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Diving northern gannets and a herring boat—a good sign of a productive tuna ground.

High consumer demand raises huge challenges in bluefin tuna management

Should the flesh of a recently harvested bluefin tuna appear a little translucent with a deep rose tone, the lucky fisherman could be in for a hefty payday.

“This type of colour is very important for a sushi chef, as presentation is vital,” a tuna buyer at the Seacow Pond wharf in western Prince Edward Island told us. The buyer was representing a Japanese sushi chef who would eventually skillfully cut the fish into thin slices and serve it over a small lump of white rice (maguro sushi).

As he ran his finger across the sample of the 375-pound tuna we just captured, the buyer further explained that fat distribution is also important. “It’s like shopping for steak; good marbling is a sign of high quality.”

After being harvested, tuna are immediately eviscerated, flash frozen, boxed, and shipped to Japanese auctions such as the famous 52-acre Tsukiji Fish Market in downtown Tokyo, where restaurant owners bid on the gigantic fish. Our tuna that the buyer examined eventually sold for $13 per pound, making the value of that single, quite small, tuna $4,875. The highest price ever paid for a single bluefin was $173,000. By the time it was sold as sushi, it was a million-dollar fish.

Yet, the Atlantic bluefin tuna fishery is, to understate the case, complicated. Characterized by a highly mobile lifestyle, bluefin tuna do not respect geopolitical boundaries and thus challenge effective management of their populations. High market demand for the succulent, sweet flesh and high prices are in direct conflict with conservation considerations.

Biological Perfection

The Atlantic bluefin tuna (Thunnus thynnus) is one of eight members of the genus Thunnus, otherwise known as the “tunas.” It is the biggest of all the tunas, with the ability to tip the scales at 1,500 pounds and attain lengths of more than 12 feet. As the name suggests, the Atlantic bluefin roams vast expanses of the sea to hunt down fast moving prey.

Kites are used to dangle mackerel on the water’s surface in hopes of enticing a strike from a bluefin tuna.

Swimming efficiently and quickly is key to being a successful open-water predator. While they share many of the same drag-reducing methods as other fishes, tunas and their relatives rely on a variety of evolutionary adaptions to survive. Recessed eyes and fins that fold into grooves help streamline the body. In addition, a crescent-shaped tail is specifically designed to reduce drag while optimizing power transfer to the water.

One of the most interesting adaptations of the bluefin tuna is their ability to heat their muscle, a trait shared with other predatory fishes such as great white sharks. The heat generated by constant movement is then circulated to tissues around the body, resulting in more efficient swimming.

A Population Divided

Atlantic bluefin tuna can be found across the entire ocean but are subdivided into western and eastern stocks. The designations relate to their spawning grounds: fish in the western stock spawn in the warm waters of the Gulf of Mexico while fish in the eastern stock spawn in the Mediterranean Sea. In Canadian waters, western stock bluefin are transient visitors, migrating here in summer and fall from the Gulf of Mexico to gorge themselves on herring and mackerel; leaving again in late fall to return to their spawning grounds.

But telemetry data for both eastern and western stock tuna indicate extraordinary trans-Atlantic migrations (by the age of 15 a bluefin will have swum an estimated million miles) that result in each stock crossing into the other’s home waters. Such stock mixing makes accurate population estimates difficult.

The International Commission for the Conservation of Atlantic Tunas (ICCAT) forms the regulatory body that synthesizes scientific data to provide management recommendations for the multi-national bluefin tuna fishery. The non-profit organization consists of 50 member nations, but only those nations that actually harvest tuna determine the total quota.

Each harvesting nation is assigned a percentage of the quota, which is further subdivided among each country’s different fishing fleets. Under the current agreement, Canada is allowed 21.8 per cent of the total quota, with Nova Scotia and Prince Edward Island allowed almost 75 per cent of the Canadian share. The balance is divided among New Brunswick, Newfoundland and Labrador, and Quebec.

The Exception to the Rule?

In general, Atlantic bluefin tuna represent an imperiled species, having been labeled “endangered” in May of 2011 by the Committee on the Status of Endangered Wildlife in Canada. However, key differences exist between the western and eastern stocks, chiefly as they pertain to how bluefin are fished and the subsequent health of each stock.

For example, underreporting of harvested bluefin tuna that occurred for nearly 10 years in European fisheries led to the establishment of inappropriate quota allotments for the eastern stock. In its 2014 stock assessment, ICCAT identified this infraction as “a major cause of stock decline” during that time frame.

Increasing pressures have also been placed on this eastern stock as purse seine operations can summarily round up entire schools of bluefin for placement into open-ocean pens. These circular containment facilities, known as “ranches,” rely on the capture of wild adults for later fattening before individuals are harvested and shipped to fish markets around the world. (This was actually conducted in St. Margaret’s Bay in Nova Scotia for several years.) The result is a very rapid removal of large numbers of fish from existing populations.

Yet, here in Atlantic Canada, fishermen are observing more and more fish entering the region’s waters, and it appears the science backs them up.

Recovering bluefin tuna populations requires increasing the numbers of sexually mature individuals. To accomplish this, ICCAT set an aggressive reduction in the western stock quota beginning in the late 1990s. Dr. Alex Hanke, a Department of Fisheries and Oceans (DFO) research scientist, explains that recent population estimates indicate the numbers of mature adult tuna are increasing. The population models thus appear to corroborate observations of Atlantic Canadian fishermen.

