12.1 What’s Special about Tuna?

Tuna are highly adapted for life in the open ocean. Their streamlined bodies, built for speed and endurance, make long-distance migrations possible. In fact, the name “tuna” comes from the Greek thunnos, derived from the verb thuo, which means “to dart” or “to rush.” One cannot help but be mesmerized when watching tuna swimming—an experience hard to come by. Only a few public aquariums have exhibits large enough for the largest tuna. Divers swim with Bluefin Tuna in floating cages in Australia and Malta. Carl Safina, one writer who swims with tuna, described the Bluefin Tuna as “half a ton of laminated muscle rocketing through the sea as fast as you drive your automobile” (Ellis 2008).

Tuna regulate their core body temperature with specialized circulation near their swimming muscles, a condition known as heterothermy. Bluefin Tuna can elevate their core body temperature up to 20°C above surrounding ocean temperature to enhance swimming efficiency. The swimming mode of tuna involves high-frequency tail beats (1–2 Hz) with a stiff tail fin and extra-long tendons that connect the large muscles directly to the tail fin. Other metabolic adaptations lead to capacities exceeding those of other fish, such as an increased heart size, large gill surface area, high blood oxygen–carrying capacity, and elevated hematocrit. When speed is required, the tuna switches into high-speed mode: large dorsal and ventral fins retract into cavities, while the pectoral fins are pressed flat against the body. Consequently, tuna are among the fastest-swimming fish.

Heterothermy also allows tuna to migrate into cold waters to follow abundant prey fish. Bluefin Tuna swim in both subtropical oceans and cold seas. Tuna are also known for remarkable daytime vertical migrations to find abundant prey in deeper and colder waters. They migrate from spawning grounds to feeding grounds that may be separated by over 5,000 miles. Therefore, the tuna cross country borders, which makes drawing boundaries around populations nearly impossible. Arrival of tuna near coastal regions is predictable, and communities hold celebrations, festivals, and fishing tournaments when they arrive. Managing tuna is hard because they travel between many different jurisdictions.

The larger tuna species have long been targets of game fish enthusiasts, such as authors Ernest Hemingway and Zane Grey. Ernest Hemingway wrote, “It is a back-sickening, sinew-straining, man-sized job even with a rod that looks like a hoe handle.” Hemingway and Grey wrote extensively about big-game fishing, thereby bringing awareness of these awesome yet hidden creatures. Sportfishing for large tuna was a transformational experience. Hemingway wrote, “But if you land a big tuna . . . and finally bring him up alongside the boat, green-blue and silver in the lazy ocean, you will be purified and will be able to enter unabashed into the presence of the very elder gods and they will make you welcome” (Hemingway 1922).

Current controversies about tuna relate to our relationship with them. For centuries, these fish have been an important ocean commodity. Today, tuna are an emblem of globalization—they swim across the globe, crossing boundaries of many countries that claim an interest in their harvest. Trade in tuna products has transformed the world into a more connected and interdependent place. At the same time, tuna (Thunnus spp.) have become a charismatic flagship genus to raise awareness of global conservation issues. Managing tuna fisheries involves substantial coordination among regional and international commissions and organizations that represent at least 48 countries. In 2017, the United Nations set May 2nd as World Tuna Day to focus on conserving the world’s tuna. The story of fishing for tuna from prehistory to today’s globalized society should prompt us to reflect on how a sustainable global economy based on tuna fishing should proceed.

12.2 Tuna of the World

Tuna are part of a large, diverse family of epipelagic (i.e., near-surface) dwellers. The ancestral fish that gave rise to these specialized fish was a deep-ocean dweller that lived and survived the Cretaceous-Paleogene mass extinction event, which eliminated approximately 80 percent of all species of animals about 66 million years ago (Miya et al. 2013). This deep-ocean dweller did not resemble tuna. The unique tuna traits did not appear in fish until the first tuna-like fish emerged about 40–50 million years ago.

Tuna are most closely related to mackerels and billfish, such as swordfish and marlins. They are members of the family Scombridae, which includes mackerels, tuna, Wahoos, and bonito (Collett and Graves 2019). There are 51 species of Scombridae, many of which are important and familiar food fish. Mackerels and tuna support very important commercial and recreational fisheries, as well as substantial artisanal fisheries throughout the tropical and temperate oceans.

All species in the family are specialized fast-swimming predators, often called the high-performance sports cars of the fish world. Their bodies show off swimming adaptations. Drag is reduced by their fusiform body shape, smooth skin made up of tiny cycloid scales, a crescent-shaped caudal fin, body depressions for tucking in their pectoral fins, finlets behind the rear dorsal fin and anal fin, and lateral keel on each side of the tail fin (Figure 12.1). The caudal fin is stiff without flexible fin rays. The keel provides greater area for attachment of ligaments that connect the huge muscle mass to the tail fin. Tuna provided inspiration for engineers interested in designing of autonomous underwater vehicles. A robotic swimming tuna, RoboTuna, was created by a doctoral student at Massachusetts Institute of Technology in 1995 to mimic the tuna’s highly efficient propulsion. The earliest versions of the RoboTuna were not able to replicate the bursts of acceleration observed in real tuna.

All of the 7 species of bonito and 15 species of tuna are harvested. Fishery statistics do not identify them all to species. Seven species of tuna dominate the global landings and values as they enter international trade as fresh, frozen, and canned products:

• Albacore (Thunnus alalunga)
• Atlantic Bluefin Tuna (Thunnus thynnus)
• Pacific Bluefin Tuna (Thunnus orientalis)
• Southern Bluefin Tuna (Thunnus maccoyii)
• Bigeye Tuna (Thunnus obesus)
• Yellowfin Tuna (Thunnus albacares)
• Skipjack Tuna (Katsuwanus pelamis)

The largest species are Bluefin Tunas. Atlantic and Pacific Bluefin Tuna have a maximum recorded weight of 685 kilograms (1,510 pounds). The size of a species is related to the type of commodity the fish supports—namely sushi, loins, or canned (Figure 12.2.). At least three-quarters of all tuna landed is canned, and most of this is Skipjack, Yellowfin, and Albacore. Skipjack Tuna is the most caught species by number and weight, representing more than half of the global volume of tuna harvested (McKinney et al. 2020). Skipjack Tuna is marketed as “light” or “chunk light” tuna. Albacore is the most expensive canned tuna, marketed as “white” meat tuna. Large Bluefin Tuna and Bigeye Tuna are “red” meat tuna and are priced substantially higher because they are destined for sashimi and sushi markets, where they sell for $45 to $55 per pound. Bigeye Tuna and Yellowfin Tuna are known locally in Hawaii and in fish markets as ahi. Other tuna, such as the Little Tunny (Euthynnus alleteratus) and Blackfin Tuna (Thunnus atlanticus), are less important in global trade but are incredibly important to coastal artisanal and subsistence fisheries.

Water temperature preferences of tuna broadly predict their distribution on a global scale (Boyce et al. 2008). Bluefin Tuna, Bigeye Tuna, and Albacore have the widest temperature preferences and are found in waters as cold as 10°C. Skipjack and Yellowfin Tuna are tropical tuna and most abundant in waters with temperatures greater than 18°C. Consequently, the number of tuna species encountered by fisheries is highest in the largest and warmest ocean, the Pacific. 

