Overfishing Bluefin Tuna
Bluefin tuna are highly sought after by both sport fishermen and commercial fisheries worldwide, and this increase in demand has resulted in overfishing bluefin tuna, reducing their populations to critically low, unsustainable levels. As a large, fast swimming fish that puts up a spectacular fight, it is attractive to big-game fishermen due to the challenge it offers, allowing them to show off their fishing skills and prowess. The dark red meat from this fish is high in demand in the sushi and sashimi industry, where an estimated 600,000 tons is consumed in Japan alone. The high demand placed on this increasingly diminishing resource results in it fetching high prices on the Japanese market, which accounts for approximately 80% of Atlantic and Pacific bluefin tuna consumption, where exclusive restaurants ask 2000 yen (around $25) for a serving of top-grade otoro . In January 2011, a huge 754 lb (342 kg) bluefin tuna sold for approximately $410,000, (a record breaking £250,000) in Tokyo. This economical incentive has put added pressure on the bluefin tuna as a commercial species, and it is now also increasingly sold by many recreational fisherman who, seeing the lucrative opportunity presented to them, have applied for commercial licenses to enable them to sell their catch for great financial reward.
With advances in technology such as faster boats fitted with modern gadgets such as fish-finders, radar, and water temperature sensors to enable fishermen to quickly find schools of fish, and the use of helicopters in commercial fisheries to scout for fish, combined with an increase in performance of modern fishing gear, the pressure on the target species has intensified.
Big-game fisherman fish with rod, reel and tackle commonly using trolling methods to lure bluefin tuna onto the moving baited hooks towed behind a big-game fishing launch. Kite fishing is another method used by sport fishermen for catching bluefin tuna.
Trolling is also used in small-scale commercial fishing operations to catch bluefin tuna. Multiple fishing lines are set using outriggers to keep the lines apart and prevent them from getting tangled.
Pelagic long-lining is commonly used by commercial fisheries to catch bluefin tuna. This involves setting a line of hundreds, or even thousands, of baited hooks near the surface of the ocean to catch bluefin tuna. Unfortunately, if mitigating measures are not followed, a high by-catch of non-target species, particularly seabirds can result. Thousands of endangered albatross species are killed each year as a result of getting hooked and drowned after being attracted to the baited hooks during deployment.
Purse seine nets is another method used by commercial fisheries to trap large numbers of bluefin tuna in a single haul, after the net, which is set around the school of tuna by the circling fishing vessel or by an auxiliary vessel known as a skiff, is drawn into the fishing boat trapping the entire school of tuna in the catch. This method of fishing also has a by-catch of non-target species such as sharks, dolphins, turtles, and other non-target fish species. However, depending on the mesh size used in the nets, smaller fish may be able to escape, thus reducing the by-catch of certain non-targeted fish species.
Cage farming of bluefin tuna is a fishery that has been established primarily in Japan to meet the demand for this species commercially and to reduce the pressure on wild stocks by producing bluefin tuna for the sushi and sashimi market in local fish farms. However, cage farming of tuna causes a whole new set of ecological problems, as they are predatory fish and have to be fed. Consequently, prey fish are being fished out of the ocean in huge numbers to support this fishery, upsetting the ecological balance and leaving other marine predators starving. Read this thought provoking article on the overfishing of prey species to find out more about this critical problem.
While the Atlantic bluefin tuna or Northern bluefin tuna (Thunnus thynnus) is classified as Data Deficient on the IUCN Red Data List, the Western Atlantic stock is classified as Critically Endangered, meaning it is facing an extremely high risk of extinction in the wild in the immediate future, and the Eastern Atlantic stock is classified as Endangered on the IUCN Red Data List.
The Southern bluefin tuna (Thunnus maccoyii) is classified as Critically Endangered on the IUCN Red Data List. It is believed that if exploitation and overfishing of this species continues at the current rate, the total number of individuals of breeding age will fall below 500 within 100 years.
The Pacific bluefin tuna (Thunnus orientalis) is currently not listed on the IUCN Red Data List.
