*I came across this document again while cleaning my laptop. This is a paper I made for my Biology 11 class back in 2008. It took me almost three months to finish this shit because my professor is as OC as OC can be. :|
Posting it here so I can erase the file and free up some space in my almost-full local disk.
Posting it here so I can erase the file and free up some space in my almost-full local disk.
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Figure 1 Bluefin tunas are voraciouseaters and they hunt in packs. They are accustomed to high-speed chases andwill eat almost anything that is around. Takenfrom http://animals.nationalgeographic.com/animals/ enlarge//bluefin-tuna image.html |
Haveyou ever wondered how it feels to eat a thousand-dollar fish? The bluefin tuna (Thunnus thynnus) is a highly popularfood among connoisseurs and can cost up to $45,000. There is a wide demand forthis prized fish because it is a good quality ingredient for sushi and sashimi.Despite the extremely high price of this delicacy, many people are still willingto buy this food item. The sad thing that comes with this is that thisthousand-dollar fish is slowly facing extinction due to the uncontrollableharvesting of this species in different parts of the world.
A fish like no other
The bluefin tuna is one of the mostinteresting fishes in existence. With a size that can reach up to 6.5 ft (2m)and a weight that’s up to 550 lbs. (250 kg), it is considered as one of thelargest world fishes (Collette 2009). Itsmetallic blue color on the top and the shimmering silver-white on the bottomserve as a camouflage and protection from enemies. It can live up to 25-30years and the most intriguing part of it is that nobody but another tuna candistinguish a male from a female one (Ellis2008).
Thebluefin is from the family of bony fishes, Scombridae. The term ‘bluefin’ actuallyrefers to three regional divisions of the specie: the Atlantic or Northern bluefin(Thunnus thynnus), Southern bluefin (Thunnus maccoyii) and the Pacificbluefin(Thunnus thynnus orientalis) (Collette 2009).
The bluefin’s torpedo-shaped, streamlinedbody is built for speed and the retractable pectoral fins and body-flushed eyesare adaptations to reduce the struggle while swimming. These explain why the bluefinis an extremely efficient swimmer and can attain a speed of 22.6 m s-1(81.4km h-1) allowing it to migrate across oceans (Bone, Blaxter and Marshall 1995).
Unlike most of the fishes, the bluefin iswarm-blooded and can maintain a temperature of up to 27 degrees Celsius (81degrees Fahrenheit), close to that of a mammal(Ellis 2008). Changes in temperature is aided by the bluefin’s ‘rete mirabile’, a unique adaptation ofits circulatory system that reduces the cooling effects of the surroundingwater by preserving 95% of internal heat produced by metabolism. Thisadaptation also account for the bluefin’s speed in swimming because its warmmuscles allow it to swim faster.
The bluefin is both epipelagic and oceanic.These fishes are found on the euphotic zone, the zone 100 m down from thesurface, but migrate to colder waters in the productive seasons. (Bone, et al.,1995) Like other epipelagicfishes, the bluefin must literally swim for its life. Its stiff body isnegatively buoyant and will sink if it stops swimming. (Ellis 2008)The bluefin isdistributed throughout the Pacific and Atlantic Oceans. Depending on the year,bluefin populations are concentrated in Japan and the Philippines.
As a carnivore, the bluefin eatswhatever it can catch which is almost everything. Bluefins hunt in packs likewolves and are designed for high-speed chases using their vision. The usualdiets for this fish are Atlantic herrings, sand lance, bluefish and squids.Italso feeds on crustaceans, zooplankton and eels (Ellis2008).
Fishingfor bluefins date back thousands of years ago even before time of Aristotle. Inthe Mediterranean, bluefin tunas were trapped and burned whole in spits. In theearly 1900’s, before tuna was served as an epicurean dish, people called it ‘horse mackerel’ and considered its stronglyflavoured red meat suitable only for the palates of cats and dogs. In the 1950’sthe tuna was regarded as nuisance because of the damage it causes to fishinggears (Ellis 2008).
Because of its astounding strength, big gamefishers from New Jersey and Nova Scotia regarded the bluefin as a worthyopponent. Although edible, the bluefin was classified only as a target forhunting and not as a food (Ellis 2008).