12.3 Historical Roots of Tuna Fishing

Tuna fishing is one of the oldest marine fishing traditions, often traced back 12,000 years. Other evidence confirms that indigenous people were tuna fishing off the northern Australian coast 42,000 years ago (O’Connor et al. 2011). Neanderthals knew that giant tuna moved through the Strait of Gibraltar every spring on their way to spawning grounds and in summer as they leave the Mediterranean. Tuna were followed by Orcas (Orcinus orca), whose breaching behavior revealed their locations. Orcas ambushed the migrating giant tuna as they swam the narrow channel at Gibraltar. Neanderthals caught Bluefin Tuna that beached themselves while trying to escape the Orcas (Adolf 2019). Extinction of the Neanderthals about 40,000 years ago corresponds to the arrival of Homo sapiens in Africa, who continued to exploit tuna as a food source.

As visual predators, tuna choose to migrate along the shallower waters along the coast where they find more abundant prey. Consequently, early fishers learned of the predictable journeys and built large traps fixed to the seabed. The term for tuna fishing is almadraba in Spain, tonnare in Italy, and madrague in France. This technique uses a maze of nets, anchored to the seabed, to catch tuna as they follow their migratory route (Figure 12.3). Once tuna are trapped in the central chamber, fishers would lift the net to the surface to harvest them. Some brave fishers even jump in the tuna-filled net to harpoon and attach ropes to the tail of each fish so that they can be lifted from the water. The trap fishing methods were described in ancient Greek and Roman literature from 1500 BC (Vargas and Corral 2007), and they are the oldest form of industrial fishing in the world. Catching a large shoal of tuna in such traps results in enormous profit.

Tuna was the first fish in human history to be captured, processed, and sold on a large industrial scale. The ancient civilization of Phoenicia (1550 BCE to 300 BCE) became prosperous because they were adept in maritime arts and shipbuilding, thereby permitting trade with ancient Greeks and other settlements in the Mediterranean. Phoenicians first began an industry based on catching, preserving, and trading tuna in the Mediterranean. The ancient Greeks, like the Japanese today, showed preference for the fatty belly cuts. The Phoenicians also invented a salting technique to conserve large quantities for trade to distant markets. Garum, a liquid fish extract derived from aging a mix of the entrails of tuna with salt water, became and remains an exclusive delicacy. Tuna trade grew from a small-scale consumption to massive trade by the sixth century BCE. Industrial fishing for tuna has expanded and persisted through the turmoil of wars, from the Punic Wars and the Fall of the Roman Empire in the Mediterranean to World War II, when the United States deployed tuna clipper ships as minesweepers.

The Roman legal concept of res communis meant that coastal fishing grounds were initially open to all. Phoenicians brought large-scale tuna fishing from the east to the west of the Mediterranean. Throughout the various shifts in ruling dynasties in Mediterranean countries, these fisheries persisted. During the Middle Ages (approximately from the 5th to the late 15th centuries), tuna fishing enriched the fortunes of Spanish dukes, who held a fishing monopoly along Spain’s southern coast.

After the Spanish Armada was defeated by the English navy in 1588, tuna catches dramatically decreased, and demand for the fish plummeted as continuing wars complicated trade. Many signs were emerging of local declines in Bluefin Tuna, which may represent the first documented fisheries collapse. In the 18th century, a monk, Brother Martín Sarmiento, referred to as the Tuna Saint, researched and wrote the first scientific study on sustainable tuna management. In the study, he warned of the decline in Bluefin Tuna and began to promote sustainable fishing, advocating for closed season and a ban on tuna fishing in the ocean. Spain had and still has the largest fishing fleet in Europe and the biggest industry for canning tuna. Tuna fisheries were on the verge of collapse as more and more almadrabas were discontinued. No one before Sarmiento had warned that overfishing was the cause of the tuna crisis. Warnings of the so-called Tuna Saint against fishing during the breeding season despite a ban were not effective at reducing fishing capacity.

The Tuna Saint’s recommendations to the duke to create catch quotas and enforce measures to protect the juvenile tuna were not accepted. Lack of regulation continued through the 19th century because of prevailing views that ocean fisheries were inexhaustible. In 1883, eminent scientist Thomas Henry Huxley declared that “Probably all the great sea fisheries are inexhaustible; that is to say, that nothing we do seriously affects the numbers of fish. Any attempt to regulate these fisheries seems consequently, from the nature of the case, to be useless.” The combined effects of fishing based on short-term profits and the increased availability of herring, cod, and salmon brought competition that doomed the giant tuna fisheries.

Despite their journeys back and forth the tuna . . . cannot avoid being eaten by larger fish, and especially by man.

—Brother Martín Sarmiento (1757)

Purse seines and longlines replaced beach seines and traps when tuna fishing effort expanded into the Atlantic Ocean. Japanese fisheries also expanded largely through pole and line fishing. Although canning methods were invented in the early 19th century, tuna were not canned until 1904, many decades after sardine, mackerel, herring, and salmon canneries became commonplace. Canning assured the consumer of a healthy protein that would keep a long time. The advent of canning and the wide distribution of tuna from tropical to subtropical oceans meant that people around the world and far from coastal areas became familiar with it. The rising demand for canned tuna at the start of the 20th century led to an expansion of the industrial fishing fleets, construction of many canneries, and control of prices by traders in the newly formed supply chain that exists to this day.

The labor-intensive almadrabas might have disappeared if not for the emerging demand in Japan for high quality Bluefin Tuna. During the 1960s, Bluefin Tuna were considered an undesirable food fish. Sport anglers caught them and sold them for cat food. Fishmongers would throw away the fatty belly meat. A restauranteur arranged to buy these for his sushi restaurant in Little Tokyo, Los Angeles. Japanese businessmen introduced American businessmen to sushi, and Hollywood, Chicago, and New York embraced sushi. Soon sushi restaurants were everywhere and sushi-quality tuna was in high demand. Improvements in freezing methods meant that tuna from around the world could be air shipped to Japan’s largest fish market, the Tsukiji Market. Japan Airlines would deliver electronics, cameras, and textiles to airports in eastern North America and return to Tokyo with crates of frozen Atlantic Bluefin Tuna.

Today, purse seines are the dominant gear used to target tuna, which form large, dense schools. The schools can be surrounded by a vertical net, after which the bottom of the net is drawn together to enclose the fish like tightening cords on a drawstring purse. Purse seines permit large catches of a single species, such as Yellowfin Tuna (Figure 1.3; Figure 12.4). Today, the demand for tuna has never been higher, and the largest super seining fishing vessel, the Albatun Tres, can net 3,000 tonnes in a single trip. As discussed in the following section, tuna fishing is highly industrialized and profit driven, depending on a complex, widespread supply chain.

12.4 Industrial Fishing, Supply Chains, and Status of the World’s Tuna

Tuna support the world’s largest global seafood companies. Commercial fisheries alone produced $40.8 billion in sales in 2018, making tuna the most valuable commercial fish on the planet. Other values include subsistence fisheries, sport fisheries, unreported catch, and ecosystem benefits. Tuna is the second-most-consumed seafood in the United States behind shrimp, and the second-most-eaten fish in Britain, behind salmon. Projected increased seafood demand in China will further complicate its management (Crona et al. 2020). Keeping tuna as an affordable seafood product requires accurate information about the supply chain. The tuna supply chain encompasses all the activities required to get a business’s products to consumers, from catching, transfer to processors, transport to distributors, retailers and, finally, to consumers. It begins with the fishing boats and ends when the final product is sold to consumers far from the site of capture (Figure 12.5). An efficient supply chain saves money and helps processors and retailers produce and transport only what they can sell. Much of the tuna catch is exported from the country of origin, and the supply chain must be coordinated with regulations imposed by governments and regional fisheries management organizations (Kresna et al. 2017; Mullon et al. 2017).

