Thunnus maccoyii (Castelnau 1872)

Die Suidelike blouvin-tuna (Thunnus maccoyii) is 'n roofvis wat voorkom in matige tot koue water van die Atlantiese-, Indiese- en Stille oseane. In Engels staan die vis bekend as Southern bluefin tuna.

Afname in vangste

Sien ook

• Alfabetiese lys van visse
• Lys van Suider-Afrikaanse visse volgens wetenskaplike name
• Lys van varswater visfamilies
• Lys van visfamilies

Verwysings

Eksterne skakel

• http://www.fishbase.org/summary/Thunnus-maccoyii.html
• Wikimedia Commons het meer media in die kategorie Suidelike blouvin-tuna.
• Wikispecies het meer inligting verwant aan: Suidelike blouvin-tuna

Mavi cənub tunesi(Thunnus maccoyii) - Xanıkimilər dəstəsindən balıq növü.

Balıq ilə əlaqədar bu məqalə qaralama halındadır. Məqaləni redaktə edərək Vikipediyanı zənginləşdirin.

Gràfica mostrant el volum total de captures d'aquesta espècie al llarg dels darrers anys.

La tonyina del sud (Thunnus maccoyii) és una espècie de peix de la família dels escòmbrids i de l'ordre dels perciformes.

Morfologia

Els mascles poden assolir els 245 cm de longitud total i els 260 kg de pes.^[3]

Distribució geogràfica

Es troba a l'Atlàntic, a l'Índic i al Pacífic.^[3]

Referències

Bibliografia

• Baillie, J. i Groombridge, B., 1996. Llista Vermella d'Animals Amenaçats de la UICN 1996. UICN, Gland, Suïssa.
• Castelnau, F. L. 1872. Contribution to the ichthyology of Australia. Núm. 1.--The Melbourne fish market (pp. 29-242). Núm. II.--Note on some South Australian fishes (pp. 243-247). Proc. Zool. Acclim. Soc. Victoria v. 1: 29-247 plus 1 p. Errata.
• Collette, B.B. i C.E. Nauen., 1983. FAO species catalogue. Vol. 2. Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. FAO Fish. Synop. 125(2). 137 p.
• Helfman, G., B. Collette i D. Facey: The diversity of fishes. Blackwell Science, Malden, Massachusetts (Estats Units), 1997.
• Moyle, P. i J. Cech.: Fishes: An Introduction to Ichthyology, 4a edició, Upper Saddle River (Nova Jersey, Estats Units): Prentice-Hall. Any 2000.
• Nelson, J.: Fishes of the World, 3a edició. Nova York, Estats Units: John Wiley and Sons. Any 1994.
• Wheeler, A.: The World Encyclopedia of Fishes, 2a edició, Londres: Macdonald. Any 1985.

Enllaços externs

• ITIS (anglès)
• AQUATAB.NET

Der Südliche Blauflossen-Thunfisch (Thunnus maccoyii) ist ein Thunfisch aus der Familie der Scombridae. Die Art ist ein vom Aussterben bedrohter Speisefisch.

Etymologie

Der Artzusatz maccoyii bezieht sich auf Frederick McCoy. Dieser war der erste Direktor des National Museum of Victoria in Australien.^[1]

Merkmale

Der Südliche Blauflossen-Thunfisch ist an der Unter- und Bauchseite weißlich gefärbt und besitzt ein laterales irisierendes blaues Band. Die erste dorsale Flosse ist tiefgelb, die Zweite und die Afterflosse weisen dagegen eine hellgelbe Färbung auf. Die Finlets sind gelb gefärbt mit schwarzen Spitzen. Das Skelett weist 18 präcaudale und 21 caudale Wirbel auf. Die Flossenformel lautet: D XII–XIV/13–16 + 8–10, A 12–15 + 7–10, pectoral 33–36, C 17, P I/5.^[1] Die Lebenserwartung beträgt circa 12 Jahre, wobei Einzelfälle von älteren Exemplaren bekannt sind. Dabei erreicht die Art eine Körpergröße von 160–200 cm, der Rekord liegt bei 225 cm. Das Gewicht beträgt für einen 180 cm großen Fisch etwa 100–130 kg.^[2]

Lebensweise

Die Art kommt in den südlichen Bereichen des westlichen Atlantik, Indischen Ozeans und der Tasmansee entlang des 30. bis 50 Breitengrads – in Ausnahmefällen auch bis 60° S – im Epipelagial vor. Dabei bevorzugt die Art während des Großteils ihrer Lebenszeit eher kühle Wassertemperaturen von 5–20 °C, allerdings werden laichende Fische und Larven in Gewässern mit Oberflächentemperaturen von 20–30 °C beobachtet. Die adulten Tiere wandern zum Laichen üblicherweise in wärmere Gewässer zwischen Australien und Indonesien bis zu 10° S. Die Laichzeit findet während des Sommers auf der Südhalbkugel von September bis März statt. Nach dem Larvenstadium migrieren die Juvenilen in die Große Australische Bucht (GAB). Bis zu einem Alter von fünf Jahren kann ein Zyklus beobachtet werden: Während des Sommers halten sich die Tiere in der GAB auf, während sie für den Winter nach Neuseeland oder Südafrika wandern. Tiere die älter als fünf Jahre sind, kehren nur selten in die GAB zurück und halten sich über die zuvor genannten Ozeane verteilt auf.^[3][2][4] Der Südliche Blauflossen-Thun ernährt sich von einer Vielzahl an unterschiedlichen Fischarten, Weich- und Krustentieren.^[2]

Wirtschaftliche Bedeutung

Insbesondere in Australien ist der Fang der Art von wirtschaftlichem Interesse. Die Fanggebiete erstrecken sich dabei entlang 10° bis 170° W entlang der Südhalbkugel, wobei jedoch eine Konzentration um Tasmanien, Neuseeland und Südafrika beobachtet werden kann. Der Fischfang erfolgt üblicherweise mittels Langleinen, während in Australien Ringwadenfischerei betrieben wird, um die Fische in Aquakulturen zu überführen.

Auf Auktionen in Tokio erzielen einzelne Exemplare teilweise hochpreisige Gebote von über 10.000 US-$. Kiyoshi Kimura, Chef einer japanischen Restaurantkette, ersteigerte 2019 ein Exemplar für 3,1 Millionen US-$.^[5] Hierbei hängt der Preis maßgeblich vom Fettgehalt und der Qualität des Fleisches ab. Dieses wird üblicherweise auf Sashimi-Märkten in Tokio verkauft. Es wird geschätzt, dass die Fischerei vom Südlichen Blauflossen-Thunfisch ein Geschäft im Umfang von über 1 Mrd. Euro ist.^[1][2]

Bedrohung

Die Art wird in der Roten Liste gefährdeter Arten als „Vom Aussterben bedroht“ aufgeführt. Ursachen hierfür sind das langsame Wachstum mit später Geschlechtsreife, eine ausgeprägte zyklische Migration und dass es nur einen einzelnen Laichort gibt. Als Hauptursache wird jedoch die intensive Befischung der Bestände seit den frühen 1950er-Jahren gesehen. Es wird angenommen, dass die Bestände von 1973–2009 um 85 % abnahmen, wobei keine Anzeichen für eine Erholung der Bestände vorhanden sind.^[4][3]

Einzelnachweise

1. ↑ ^{a b c} Dianne J. Bray, Martin F. Gomon: Southern Bluefin Tuna,Thunnus maccoyii (Castelnau 1872). In: Fisches of Australia. Abgerufen am 26. November 2018 (englisch).
2. ↑ ^{a b c d} Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. Band 2. Rom 1983, ISBN 92-5101381-0, S. 87–88 (fao.org [PDF; 6,0 MB; abgerufen am 27. November 2018]).
3. ↑ ^{a b} Takasho Kitagawa, Shingo Kimura (Hrsg.): Biology and Ecology of Bluefin Tuna. CRC Press, 2015, ISBN 978-1-4987-2488-3, Kap. 8, S. 189–195 (eingeschränkte Vorschau in der Google-Buchsuche [abgerufen am 27. November 2018]).
4. ↑ ^{a b} B. Collette et al.: Thunnus maccoyii,Southern Bluefin Tuna. In: Rote Liste gefährdeter Arten. 2011 (iucnredlist.org [abgerufen am 27. November 2018]).
5. ↑ Japan’s ‘tuna king’ shells out $3.1 million for bluefin at Tokyo’s new fish market. thenational.ae, 5. Januar 2019, abgerufen am 17. April 2020 (englisch).

Sisék anoe (nan Latèn: Thunnus maccoyii) nakeuh saboh jeunèh eungkôt nyang na di la’ôt Acèh. Lam bahsa Indônèsia eungkôt nyoë geupeunan eungkôt tuna sirip biru selatan. Eungkôt nyoe kayém geudrop lé ureueng meula'ôt^[1] biasa geupubloe u Jeupun. Di Jeupun yum saboh eungkôt nyang geuhon 70-80 kg trôk 3,2 milyar.^[2]

Nè

The southern bluefin tuna (Thunnus maccoyii) is a tuna of the family Scombridae found in open southern Hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S. At up to 2.5 metres (8 ft 2 in) and weighing up to 260 kilograms (570 lb), it is among the larger bony fishes.

Southern bluefin tuna, like other pelagic tuna species, are part of a group of bony fishes that can maintain their body core temperature up to 10 °C (18 °F) above the ambient temperature. This advantage enables them to maintain high metabolic output for predation and migrating large distances. The southern bluefin tuna is an opportunistic feeder, preying on a wide variety of fish, crustaceans, cephalopods, salps, and other marine animals.

Environmental/physical challenges

The southern bluefin tuna is a predatory organism with a high metabolic need. These are pelagic animals, but migrate vertically through the water column, up to 2,500 m (8,200 ft) in depth. They also migrate between tropical and cool temperate waters in the search for food.^[4] The seasonal migrations are between waters off the coast of Australia and the Indian Ocean. Although the preferred temperature range for southern bluefin tuna is from 18–20 °C (64–68 °F), they can endure temperatures as low as 3 °C (37 °F) at low depths, and as high as 30 °C (86 °F), when spawning.^[5]

This wide range of temperature and depth changes poses a challenge to the respiratory and circulatory systems of the southern bluefin tunas. Tuna swim continuously and at high speeds and, therefore, have a high demand for oxygen. The oxygen concentration in the water changes with the change in temperature, being lower at high temperatures.^[5] Tuna are, however, driven by the availability of food, not by thermal properties of water. Bluefin tuna, unlike other species of tuna, maintain a fairly constant red muscle (swimming muscle) temperature over a wide range of ambient temperatures. So, in addition to being endotherms, bluefin tuna are also thermoregulators.^[6] The species is listed as Endangered by the IUCN.

