Southern
Bluefin Tuna (Thunnus maccoyii)
This page was last updated on
the 8th April 2008
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Other Names
Bluefin;
tuna
- Size
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- Commonly grow to 180 cm with a weight
of 100kg
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- Physical Features
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- Short pectoral fins.
No white outer edge on caudal fin. 31-40 gill rakers on first gill
arch. Small scales on posterior half of body. Upper surface dark
blue without dark spots or striped pattern. Top of tongue has two
longitudinal ridges. Pronounced thickened scale patch near pectoral
fin base. Large fleshy keel on caudal peduncle flanked by two smaller keels.
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- Habitat
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- Marine. Pelagic in the open
ocean. Found mainly in cool temperate waters.
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Southern
bluefin tuna
Photo:
Alistair Douglas
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(Information kindly supplied by Mr Brian Jeffriess,
CE0 of the Australian Southern Bluefin Tuna Industry Association, South
Australia)
Commercial tuna farming is a relatively new industry. It celebrated only its
16th birthday in 2007, but the progress of the industry has been very
exciting and certainly impressive.
All southern bluefin tuna (SBT) ranching occurs in a small region offshore
of Port Lincoln, South Australia. This industry was initiated in 1991 with a
research trial, and has now developed to be the largest farmed seafood
sector in Australia.
Tuna farming began as a result of a declining wild fishery. Australian SBT
catch peaked in 1982 at 21,500 tonnes. In response to increasing concerns
about sustainability, Australia, Japan and New Zealand in 1984, joined to
limit and manage the total allowable catch (the Australian share has been
5,265 tonnes since 1990). As a result, the Australian tuna fishers
investigated the potential for value-adding their catch through aquaculture.
The tuna are mainly caught from December to March when they are present
along the continental shelf in the Great Australian Bight region. The
schools are found, seined and transferred through underwater panels between
nets to specialised tow pontoons, and then towed back at about 1 knot to the
farm areas adjacent to Port Lincoln. The total process takes several weeks.
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On arrival at the farm sites, the tuna are swum from
the tow pontoons into 40-50m diameter farm pontoons. They are then fed bait fish
six days per week, twice per day. This is done by feeding fresh local pilchards
or placing frozen blocks of bait fish in a mesh cage within each pontoon.
The exciting advances in the industry are reflected in the recovering southern
bluefin wildstock, and an increased export of farmed SBT. The conclusion of the
CCSBT scientists indicated that the SBT global catch was at about "replacement
yield". This provided a more positive conclusion built partly on the data from
the spawning ground that large numbers of young spawners, as young as 7 years,
were now entering the spawning stock. Exports in CY2002 exceeded $300 million
for the first time, and have remained between $200-300 million.
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Frozen
tuna at the Japanese market
Photo:
Alistair Douglas |
The surge in super low temperature
shipments in July/September pushed the 2007 exports to over 9,500 tonnes.
tonnes. This increased tonnage reflects the movement to longer growout, partly
due to the movement to super low temperature freezing.
In 2007, the price of ranched SBT has continued to rise. This is partly due to
lower supplies from Europe and Mexico of farmed Northern Bluefin Tuna (NBT).
However, the strong Australian dollar, and weak Yen, meant that total income
increased much less than the price.
The Japanese market appears likely to be stronger in 2008, but still below 2002
levels. The Australian industry has adjusted to the new market situation, but
retains its commitment to continuous improvement through research and training.
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