Three main distribution channels for captured tuna include (1) fresh fish landings to processing facilities from fishing vessels or carrier boats; (2) frozen fish landings directly from fishing vessels; and (3) frozen fish transshipped from fishing vessels onto carrier vessels and then to canneries. Because the tuna purchased in your local restaurant or fish market could originate halfway across the globe, consumers may be unaware of how and where it was captured. The long and complex supply chain makes it challenging to guarantee that the tuna on your plate is really the one that it is supposed to be. Furthermore, financial interests of distributors all serve to deprive actual fishers of profits while enriching middlemen and distributors. Consumers have many questions that are often difficult to answer. How can we ensure that the tuna we buy is slavery free? Do fishers have safe working conditions and fair pay? Were the fish captured with minimal bycatch of threatened species? Is the fishery managed sustainably? One tool to ensure the standard safety and quality is the traceability database system along the supply chain. It is very crucial, because every actor in the chain has a responsibility to ensure food safety and quality through handling, manufacturing, packaging, and transporting the product. Additionally, major tuna-consuming countries are adopting import controls to permit traceability of illegal, unreported, unregulated fishing and to support sustainability certification.

Tuna are highly migratory; therefore, a global and interconnected framework of organizations and policies is in place for managing stocks around the world. Commercial tuna fishing occurs in all the world’s oceans and more than 70 countries. At least 580 industrial-scale tuna purse seine vessels are in operation globally (Hamilton et al. 2011). The largest companies, including Bumble Bee®, Chicken of the Sea®, and StarKist®, are pressured by consumers to adopt principles of responsible and sustainable fishing while keeping prices competitive. The global canned tuna market alone was valued at U.S. $8.57 billion in 2020 and is expected to grow up to $12.5 billion by 2028 (Grand View Research 2020).

The trend in per capita consumption of canned tuna in the United States (Figure 12.6) shows a steady rise before, during, and after World War II, when the tuna industry touted the fish’s health benefits and claimed that it tasted like chicken. By 1950, it had overtaken salmon as America’s most popular fish. Charlie the Tuna was a cartoon character created in 1961 to advertise StarKist® tuna. Charlie resembled the beatnik of the day, with a beret to show his hip, cultured tastes (Figure 12.7). The popular catch phrase was, “Sorry Charlie, StarKist doesn’t want tuna with good taste, but tuna that tastes good!” Consumption peaked at nearly 4 pounds per person in 1989, when Americans consumed between half to two-thirds of the global supply of canned tuna. Clearly, decades of advertising, such as Charlie the Tuna, worked on American consumers. However, since the peak, consumption has fallen by half. One reason for this recent and substantial decline is changing consumer preferences for convenience foods. Additionally, consumer concerns over the killing of dolphins may have played a role.

Dolphin-safe labeling began in the United States, in response to consumer reactions to dolphins killed in purse seines. Commercial tuna fisheries in the tropical oceans began to catch Yellowfin Tuna by spotting large aggregations of dolphins and seabirds associated with shoals of tuna and encircling them with purse-seine nets. These dolphin sets deployed very large nets (1,500–2,000 m long and 120–250 m deep) to encircle entire schools of tuna. Incidental take of dolphins was estimated at 550,000 in 1961 alone, and population estimates of spinner and spotted dolphins declined by more than half. Dolphin mortality was a problem for the purse-seine tuna industry, and many modifications in fishing methods and gears were tested. Principal innovations that were responsible for mortality reduction were “backing down” the net to allow dolphins to escape; and the Medina panel, which prevented dolphins from getting their snouts entangled in nets. The passage of the U.S. Marine Mammal Protection Act (1972), international agreements to limit dolphin mortality, and economic incentives, such as the dolphin-safe label, encouraged fishers to adopt improved fishing methods to minimize dolphin fatalities during fishing for tuna destined for canning. By 1988, a coalition of environmental groups called for a consumer boycott of the tuna caught by purse seines. Demonstrators carried signs saying, “Sorry Charlie—StarKist Kills Dolphins.”

In 1990, Bumble Bee, Chicken of the Sea and StarKist, the three largest tuna canners, voluntarily declared that they would no longer purchase tuna captured in association with dolphins. Soon the Marine Mammal Protection Act was amended to mandate that U.S. retailers exclude tuna caught using methods that set nets on schools of dolphins. Dolphin-safe tuna fishing must meet several standards: (1) no use of drift gill nets to catch tuna; (2) no accidental killing or serious injury to any dolphins during net sets; (3) no mixing of dolphin-safe and dolphin-deadly tuna; and (4) an independent observer must be on board attesting to the compliance. Recent observations show that entanglement mortality of dolphins has been reduced by 99% (Balance et al. 2021).

Today most tuna are captured in purse seines, and longlines are the second-most-common gear. Indonesia and Japan are consistently the top-two fishing nations (Figure 12.8). Five of the top tuna fishing nations—Japan, Taiwan (Republic of China), Spain, Korea, and the USA—have large fishing fleets that operate far from their home waters, whereas the others have large local or regional fleets. New technologies, such as sonar, have made tuna fishing much more effective. In response, the use of spotter planes is banned for fishing Atlantic Bluefin Tuna in the Mediterranean (Di Natale 2020). Many recreational tuna boats also use spotter planes in the eastern Atlantic Ocean, although the traditionalist harpoon fishers shun the technology (Whynott 1995; Decker 2016).

The Pacific Ocean has consistently had the highest landings, about 66% of the world’s tuna catch. The western and central Pacific Ocean is where many artisanal and industrial fisheries overlap. For the small island nations, fishing provides a major source of income, jobs, and food security (Bell et al. 2019). Yet, Pacific island nations have not fully realized the economic potential with the global tuna industry, despite the fact that 80% of it is caught within their exclusive economic zones (EEZs, i.e., within 200 miles). The 1982 United Nations Convention on the Law of the Sea awarded coastal states sovereign rights to (1) exploit and manage all living resources within their EEZ, (2) exclude distant water fleets in favor of developing their own fleets, and (3) charge distant water fleets rent for access. Eight island nations—the Federated States of Micronesia, Kiribati, Marshall Islands, Nauru, Palau, Papua New Guinea, Solomon Islands and Tuvalu, which support 80% of the purse-seine catch in their waters—formed an alliance and require collective bargaining to set rents for access by foreign vessels. The alliance also prioritized domestic over foreign vessels and set limits on the number of purse-seine vessels. The issue of sovereignty over tuna that migrate freely among EEZs remains a concern for small island nations (Bailey et al. 2012). Working to establish fair and equitable allocations of total allowable catches to the many parties will require more equitable sharing with the larger tuna-fishing nations.