Physiology

Respiratory physiology

Respiratory systems of southern bluefin tunas are adapted to their high oxygen demand. Bluefin tunas are obligate ram ventilators: they drive water into the buccal cavity through their mouth, then over the gills, while swimming.^[7] Therefore, unlike most other teleost fish, the southern bluefin tuna does not require a separate pump mechanism to pump water over the gills. Ram ventilation is said to be obligatory in southern bluefin tunas, because the buccal-opercular pump system used by other teleost fish became incapable of producing a stream of ventilation vigorous enough for their needs. All species of tuna in general have lost the opercular pump, requiring a quicker movement of oxygenated water over the gills than induced by the suction of the opercular pump. Therefore, if they stop swimming, tunas suffocate due to a lack of water flow over the gills.^[6]

The oxygen need and oxygen uptake of the southern bluefin tuna are directly related. As the tuna increases its metabolic need by swimming faster, water flows into the mouth and over the gills more quickly, increasing the oxygen uptake.^[8] Additionally, since there is no energy required to pump the water over the gills, the tunas have adapted an increased energy output to swimming muscles. The oxygen and nutrient uptake in the circulatory system is transported to these swimming muscles rather than to tissues required to pump water over the gills in other teleost fish.

Based on the principles of the Fick equation, the rate of the gas diffusion across the gas exchange membrane is directly proportional to the respiratory surface area, and inversely proportional to the thickness of the membrane. Tunas have highly specialized gills, with a surface area 7–9 times larger than that of other aquatic environment organisms.^[7] This increased surface area allows more oxygen to be in contact with the respiratory surface and therefore diffusion to take place more quickly (as represented by the direct proportionality in the Fick equation). This massive increase in surface area of the gills of the southern bluefin tuna is due to a higher density of secondary lamella in the gill filaments.

The southern bluefin tuna, like other tuna species, has a very thin gas-exchange membrane.^[7][9] Tunas have a barrier thickness of 0.5μm, compared with 10μm of dogfish, 5μm of toadfish and less than 5μm of trouts. This means that the oxygen must diffuse a short distance across the respiratory surface to get to the blood. Similarly to the increased surface area, this allows the highly metabolic organism to take oxygenated blood into the circulatory system more quickly. On top of a quicker rate of diffusion in the respiratory system of southern bluefin tuna, there is a significant difference in the efficiency of the oxygen uptake. While other teleost fish typically utilize 27–50% of the oxygen in the water, the tuna's utilization rates have been observed as high as 50-60%. This overall high oxygen uptake works in close coordination with a well-adapted circulatory system to meet the high metabolic needs of the southern bluefin tuna.

The oxygen dissociation curves for southern bluefin tunas show a reverse temperature effect between 10 and 23 °C (50–73 °F), and temperature insensitivity between 23 and 36 °C (73–97 °F).^[10] Reverse temperature shift might prevent premature oxygen dissociation from hemoglobin as it is warmed in rete mirabile.^[8] Root effect and a large Bohr factor were also observed at 23 °C (73 °F).^[10]

Circulatory physiology

The cardiovascular system of tunas, as in many fish species, can be described in terms of two RC networks, in which the system is supplied by a single generator (the heart). The ventral and dorsal aorta feed resistance of the gills and systemic vasculature, respectively.^[11] The heart in tunas is contained inside a fluid-filled pericardial cavity. Their hearts are exceptionally large, with ventricle masses and cardiac output roughly four to five times larger than those of other active fishes.^[12] They consist of four chambers, as in other teleosts: sinus venosus, atrium, ventricle, and bulbus arteriosus.^[9]

Tunas have type IV hearts, which have more than 30% compact myocardium with coronary arteries in compact and spongy myocardium. Their ventricles are large, thick-walled, and pyramidal in shape, allowing for generation of high ventricular pressures. The muscle fibers are arranged around the ventricle in a way that allows rapid ejection of stroke volume, because ventricles can contract both vertically and transversely at the same time. Myocardium itself is well vascularized, with highly branched arterioles and venules, as well as a high degree of capillarization.^[7]

Major arteries and veins run longitudinally to and from the red swimming muscles, which are found close to the spinal column, just underneath the skin. Small arteries branch off and penetrate the red muscle, delivering oxygenated blood, whereas veins take deoxygenated blood back to the heart.^[6] The red muscles also have a high myoglobin content and capillary density, where many of the capillaries branch off. This helps increase surface area and red-cell residence time.^[13] The veins and arteries are organized in a way that allows countercurrent heat exchange. They are juxtaposed and branched extensively to form rete mirabile. This arrangement allows the heat produced by the red muscles to be retained within them, as it can be transferred from the venous blood to the ingoing arterial blood.^[6]
Tunas have the highest arterial blood pressure among all fishes, due to a high resistance of blood flow in the gills. They also have a high heart rate, cardiac output, and ventilation rate. To achieve high cardiac outputs, tunas increase their heart rate exclusively (other teleosts may increase their stroke volume as well). High cardiac outputs in southern bluefin tuna are necessary to achieve their maximum metabolic rates.^[7][9] The bulbus arteriosus can take up an entire stroke volume, maintaining a smooth blood flow over the gills through diastole. This might, in turn, increase the rate of gas exchange.^[7] Their heart rate is also affected by temperature; at normal temperatures can it reach up to 200 beats/min.^[13]

The blood of southern bluefin tuna is composed of erythrocytes, reticulocytes, ghost cells, lymphocytes, thrombocytes, eosinophilic granulocytes, neutrophilic granulocytes, and monocytes.^[14] Southern bluefin tuna has a high blood hemoglobin content (13.25—17.92 g/dl) and, therefore, a high oxygen carrying capacity. This results from an increased hematocrit and mean cellular hemoglobin content (MCHC). The erythrocyte content in the blood ranges from 2.13 to 2.90 million/l which is at least twice that of adult Atlantic salmon, reflecting the active nature of southern bluefin tuna.^[8][14] Because the MCHC is high, more blood can be delivered to tissues without an increase in energy used to pump more viscous blood. For southern bluefin tuna, this is important in blood vessels that are not protected by heat exchangers when they migrate to colder environments.^[8]

Integration of respiratory and circulatory organs

Tunas are more mobile than any terrestrial animals and are some of the most active fish; therefore, they require highly efficient respiratory and circulatory systems. Southern bluefin tuna, as well as other species of tunas, have developed many adaptations in order to achieve this.^[6]
Their respiratory system has adapted to rapidly take up oxygen from water. For example, tunas switched from a buccal-opercular pump system to ram ventilation, which allows them to drive large quantities of water over their gills. Gills have, in turn, become highly specialized to increase the rate of oxygen diffusion. The circulatory system works together with the respiratory system to rapidly transport oxygen to tissues. Due to high hemoglobin levels, the blood of southern bluefin tuna has a high oxygen carrying capacity. Furthermore, their large hearts, with a characteristic organization of muscle fibres, allow for comparatively high cardiac outputs, as well as rapid ejection of stroke volume. This, together with the organization of blood vessels and a countercurrent heat exchange system, allows the southern bluefin tuna to rapidly deliver oxygen to tissue, while preserving energy necessary for their active lifestyle.^[6][7]

Osmoregulation

Environmental osmotic conditions

Southern bluefin tuna migrate between a variety of different ocean regions, however the osmotic conditions faced by the tuna stay relatively similar. This species of tuna inhabits ocean areas that are relatively high in salinity compared to the rest of the world's oceans.^[15] Like other marine teleost fish, the southern bluefin tuna maintain a constant ion concentration in both their intracellular and extracellular fluids. This regulation of an internal ion concentration classifies southern bluefin tuna as osmoregulators.^[6]

The blood plasma, interstitial fluid, and cytoplasm of cells in southern bluefin tuna are hyposmotic to the surrounding ocean water. This means that the ion concentration within these fluids is low relative to the seawater. The standard osmotic pressure of seawater is 1.0 osmole/L, while the osmotic pressure in the blood plasma of the southern bluefin tuna is approximately half of that.^[16] Without the mechanism of osmoregulation present, the tuna would lose water to the surrounding environment and ions would diffuse from the seawater into the fluids of the tuna to establish equilibrium.^[6]

The southern bluefin tuna acquires its water by drinking seawater: its only available water source. Since the osmotic pressure of the fluids in the tuna must be hyposmotic to the seawater that has been taken up, there is a net loss in ions from the tuna. Ions diffuse across their concentration gradient from the fluids of the tuna to the external seawater. The result is a net movement of water into the fluid of the bluefin tuna, with the net movement of ions being into the seawater. Southern bluefin tuna, along with other marine teleost fish, have acquired a variety of proteins and mechanisms which allow the secretion of ions through the gill epithelium.^[6]

Due to the southern bluefin tuna's high metabolic need, ions must be taken up relatively quickly to ensure sufficient concentrations for cellular function. Tuna are able to drink the seawater as they constantly swim in order to ensure sufficient ion concentrations. The seawater is specifically high in sodium and chloride ions which together make up approximately 80% of the ions in the water.^[15] The intake of sodium and chloride, along with lower relative concentrations of potassium and calcium ions in the seawater allow southern bluefin tuna to generate the action potentials required for muscle contraction.^[6]

Primary osmoregulatory system and features

Tunas have elevated levels of ion and water transfer due to their elevated gill and intestinal Na⁺/K⁺ ATPase activity, in which this activity is estimated to be about four to five times higher when compared to other freshwater vertebrates, such as rainbow trout.^[17] The gills, due to their large surface area, play a significant role toward osmoregulation in the tuna to maintaining water and ionic balance by excreting NaCl. The intestine also contributes toward compromising for the osmotic loss of water to the surroundings by absorbing NaCl to withdraw the needed water from the lumen contents.^[18]

The kidney also plays a crucial role toward tuna osmoregulation by excreting divalent ionic salts such as magnesium and sulfate ions. By the use of active transport, the tuna could move solutes out of their cells and use the kidneys as a means to preserve fluidity.

