The Bluefin Tuna – a majestic marine giant



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The Bluefin Tuna – a majestic marine giant

Dr. Alan Deidun


Tuna and its exploitation has been hogging the limelight for quite some time now. Dr. Alan Deidun gives an insight into the biology of the bluefin tuna and what’s stoking the white-hot demand for tuna meat.
The term tuna is too vague a term, since together with the mackerels, tuna species make up a 50 species-strong family of bony fish. The seven different species of tuna of commercial interest include the bluefin tuna (ton in Maltese), albacore (allungi in Maltese), skipjack (palamit in Maltese – the stuff gracing your tuna salads), bonito, yellowfin tuna and bigeye tuna. To fully unravel the intricate net of terminology, there are actually three different species of bluefin tuna – the one normally encountered in Mediterranean waters is the Atlantic bluefin tuna, whose range girdles the entire Atlantic Ocean, from the coasts of North Carolina to the waters off north-western Africa and into the Mediterranean.
The Atlantic bluefin tuna species (Thunnus thynnus) is head and shoulders above other fish species for two major reasons: firstly, contrary to most of the other approximately 20,000 fish species, it is warm-blooded, maintaining a body temperature of twenty-seven degrees Centigrade, despite diving to depths of up to one kilometer, where the ambient sea temperature can plummet to around five degrees Centigrade. Secondly, the species is truly a juggernaut, attaining gargantuan dimensions close to three quarters of a ton and a length of four meters, dimensions which are normally reserved for marine mammals such as whales. Despite its prohibitive size, the bluefin tuna cleaves the water at a breakneck speed (being able to reach speeds of up to 55 mph or 90 km per hour), by means of its scimitar-shaped tail and by keeping its operculum continuously open in order to bolster ventilation (ram ventilation). The full life span of a bluefin is approximately 30 years and they reach maturity around the age of 8.
Blue fin is caught commercially by two main methods, purse seine and long lining. It has become almost a cliché but most the bluefin tuna is destined to satiate the ravenous Japanese appetite for tuna – at the Tsukiji fish market in Tokyo, a single bluefin tuna sold for a staggering $173,600! The bluefin tuna scaled new heights, from being a fish that samurai would not eat since they perceived it as being unclean to maguro, a delicacy that can be expensive as truffles or caviar. Toro, the best quality maguro, comes from the fatty belly meat of the adult bluefin. The crave for raw tuna meat in the form of sushi and sashimi has recently exploded worldwide, with Mediterranean bluefin tuna being especially sought after for their oil-rich tissue. The food dispensed to tuna in pens are closely monitored so as to bestow the most appealing colour and taste to the final product.
The history of catching Blue fin dates back into B.C and even people such as Aristotle wrote about Blue fin before he died in 322 B.C. Nowadays, the movements of bluefin tuna area tracked by means of pop-off satellite tags. Locally, bluefin tuna used to approach very closely our shores and in fact some coastal stretches are named after such an annual occurrence – e.g. Dawret it-Tonn in Mellieha, where the old tunnery building has been reinstated and opened as a museum recently.
Made from netting and stretching like a wall vertically from seafloor to sea surface, a Mediterranean tuna trap is called a tonnara or madrague and is set in places known from long experience. A net wall stretches out from the coast to over a mile offshore, steering migrating tuna towards an offshore netted enclosure about one hundred feet or more to a side and plunging down to the sandy bottom at 130 feet. Through a vertical opening, the tuna find their way into this netted enclosure, but once inside and circling as a school, cannot find their way out to escape. The Egadian Islands off the western coast of Sicily have been since the remotest of times the hubs of the tunny fisheries. The world-renowned bloodbath known as Mattanza (from the Spanish Matar, to kill) is suffused in deeply-rooted rituals and reeks of Arab ancestry. In fact, the men involved in the tuna haul are led by a captain, or Rais (word of Arab ancestry), whose authority is undisputed and who has the final word over all aspects of the kill. It is he indeed, in his six-oared boat (called la ‘muciara’) who directs the congregation of fishermen (or ‘Ciurma’) as to when there are enough tuna in the death chamber to start the kill proper.
