they school with. Yellowfin associate with various species of dolphins, porpoises, and whales, as well as whale sharks. They’ll also hang around with drifting flotsam such as logs and pallets, and some follow moving vessels. Schooling with dolphins and such is presumed to be protection against sharks, but commercial fishing vessels learned to exploit this affiliation. They would capture the whole school, dolphins and all. Of course, public outcry eventually led to more “dolphin-friendly” methods. That’s all old news (great news, but old news). However, dolphins aren’t the only animals adversely affected by tuna fishing, and sometimes practices designed to reduce dolphin mortality cause greater bycatch in other species such as sharks and turtles.

Japan and the United States are the largest consumers of tuna. The majority of the market consists of four species: skipjack, yellowfin, albacore, and bigeye. Though the methods of catching tuna have been refined and improved over the years, the conservation and management has not kept up. Taking into account that tuna are highly migratory species – some crossing the entire Atlantic Ocean to feed off the coast of Europe, and then swimming all the way back to the Gulf of Mexico to spawn – how are tuna stocks managed? The Regional Fisheries Management Organizations (RFMOs) are the bodies responsible for the management of tuna populations; they monitor the activity and set catch limits within fishing countries in each region. They are also responsible for regulating the fishing fleets and controlling the health of stocks. Currently, these are the active tuna RFMOs in the world:
- Commission for the Conservation of Southern Bluefin Tuna (CCSBT)
- Inter-American Tropical Tuna Commission (IATTC)
- International Commission for the Conservation of Atlantic Tunas (ICCAT)
- Indian Ocean Tuna Commission (IOTC)
- Western and Central Pacific Fisheries Commission (WCPFC)

However, the RFMOs can only do what their member governments instruct and allow them to. They can recommend, but they have no powers to enforce and no sanctions with which to punish. These remain with the national governments, and the European Union. Recommendations from the RFMO scientists are sometimes whittled down, first by the RFMO, and then by the governments. In 2006, forty-two member governments of ICCAT agreed to a recovery plan for the northern bluefin. Quotas were lowered, the fishing season shortened, and mechanisms established to reduce illegal, unreported, and unregulated fishing. ICCAT scientists recommended quota cuts of about 50 percent and closing the fishery at the beginning of June. This would allow the stock to rebound and allow fleets to catch almost as much as they had ever done, and do so sustainably, ensuring an income for the foreseeable future. The government implemented a 20 percent quota cut and closed the fishery at the end of June. In 2007, ICCAT researchers recommended a global quota of 15,000 tonnes to maintain the current populations, or 10,000 tonnes to allow the populations to recover. ICCAT chose a quota of 36,000 tonnes. The EU even provides monetary incentives for putting vessels out of commission. But some have apparently taken the money and spent it on newer and bigger vessels, while redeploying the old boats to countries where fresh quota is available. It is difficult to comprehend the mentality that would exploit a fishery to collapse, even, especially, from a commercial point of view.

Even if bluefin tuna aren’t fished to extinction, they could become ecologically trapped at a low population level, unable to rebound, like the cod off Grand Banks near Newfoundland. Cod fishing was banned there in 1992, and there are still cod in the area, but while the ecosystem has moved into a new, probably stable, state, cod numbers don’t appear to be increasing. Species that the cod used to prey upon, such as herring, capelin, and sand lance, have “increased in abundance…[and] are now thought to prey heavily on the larvae and eggs of cod; so the prey now is the predator, and that may diminish the ability of cod to recover,” according to Boris Worm from Dalhousie University.

Of course, eating tuna isn’t the only way to enjoy them! Many species are caught frequently as game fish. Larger specimens can put up a great fight when hooked. The annual Rhode Island Tuna Tournament became one of the world's largest of such events in the late 1960s and early 1970s. It continues today, but with roughly a 50 percent drop in participation, both from the anglers and the tuna. Increasing emphasis is being placed on tag-and-release fishing in the recreational world. At least with catch and release, you don’t have to worry about mercury content. But if you’re like many, and can’t resist the taste of tuna every once and a while, the Environmental Protection Agency and the Natural Resources Defense Council (and probably several other organizations) provide guidelines on how much tuna is safe to eat. Roughly speaking, a 130-pound woman can eat about 12 ounces of light or skipjack tuna (canned) a week. A four- or five-year-old child should eat only about four ounces, unless it’s albacore; they should avoid that altogether. When in doubt, pick the little guys – anchovies, sardines, eels, crabs, clams, and scallops; they’re lower in mercury.

I embrace you with chopsticks, eyes closed, and place you on my tongue;

And your flavor love-making that proceeds keeps me feeling young.
O Toro, my Toro!
 You leave me and my appetite so Zen,

And I’ll be dwelling in our memories until we meet again.
~Ryan Unger, excerpt from “Fatty Tuna: A Love Poem”

Where I learned about tuna, and you can too!

World Wildlife Fund
www.worldwildlife.org/species/tuna

Science Encyclopedia
science.jrank.org/pages/7020/Tuna-Biology-tuna.html

Science Direct
www.sciencedirect.com/science/article/pii/S0308814608004603

MarineBio
marinebio.org/species.asp?id=236

BioExpedition
www.bioexpedition.com/atlantic-bluefin-tuna/

Atuna
www.atuna.com/index.php/en/tuna-info/tuna-species-...

World Billfish Series Species Identification
dennisalbert.com/FISH/TunaSpecies.htm

Rhode Island Sea Grant
web.archive.org/web/20120712070954/http://seagrant.gso.uri.edu/factsheets/tuna.html

Encyclopedia of Life
eol.org/pages/223943/overview

IUCN Red List
www.iucnredlist.org/details/170310/0
www.iucnredlist.org/details/21857/0
www.iucnredlist.org/details/21856/0
www.iucnredlist.org/details/21859/0
www.iucnredlist.org/details/21860/0
www.iucnredlist.org/details/155276/0

NRDC
www.nrdc.org/stories/mercury-guide

EPA
www.epa.gov/fish-tech/2017-epa-fda-advice-about-ea...

University of Texas Marine Science Institute
utmsi.utexas.edu/

BBC News
news.bbc.co.uk/2/hi/science/nature/7040011.stm

The New York Times
www.nytimes.com/2010/03/19/science/earth/19species.html?src=sch&pagewanted=all

United States Department of the Interior
www.fws.gov/news/Historic/NewsReleases/1965/196503...

Wikipedia
en.wikipedia.org/wiki/Tuna