Supply-chain management of tuna focuses mostly on the at-sea operations and marketing and processing standards. Throughout the world, tuna fishing is a male-dominated activity. Yet, women play essential roles in different nodes of the supply chain (Barclay et al. 2021). Management organizations typically exclude women for policy making, and existing policies fail to recognize women’s work in tuna supply chains and in supporting men who fish at sea. Weak gender-based policies make women more vulnerable or easily subjected to sexual harassment, exploitation, and abuse in the workplace.

The tuna fishing industry has long been plagued by overfishing, corruption, human rights abuses, fraud, and illegal, unreported, and unregulated fishing, all of which compromises the well-being of environments and communities. Pacific island fisheries are particularly imperiled by corruption and lack of strong governance (Hanich and Tsamleyi 2009). Additionally, illegal, unreported, and unregulated tuna fishing is a major problem, especially in the Pacific Ocean, where estimates show the value lost annually to coastal nations is approximately $333.5 million (MRAG Asia Pacific 2021).

12.5 Recent Advancements in Tuna Fisheries

High-profile tuna brands have adopted corporate social responsibility guidelines to ensure that issues such as sustainability, IUU fishing, and social welfare are considered in business operations. French explorer Jacques Cousteau (1910–1997) had a way of making people passionate about marine life via his documentaries on underwater life and consequences of human negligence. After Cousteau visited an almadraba in action and dove in the innermost chamber surrounded by Bluefin Tuna and bonito, he wrote, in The Silent World (French: Le Monde du silence, 1956), that it was one of the “most horrible and grand” marine spectacles to be seen (Adolf 2019). Subsequently, nongovernmental organizations developed campaigns to reduce large-scale industrial fishing and promote sustainable fishing practices and the need for traceable tuna products (Bailey et al. 2016).

The supply-chain harvesters and retailers are playing a much larger role in shaping the international governance of tuna fishing. The number of fisheries that hold or are seeking sustainability certification have greatly increased over the past decade (Schiller and Bailey 2021). For example, the Marine Stewardship Council certifies pole-and-line–caught tuna (Figure 12.9), such as the Maldives Skipjack Tuna fishery of the Indian Ocean. Here the tuna are captured one by one and have low levels of bycatch and fish at levels that are sustainable. Tuna fishing is the second major source of income for the Maldives, after tourism. Fair Trade-certified fisheries meet a set of rigorous, audited criteria that work to protect the fundamental human rights of fishermen, as well as the ecosystems impacted by the trade. Consumers are willing to pay more for ecofriendly canned tuna, and sales at supermarkets have been trending upward (Sun et al. 2017).

Despite growing public concerns and efforts across the seafood sector to address corporate social responsibility, corruption and price fixing among the big-three tuna canning companies was recently exposed in a lawsuit brought by 25 major U.S. retailers. The big-three tuna brands control almost three-fourths of the shrinking American consumer market. Cans of tuna on grocery shelves were getting smaller and quality was dropping, yet prices increased. Guilty pleas were filed by all three tuna companies and several of their executives. The CEO of Bumble Bee Foods was sentenced to a 40-month prison sentence. Bumble Bee admitted to price fixing and agreed to pay a $25 million fine as part of a plea agreement, and StarKist was sentenced and ordered to pay a $100 million fine.

Globally, the abundance of tuna has declined by more than 50% over the past century, with steepest declines observed in the largest, longest-lived, highest-valued tuna (Juan-Jordá et al. 2011). Stocks are either overfished or fished at levels near the maximum sustainable yield levels, preventing further expansion of catches. Tuna fisheries that are overfished must be rebuilt with stricter measures to reduce overcapacity in the face of rising demand.

Two sources provide assessment of conservation status. The International Union for Conservation of Nature (IUCN) provides a global classification based on population decline and threats other than fishing pressure (Collette et al. 2011; Collette 2017). The status of world fisheries is periodically assessed for the seven species of major commercial tuna stocks. The assessment is challenging because of their migratory behavior and often differing spawning locations. Regional fisheries management organizations (RFMO) are responsible for stock assessment and management of 23 tuna stocks (6 Albacore, 4 Bigeye, 4 Bluefin, 5 Skipjack, and 4 Yellowfin stocks). Ideally, sustainable fishing means spawning-size fish abundance is at or above the level that produces maximum sustainable yield, fishing mortality is less than that which would produce the maximum sustainable yield, and there is minimal bycatch of nontarget species (ISSF 2022; Medley et al. 2022). There are five tuna RFMOs, which are responsible for assessing and managing the 23 stocks of the seven major commercial oceanic tuna species:

• IATTC: Inter-American Tropical Tuna Commission
• ICCAT: International Commission for the Conservation of Atlantic Tuna
• CCSBT: Commission for the Conservation of Southern Bluefin Tuna
• IOTC: Indian Ocean Tuna Commission
• WCPFC: Western and Central Pacific Fisheries Commission

Albacore are not overfished or experiencing overfishing. However, lack of reporting remains a concern, and the IUCN classifies them as Near Threatened. Atlantic Bluefin Tuna are rebuilding and classified as Near Threatened in eastern stock and Endangered in the smaller western stock. Both stocks are in a rebuilding phase. See section 12.6 for more details. Pacific Bluefin Tuna are overfished and down to 4.5% of their historic biomass (ISC 2022) and in need of a rebuilding plan. The Atlantic Bluefin Tuna (Thunnus thynnus) moved from Endangered to Least Concern, while the Southern Bluefin Tuna (Thunnus maccoyii) moved from Critically Endangered to Endangered. The Albacore Tuna (Thunnus alalonga) and Yellowfin Tuna (Thunnus albacares) both moved from Near Threatened to Least Concern. The Pacific Bluefin Tuna (Thunnus orientalis) moved from Vulnerable to Near Threatened in this update due to the availability of newer stock assessment data and models. Other tuna species reassessed for this Red List update include the Bigeye Tuna (Thunnus obesus), which remains Vulnerable, and the Skipjack Tuna (Katsuwonus pelamis), which remains Least Concern. Harvesting Bigeye Tuna with purse seines near FADs (fish aggregating devices) targets smaller Bigeye Tuna. Yellowfin Tuna are fully fished or overfished, and overfishing continues in the eastern Pacific and Indian oceans.

Currently, the traceability system in the tuna industry, even in the largest exporting country of Indonesia, is conducted through a paper-based system. However, a computer-based network, known as the blockchain, could revolutionize catch documentation and traceability through real-time data acquisition and integrated data access and transparency at every step along the supply chain. Under a blockchain-based system, fishing vessels are tracked with satellites (Taconet et al. 2019), and, from the time of capture, each tuna can be given a unique identification that is permanent and fully traceable across the blockchain database. At its core, blockchain technology is simply a digital, tamper-proof record of information that is accessible to businesses, restaurants, supermarkets, and, ultimately, even consumers. By tracking the fish from the moment it’s caught, blockchain would make it nearly impossible for any illegal or unreported tuna to enter the market over time. The traceability allowed by blockchain technology would allow consumers to be confident about what they are eating, where it came from, how it was produced, and how it got to them. Such new technology was piloted by the World Wildlife Fund (WWF) in 2017 and remains under development across several fisheries. Fisheries specialist Bubba Cook with WWF says, “If you have the opportunity as a consumer to know with confidence that you’re buying from a fishery that engages in sustainable and ethical practices, then of course you would want to do that” (Whiting 2020).