Anatomy and biochemistry involved in osmoregulation

The primary sites of gas exchange in marine teleosts, the gills, are also responsible for osmoregulation. Because gills are designed to increase surface area and minimize diffusion distance for gas exchange between the blood and water, they may contribute to the problem of water loss by osmosis and passive salt gain. This is called the osmo-respiratory compromise. To overcome this, tunas constantly drink seawater to compensate for water loss.^[19] They excrete highly concentrated urine which is approximately isosmotic to blood plasma, i.e. urine solute to plasma solute ratio is close to 1 (U/P≅1). Because of this, solely excreting urine is not sufficient to resolve the osmoregulatory problem in tunas. In turn, they excrete only the minimum volume of urine necessary to rid of solutes that are not excreted by other routes, and the salt is mostly excreted via gills. This is why the composition of solutes in urine differs significantly from that of the blood plasma. Urine has a high concentration of divalent ions, such as Mg²⁺ and SO₄²⁻ (U/P>>1), as these ions are mostly excreted by the kidneys keeping their concentration in blood plasma from rising. Monovalent ions (Na⁺, Cl⁻, K⁺) are excreted by the gills, so their U/P ratios in the urine are below 1. The excretion of inorganic ions by structures other than kidneys is called the extrarenal salt excretion.^[6]

In southern bluefin tuna and other marine teleosts, specialized ion-transporting cells called ionocytes (previously known as mitochondrion-rich cells and chloride cells) is the primary sites of NaCl excretion^[20] Ionocytes are usually found on the gill arch and filament,^[20][21] though in some cases can be also found on the gill lamellae when exposed to various environmental stressors.^[22] Ionocytes are interspersed between pavement cells which occupy the largest proportion of the gill epithelium. Ionocytes are highly metabolically active, as indicated by the large number of mitochondria (which produce energy in the form of ATP). They are also rich in Na⁺/K⁺ ATPases, in comparison to other cells.^[6] Ionocytes have an elaborate intracellular tubular system, continuous with the basolateral membrane (facing blood). The apical side (facing the environment) is typically invaginated below the surrounding pavement cells, forming apical crypts. Leaky paracellular pathways exist between the neighbouring ionocytes.^[23]

Ionocytes of marine teleosts, such as the southern bluefin tuna, employ specific transport mechanisms to excrete salt. By ingesting seawater they uptake water and electrolytes, including Na⁺, Cl⁻, Mg²⁺ and SO₄²⁻.^[24] As seawater passes through the esophagus it is quickly desalinated as Na⁺ and Cl⁻ ions move down their concentration gradients into the body. In the intestine, water is being absorbed in association with NaCl cotransport.^[19]

Inside the gill ionocyte, the Na⁺/K⁺ ATPases on the basolateral membrane maintain a low sodium concentration.^[19][20] The NKCC (Na⁺-K⁺-Cl⁻ channel) cotransporter moves K⁺ and Cl⁻ ions inside the cell, while Na⁺ diffuses in, down its concentration gradient.^[19][20] The K⁺ ions can leak out of the cell through their channels on the basolateral membrane, whereas Cl⁻ ions diffuse out, through their channels on the apical membrane. The gradient created by Cl⁻ allows Na⁺ ions to passively diffuse out of the cell via paracellular transport (through tight junctions).^[19][20]

Special adaptations for osmoregulation

The southern bluefin tuna have a large gill surface area which is important for oxygen consumption and handling high osmoregulatory costs, associated with the high resting metabolic rate.^[25] They can adapt to increasing water salinity, where the ionocyte increase in size, gill filaments become thicker, the surface area of the basolateral membrane increases, and the intracellular tubular system proliferates.^[6] Teleost fish do not have the loop of Henle in the kidneys and are, therefore, not able to produce hyperosmotic urine. Instead, they secrete small amounts of urine frequently in order to prevent water loss and excrete NaCl thorough the gills.^[19] Additionally ram-ventilators such as tunas and billfishes have specialized gill structures: adjacent lamellae and filaments are fused to prevent gill filaments and lamellae from collapsing under high water flow.^[26][27] Here, ionocytes have also been found on these specialized interlamellar, lamellar, and filament fusion in larval and adult Yellowfin Tuna (Thunnus albacares).^[21]

Thermoregulation and metabolism

Physiological challenges

Southern bluefin tunas are thermo-conserving and can function over a wide range of temperature conditions, which allows them to dive from the surface of the water to depths of 1,000 m (3,300 ft), in only a few minutes.^[28] They forage in temperate waters of the southern hemisphere oceans, during winter in Australia, and migrate to tropical areas in the north-western Indian Ocean, from spring to autumn, for the spawning season.^[5] Their preferred temperature range is 18–20 °C (64–68 °F), with most of their time (91%) spent below 21 °C (70 °F). Southern bluefin tunas experience a wide range of ambient water temperatures, from a minimum of 2.6 °C (36.7 °F) to a maximum of 30.4 °C (86.7 °F).^[5] All species of tuna are reported to spawn in water temperatures above 24 °C (75 °F).^[29] However, 24 °C (75 °F) is outside, or at the upper limit, of temperature tolerances for bluefin tunas. Large individuals have been found to withstand temperatures of less than 10 °C (50 °F) and as low as 7 °C (45 °F) for over 10 hours, possibly to search for prey.^[5] During the day they migrate through depths between 150–600 m (490–1,970 ft), but at night they stay in waters that are 50 m (160 ft) or less in depth.^[5]

Heat exchange in southern bluefin tuna is a unique adaption among teleost fishes. They are endotherms, which means that they can maintain their internal temperature elevated above water temperature. Heat is lost through heat transfer throughout the whole body surface and the gills, so prevention of metabolic heat loss is important. This is an adaptive feature, because it is far more difficult for an organism to maintain a temperature differential with its environment in water than in air.^[30] It allows tunas to have faster metabolic reactions, to be more active, and to exploit colder environments. A disadvantage is that they require a high energy input and insulation, and there is potential for greater heat loss, because of the high temperature gradient with the environment.^[30] To reduce heat loss, southern bluefin tunas have reduced their heat conduction by the presence of oxidative muscle tissues and fat, as muscle and fat have low heat conductivity, according to Fourier's law of heat conduction.^[30] Their heat convection is also reduced. Since the heat transfer coefficient depends on an animal's body shape, tunas increased their body size, adopted a fusiform shape, and their internal tissue arrangement is based on different thermal conductances.^[30]

Adaptations involved in temperature regulation

Southern bluefin tunas often migrate vertically through the water column in search of their preferred temperature, and they spend time in cooler waters seeking prey. Some have hypothesized that they take refuge in warmer areas of water fronts and eddies after these foraging periods, but others suggest that these migrations are only associated with the aggregation of prey. Either way, it is clear that southern bluefin tuna have developed complex physiological mechanisms to maintain their body temperature (T_B) significantly above the ambient water temperature in these changing conditions.^[5] In fact, tuna can maintain the temperature of their muscles at 5–20 °C (9–36 °F) above the temperature of surrounding water.^[31] Overall, tuna do not have a set body temperature point; rather it maintains its T_B within a narrow range, with variations of only 4–5 °C (7–9 °F) over time and from individual to individual.^[31][32]

In contrast to the warm muscle and viscera of swimming bluefin tunas, the heart and gills remain at or near ambient water temperature in all tuna species.^[33] Tunas achieve regulation of body temperature by employing complex vascular structures called rete mirabile.^[31] In bluefin tuna, large lateral cutaneous vessels that branch off into the arteries and veins of rete mirabile supply blood to the red muscle, instead of a centrally located aorta.^[34] Rete mirabile function as countercurrent heat exchangers that prevent metabolic heat loss at the gills. Warm-bodied fish, such the southern bluefin tuna, maintain their T_B by varying the efficiency of heat exchangers. Some oxygen is typically lost to outgoing venous blood in the process of heat exchange, depending on heat exchanger efficiency, which can be influenced by the rate of blood flow and blood vessel diameter.^[32]

As tunas migrate to greater depths, often looking for prey, they encounter cooler water temperatures at the gill surface. To maintain normal levels of oxygen transport in these conditions, they have developed unique blood respiratory properties. The oxygen carrying capacity in southern bluefin tuna is high, due to the high hemoglobin (Hb) concentration. The blood affinity for oxygen is also elevated. Normally, blood affinity for oxygen would change with changes in temperature experienced at gills (in comparison to warmer adjacent tissues); however, Hb in southern bluefin tuna shows insensitivity to temperature, and a reverse temperature effect between 10 and 23 °C (50 and 73 °F) (Hb-O₂ binding is endothermic). Due to their anatomical positioning, the heart and the liver are the coldest organs and significant work needs to be expended for them to serve a regionally warmer body. It is likely that the reversed temperature effect on oxygen binding was developed to ensure adequate unloading of oxygen at the heart and liver, especially in colder waters when the difference in temperature between these organs and the swimming muscle is the greatest.^[4][35]

Since southern bluefin tunas must constantly be swimming to drive water over the gills and provide their bodies with oxygen, there is a requirement for their metabolic rate to constantly be high. Unlike other organisms, the southern bluefin tuna cannot expend more energy to produce heat in cold temperatures, while slowing down metabolism to cool down in high temperature waters and maintain a homeostatic temperature. Instead, the southern bluefin tuna seems to implement a system that regulates how actively the rete mirable system heats the tissues. Experiments involving the southern bluefin tuna have led researchers to believe that this species of tuna has developed a shunting system. When the southern bluefin tuna experiences cold temperatures, more blood is directed to the rete vascular system, heating muscle tissue, while in warm temperatures, blood is shunted to the venous and arterial systems, reducing the heat in the muscle tissues.^[34]

The tuna's heart must pump blood to the bodily extremities at a quick rate to conserve heat and reduce heat loss. The heart of tunas is able to adapt to colder water temperatures, mainly by increasing blood flow and pumping warm blood to the muscle tissues at a faster rate.^[32]

In addition to the main source of heat loss at the gills, there is a significant amount of heat lost to the lower temperature water through the body surface. The southern bluefin tuna, being considered a large fish, has a relatively low surface-area-to-volume ratio. This low surface-area-to-volume ratio explains why there is a more significant amount of heat lost at the site of the gills compared to the body surface. As a result, the rete vascular system is located mostly at the site of the gills, but also at several other organs in the tuna. Specifically, due to the high metabolic demand of the southern bluefin tuna, the stomach is an organ requiring a high demand of thermoregulation. It is only able to digest food at specific temperatures, often much higher than the temperature of the surrounding water. Since the food is ingested along with a large amount of seawater, the contents must be heated to a temperature that allows the food to be digested and the nutrients and ions taken up. The southern bluefin tuna seems to increase blood flow to the stomach at times of increased digestion, by increasing the diameter of blood vessels flowing to the stomach, allowing more warm blood to reach the organ at a quicker rate.^[32]

The eyes and the brain of the southern bluefin tuna are a common area of research involving the thermoregulatory systems of this species. Both the eyes and the brain maintain a remarkably high temperature when compared to the surrounding water environment, often 15–20 °C (27–36 °F) higher than the temperature of the water. The carotid rete carries blood to the brain and seems to play a role in the elevated temperatures of both the brain and the eyes of the southern bluefin tuna. The carotid rete has been observed to have strong insulation properties, allowing blood to travel a great distance throughout the body while reducing the amount of heat lost to surrounding tissues prior to the brain and eyes. The elevated temperatures in the brain and eyes allow the southern bluefin tuna to search for food more effectively by reducing reaction time and creating stronger vision. This is due to the increased axon activity that is directly correlated to temperature: high temperatures allowing signal transduction to take place more quickly.^[36]

Special adaptations unique to habitat/lifestyle

One of the adaptations that allow bluefin tunas to have large migratory patterns is their endothermic nature, whereby they conserve heat in their blood and prevent its loss to the environment. They maintain their body temperature above the ambient water temperature in order to improve their locomotor muscle efficiency, especially at high speeds and when pursuing prey below the thermocline region.^[37] It has been hypothesized that tunas can rapidly alter their whole-body thermal conductivity by at least two orders of magnitude.^[37] This is done by disengaging the heat exchangers to allow rapid warming as the tuna ascend from cold water into warmer surface waters, and are then reactivated to conserve heat when they return into the depths.^[37] Through this unique ability, tunas can reach out into otherwise hazardously cold water in order to hunt for food or escape from predators. Variations in their muscle temperatures are not necessarily influenced by water temperatures or that of swimming speeds, which indicates the ability of the bluefin tuna to control the level of efficiency of their heat exchange system.^[38] Relating to the efficiency of oxygen extraction, tuna gill structure maximizes contact between water and the respiratory epithelium, which minimizes anatomical and physiological “dead space” in order to enable more than 50% oxygen-extraction efficiencies.^[39] This allows the fish to maintain a high rate of oxygen consumption as it continually swims out to others areas of oceans in search of food and ground for growth and reproduction.