The extreme popularity of the bluefin tuna asa valued food came only with the introduction of sushi and sashimi in the worldcuisine. Japanese, who rely mostly onthe sea for their food, used to smoke and pickle their fishes and otherseafoods to prevent spoiling. But with the advent of refrigerators, theJapanese’s eating habit changed and the craze for raw food started (Ellis 2008).
Tuna, which was previously regarded as dogfood became maguro, a Japanesedelicacy as expensive as truffles and caviar. Toro, the best quality maguroobtained from the fatty belly of the adult bluefin, is highly demanded inthe market. This high demand resulted to an increase in the tuna price in theJapanese market. In 2001, a single tuna weighing 444 lbs. (201 kg) was sold for$173,000 (¥20.2 million), making it a world record as the highest priced fishin a market (Ellis 2008).
In the Tsukuji market, hundreds of bluefinsare lined up and auctioned almost every day. (Grescoe,2008). This love forsushi and sashimi extended to every part of the world including the UnitedStates of America. Tuna became expensive with a single slice costing $350 (Ellis 2008).
The high price of tunas in the marketattracted fishing fleets from all over the world. Tuna fishing intensified.Fishers discovered that bluefins in the Atlantic are larger and more bountifulcompared to the Pacific bluefins. The rush to provide tuna to the Japanesetable drove buyers and importers to the American ports such as Gloucester andBarnstable in Massachusetts (Ellis 2008).
In 1969, a regulatory board, the International Commission for theConservation of Atlantic Tunas (ICCAT), was established and quotas for tunafishing was enforced. Large catches were allowed in the eastern Atlantic whilefishing in the western Atlantic was limited. This was based on their beliefthat there were two populations of Atlantic bluefins. This belief was refinedwith the discovery that the foraging grounds for these two populationsoverlapped and that migration of fishes occurred. The ICCAT failed to stopoverfishing in the eastern Atlantic which resulted to a collapse of the bluefinstock throughout the ocean (Ellis 2008).
In the Mediterranean, the situation wasworse. Fishers capture half grown tuna, hold them in tuna ranches and floatingfish pens where they are fed and fattened until they are big enough to bekilled and shipped to Japan. Mediterranean countries take advantage ofloopholes in the tuna fishing law and established tuna ranches which guaranteedthe decimation of the bluefins’ population (Ellis2008).
Despite calls from conservationistorganizations such as the World Wildlife Fund (WWF), the ICCAT can’t stop the overharvestingof bluefins in the Mediterranean because of the high income that the status quois bringing. Moreover, the rampant illegal fishing of Japanese fleets thatignores the quotas and rules set by authorities along with the Japanese marketsoverly eager consumption of tuna, regardless of its way of capture, makes iteven harder to protect the dwindling population of the bluefins (Ellis 2008).
What’s in a slice of tuna?
Bluefinis low in sodium. It is a great source of vitamins A, B6 and B12, selenium andphosphorus. It is the darkest and fattiest of the tuna specie. This high fatcontent makes it a prized ingredient of sushi and sashimi. A higher fat contentalso makes it a higher quality product. Cooking is not advised because a strongodor and taste is released when the bluefin is cooked (Osher 2007).
In a single serving (100g), a bluefincontains 4.9 g of fat, 1.257 g of saturated fatty acids, 38 mg of cholesterol,36.5 mcg of selenium, 39 mg of sodium and 23.33 g of protein. Bluefin isregarded as a healthy food choice especially for those with heart problemsbecause of its low level of cholesterol (Osher2007).
Capturingthe Bluefin
Theoldest way of catching bluefin tunas is the tuna trap. Traps are placed instrategic locations where bluefins are known to travel. The fish enters thetrap and follows a chute towards a wider “holding area” where it will be unableto escape. Only few fishers in the Atlantic use this trap at present.
More popular and efficient ways of catchingthe bluefin such as purse seine, harpoon and rod and reel/hand line replacedthe tuna trap. The purse seine vessels capture tuna by encircling the school oftuna with a net and then closing or “pursing” the net to hinder the fishes’ escape.The vast majority of fishers who use this method is found in theMediterranean. Harpoon boats also huntbluefin throughout the Gulf of Maine. Both the harpoon and purse seine methodare referred to as fair weather fishery because it requires a calm sea to beeffective. “Show days” are days when fishes are visible close to the surface.Bluefin tunas can be observed busting the surface often either catching forprey or sunning in the warm water ( Lutcavage, 2008).