Thanks to demand for the highest-quality tuna for sushi and sashimi, the Japanese developed a new and more humane killing method that maintains the quality of the flesh. Any stress to a recently captured fish reduces the eating quality and shortens the storage life of the flesh (Poli et al. 2005). Some fish consumers have changed eating patterns as they learn that fish have consciousness, experience pain, are social, know how to use tools, and are able to communicate (see Chapter 5 in this book). Yet, even if the consumer is not concerned with the welfare of the tuna, preventing muscle spasms in dying tuna will improve the flesh quality. Spasms cause muscles to release lactic acid, which in turn leads to bacterial changes that acidify muscular tissue and give the meat a brownish tint and bitter taste.

The ikejime killing method is similar to pithing a frog. A spike is inserted quickly and directly into the hindbrain, thereby causing immediate brain death. Then, a thin needle or wire is inserted into the spinal column ceasing all muscle movement. The tuna is then bled and placed on ice. Tuna killed in this way have better flesh quality than those killed by suffocation or bleeding.

12.6 Atlantic Bluefin Tuna

Atlantic Bluefin Tuna are one of three different species of Bluefin Tuna (Figure 12.10). The other very similar species are the Pacific Bluefin Tuna and the Southern Bluefin Tuna. Bluefin Tuna is one of the sea’s most valuable species, a highly migratory fish that has been harvested for many centuries. After a long history where fishing was primarily in the Mediterranean, new fisheries emerged throughout the Atlantic Ocean. The new fisheries adopted purse seines and longlines instead of beach seines and traps. The new gears were more effective, and increased fishing effort after World War II led to substantial declines in the harvest of Atlantic Bluefin Tuna and calls to develop an improved governance system to regulate fishing.

Bluefin Tuna were not always popular food fish. In the 1800s, the Japanese referred to tuna as neko-matagi, meaning “fish that even a cat would disdain.” Until recently, the red flesh and robust taste of Bluefin Tuna were not desirable for consumption. It was primarily a sport fish caught for fun along the Atlantic Coast from Nova Scotia to Massachusetts in the 1940s, 50s and 60s. The big tuna were weighed and photographed, then sent to landfills or sold for under $1 per pound to be turned into pet food. Chasing giant Bluefin Tuna always attracted big-game anglers to tournaments, such as the International Tuna Cup Match, which began in 1937. Atlantic Bluefin Tuna recreational fishing increased as a specialized sport, some with hook-and-line fishing and others devoted to the use of harpoons (Decker 2016). The record Atlantic Bluefin Tuna landed in 1979 weighed 1,496 pounds—a record that continues to stand today. Television series, such as Wicked Tuna, brought broader attention to rod-and-reel fishing for Atlantic Bluefin Tuna.

Growth in market demand for Bluefin Tuna exploded in the 1970s, after Kobe beef, a fatty, well-marbled product, was first introduced and marketed in Japan (Longworth 1983). This resulted in appreciation of strong flavors and dark flesh, and Japanese developed a taste for toro, the fatty belly flesh of the Bluefin (toro means “to melt,” in reference to its buttery texture). Fish wholesalers wear masks and sanitize their hands as they examine the texture of tail meat from fresh and frozen tuna by touching, smelling, and sometimes tasting pieces of it. Sushi chefs handle and serve different cuts of Bluefin Tuna flesh. Every cut has a different name and purpose. The cuts from the cheeks and top of head are found only at a few high-end Japanese restaurants.

Japanese fishmongers were the first to store and age tuna to soften the rich flavor (Goulding 2000). When Bluefin Tuna was introduced to high-end restaurants, demand continued to skyrocket. Demand for high-quality sushi led to another expansion in Bluefin Tuna fishing well before tuna management was ready to adapt. Soon a heavily subsidized European Union fleet of giant, specialized purse-seining vessels vastly expanded the catch of Atlantic Bluefin Tuna. Bluefin Tuna caught from the Pacific, Atlantic, and Southern oceans were flash-frozen and shipped for auction at Japan’s Tsukiji Market, the biggest wholesale fish and seafood market in the world (Figure 12.11). At the first auction of the year, the first Bluefin Tuna auctioned receives special attention. The owner of a Japanese sushi restaurant chain set a record by paying more than $3.1 million for a 278-kg (613-lb) Bluefin Tuna. These high bids receive a lot of press attention, which inspires customers to flock to sushi restaurants. However, the auction price is highly symbolic and not an accurate measure of the price of tuna.

Landing records for Atlantic Bluefin Tuna date back to 1525, from almadrabas in the western Mediterranean and the Strait of Gibraltar (Ganzedo et al. 2016). Landings have always shown short-term and long-term fluctuations associated with conditions that modify fishing conditions or spawning behavior and early survival of young Bluefin Tuna. One constraint to management of the Atlantic Bluefin Tuna has always been the lack of certainty over the spawning locations and migratory path. Atlantic Bluefin Tuna feed in the productive waters off the coasts of North America, Europe, and Africa (Block 2019). Each year mature fish make long migrations so they can reproduce in warm waters >24°C suitable for eggs and larvae. Tuna from each spawning ground mix during the rest of the year (Rooker et al. 2007). Therefore, an Atlantic Bluefin Tuna caught anywhere in the Atlantic cannot be identified to its spawning stock. The mid-Atlantic region has the highest mixing levels (Siskey et al. 2016).

Since 1950, landings of both stocks fluctuated, but landings demonstrated that the Eastern stock was larger (about 10-fold) (Figure 12.12). The Japanese fishing fleet started to actively fish Bluefin Tuna in the Atlantic in the 1950s. In 1966, tuna fishing nations formed the International Commission for the Conservation of Atlantic Tuna (ICCAT), and management decisions were made by representatives from 51 countries. Few regulations were in place in the early years of ICCAT. While ICCAT does not have regulatory or enforcing powers (Korman 2011), it is entrusted with collecting and compiling statistical data, generating scientific reports, proposing nonbinding management recommendations based on its findings, and creating an arena for contracting parties to meet and discuss recommendations. Scientific advice from ICCAT has often been watered down or manipulated for political purposes (Telesca 2020). Member states are responsible for the implementation of regulations, monitoring, sanctioning, and collection of data. It was 1975 before ICCAT recommended a minimum size of 6.4 kg (~age two and still immature), reflecting recommendations by the Tuna Saint in the 1800s (Mather et al. 1995). One of the most significant changes occurred in 1981, when ICCAT elected to divide governance into Eastern and Western management units using an effectively arbitrary boundary of 45°W longitude. In the 1990s, long-liners and purse seiners with spotting planes were prohibited in Mediterranean Sea at vulnerable times of year when ICCAT and others recognized that the Atlantic Bluefin Tuna were overfished (MacKenzie et al. 2009).

It was 1998 before ICCAT would establish the first country-based quotas for Bluefin Tuna. Quotas were set too high in response to economic and political pressures. The period from 1997 to 2007 (Figure 12.12) was time of fraud, blatant overfishing, and rule breaking, with catches over twice the annual quota. At this time of peak landings, a black market worth an estimated $4 billion caught more than one out of every three Atlantic Bluefin Tuna (Guevara et al. 2012). Not surprisingly, by the turn of the century, the spawning stock hit a new low. Countries were forced to reveal their true catches; for example, France revealed its true catch was almost double the ICCAT quota. In 2010, some sushi consumers boycotted Bluefin Tuna over concerns about population declines.