Commercial fishing

Southern bluefin tuna catch - Australia & Japan (1952-2013)

Southern bluefin tuna are targeted by fishing fleets from a number of nations. This occurs on the high seas and within the Exclusive Economic Zones of Australia, New Zealand, Indonesia and South Africa. The onset of industrial fishing in the 1950s, in conjunction with ever-improving technologies such as GPS, fishfinders, satellite imagery, etc., and the knowledge of migration routes, has led to the exploitation of southern bluefin tuna across its entire range. Improved refrigeration techniques and a demanding global market saw global SBT catch plummet from 80,000 tonnes a year during the 1960s to 40,000 tonnes a year by 1980.^[40] Australian catch peaked in 1982 at 21,500 tonnes, and the total population of SBT has since declined by about 92 percent.^[41] There was a pressing obligation to reduce harvesting pressure southern bluefin tuna populations in the mid-1980s. The main nations fishing the species adapted their practise to manage their catches, although no official quotas were put in place.

Convention for the Conservation of Southern Bluefin Tuna

In 1994, the Convention for the Conservation of Southern Bluefin Tuna formalised existing voluntary management measures between Australia, New Zealand and Japan. The Convention created the Commission for the Conservation of Southern Bluefin Tuna (CCSBT). Its objective was to ensure, through appropriate management, the conservation and optimum utilisation of the global fishery. The convention applies to southern bluefin tuna (Thunnus maccoyii) throughout its entire migratory range, rather than within a specified geographic area. South Korea, Taiwan, Indonesia and the European Union have since joined the Commission and South Africa and the Philippines are cooperating with it as non-members. The CCSBT is headquartered in Canberra, Australia.

Current quota limits were reduced in 2010 to reflect the vulnerable nature of wild stocks. Quotas for the 2010/2011 seasons were reduced to 80% of years previous. The global total allowable catch (TAC) was reduced from 11,810 tonnes from the previously allocated global TAC to 9,449 tonnes.^[42] After the quota reduction, Australia had the highest "effective catch limit" with 4,015 tonnes, followed by Japan (2,261), Republic of Korea (859), Fishing Entity of Taiwan (859), New Zealand (709), and Indonesia (651).^[42] Fishing pressure outside the allocated global TAC remains a major concern. The Australian government stated in 2006 that Japan had admitted to taking more than 100,000 tonnes over its quota over the previous 20 years.^[43] The reduced quotas reflected this, with Japan's cut by half, as supposed punishment for over-fishing.

Australia's quota bottomed out at 4,015 tonnes pa in the 2 years ending 2010/11, then increased to 4,528 tonnes in 2011/12, and 4,698 tonnes in 2012/13.

Total allowable catch (tonnes)

The quota system increased the value of the catch. Fishermen that once earned $600 a ton selling fish to canneries began making more than $1,000 per ton of fish, selling them to buyers for the Japanese market. Quotas are expensive and are bought and sold like stocks within their national allocations.^[48]

In 2010, the Australian wild catch quota was cut, following concerns about the viability of the stock.

In 2012, Japan expressed "grave concerns" that Australian catch numbers were falsely counted. In response, Australia committed to implementing video monitoring to verify their catches. However, in 2013 Australia withdrew its commitment stating that such monitoring would impose an "excessive regulatory and financial burden".^[49]

In October 2013, the Commission for the Conservation of Southern Bluefin Tuna increased the wild catch quota to Australian tuna ranchers. The increases, staged over two years, were to take the quota to 5665 tonnes in 2015. The tuna quota rose 449 tonnes to 5147 tonnes in 2014 and then by another 518 tonnes in 2015. The quota increases were expected to allow the ranchers to increase their output by approximately 2000 tonnes per year from 2015 onwards.^[50]

Australia's reported catch has exceeded that of Japan every year since 2006.

Recreational fishing

Southern bluefin tuna are targeted by recreational and game fishers in Australian waters. Allowable catch is regulated by legislation and varies from state to state.

Fishing competitions

Several fishing competitions targeting southern bluefin tuna are held annually. In 2015, the inaugural Coast 2 Coast Tuna Tournament was held in Victor Harbor.^[51] The event attracted 165 competitors and 54 boats. 164 fish were weighed in during the tournament, approaching 2500 kg of tuna in total. The average weight of the fish was 14.76 kg.^[52] 324 southern bluefin tuna were caught by 18 boats during the Riveira Port Lincoln Tuna Classic competition In April 2015. The largest fish caught during the competition weighed 13.2 kilograms.^[53]

The longest running tuna fishing competition in Australia is held annually in Tasmania by the Tuna Club of Tasmania, and was first held in 1966.^[54] Other competitions are held in Port Macdonnell, South Australia^[55] and Merimbula, New South Wales.^[56]

Recreational fishing regulations in Australian states

Aquaculture

Ranching

The rapidly declining fishery led Australian tuna fishers to investigate the potential for augmenting their catch through aquaculture. All SBT ranching occurs offshore of Port Lincoln, South Australia; the nearby town hosting almost all of the SBT fishing companies in Australia since the 1970s.^[62] Tuna ranching commenced in 1991 and developed into the largest farmed seafood sector in Australia.^[62] The industry grew steadily, maintaining production levels of 7000 to 10,000 tonnes per annum from the mid-2000s.^[63]

Southern bluefin tuna spawn between September and April each year in the only known spawning grounds in the Indian Ocean, between the north-west Coast of Australia and Indonesia. The eggs are estimated to hatch within two to three days, and over the next two years attain sizes of approximately 15 kilograms. The principal wild catch of the Australian SBT industry is fish aged two to three years.^[64] It is believed that SBT become sexually mature between 9 and 12 years in the wild,^[62] which highlights the major negative impact of removing pre-spawning populations from the wild.

Juvenile tuna are mainly caught on the continental shelf in the Great Australian Bight region from December to around April each year, and weigh on average 15 kg (33 lb). The tuna that are located are purse seined, and then transferred through underwater panels between nets to specialised tow pontoons. They are then towed back to farm areas adjacent to Port Lincoln at a rate of about 1 knot; this process can take several weeks. Once back at the farm sites, the tuna are transferred from the tow pontoons into 40–50 m (130–160 ft) diameter farm pontoons. They are then fed bait fish (usually a range of locally caught or imported small pelagic species such as sardines) six days per week, twice per day and "grown out" for three to eight months, reaching an average of 30 to 40 kg (66–88 lb).^[40][62] Because SBT swim so fast and are used to migrating long distances, they are difficult to keep in small pens. Their delicate skin can be easily damaged if touched by human hands and too much handling can be fatal.

As with most aquaculture ventures, feeds are the biggest factor in the cost-efficiency of the farming operation, and there would be considerable advantages in using formulated pellet feed to supplement or replace the baitfish. However, as yet the manufactured feeds are not competitive with the baitfish.^[65] A further future prospect in enhancing the ranching of SBT is the plan of Long Term Holding. By holding its fish for two successive growing seasons (18 months) instead of one (up to 8 months), the industry could potentially achieve a major increase in volume, greater production from the limited quota of wild-caught juveniles, and ability to serve the market year round.^[65] This presents several uncertainties, and is still in the planning stage.

Around April, harvest begins and fish are gently guided into a boat (any bruising lowers the price) where they are killed, flash frozen and most placed on Tokyo-bound planes. Armed guards are paid to watch over them as 2,000 tuna kept in a single pen are worth around $2 million.^[48] Australia exports 10,000 metric tons of southern bluefin tuna worth $200 million; almost all is from ranched stocks.^[48]

The southern bluefin tuna ranching industry is worth between 200 and 300 million Australian dollars annually to the economy of South Australia. The industry's value peaked in 2004 at $290 million, according to industry representative, Brian Jeffriess.^[66] In 2014, following an increase in Australia catch quota and emerging export opportunities to China, the sector anticipated an annual turnover of $165 million.^[67]

The capture and transportation of southern bluefin tuna to aquaculture pens near Port Lincoln is shown in the 2007 documentary film Tuna Wranglers.

Feeds

Scientists have tried and continue to try to develop less expensive fish feed. One of main obstacles is creating a processed food that doesn't affect the taste of the tuna. Southern bluefin tuna are largely fed fresh or frozen small pelagic fishes (including Sardinops sagax) and the use of formulated pellets is not yet viable.^[65] This cost is largely due to the expense of dietary research. The annual costs of diet for research alone is approximately US$100,000^[35] and there are additional problems associated with working with large, fast-swimming marine animals. Farm-raised tuna generally have a higher fat content than wild tuna. A one-metre tuna needs about 15 kg (33 lb) of live fish to gain 1 kg (2 lb) of fat, and about 1.5 to 2 tonnes of squid and mackerel are needed to produce a 100 kg (220 lb) bluefin tuna.^[48] Research evaluating ingredients for use in southern bluefin tuna feed is ongoing, and gathering information on ingredient digestibility, palatability and nutrient utilisation and interference can improve lower costs for tuna ranchers.^[68]

Dietary supplements

The use of dietary supplements can improve the shelf life of farmed SBT flesh. Results of a study by SARDI (South Australian Research and Development Institute) indicated that feeding a diet approximately 10 times higher in dietary antioxidants raised levels of vitamin E and vitamin C, but not selenium, in tuna flesh and increased the shelf life of tuna.^[69] This is important as the frozen baitfish diets are likely to be lower in antioxidant vitamins than the wild tuna diet.