The intricate system of underwater passageways formed from fishing nets (called ‘U Calatu’) is a feat worth mentioning. La ‘coda’ is a long perpendicular net which coerces the fish to enter, through an inlet called ‘Ucca Nassa’, the web of underwater ‘camere’ which can be individually closed and which culminate into the ‘Camera della Morte’ (death chamber) which is surrounded all along its rectangular perimeter by fishing boats and trawlers. It is here that the Ciurma start heaving the net up on the boats and consequently harpooning the surfacing fish, donning the sea with a vivid crimson hue. A plaque at Favignana records the annual quantities of tuna caught – the 1848 kill, with 4353 fish killed, has etched an indelible mark in the islands’ history.
The timing of la mattanza is finely-tuned with the fish’s migratory timepiece. In fact, in the April-June period, tuna skirt the Egadian Archipelago during the ‘Corsa’ to lay eggs on the shallow bottom, whilst in the July-August period they again pass by during the ‘Ritorno’ to reach their native waters of the Atlantic Ocean. Local acumen has it that the first fifteen days of June, or la ‘Cafara’, is the optimum period for tuna kills. Today, the mattanza at the Egadian Islands is just a dying flourish of the traditional tuna fishery industry, now much less romantic and the hegemony of the Japanese fishing firms. Bonagia, also close to Trapani, is the other site besides the Egadian Islands where la mattanza is still carried out – some locals have it that the chores are still performed to please the visiting tourists. The majestic tunny-fish processing factories (the ‘Florio Family’ as they were purchased by the magnate family themselves from the Pallavicino family of Genoa in 1874 for two million lire – ca. Lm 420) now lie redundant in the port of Favignana – a facelift for them so as to host a museum of local traditions is in the offing. The tunnery fish-boats are still in use however.
Tuna is ubiquitous on the Egadian islands also in the culinary aspects. A number of local shops and restaurants bear flamboyant tuna-related names, such as ‘Casa del Tonno’, and offer a welter a tuna-based dishes, such as Spaghetti alla Bottarga (using tuna eggs), Ventresca di Tonno (using the lower belly part of the tuna), Tarantello di Tonno (using the upper belly part), Sosizella di Tonno (using ground tuna meat), Mosciamo di Tonno (using the most coveted part of the fish), Buzzonaglia di Tonno (the dark part of the tuna meat) and even the Lattume di Tonno (using the male seminal fluid!).
The International Commission for the Conservation of Atlantic Tunas (ICCAT) is a regulatory body established in 1969 which establishes annual quotas for each tuna-country nation, quotas which are repeatedly flouted. The annual establishment of such quotas results in the pitting of ICCAT against the European Commission, the latter eager to safeguard the interests of fishing nations. The Mediterranean branch of the World Wildlife Fund (WWF) has long campaigned for a drastic reduction of the annual catch quotas and in fact issues a monthly bluefin tuna bulletin. This year’s tuna fishery was abruptly and prematurely shut down in view of the flagrant disrespect towards established quotas. Our islands have assumed over recent years a key role in the fattening of tunas, caught by purse seining during the May-July period, in pens and in the export of such tuna to Japan (almost 7 million kg of tuna of local provenance exported over the last 12 months from Malta to Japan). Spotter planes are sometimes deployed for the location of large tuna schools – their use is permitted only during a few weeks in June.
Nowadays, one can even swim in enclosed quarters with these gentle giants – the marine adventure park (www.marineadventurepark.com) is one such venture, offering visitors the possibility to come in close contact with these pelagic masters.
A possible panacea to the current tuna depravation could be its taming – i.e. breeding the fish in captivity, to avoid taking it from the wild, as is the norm for countless other fish-farmed species. After such attempts by the Americans in the past floundered, the Australians are now bristling with optimism as a pilot project conducted by Clean Seas in Port Lincoln, South Australia. In 2005, a research team at the Spanish Institute of Oceanography in Puerto de Mazarron, Spain, successfully retrieved eggs and sperm from captive Atlantic bluefin broodstrock, performed in vitro vertilisation which yielded larvae. Hence, current omens are pointing towards this sleek giant becoming yet another ‘cattle of the seas’.
Alan.deidun@gmail.com, alan.deidun@um.edu.mt


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