Atlantic Bluefin Tuna are large as adults, have high fecundity, low early survival, and moderate longevity (>30 years). A 5-year-old female produces about 5 million small eggs (~1mm), while a 15-year-old female can carry up to 45 million (Rodriguez-Roda 1967). However, environmental conditions during early life greatly influence survival of the eggs and larvae. Therefore, Atlantic Bluefin Tuna depend on a broad representation of multiple age groups because not all spawning seasons provide favorable conditions for spawning and larval conditions to lead to large year classes. Spawning biomass of both stocks of Atlantic Bluefin Tuna dropped below the limits set by management organizations (Figure 12.13), triggering more regulations (Fromentin and Powers 2005; Fromentin 2009; Taylor et al. 2011; Fromentin et al. 2014; Cort and Abaunza 2015; Porch et al. 2019; Lauretta et al. 2020; Telesca 2020).

Illegal and unreported tuna fishing meant that catch statistics (Figure 12.13) were underreported, and stock assessments were biased toward estimating steep declines. Unreported catches from the Mediterranean (19,400 in 2006 and 28,600 in 2007) significantly contributed to the rapid decline in the stock (Agnew et al. 2009). Because of the mixing in the Atlantic, the successful rebuilding of the western population was tied to controlling the much larger fishing mortality rates that occur on the eastern stock (Taylor et al. 2011; Porch et al. 2019). For example, continued high fishing mortality rates in the Mediterranean Sea and eastern Atlantic compromise rebuilding efforts for the western Atlantic population.

Nongovernmental organizations also started campaigns to reduce fishing of Atlantic Bluefin Tuna. In 2007, ICCAT developed a plan to increase the minimum weight limit to 30 kg and implement surveillance and enforcement of quotas, with funding support from the European Unions. Nongovernmental organizations petitioned the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to restrict international trade in 2010. With 183 member states (including the EU countries), CITES is an unwieldy international group. Moreover, big tuna-fishing nations objected to the petition at the 2010 annual CITES conference, making deals with developing countries in return for their objecting to the proposal. The deciding incident was the screaming from the delegate from Libya over “imperialist nations” depriving Libya of its fair share of tuna. At the time, Libyan leader Muammar Gaddafi’s family was deeply involved in massive illegal tuna fisheries and smuggling and had expanded its EEZ to keep other countries out. The proposal to CITES was voted down by a clear majority, leaving ICCAT to enforce existing quotas to recover Mediterranean stock.

Also in 2010, the Center for Biological Diversity petitioned the National Marine Fisheries Service (NMFS) to list the Atlantic Bluefin Tuna (western stock) as endangered (Atlantic Bluefin Tuna Status Review Team 2011). The review by NMFS acknowledged the threats to coastal habitats but concluded that they do not represent a substantial risk to long-term persistence of the species. Furthermore, they judged that lowered quotas would allow for an increase in abundance. The ICCAT plan included an emergency clause that specified that if serious threat of stock collapse is detected in future stock assessments, ICCAT shall suspend all Atlantic Bluefin Tuna fisheries in the western Atlantic for the following year.

The path to eventual recovery of the Atlantic Bluefin Tuna is far from certain (Lauretta et al. 2020). Although overfishing is not occurring, the abundance measures are still below targets set by the ICCAT. If landings continue to stay below the total allowable catch, the population should grow. However, the giant specimens of tuna, as well as other newsworthy ginormous fish, are now rarer than in previous decades and centuries (Francis et al. 2019). There are signs that Atlantic Bluefin Tuna are expanding in the North Sea, Norwegian Sea, and northeast Atlantic as herring and mackerel have increased in abundance (MacKenzie et al. 2022). Hopeful signs for the Atlantic Bluefin Tuna may encourage adoption of similar strategies to recover the Southern Bluefin Tuna, the population of which was just 2.6% of the original unfished stocks (Nickson 2016).

The case of the Atlantic Bluefin Tuna highlights the challenge of managing fish populations in a complex global fishing supply chain. What has emerged may be viewed as a sociological and political problem or a “wicked problem,” difficult to solve because of the complex and interconnected nature and competing goals. Regional fisheries management organizations are reactive instead of proactive and respond to complaints from powerful constituencies with effective or ineffective policies, while marginalized peoples have little power to effect change (Webster 2015; Nakatsuka 2017). A large global and borderless economy easily leads to overcapacity of subsidized fishing fleets and competing interests and indifference. Marginalized groups have less political clout to mobilize efforts to address problems. Japan is the largest importer of Bluefin Tuna and considers sushi from them an acquired right. Consequently, when quotas are reduced, each country must adjust to meet the quota, creating incentives for fraud in reporting catches.

Consumption of Bluefin Tuna is an example of conspicuous consumption, which is the display of ostentatious wealth to gain status and reputation. Bluefin Tuna is a Veblen good, meaning the demand for it increases as one’s income rises (Veblen 1912). A Veblen good has an upward-sloping demand curve, which runs counter to the typical downward-sloping curve (Figure 12.14, top portion of curve). A rational consumer would consider alternative goods available in the market, and when the price for certain goods decreases, the demand should increase, and vice versa (Figure 12.14, bottom portion of curve). However, consumers have increasingly prized Bluefin Tuna as a status symbol as it becomes more and more uncommon and thus more expensive. The fewer Bluefin there are, the more sushi made, and so the more consumers want it, and thus the more it is overfished. Consumer behavior—that is, demand for a rare and expensive commodity—contributes to the decline in Bluefin Tuna abundance (Barclay 2015).

12.7 Tuna Ranching

Tuna ranches may have revolutionized the Bluefin Tuna industry, bringing fantastic profits. Increasingly, captured Bluefin Tuna are destined for aquaculture (Metian et al. 2014). However, they are controversial and have not reduced demands on wild stocks. Rather, tuna ranches became a point of conflict in the 1990s during the height of overfishing on all three species of Bluefin Tuna. An estimated 67 ranches spread across the Mediterranean, along with other ranches in Japan, Australia, and Mexico. Australia piloted tuna ranching in 1991 with funding from the Australian government, a Japanese fisheries foundation, and tuna boat owners in Australia. Tuna ranching is based on the capture of young Bluefin Tuna in purse seines. Because the entire process happens underwater, ranching made it impossible to verify the weight or number caught, leading to undersized tuna captured. These juveniles were transferred to large circular pens where they were fattened by feeding them sardine, herring, and mackerel. Tuna ranching has economic advantages: the fish are sold to ranches instead of being sold cheap to the Japanese; also, they have grown large enough (>25 kg) for the market to have improved fatty flesh quality.

Financing for many of the tuna ranches was traced largely to Japanese fish trading houses and Mitsubishi Corporation, a corporate giant that owns subsidiary companies that control much of the Bluefin Tuna market in Japan. Laundering tuna allowed the new industry to dodge quotas. Catches were underreported or traded with ranches in less-regulated countries and mixed with legal catches (Center for Public Integrity 2012). Some visionaries see a time when Bluefin Tuna aquaculture will not require harvesting young tuna to stock pens. Efforts to breed Bluefin Tuna in captivity have been successful in establishing a domestic population (Ortega and de la Gándara 2019). Selective breeding programs may reduce the feed requirements and grow-out times (Klinger and Mendoza 2019). Bluefin Tuna farming still presents many environmental concerns associated with other farmed carnivores, including the need to harvest forage fish for feed (Naylor et al. 2021). Time will tell if aquaculture can solve the problems of meeting the demands for the most expensive fish in the world today.