Parasites and pathology

The risk of parasite and disease spreading for southern bluefin aquaculture is low to negligible; the modern SBT aquaculture industry has total catch to harvest mortalities of around 2-4%.^[70] A diverse range of parasite species has been found hosted by the southern bluefin tuna, with most of the parasites examined posing little or no risk to the health of the farms—with some southern bluefin actually showing antibody responses to epizootics^[71]—however, blood fluke and gill fluke have the greatest risk factors.^[72][73] Hypoxia is also a significant issue, and can be escalated due to unforeseen environmental factors such as algal blooms.^[70]

Complete aquaculture

Initially, difficulties in closing the life cycle of the species dissuaded most from farming them. However, in 2007, using hormonal therapy developed in Europe^[74] and Japan (where they had already succeeded in breeding northern Pacific bluefin tuna to third generation^[75]) to mimic the natural production of hormones by wild fish, researchers in Australia managed for the first time to trigger spawning in landlocked tanks. This was done by the Australian aquaculture company, Clean Seas Tuna Limited.^[76] who collected its first batch of fertilized eggs from a breeding stock of about 20 tuna weighing 160 kg (350 lb).^[48] They were also the first company in the world to successfully transfer large SBT over large distances to its onshore facilities in Arno Bay which is where the spawning has taken place. This led Time magazine to award it second place in the 'World's Best Invention' of 2009.^[77]

The state-of-the-art Arno Bay hatchery was purchased in 2000, and undertook a $2.5 million upgrade, where initial broodstock facilities catered for kingfish (Seriola lalandi) and mulloway (Argyrosomus japonicas), along with a live-feed production plant. This facility has more recently been upgraded to a $6.5 million special purpose SBT larval rearing recirculation facility. During the most recent summer (2009/2010), the company completed its third consecutive annual on-shore southern bluefin tuna spawning program, having doubled the controlled spawning period to three months at its Arno Bay facility.^[78] Fingerlings are now up to 40 days old with the grow-out program, and the spawning period has been extended from 6 weeks to 12, but as yet, grow-out of commercial quantities of SBT fingerlings has been unsuccessful.^[78] Whilst aquaculture pioneers Clean Seas Limited have not been able to grow out commercial quantities of SBT fingerlings from this season's trials, the SBT broodstock were wintered and conditioned for the 2010-11 summer production run.^[78]

With collaboration secured with international researchers, in particular with Kinki University in Japan,^[78] commercial viability was hoped to be achieved.

However, after experiencing financial difficulty, the board of Clean Seas decided during December 2012 to defer its tuna propagation research and write-off the value of the intellectual property it developed as part of its research into SBT propagation. According to the chairman and chief executive's report for the financial year ending 30 June 2013, the production of SBT juveniles had been slower and more difficult than anticipated. Clean Seas will maintain its broodstock to enable discrete research in the future, however they do not expect commercial production to be achieved over the short to medium term.^[79]

Clean Seas' attempts to close the life cycle of the species appear in the 2012 documentary film Sushi: The Global Catch. At the time of filming, Clean Seas' director Hagen Stehr was optimistic having experienced early success.

Human consumption

Southern bluefin tuna is a gourmet food, which is in demand for use in sashimi and sushi. It has medium flavoured flesh.

By far the largest consumer of SBT is Japan, with USA coming in second, followed by China. Japanese imports of fresh bluefin tuna (all 3 species) worldwide increased from 957 tons in 1984 to 5,235 tons in 1993 [7]. The price peaked in 1990 at $34 per kilogram when a typical 350 pound fish sold for around $10,000.^[40] As of 2008, bluefin was selling for $23 a kilogram.^[40] The drop in value was due to the drop in the Japanese market, an increase in supply from northern bluefin tuna from the Mediterranean, and more and more tuna being stored (tuna frozen with the special "flash" method can be kept for up to a year with no perceivable change in taste).

Frozen tuna at the Tsukiji fish market.

The Tsukiji fish market in Tokyo is the largest wholesale market of SBT in the world. Tsukiji handles more than 2,400 tons of fish, worth about US$20 million, a day, with pre-dawn auctions of tuna being the main feature.^[80] No tourists are allowed to enter the tuna wholesale areas, which they say is for purposes of sanitation and disruption to the auction process.^[81] Higher prices are charged for the highest quality fish; bluefin tuna worth over $150,000 have been sold at Tsukiji. In 2001, a 202-kilogram wild Pacific bluefin tuna caught in Tsugaru Straight near Omanachi I Aomori Prefecture sold for $173,600, or about $800 a kilogram.^[40] In 2013, a 222-kilogram Pacific bluefin tuna was sold at Tsukiji for $1.8 million, or about $8,000 per kilogram.^[82]

Conservation

The southern bluefin tuna is classified as Endangered species (IUCN status) on the IUCN Red List of Threatened species.^[1] It had been reclassified from Critically Endangered in September 2021.^[83] As of 2020, the current mean population estimate is 13% of unfished levels. Its stock status remains "overfished", though it is not currently subjected to overfishing.^[84]

In Australia, the southern bluefin tuna is listed as Conservation Dependent under the EPBC Act. This listing allows for the commercial exploitation of the species,^[85] despite their accepted global status as an over-fished species.^[86] The species is listed as Endangered under the Fisheries Management Act 1994 (New South Wales) and as Threatened under the Flora and Fauna Guarantee Act 1988 (Victoria). Recreational fishing targeting southern bluefin tuna is permitted in all states and territories and is regulated by various combinations of bag, boat and possession limits.

In 2010, Greenpeace International added the SBT to its seafood red list. It is a list of fish that are commonly sold in supermarkets around the world which Greenpeace believes have a very high risk of being sourced from unsustainable fisheries.^[87] Other environmental organisations have challenged the sustainability of southern bluefin tuna fishing and ranching including the Australian Marine Conservation Society,^[88] Sea Shepherd^[89] and the Conservation Council of South Australia.^[90]

Attempts to establish or expand tuna ranching in waters close to the Sir Joseph Banks group, Kangaroo Island,^[91] Louth Bay^[90] and Granite Island^[92] have been met with public opposition on environmental grounds. Successful court challenges and appeals of planning decisions have occurred in association with plans near the Sir Joseph Banks group and Louth Bay.

Environmental impacts

Feed conversion ratios (feed input to tuna weight gain) of approximately 15:1 or higher result in significant feed requirements for captive southern bluefin tuna and resultant nutrient pollution. The feed conversion ratio is a consequence of the fish's carnivorous diet and the high metabolic costs of the species. Removing tuna from the wild before they have reached sexual maturity also impacts wild populations. Clean Seas has attempted to address this by focusing research effort on closing the life-cycle of the species with the potential benefit of alleviating some of the fishing pressure on declining stocks, but has not succeeded.

In 2016, South Australia's southern bluefin tuna ranching industry received a Sustainability Certificate from Friend of the Sea. Industry spokesperson Brian Jeffriess said of the certification: "This is one of the few awards to actually cover both the wild fish catching and the whole farming supply chain and within that labour standards, crew safety, traceability, carbon footprint... every conceivable sustainability test."^[93]

Pollution

Tuna farms are point sources of solid waste onto to the benthos and dissolved nutrients into the water column. Most farms are more than a kilometre off the coast, thus the deeper water and significant currents alleviate some of the impact on the benthos. Due to the high metabolic rates of SBT, low retention rates of nitrogen in tissue is seen, and there are high environmental leaching of nutrients (86-92%).^[70]

Ranching of southern bluefin tuna is the largest contributor of industrial nutrient pollution to Spencer Gulf's marine environment. The industry contributes 1,946 tonnes per annum, distributed across Boston Bay & Lincoln Offshore aquaculture zones. Kingfish aquaculture is the region's next largest nutrient polluter (734 tonnes per annum) but is distributed across a larger area which includes Port Lincoln, Arno Bay, Port Neill and Fitzgerald Bay (near Whyalla). These combined nutrient inputs are ecologically significant, as Spencer Gulf is an inverse estuary and a naturally low-nutrient environment. Wastewater treatment plants from the region's largest settlements at Port Augusta, Port Lincoln, Port Pirie and Whyalla contribute a combined total of 54 tonnes of nitrogenous nutrient to Spencer Gulf.^[94]

Other polluting processes include the use of chemicals on the farms, which leach into the surrounding environment. These include anti-foulants to keep the cages free from colonial algae and animals, and therapeutants to deal with disease and parasitism. Toxicants, such as mercury and PCBs (polychlorinated biphenyls), can build up over time, particularly through the tuna feed, with some evidence of contaminants being more elevated in farmed fish than in wild stocks.^[95]

Sardinops sagax

Sardine fishery

South Australian sardine fishery - Total catch (1990-2012)

Australia's largest single species fishery (by volume) has been developed since 1991 to provide feedstock for the southern bluefin tuna farming industry. Catches in the fishery increased from 3,241 tonnes in 1994 to 42,475 tonnes in 2005.^[96] According to the South Australian Sardine Industry Association, 94% of its annual catch is utilized as feedstock for farmed SBT, with the remainder used for human consumption, recreational fishing bait and premium pet food.^[97] Fishing effort is largely concentrated in southern Spencer Gulf and Investigator Strait near Kangaroo Island in South Australian state waters. Some fishing also occurs off the Coffin Bay Peninsula in the Great Australian Bight.^[96]

Reduced availability of baitfish species is known to impact seabird populations. In 2005, the potential impact of this fishery upon colonies of little penguins was considered a future research priority, due to the relative paucity of alternative prey species.^[98] As of 2014, no such studies have been undertaken.

The fishery uses large purse seine nets up to 1 km in length to catch sardines.^[97] Bycatch mortalities of the fishery include the common dolphin (Delphinus delphis) which is a protected species under state and federal legislation. The species is protected federally under the Environment Protection Biodiversity & Conservation Act.^[96]

Great white shark

Interactions with sharks

Tuna cages attract sharks, which are drawn to fish which sometimes die in the pens and settle in the bottoms of the floating nets. Inquisitive sharks may bite holes in nets and enter the cages or become entangled in the nets and subsequently become distressed or drown. In response, employees of tuna ranching operations will either enter the water and attempt to wrestle the sharks out of the pens, or kill the shark. Species known to interact with southern bluefin tuna operations include hammerhead sharks, bronze whalers and great white sharks. The latter species is protected under federal Australian legislation while the former two are not. Some of these interactions are shown in the documentary film, Tuna Wranglers (2007).

In South Australia prior to 2001 there were nine recorded deaths of great white sharks in tuna pens during a five-year period. Six of the animals were killed and the remaining three were found already deceased.^[99] Some successful releases have also occurred since,^[100] though official records of mortality and releases are not available to the public and some incidents are likely to have gone unreported.