One could argue that the late 1990s quota reductions are to be credited for the improved numbers, but the predominant use of rod-and-reel harvest techniques in North America, versus the purse seine nets in European fisheries, which now account for more than 70 per cent of the European Union’s bluefin harvest, may be facilitating population recovery.

“All methods are potentially sustainable, however some are more likely to leave the population in a close to virgin state,” said Hanke. “Two keys to successful management are to ensure that fishing-related mortality remains less than what would otherwise occur in nature and that fish should be allowed to grow and reproduce,” he says.

Tackle Busters

The first record of a sport fisherman pursuing bluefin tuna in the Canadian Maritimes (Liverpool, NS) was in 1871. The heyday became the world-renowned International Tuna Cup fished out of Wedgeport, NS, and attracting the rich and famous from all over the western world. Today, international anglers still flock to the region to test their skill and staying power against these giant creatures.

“There is really nothing else like it on Earth,” says Larry Dahlberg of the Outdoor Channel’s Hunt For Big Fish. “The sheer size and power of these beasts is what excites most anglers.”

Although bluefin tuna can be caught in New England waters, Canadian waters have two assets that US waters do not—fish size and proximity to shore. Jamie Bruce of Bruce Brothers Charters in North Lake, Prince Edward Island, says that when an angler wants to tangle with a 1,000-pound fish and do so within sight of the shore, they come to Atlantic Canada. “We’re so close at times that we can see people swimming along the beach,” he says.

People are lured to Atlantic Canada with hopes of witnessing spectacular tuna feeding frenzies. One need only search YouTube videos online to find scores of amazing footage showing massive 500- to 1,000-pound tuna gracefully gliding through the water to devour dead herring and mackerel.

“Seeing the fish come up next to the boat and fearlessly eat a herring literally out of your hand is hard to beat,” says Dahlberg. Other techniques include using kites to keep mackerel skittering across the water’s surface or trolling large rigs containing a dozen or more lures.

A full day tuna fishing charter costs at least $1,200, depending on distance to the fishing grounds. However, anglers can often split the cost of a trip with several other people.

Bruce explains that the charter season is two-pronged, with late July and August dominated by anglers visiting the region with their families, and September through October—historically the peak fishing time for the largest bluefin—reserved for more hardcore anglers.

Catch, and Catch Again?

The concept of releasing one’s catch is not new, but its application in bluefin tuna fisheries is very recent. Six years ago, DFO initiated an experimental catch-and-release charter fishery to determine if the bluefin tuna resource could be used without placing any additional pressures on the existing stock.

Of course, the success of a catch-and-release fishery hinges on one fundamental and crucial assumption: a released fish will survive the angling event. Fortunately, research published in 2011 by Acadia University’s Dr. Michael Stokesbury and colleagues confirms just that, indicating a very high survival rate of released tuna.

Movement data from special satellite transmitters informed the researchers when, or if, a fish died. “We had two mortalities out of 59 tagged and released fish. So, the mortality estimate was 3.4 per cent,” said Stokesbury.

Anglers participating in the study followed guidelines set forth by DFO, including the use of special barbless circle hooks designed to hook the fish in the corner of the jaw. They were also encouraged to land the tuna in 45 to 60 minutes and to use heavy lines and leaders to expedite the landing process.

Stokesbury says, “If the fishers execute the fishery in the manner that is laid out by [the department of] Fisheries and Oceans, Canada, the 3.4 per cent mortality estimate should be an accurate representation of the actual impact on the fish.”

An economic study commissioned by the Ecology Action Centre in Halifax indicated that each tonne of tuna landed in the catch-and-release fishery could bring more than six times the revenue generated by commercial harvesting. While a complete switch to a catch-and-release only fishery is highly unlikely, at least for the moment, the results of this study suggests that promoting a catch-and-release fishery may be an endeavor worth pursuing.

Here in Atlantic Canada, the bluefin tuna is a regional fixture, and with careful management and co-operation from all stakeholders involved in the fishery we might continue to have these magnificent fish for many generations to come.

Fishing For Answers

Managing bluefin tuna stocks is a joint venture involving scientists and fishermen. Aside from catch data logged by each fisherman, the head from every tuna successfully landed is removed for analysis by researchers. Arguably the most valuable tissue to scientists in the entire bluefin tuna is a tiny, calcium-derived structure called an “otolith,” which is akin to our ear stones and helps maintain equilibrium.

“The otoliths are paired calcareous structures in the head that grow as the fish ages,” says Hanke. Like rings on a tree, each year of growth is reflected in thin bands on the inner structure of the otolith that can be counted to determine a fish’s age. Hanke notes that bluefin can live more than 30 years and that fish in the western stock reach sexual maturity at about nine years of age.

The otoliths also record information on the chemicals and trace elements of the fish’s environment. Scientists can then match chemical signatures to specific locations, giving them the ability to determine where a fish moved or even where it was born. “In total the samples help us determine where the fish was hatched and thus its stock of origin as well as the age structure of the stock,” Hanke explains.

Otoliths, like fingerprint scans, give scientists the ability to perform background checks on individual tuna. The information gleaned is critical to ensuring the sustainability of bluefin tuna stocks throughout the Atlantic.

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