The largest and most popular method interms of the number of participants is the rod and reel fishery. Trolling andchunking are the most widely used. Trolling includes anchoring and sendingeither live or cut bait for the tunas (Lutcavage, 2008).
The bluefin tuna is also a famous game fishespecially in America. It is caught by a hook and line. According to somereports, bluefin do not readily take bait. They will only do so when it they arein mixed schools that include albacore or yellowfin. Scientists speculate thatthe intense feeding activity of the other species may stimulate the bluefintuna into a wild feeding frenzy (Lutcavage, 2008).
The methods of catching bluefin tuna do notbring serious damage to the physical habitat of the fish. But the excessivecatching of the bluefin tuna has a huge implication in the status of itspopulation. Most fishing fleets, as mentioned earlier, catch young tuna andfatten them in tuna ranches until they are ready for harvest. This lessenschances of reproduction and breeding among the bluefins and may result todepletion of the specie (Ellis 2008). Moreover,depletion of the bluefin stock causes an imbalance in the ecosystem of itsnatural habitat. The Atlantic bluefin tuna is towards the top of the food chainand preys on other aquatic organisms. With the depletion of the stock, thebluefin’s prey is slowly increasing in number and the whole food chain isdisturbed.
Breeding in captivity
Because of the alarming depletion of thebluefin stock, international organizations and other concerned parties takestep to conserve the endangered fish.
In South Australia, the CleanseasAquaculture Growout, a company owned by the Stehr Group, is attempting to breedthe bluefin in captivity. The Australian government granted Cleanseas 4.1million Australian dollars to assist in the commercialization of the southernbluefin breeding (Ellis 2008).
In October 2006, Cleanseas airlifted a broodstock of bluefin tunas and transferred them to a computer regulated threemillion litre tank designed to imitate the spawning conditions of the fishes.Through the computer, the temperature can be controlled as well as the lightingof the tank. This brood stock was not successful in producing offspring butCleanseas continues on improving their method of breeding in captivity (Ellis 2008).
In 2005, a research team at the SpanishInstitute in Puerto de Mazarrón, Spain successfully recovered sperm and egg fromcaptive broodstock of the Atlantic Bluefin tuna and performed in vitrofertilization. They were able to produce larvae(Ellis 2008).
The ICCAT also tries to enforcelaws that are aimed at preserving the bluefin’s population that is nearing extinction. But this efforts are matched bytremendous amount of illegal fleets from fishermen across the globe.
Ellis(2008)argues in his article, Bluefin Tuna inPeril, that the only way for the bluefin population to survive is eitherthrough bred captivity or a change in human nature. Rampant overfishing willresult in disadvantages for the our race in the future. The worst scenario willbe the extinction of the bluefin population. Parfit(1995) said in his article, Diminishing Returns, the trouble we haveis that there are many fishermen and not enough fish.
The alarming depletion ofbluefin population has serious implications to our environment. Not only doesit spell danger for the bluefin specie but it also affect the balance of thewhole ecosystem. The overharvesting of the tuna population should be stopped before it finally destroys the natural orderof our planet. We are all interconnected and in this cycle of life, a simpleaction may have serious repercussions to the rest of us.
References:
Bone,Quentin, N.B. Marshall and J.H.S. Blaxter. 1995. Biologyof Fishes. 2 ed. London, Chapman& Hall.
Ellis,Richard, 2008. The Bluefin in Peril. Scientific American 298: 59-65
Grescoe,Taras. 2008. Bottomfeeder. How to Eat Ethically in a World of Vanishing Seafood. NewYork, Bloomsbury.
Parfit,Michael. (1995) DiminishingReturns. Exploiting the Ocean’s Bounty. NationalGeographic 188:2-37
Collette,Bruce B. (2009). Thunnus Thynnus (NorthernBluefin Tuna). http://www.fishbase.org(accessed March 22, 2009).
Lutcavage,Molly. (2008). Large Pelagics Research Lab. http://www.tunalab.unh.edu(accessed December 27, 2008)
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