Compatibility with Marine Parks

When State Government managed Marine Parks were proclaimed in South Australia in 2009, a "whole of Government" commitment was made to prevent adverse impacts to the aquaculture sector. This included the preservation of existing aquaculture operations and zones. A further commitment was made to allow for the expansion of aquaculture within South Australian marine park boundaries. The commitment states that "DENR and PIRSA Aquaculture have identified areas that may support marine parks through appropriate mechanisms."^[101] An example of a pilot lease being issued within a marine park exists in the Encounter Marine Park, where Oceanic Victor received approval to establish a pen containing southern bluefin tuna for tourism purposes in 2015. In this case, the lease has been issued within a Habitat Protection Zone.

Film and television

The southern bluefin tuna industry has been the subject of several documentary films, including Tuna Cowboys (circa 2003) and Tuna Wranglers (2007), which were produced by NHNZ for National Geographic and Discovery Channel respectively. Some historical fishing footage and the process of harvesting the fish are shown in Port Lincoln home of the bluefin tuna (circa 2007) produced by Phil Sexton.^[102] Clean Seas' attempts to close the life cycle of the southern bluefin tuna feature in Sushi: The Global Catch (2012). In 2019, fisherman Al McGlashan produced the documentary Life on the Line - The Story of the Southern Bluefin Tuna with $145,000 funding from the Australian Government via the Australian Fisheries Management Authority and the Fisheries Research and Development Corporation.^[103][104]

References

• Froese, Rainer; Pauly, Daniel (eds.) (2006). "Thunnus maccoyii" in FishBase. March 2006 version.
• Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd., Auckland, New Zealand 1982) ISBN 0-00-216987-8
• Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 978-0-09-189780-2
• Bye bye bluefin: Managed to death The Economist. 30 October 2008. Retrieved 6 February 2009.

La Suda blunaĝila tinuso, Thunnus maccoyii, estas tinuso de la familio Skombredoj troviĝanta en malfermaj akvoj de suda hemisfero el ĉiuj tutmondaj oceanoj ĉefe inter 30°S kaj 50°S, al preskaŭ 60°S. Ili estas ĝis 2.5 m longaj kaj pezas ĝis 260 kg, pro kio ĝi estas inter la plej grandaj ostaj fiŝoj.

La Suda blunaĝila tinuso, kial aliaj pelagaj tinusaj specioj, estas parto de grupo de ostaj fiŝoj, kiuj povas elteni ilian korpan temperaturon ĝis 10 gradoj super la media temperaturo. Tiu avantaĝo permesas al ili elteni altan metabolan rezulton por predado kaj migrado al grandaj distancoj. La Suda blunaĝila tinuso estas oportunema manĝanto, kiu predas ampleksan varion de fiŝoj, krustuloj, cefalopodoj, salpedoj, kaj de aliaj marbestoj.

Bibliografio

• "Thunnus maccoyii". FishBase. Red. Rainer Froese kaj Daniel Pauly. Versio de Marto, 2006. N.p.: FishBase, 2006.
• Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8
• Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 978-0-09-189780-2
• Bye bye bluefin: Managed to death The Economist. 30 October 2008. Retrieved 6 February 2009.

El atún rojo del sur (Thunnus maccoyii) es una especie de peces de la familia Scombridae en el orden Perciformes. La sobrepesca es la mayor amenaza conocida para el atún rojo del sur. Este depredador se encuentra en lo alto de la cadena alimentaria marina y el descenso de su población podría tener repercusiones en otras especies. La especie es altamente preciada en el mercado de shashimi japonés, donde se vende la inmensa mayoría de la captura global. Es objetivo de las flotas pesqueras por parte de varias naciones, dentro de la Zonas Económicas Exclusivas de Australia, Nueva Zelanda, Indonesia y Sudáfrica. Si su población sigue disminuyendo, la especie se enfrenta a la posibilidad de la extinción. No hay indicios de que la población se esté recuperando. La especie está clasificada como en “Peligro Crítico” por la Unión Internacional para la Conservación de la Naturaleza.

Morfología

Los machos pueden llegar alcanzar los 245 cm de longitud total y los 260 kg de peso.^[2]​

Atún rojo del sur

Distribución geográfica

Se encuentra en el Atlántico, en el Índico y en el Pacífico.

Referencias

Bibliografía

• Fenner, Robert M.: The Conscientious Marine Aquarist. Neptune City, Nueva Jersey, Estados Unidos : T.F.H. Publications, 2001.
• Helfman, G., B. Collette y D. Facey: The diversity of fishes. Blackwell Science, Malden, Massachusetts, Estados Unidos , 1997.
• Hoese, D.F. 1986: . A M.M. Smith y P.C. Heemstra (eds.) Smiths' sea fishes. Springer-Verlag, Berlín, Alemania.
• Maugé, L.A. 1986. A J. Daget, J.-P. Gosse y D.F.E. Thys van den Audenaerde (eds.) Check-list of the freshwater fishes of Africa (CLOFFA). ISNB Bruselas; MRAC, Tervuren, Flandes; y ORSTOM, París, Francia. Vol. 2.
• Moyle, P. y J. Cech.: Fishes: An Introduction to Ichthyology, 4a. edición, Upper Saddle River, Nueva Jersey, Estados Unidos: Prentice-Hall. Año 2000.
• Nelson, J.: Fishes of the World, 3a. edición. Nueva York, Estados Unidos: John Wiley and Sons. Año 1994.
• Wheeler, A.: The World Encyclopedia of Fishes, 2a. edición, Londres: Macdonald. Año 1985.

Thunnus maccoyii Thunnus generoko animalia da. Arrainen barruko Scombridae familian sailkatzen da.

Banaketa

Erreferentziak

• FishBase.org

Ikus, gainera

• Thunnus
• Scombridae

Sinievätonnikala (Thunnus maccoyii) eli eteläntonnikala on äärimmäisen uhanalainen tonnikalalaji.

Koko ja ulkonäkö

Sinievätonnikala kasvaa suurimmillan 2,5 metrin pituiseksi ja 260 kilon painoiseksi. Sinievätonnikalan ruumiin väri on sinimusta selässä ja hopeanvalkoinen vatsassa, leuassa ja evissä. Eväkkeet ovat keltaisia. Vanhin tavattu Sinievätonnikala on 20-vuotias.

Esiintyminen

Sinievätonnikala elää Atlantin, Tyynenmeren ja Intian valtameren eteläosissa, 30. ja 55. eteläisen leveysasteen välissä. Sinievätonnikala voi elää matalassakin 50 metrin vedessä, mutta myös yli 2000 metrissä.

Ravinto

Sinievätonnikalat syövät pääasiassa äyriäisiä, pääjalkaisia eli mustekaloja ja muita pienehköjä mereneläviä. Ne voivat sukeltaa ravinnon perässä 500 metrin syvyyteen.

Harvinaistuminen ja suojelu

Sinievätonnikalakannat ovat heikentyneet liikakalastuksen takia 1950-luvulta lähtien 92 prosenttia. Lajin tulevaisuus näyttää synkältä ellei harvinaistumista saada kuriin kiintiöiden avulla.

Lähteet

• www.fishbase.org (englanniksi)

Le thon rouge du Sud (Thunnus maccoyii) est une des trois espèces de thons rouges, avec le thon rouge du Pacifique (Thunnus orientalis) et le thon rouge du Nord (Thunnus thynnus).

Cette espèce est inscrite sur la liste rouge de l'UICN, c'est-à-dire qu'elle est en danger critique d'extinction^[1].

Captures et gestion des stocks

Depuis les années 1950 et l'accentuation de la pêche industrielle, l'espèce a été amenée au bord de l'extinction (les populations totales ont diminué d'environ 92 %)^[2].

En 1994, la volonté de gestion entre l'Australie, le Japon et la Nouvelle-Zélande prit forme lorsque la convention sur la conservation du thon rouge du Sud entra en vigueur. Cette convention créa la « Commission pour la conservation du thon rouge du Sud » (Commission for the Conservation of Southern Bluefin Tuna ou CCSBT). Ses objectifs sont d'assurer la conservation de l'espèce et d'optimiser les moyens de pêche. Plus tard la Corée du Sud, Taïwan et les Philippines se sont joints ou ont coopéré avec la commission. Elle siège à Canberra en Australie.

Captures de thons rouges du Sud depuis 1952 en tonnes. La tendance reflète la baisse des stocks.

Références

Tuna sirip biru selatan (Thunnus maccoyii) adalah spesies tuna sirip biru dari familia skombride yang ditemukan di perairan belahan selatan samudra dunia antara Lintang 30°LS dan 50°LS, hingga 60°LS. Ikan ini dapat mencapai panjang 2,5 m (8,2 ft) dan berat mencapai 260 kg (570 lb), ikan ini termasuk salah satu ikan bertulang sejati terbesar. Daerah sebar ikan ini terdapat baik di perairan laut lepas ataupun sekitar pesisir.^[2]

Tuna sirip biru selatan adalah ikan besar berbentuk memanjang seperti torpedo, bersirip langsing dan agak pendek. Tubuhnya dilapisi sisik kecil. Warna tubuhnya adalah hitam kebiruan pada punggungnya dan putih keperakan pada bagian sisi dan bawah tubuh, dengan warna kuning terang pada sirip ekor spesimen dewasa. Sirip dada pertama berwarna abu-abu dengan sedikit warna kuning, sirip dada keduanya berwarna merah kecokelatan, sementara sirip-sirip kecilnya berwarna kuning bertepi gelap.

Tuna sirip biru selatan, seperti spesies tuna pelagik lainnya, termasuk kelompok ikan bertulang yang dapat menjaga suhu inti tubuhnya hingga 10 di atas suhu rata-rata lingkungannya. Keunggulan ini memungkinkan mereka menjaga metabolisme tubuh mereka agar dapat berburu mangsa atau bermigrasi jarak jauh. Tuna sirip biru selatan adalah pemangsa oportunistik, memangsa berbagai jenis ikan, krustasea, sefalopoda, salpida, dan satwa laut lainnya.

Referensi

Pranala luar

• Tuna sirip biru selatan di CSIRO
• Tuna sirip biru selatan di MarineBio.org
• Homepage resmi Commission for the Conservation of Southern Bluefin Tuna

Il tonno australe^[2] (Thunnus maccoyii Castelnau, 1872), comunemente noto come tonno rosso australe o tonno rosso del sud (Regolamento (UE) 2017-2107), è un pesce osseo marino della famiglia Scombridae.

Descrizione

L'aspetto esteriore di questo pesce è quasi indistinguibile da quello del tonno rosso atlantico. Alcuni caratteri della colorazione sono però diversi: Sulla parte inferiore dei fianchi sono presenti fasce verticali indistinte formate da macchie chiare, la prima pinna dorsale può avere colore giallo o azzurro, la pinna anale e le pinnule sono giallo opaco con bordo nero, anche la carena centrale presente sul peduncolo caudale è gialla negli individui maturi. È un tonno di grandi dimensioni: la taglia massima nota è di 245 cm, la taglia media è sui 160 cm. Il peso massimo che sia noto è di 260 kg^[3].