12.8 Outlook for Sustainability of Tuna Fisheries

Our relationship with tuna will continue to focus on these fish as a commodity and not a key part of the ocean ecosystems. Tuna fisheries continue to provide an important source of employment and foreign exchange for major fishing countries. Problems, such as overfishing, subsidies, human rights abuses, and fraud, as well as illegal, unreported, and unregulated fishing, are well recognized, and the experts have differing views of the future for sustainable tuna fisheries (Adolf 2019; Telesca 2020). The difference of opinions is due to a mix of positive signs and continuing challenges:

• Improved governance
• Traceability and ecocertification of tuna products
• Mercury contamination
• Oil spills
• Climate change and shifting baselines
• Ecosystem connections

Improved Governance

Countries that subsidize tuna fishing fleets can overfish stocks, while smaller subsistence fisheries are disadvantaged (Sumaila et al. 2014; Bush and Roheim 2018). Larger tuna fleets also target high-value species for export to the luxury market (Willis and Bailey 2020). Fishing fleets can target fishing in countries with little enforcement, and once the fish are landed at a port, it is very difficult to determine where, how, and by whom the fish were caught.

The FAO Code of Responsible Fisheries sets out international principles and standards of behavior to ensure effective conservation, management, and development of living aquatic resources (FAO 1995). These principles are intended to prevent overfishing, while meeting the needs of present and future generations in the context of food security, poverty alleviation, and sustainable development. Limiting access to tuna fishing via individual transferable quotas is controversial, as it focuses only on the aggregate economic performance through profit generation and not the well-being of tuna-fishing communities (Hallman et al. 2010). For example, led by powerful ranching investors, tuna fisheries in Malta transitioned from an open-access artisanal activity to an industrial one with an individual transferable quota system. The shift raised questions over who had legitimate fishing rights and decreased profitability for artisanal due to competition with industrial fishing (Said et al. 2016). The artisanal fishing of Bluefin Tuna in Malta has been ongoing since the 1700s, yet the future livelihood of artisanal fishers is now at risk. Furthermore, tuna ranching, owned by only five foreign companies, dominates much of the fishing for Bluefin Tuna in Malta. In Malta, the transition to industrialized tuna fishing resulted in very unequal benefits and was not aligned with FAO’s principles of responsible fishing.

Future decisions over tuna fishing can be improved by enhancing the function of the existing regional fisheries management organizations to counteract overcapacity of fishing fleets (Aranda et al. 2012). Some form of right-based management is being debated across multiple RFMOs, raising ethical questions in a world where food security, not profits, may become a top priority (DeBruyn et al. 2012; Dueri et al. 2016).

Policy changes that facilitate industrialization of tuna fishing and use of transferable quotas may be the beginning of the end for the artisanal tuna fishers. An alternative to individual transferable quotas was adopted by a coalition of eight island nations, dispersed over thousands of islands and atolls (Yeeting et al. 2018). The combined EEZs of the coalition support half of global catches of Skipjack Tuna and a quarter of all total global tuna catches. This agreement was designed to cap the number of purse-seine vessels by setting a benchmark price and allocating tradable fishing days. After this agreement was implemented, the price of fishing licenses rose, and tuna stocks increased (Adolf 2019). This partnership protects the food sovereignty of the island nations and may be the first step toward managing ownership of tuna resources.

There are signs from the most recent decade that more major stocks are being fished sustainably. Tuna stocks were more depleted for stocks with high commercial value, large size, and long lifespans. In addition, implementing and enforcing total allowable catches (TACs) had the strongest positive influence on rebuilding overfished tuna (Pons et al. 2017). RFMOs have made progress in implementing stock assessments for a wide range of taxa (Heidrich et al. 2022).

Traceability and Ecocertification of Tuna Products

The efforts to manage highly migratory tuna stocks have taught us that different governance arrangements, from state-based, public regulation to market-based, private initiatives, each have a role to play. Many consumers are concerned about illegal and unsustainable tuna fishing and will pay a premium price if they can verify the source of the product. Changes in management come from fishing companies that seek to differentiate their tuna products with a certification of sustainable fishing and global initiatives, such as the World Wildlife Fund’s Smart Fishing Initiative (Bailey et al. 2018). New tools, such as certification, recommendation lists, and traceability increasingly play important roles in modifying the purchasing behavior of consumers (Bush and Roheim 2018).

Improvements come from promoting the use of technology in fishing operations that permits both transparency and traceability of tuna products. Market incentives such as ecolabels can reduce illegal and unsustainable fishing by driving buyers toward more ethical and transparent producers while simultaneously excluding the rest. Electronic monitoring using cameras and other sensors on industrial tuna fishing boats supplements catch and effort information collected through logbooks, port sampling, and observer data. These procedural and technological advancements detect a vessel’s position and activity (Whiting 2020), while cameras record key aspects of fishing operations, such as observing bycatch of at-risk species. Local fishers and processors along the supply chain may then enter data into a database, such as a blockchain, via their mobile electronic devices (Figure 12.15). Consequently, the consumers at the end of the chain can see mobile-accessible information about location of the catch and suppliers along the entire supply chain. As of 2019, approximately 47% of the global tuna catch came from fisheries that either held or were seeking ecocertification from the Marine Stewardship Council (Schiller and Bailey 2021). An increase in certified tuna fisheries is expected as standards are established for electronic monitoring systems (Murua et al. 2022).

Mercury Contamination

Mercury is a persistent substance that can build up, or bioaccumulate, in living organisms. Bacteria and other living organisms convert mercury in the water to methylmercury, a highly toxic organic compound. Fish absorb methylmercury from their food as well as from water as it passes over their gills. As mercury-contaminated organisms are eaten and transformed at higher trophic levels, the concentration of methyl mercury increases through a process known as biomagnification (Figure 12.16). Because tuna are top predators as adults, they have high concentrations of mercury (Moura Reis Manhães et al. 2020). All three species of Bluefin Tuna have high concentrations of methylmercury that increase with age (Tseng et al. 2021). For example, the biggest Atlantic Bluefin Tuna ever caught off Delaware (873 pounds) had 2.5 parts per million, making it 2.5 times higher than the FDA action level for commercial fish (Absher 2005).

Mercury in fish is bound to proteins in fish tissues, including muscle. There is no method of cooking or cleaning fish that will reduce mercury levels. Both elemental and methylmercury can cross the blood-brain and placental barriers. The adult and fetal brains are targets for elemental mercury, and the brain and the kidneys are critical target organs for methylmercury. Methylmercury interferes with a cell’s ability to divide, and its effects on brain development can be permanent. Chronic exposures to children and developing fetuses show up later in the form of reduced performance on some tests of language, coordination, and intelligence. Chronic exposure to mercury in adults may be associated with an increased risk of cardiovascular diseases, reproductive harm, kidney disease, risk of dementia, and cancer (Ye et al. 2016).