Fisheries Management of Bluefin Tuna
The International Commission for the Conservation of Atlantic Tunas (ICCAT) was established after the International Convention for the Conservation of Atlantic Tunas was signed in 1966 in an effort to manage this fishery more efficiently so as to conserve tuna numbers in the Atlantic Ocean and surrounding seas. The management goals of the ICCAT are to attain data through research into the biology and ecology of tuna species, primarily focussing on population studies and the effects of fishing on stock abundance in order to make recommendations for fisheries resource management of tuna species. The ICCAT also undertakes research in the by-catch of non-targeted species caught during commercial fishing for tuna. The ICCAT is responsible for setting restrictions such as total allowable catch, and minimum commercial size limits, in an effort to maintain tuna stocks at levels that will permit maximum sustainable catch.
Following an increased demand for bluefin tuna for sushi and sashimi dishes, and the resultant high prices that the meat from bluefin tuna fetches on the market, this species has been heavily exploited in recent years. This is exacerbated by the improvements in fishing technology, and the fact that bluefin tuna are a relatively long-living species, and hence reach sexual maturity later in life. Therefore, if young sexually immature fish under 5 years (depending on species, up to 8 years) of age are harvested, they will not have had the chance to breed, resulting in the fishery becoming unsustainable as the number of fish being removed from the population far outweighs the number of fish being replenished by reproduction.
Overfishing bluefin tuna has severely depleted wild populations worldwide, and drastic management measures are urgently needed to allow stocks to recover to sustainable levels in order for this fishery to continue being a viable resource in the future. While cage farming of bluefin tuna may help supply the needs of sushi and sashimi connoisseurs in the interim, and hopefully reduce the demand for wild stocks to allow populations in the wild to recover to acceptable levels, this is a double-edged sword, as the prey fish that the wild stocks depend on for survival are being depleted to support this aquaculture initiative. A holistic approach to fisheries management is urgently required, and prudent management of this fishery, and compliance by all fisheries, is critical if we want to save the bluefin tuna before it’s too late.
Fromentin, J-M. & Powers, J.E. “Atlantic bluefin tuna: population dynamics, ecology, fisheries and management.” Fish and Fisheries. Blackwell Publishing, Dec 2005; 6(4): 281-306.
International Commission for the Conservation of Atlantic Tunas, https://www.iccat.int/en/
McCurry, Justin. “Huge bluefin tuna fetches record price in Tokyo, but whale is left on the shelf”. The Guardian. Jan 2011. https://www.guardian.co.uk/world/2011/jan/06/japan-bluefin-tuna-record-price
Punt, A. 1996. Thunnus maccoyii. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 05 April 2011.
Safina, C. 1996. Thunnus thynnus. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 05 April 2011.
Safina, C. 1996. Thunnus thynnus (Eastern Atlantic stock). In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 05 April 2011.
Safina, C. 1996. Thunnus thynnus (Western Atlantic stock). In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. <www.iucnredlist.org>. Downloaded on 05 April 2011.
Whitehead, S.S. “Fishing Methods for the Bluefin Tuna (Thunnus thynnus) and an Analysis of the Catches.” Fish Bulletin No. 33. Division of Fish and Game of CaliforniaBureau of Commercial Fisheries_._ 1931.
Image Credit, Tuna rolls: Wikimedia Commons/BrokenSphere
Image Credit, French purse seine tuna boat with helicopter: Wikimedia Commons/NOAA
Image Credit, Big-game fisherman with giant tuna: Wikimedia Commons/NOAA
Image Credit, Trolling for tuna: Wikimedia/NOAA
Image Credit, Illustration of purse seine netting operation: Wikimedia/US National Parks Service
Image Credit, Cage farming tuna: Wikimedia/Sudika
Image Credit, Tuna for sale at fish market: Wikimedia/Fisherman
This post is part of the series: Bluefin Tuna Facts: Biology, Ecology, and Conservation Status
Bluefin tuna is a highly sought after fisheries resource but stock levels are declining at an alarming rate. Discover why these fish are so in demand and how they are fished. Learn bluefin tuna facts like their reproduction, feeding behavior, habitat, their conservation status and management.