Distribuzione e habitat

Questa specie è diffusa nella parte meridionale con acque temperate e anche fredde dei tre oceani. Durante l'epoca riproduttiva vengono effettuate migrazioni verso le acque tropicali dell'Australia occidentale. Fa vita pelagica oceanica^[3].

Biologia

La longevità arriva a 20 anni^[3].

Alimentazione

Si tratta di un predatore versatile, si nutre di pesci, cefalopodi, crostacei, salpe e altri organismi^[3].

Riproduzione

Si sa poco sulla biologia riproduttiva di questa specie, non si sa, per esempio, se si riproduca annualmente, ogni qualche anno o una sola volta. La deposizione avviene in acque tra 20 °C e 30 °C^[3].

Pesca

Andamento delle catture globali di Th. maccoyii dal 1952 al 2006

Viene pescato soprattutto lungo le coste australiane dove ha una certa importanza e dove vengono catturati anche esemplari immaturi da destinarsi alla piscicoltura in gabbie galleggianti. Viene destinato principalmente alla produzione di tonno in scatola e di sashimi^[1][3].

Conservazione

Le popolazioni di Th. maccoyii sono diminuite di oltre l'85% dal 1973 al 2006 a causa della sovrapesca e le popolazioni risultano in ulteriore contrazione. Per questo motivo la IUCN classifica questa specie in pericolo critico di estinzione. Sono state prese numerose iniziative per la conservazione e il ripristino degli stock^[1].

Note

De zuidelijke blauwvintonijn (Thunnus maccoyii) is een straalvinnige vis uit de familie van makrelen (Scombridae) en behoort derhalve tot de orde van baarsachtigen (Perciformes). De vis kan een lengte bereiken van 245 cm. De hoogst geregistreerde leeftijd is 20 jaar.

Leefomgeving

De zuidelijke blauwvintonijn is een zoutwatervis. De vis prefereert een gematigd klimaat en heeft zich verspreid over de drie belangrijkste oceanen van de wereld (Grote, Atlantische en Indische Oceaan). De tonijn komt echter alleen in de zuidelijke delen voor, tot ongeveer de 20e breedtegraad. In het centrale en noordelijke deel van de Atlantische Oceaan komt de gewone blauwvintonijn voor en in het centrale en noordelijke deel van de Grote Oceaan leeft de soort Thunnus orientalis.^[2] De diepteverspreiding is 50 tot ruim 2700 meter onder het wateroppervlak.

Relatie tot de mens

De zuidelijke blauwvintonijn is voor de visserij van aanzienlijk commercieel belang. In de hengelsport wordt er veel op de vis gejaagd.

Externe link

• Foto's van Thunnus maccoyii op FishBase

• Froese, R., D. Pauly. en redactie. 2005. FishBase. Elektronische publicatie. www.fishbase.org, versie 06/2005.

Fangst av Thunnus maccoyii 1950–2009

Thunnus maccoyii er en tunfiskart. På engelsk kalles den southern bluefin tuna, og den er altså en av tre ettertraktede og truede artene av «blåfinnet tunfisk».

Den dypeste delen av kroppen er under midten av første ryggfinne. Brystfinnene er svært korte, mindre enn 80 prosent av hodets lengde. Arten har svømmeblære. Nedre del av sidene og buken er sølvhvit med fargeløse tverrstriper som veksler med rader av fargeløse flekker.

Den første ryggfinnen er gul eller blå. Gattfinnen og småfinnene er grågule med svart kant. Den store kjølen midt på sporden er gul hos voksne eksemplarer. Den er blant de største tunfiskartene og maksimal lengde er 225 cm. Vanlig lengde er 160–200 cm. En 180 cm lang fisk kan ha en vekt på 102–134 kg etter at den er renset.

Thunnus maccoyii lever epipelagisk ute på åpent hav i kaldt tempererte farvann. Den er for det meste begrenset til vann med en temperatur på 5–20 °C. Gytende fisk og larver påtreffes derimot i vann med en overflatetemperatur på 20–30 °C. Generasjonslengden er omtrent 12 år og maksimal levealder kanskje 20 år.

Utbredelsen er sirkumpolar i de sørlige verdenshavene, for det meste mellom 30°–50° sør, men av og til lenger sør eller nord. Arten vandrer etter årstidene mellom gyteområder med varmt vann og områder med mye næring og kaldere vann. Den er en opportunist som eter mange forskjellige fiskearter, krepsdyr, bløtdyr og salper. Selv blir den jaktet på av haier, delfiner, seler og seilfisker.

Det har vært drevet et intenst fiske etter Thunnus maccoyii, spesielt utenfor Australia, New Zealand og Sør-Afrika. Den var ettertraktet i Japan som råstoff for sashimi, og det hendte at det ble betalt 10 000 amerikanske dollar for en enkelt fisk på fiskemarkedet i Tokyo. Fangsten var størst mellom 1960 og 1985 med en rekord på 55 487 tonn i 1972. Bestanden kollapset i siste halvdel av 1980-tallet på grunn av overfiske. Arten regnes som kritisk truet, og fangsten i 2010 var bare på 9 253 tonn.

Litteratur

• B.B. Collette og C.E. Nauen (1983). FAO species catalogue: Vol.2. Scombrids of the world: An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. FAO Fish.Synop. s. 87–88. ISBN 92-5-101381-0.

Eksterne lenker

• (en) Thunnus maccoyii – oversikt og omtale av artene i WORMS-databasen
• (en) Thunnus maccoyii i Encyclopedia of Life
• (en) Thunnus maccoyii i Global Biodiversity Information Facility
• (en) Thunnus maccoyii hos Fossilworks
• (en) Thunnus maccoyii hos NCBI
• (en) Thunnus maccoyii hos ITIS
• (en) Thunnus maccoyii hos FishBase
• (en) Kategori:Thunnus maccoyii – bilder, video eller lyd på Wikimedia Commons
• (en) Thunnus maccoyii – galleri av bilder, video eller lyd på Wikimedia Commons
• Thunnus maccoyii – detaljert informasjon på Wikispecies
• (en) Thunnus maccoyii (Castelnau, 1872) Southern bluefin tuna - FishBase
• B. Collette m.fl. (2011). «Thunnus maccoyii». IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1. Besøkt 20. august 2012.
• Thunnus maccoyii i FAO FishFinder

Thunnus maccoyii (Castelnau, 1872) é uma espécie de atum pertencente à família Scombridae com distribuição natural nas águas marinhas temperadas e subtropicais do hemisfério sul, em particular entre as latitudes 30° S e 50° S, mas estendendo-se ocasionalmente até aos 60° S. Tem um comprimento de até 2,5 m e um peso que pode atingir os 400 kg, sendo um dos maiores peixes ósseos extantes.

Notas

Referências

• Ed. Froese, Rainer; Pauly, Daniel. «"{{{género}}} {{{espécie}}}"». www.fishbase.org (em inglês). FishBase
• Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8
• Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 978-0-09-189780-2
• Bye bye bluefin: Managed to death The Economist. 30 October 2008. Retrieved 6 February 2009.

Güney mavi yüzgeçli orkinosu (Thunnus maccoyii), uskumrugiller (Scombridae) familyasına ait bir balık türü.

Dünyanın güney küresinde sıcak ve ılıman denizlerde yaşar. 2,5 metre uzunluğa ve 400 kilo ağırlığa ulaşabilir, ve böylece kemikli balıklar sınıfının en büyük balıklarından birisidir. Büyüklüğüne ve yüzgeçlerinin diğer orkinoslara nazaran küçük olmasına rağmen çok iyi ve hızlı bir yüzücüdür.

Sırtının rengi lacivertdir ve rengi karnına doğru beyaz-gri'ye dönüşür. Öndeki sırt yüzgeci gri-sarıdır, ikinci sırt yüzgecinin rengi ise koyu kırmızı-kahverengidir. Diğer yüzgeçlerinin kenarları koyu gerisi sarı renklidir.

Fazla yemek seçmeyen bir balıktır. Bir sürü farklı balık türleri, yumuşakçalar, kabuklular ve diğer deniz hayvanları ile beslenebilir.

Aşırı avlanmasından dolayı (özellikle Japon balıkçıların avlamaları ile) nesli tehlikeye girmektedir.

Kaynakça

• Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8

Cá ngừ vây xanh phương Nam (Danh pháp khoa học: Thunnus maccoyii) là một loài cá ngừ trong họ họ cá thu ngừ Scombridae,^[3][4][7] trong nhóm cá ngừ vây xanh thường sống ở vùng nam Đại Tây Dương, Thái Bình Dương và Ấn Độ Dương, chúng có quan hệ gần với cá cờ và cá kiếm. Chúng là loài cá ngừ được xếp loại cực kỳ nguy cấp do đánh bắt quá mức vì được cho là có thịt ngon, đặc biệt ở Nhật Bản (làm sushi và sasimi).

Đặc điểm

Cá có màu xanh đậm phía trên và màu trắng bạc phía dưới, một dải vàng ở bên hông. Là loài cá bơi rất nhanh, chúng đạt tới tốc độ hơn 90 km/giờ và có thể dài tới 2 m và nặng 135 kg. Cá ngừ vây xanh phương nam có đuôi cong, hai vây lưng, và các vây có thể gấp lại để giảm bớt sức cản khi cá bơi trong đại dương. Là loài di cư trong tự nhiên, cá ngừ vây xanh sở hữu những hệ thống hô hấp và tuần hoàn độc đáo giúp nó di chuyển quãng đường rất xa.

Cá có thể giữ nhiệt độ cơ thể ổn định thường ấm hơn nhiệt độ vùng nước mà chúng đi vào. Chúng cũng có tim lớn hơn những loài cá khác, cho phép nó đẩy rất nhiều ô-xy năng lượng trong các chuyến du hành xa. Cá sử dụng hệ thống thị giác và thính giác phát triển cao của chúng để bắt mồi, như là tôm krill, mực, bạch tuộc, giáp xác. Các động vật săn cá ngừ vây xanh gồm cá mập, chim, cá voi sát thủ, và ngay cả các cá ngừ khác.