Unfortunately, few consumers are aware of the mercury content in the tuna they eat. Some grocery chains now include FDA warnings to limit consumption of fresh or frozen tuna. California passed Proposition 65, which required warning about exposures to chemicals, including mercury, that cause cancer, birth defects, or other reproductive harm. However, tuna companies appealed the ruling requiring warning labels, and the court ruled that mercury in canned tuna is “naturally occurring” and therefore exempt from Proposition 65. However, whether the mercury is naturally occurring or added by human actions is irrelevant to the consumer. Jane Hightower, MD, found that many of her fish-loving patients had chronic methylmercury poisoning, which caused numerous symptoms that were not thought to be due to mercury until mercury levels were measured in the patient’s blood (Hightower 2008).

Concerns over mercury contamination will continue in the future, as the human health impact of chronic exposure to mercury is a topic of great controversy. Although aggressive regulation of mercury in North America and Europe since the 1970s reduced mercury emissions (Conniff 2016), the warming of the oceans will increase accumulation of mercury in tuna and other top predators (Shartup et al. 2019). Consumers should choose to substitute other lower-mercury fish for tuna. According to the FDA and the EPA, canned light tuna is the better, lower-mercury choice. Canned white and Yellowfin Tuna are higher in mercury, but still okay to eat one time per week. Bigeye Tuna and Bluefin Tuna, not typically used in canned tuna, should be avoided completely (Ballance et al. 2021).

Oil Spills

The Deepwater Horizon oil spill released ~4 million barrels of oil in the northern Gulf of Mexico in areas of known for spawning of Atlantic Bluefin Tuna. Oil can cause deformities and death in tuna eggs and larvae. Even short-term exposure of adults interferes with heart function in Atlantic Bluefin Tuna, which may lead to life-threatening arrhythmias (Brette et al. 2014). The Deepwater Horizon spill influenced less than 10% of the spawning area for Atlantic Bluefin Tuna and influenced only a single-year class (Hazen et al. 2016; Gracia et al. 2019).

Climate Change and Shifting Baselines

Long-term shifts in tuna are expected with climate change. Like other fish, the distribution of tuna has shifted northward in the Northern Hemisphere and southward in the Southern Hemisphere (Erauskin-Extramiana et al. 2019; Townhill et al 2021). These shifts will undoubtedly influence productivity of tuna and potential yields. Additionally, seafood rating systems (e.g., Monterey Bay Aquarium Seafood Watch) and seafood certifications (e.g., MSC) to inform purchasing decisions may consider the rising costs of fossil fuels in their rating systems (McKuin et al. 2021). Furthermore, setting appropriate baselines for recovery of tuna populations present a new challenge as old data sets are abandoned or forgotten. The average size of harvested tuna has been reducing over time. It is unlikely we will see a return of abundant giant tuna in our lifetimes. Shifting baselines affect our vision for the future.

Ecosystem Connections

Finally, the management of tuna seldom considers that they are also preyed upon in ocean ecosystems. Yet, predators such as large pelagic sharks and Orcas feed on tuna. Predators also depredate tuna caught in longline fisheries. Survival of killer whale calves was reduced and recruitment ceased when tuna stocks declined near the Strait of Gibraltar (Esteban et al 2016). Consequently, future stock assessments should consider the tuna predators when setting harvest quotas.

Profile in Fish Conservation: D. G. Webster, PhD

D. G. Webster is Associate Professor of Environmental Studies at Dartmouth University. Her major research interest is understanding feedbacks within global-scale social-ecological systems in order to improve environmental governance. Thus, she brings an important yet underutilized perspective from political science and organizational theory to bear on preventing collapse of international fisheries. She is author of two books, including Beyond the Tragedy in Global Fisheries, which explains the evolution of global fisheries governance through a responsive governance lens. Her research showed how fisheries all over the world may cycle through periods of effective and ineffective governance in what she calls the “management treadmill.” Her first book, Adaptive Governance: The Dynamics of Atlantic Fisheries Management, which won the International Studies Association’s Harold and Margaret Sprout Award, tested her vulnerability-response framework. Her contributions are relevant to the competition for fish associated with open access and declining fish stocks.

Webster’s concept of the governance treadmill helps to understand barriers to change and informs a wide range of crises. The concept was applied to the Maine lobster fishery, where governance shifted back and forth between effective and ineffective periods of management over a 200-year period. Recently, this concept helped scientists to demonstrate factors that help or hinder the alignment of government capacities toward prevention during public health crises, such as the COVID-19 pandemic. Stagnation in governance includes maladaptive responses by government, economy, and society that are ineffective. Often the very people with access to information and resources lack understanding to be effective. This was also evident in the response of ICCAT parties during the low ebb in Atlantic Bluefin Tuna populations.

Dr. Webster has explored new methods for exploring social-ecological systems as the lead investigator on a multi-institutional project called Fishscape: Modeling the Complex Dynamics of the Fishery for Tropical Tuna in the Eastern Pacific Ocean. This research focuses on international tuna fisheries, which are very difficult to manage. In the eastern Pacific alone, an area of about 10 million km², over 200 purse-seine vessels from more than 10 countries fish for tuna. In this project, her research team uses a unique form of analysis, called “agent-based modeling,” to better model vessel search processes and better understand how different types of regulations will affect the fish and tuna fishers who rely of them. This project wrapped up in 2015.

Dr. Webster teaches courses related to global environmental governance, green business, marine policy, and environmental economics. She earned her PhD from the University of Southern California’s Political Economy and Public Policy program in 2005.

This chapter was reviewed by Alfred “Bubba” Cook.

Long Descriptions

Figure 12.2: Illustration of seven common tunas; largest to smallest: 1) bluefin, 2) yellowfin, 3) bigeye, 4) albacore, 5) blackfin, 6) little, and 7) skipjack. Jump back to Figure 12.2.

Figure 12.5: Key: Green arrow – products and information flow; brown arrow – coordination and information flow; packaging material, vertical green arrow points to fish processing unit within a horizontal green arrow that includes, 1) tuna fish, 2) fishing vessel, 3) transit, 4) fish processing unit, 5) transporter, 6) distributor, 7) retailer; fish processing unit vertical brown arrow points both ways from fish processing unit to government. Jump back to Figure 12.5.

Figure 12.8: Top 10 tuna fishing nations (2018): 1) Indonesia (575,000 metric tons); 2) Japan (474,000 metric tons); 3) Papua New Guinea (325,000 metric tons); 4) Taiwan, China (320,000); 5) Spain (305,000); 6) Ecuador (300,000); 7) Republic of Korea (300,000); 8) USA (240,000); 9) Kiribati (195,000); 10) Philippines (150,000). Jump back to Figure 12.8.

Figure 12.12: Trends from 1950 to 2020, including 1) brown: new landings from eastern Atlantic and Mediterranean; 2) blue: eastern Atlantic and Mediterranean; 3) green Western Atlantic. Highest landing in 1995 with 55,000 metric tons of Eastern Atlantic and Mediterranean tuna. Jump back to Figure 12.12.

Figure 12.13: Two graphs show estimated spawning biomass; 1) Western: overfished 1970-2020; shaded line band is highest (105) in 1950 and declines through approx 2015; 2) Eastern: overfished 2000-2020; shaded line band is highest (900) in 1950 and 1980, then declines in 2010. Jump back to Figure 12.13.

Figure 12.16: Line graph shows increase in mercury with increasing trophic level with, 1) mercury in water, 2) mixed phytoplankton, 3) copepod, 4) menhaden, 5) tuna. Jump back to Figure 12.16.

Figure References

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