Sinh sản

Khoảng 9 năm tuổi, cá ngừ vây xanh phương nam thuần thục về mặt giới tính. Chúng sinh sản vào giữa tháng chín và tháng 4 năm sau và thường hướng về Ấn độ dương để đẻ trứng ở vùng nước ôn đới gần đảo Java,Indonesia. Thông thường cá ngừ đẻ trong nước có nhiệt độ 20 – 30 độ C. Một lần, cá cái có thể đẻ hàng triệu trứng. Trứng chỉ cần một ít ngày thì nở, trở thành một chú cá ngừ con dài chỉ 2,5 cm. Cá ngừ con trải qua thời gian 5 năm ở gần bờ biển nước Úc trước khi chuyển ra vùng nước sâu hơn nơi chúng có nhiều lựa chọn về thức ăn. Cá ngừ vây xanh phương nam có thể sống gần 40 năm

Khai thác

Cá ngừ vây xanh phương nam bị đánh bắt nặng nề vì chúng luôn được thèm muốn do thịt nhiều dầu, được ưa chuộng để làm sushi và fillet. Các nước như Nhật bản, Úc,New Zealand đã hạn chế số lượng cá ngừ vây xanh phương nam được phép đánh bắt. Hạn ngạch (Quota) cá ngừ vây xanh phương nam của Nhật bản là 6.000 tấn trong năm 2006. Theo Ủy ban Bảo vệ Cá ngừ Vây xanh Phương nam (CCSBT), Nhật bản đánh bắt gấp hai lần số lượng cá ngừ vây xanh phương nam được phép đánh bắt giữa năm 2003 và 2005. Các ngư dân Nhật bản nói rằng họ chỉ đánh bắt vượt mức 6.000 tấn một năm nhưng dựa trên số lượng cá được bán, CCSBT tính toán rằng từ 10.000 tấn tới 16.000 tấn thực sự đã bị đánh bắt.

Chú thích

Tham khảo

• Thông tin "Thunnus maccoyii" trên FishBase, chủ biên Ranier Froese và Daniel Pauly. Phiên bản tháng March năm 2006.
• Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8
• Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 978-0-09-189780-2
• Bye bye bluefin: Managed to death The Economist. ngày 30 tháng 10 năm 2008. Truy cập ngày 6 tháng 2 năm 2009.

Liên kết ngoài

• Southern Bluefin Tuna at CSIRO
• Southern Bluefin Tuna at MarineBio.org
• Official homepage of the Commission for the Conservation of Southern Bluefin Tuna

Ежегодный улов австралийского тунца (1952-2013)

Взаимодействие с человеком

Мясо австралийских тунцов является деликатесом. Считается прекрасным сырьём для суши и сашими помимо мяса обыкновенного тунца^[20]. Сырое мясо тёмно-красного цвета, после термической обработки белеет или приобретает цвет слоновой кости. Текстура плотная, по внешнему виду напоминает говядину. Прекрасный источник белка (содержание 23,3 г на 100 г), тиамина, селена, витамина B6 и омега-3-ненасыщенных жирных кислот. Калорийность 144 кКал^[21]. В мясе этих рыб, как и в мясе прочих тунцов может накапливаться ртуть^[22] и гистамин^[23]. Этот вид ценится рыболовами любителями. Максимальная масса трофейной рыбы составляет 167,5 кг^[14].

Промысловое значение

См. также Промысел тунцов

Тунцы издавна были и остаются важным промысловым объектом. Ценятся рыболовами-любителями. Тунцов промышляют ярусамии, кошельковыми неводами, и крючковыми орудиями лова^[4]. Охлаждённые и замороженные туши используют в ресторанном бизнесе и производстве полуфабрикатов^[24]. До 80-х годов XX века мясо австралийских тунцов в основном использовали для производства консервов.

Промысел австралийского тунца находится под контролем Рыболовная комиссия Центральной и Западной части Тихого океана^ru_en и Комиссия по сохранению южного голубого тунца^ru_en.

Меры по сохранению вида

Интенсивный промысел австралийского тунца ведётся с 50-х годов прошлого века. В 60-х годах наблюдалось существенное снижение нерестовой биомассы до 7—15 % от объёма начала исторического учёта. В за 36 лет с 1973 по 2009 нерестовая биомасса сократилась на 85,4 %^[4]. Гринпис внёс голубого тунца в «Красный список продуктов», от употребления которых рекомендовано воздерживаться, чтобы не усугублять вред, наносимый экосистеме^[25].Установлены квоты на вылов. С 1991 года в Австралии тунцов стали выращивать на фермах. Неполовозрелых диких тунцов отлавливают и доращивают искусственно^[4].

Ссылки

• Вид Thunnus maccoyii (англ.) в Мировом реестре морских видов (World Register of Marine Species).

Примечания

蓝鳍金槍魚為輻鰭魚綱鱸形目鯖亞目鯖科的其中一種，被IUCN列為極危保育類動物，分布於全球各大洋熱帶至溫帶海域，棲息深度50-2473公尺，體長可達245公分，為大洋性洄游性魚類，成群活動，屬肉食性，以魚類、頭足類、甲殼類為食，可做為食用魚、遊釣魚及養殖魚類，臺灣稱為「南方黑鮪」。

参考文献

• Froese, Rainer & Daniel Pauly, eds. (2012). Thunnus maccoyii in FishBase. 2012年7月版本

擴展閱讀

ミナミマグロ（南鮪、学名 Thunnus maccoyii）は、スズキ目サバ科に分類される魚の一種。和名通り南半球の中緯度海域に広く分布するマグロである。

インド洋で多く漁獲されることから、日本ではインドマグロ^[2]とも呼ばれる。漁獲されたものは食用として日本に多く輸入される。人気が高いが、マグロ類の中でも特に絶滅が危惧されている種類にもなっている。

特徴[編集]

成魚は最大で全長245 cm・体重260 kgに達する。マグロ8種の中ではメバチ、キハダと並ぶ中型種で、タイセイヨウクロマグロ、クロマグロに次ぐ大きさである。

メバチやキハダよりも胸鰭が比較的短く、第二背鰭まで達しない。体表は胸甲部以外も小さな鱗に覆われる。体色は背面が濃い藍色、側面と腹面が銀白色をしている。各鰭は第一背鰭が黄灰色、第二背鰭が赤褐色、小離鰭が黄色、尾鰭の付け根の水平隆起線（尾柄キール）は黄白色をしている。

生態[編集]

太平洋・インド洋・大西洋の南半球のみに分布する。主に南緯30度から60度にかけての中緯度海域に多い。比較的温暖な海域ではメバチやビンナガと分布域が重複する。また、マグロに似たサバ科の大型魚であるガストロはミナミマグロと同様の分布を示す。

外洋域の中層に生息し、群れをなして広範囲を回遊する。食性は肉食性で、他の小魚、甲殻類、頭足類、サルパなど小動物を幅広く捕食する。

オーストラリア北西・ジャワ島南方の暖海域が産卵場として知られており、繁殖に参加する成魚と幼魚は水温20-30℃の表層水域で見られる。

人間との関わり[編集]

ミナミマグロは延縄、巻き網などの遠洋漁業で漁獲され、その大部分が日本で消費されている。漁獲量は1960年代から年間5万t前後、1980年代後半からは2万t前後で推移している。身は脂肪が多く、日本ではクロマグロに次ぐ高級品として珍重されている。刺身や寿司種に利用される。

ただし、漁獲の結果として50年余りで92%もの個体数減少が起こったとされている。IUCNのレッドリストでは、1994年に"CR"(Critically endangered)、マグロ類のみならず野生動物としても最も絶滅が危惧されている動物の一つとして記載された。このまま漁獲を続けると、100年以内に個体数が500匹を下回るともいわれる。

1994年には主要な漁業国だった日本・オーストラリア・ニュージーランド三国によって「みなみまぐろ保存委員会」（CCSBT - Commission for the Conservation of Southern Bluefin Tuna : 本部キャンベラ）が設置され、資源管理への取り組みが本格化した。その後韓国、フィリピン、南アフリカ、EUなども加盟国、または協力的非加盟国としてCCSBTに参加を表明した。

しかし割り当てられた漁獲量以上の漁獲が発覚（日本、1996年－2005年までに約10万トン前後^[3]）したり、日本とオーストラリア・ニュージーランドが国際海洋法裁判所で対立したり（みなみまぐろ事件^[4]）、非加盟国による漁獲も続いたりと、課題は多い。

また、ミナミマグロを狙った延縄にワタリアホウドリなどのアホウドリ類が掛かって溺死するため、これも問題となっている。

食料として見た場合、ミナミマグロの体内に含まれる微量の水銀に注意する必要がある。 厚生労働省は、ミナミマグロを妊婦が摂食量を注意すべき魚介類の一つとして挙げており、2005年11月2日の発表では、1回に食べる量を約80gとした場合、ミナミマグロの摂食は週に2回まで（１週間当たり160g程度）を目安としている^[5]。

資源の保護[編集]

日本では、大西洋まぐろ類保存国際委員会の取り決めに従い、ミナミマグロ等を輸出又は再輸出する際には、漁獲証明書、統計証明書、輸出証明書又は再輸出証明書の添付するなど原産地証明を確実なものとすることが求められる^[6]。

参考文献[編集]

1. ^ Punt, A. 1996. Thunnus maccoyii. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. . Downloaded on 28 April 2008.
2. ^ “魚介類の名称表示等について（別表1）”. 水産庁. オリジナルよりアーカイブ。^ これが2006年のみなみまぐろ保存委員会での日本の割り当て漁獲枠半減（3千トン／年）の背景になったとされる。ただし水産庁はこれの懲罰的意味合いは否定し、資源管理への前向きな姿勢だとしている（日本の捕りすぎ１０万トン超か　国際機関調査委が報告書）。
3. ^ 1998年と1999年に日本が豪などとの合意が得られない状況で実施した調査漁獲について、オーストラリアとニュージーランドが国連海洋法条約等に違反するとして訴えた事件。調査漁獲は慎むべきとする暫定措置命令が日本に下った。しかし2000年、この問題を審理していた国際海洋法裁判所の仲裁裁判所は、この問題は審理の管轄外であり以前の暫定措置命令は無効とする判断を下して日本が逆転勝訴している。（外務省_国際海洋法裁判所）
4. ^ 厚生労働省医薬食品局食品安全部基準審査課 (妊婦への魚介類の摂食と水銀に関する注意事項の見直しについて(Q&A)（平成17年11月2日）”. 魚介類に含まれる水銀について. 厚生労働省. オリジナルよりアーカイブ。^ “マグロ類の輸出手続きについて”. 水産庁. Southern bluefin tuna
5. Fishbase - Thunnus maccoyii（英語）
6. みなみまぐろ保存委員会（CCSBT） - 日本語版トップページ。英語版へのリンクもある
7. 本田崇・魚住雄二・熊井英水『マグロはいつまで食べられるか』Newton2007年3月号
8. 小松正之・遠藤久『国際マグロ裁判』， 岩波新書， 2002.

関連項目[編集]

ウィキスピーシーズにミナミマグロに関する情報があります。 ウィキメディア・コモンズには、ミナミマグロに関連するメディアがあります。