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Because of their popularity Bluff
oysters were among the first to be managed under a rudimentary quota
system. This was introduced in 1963 (it was not introduced for other
fish stocks until 1986) when seasonal harvest of 170,000 sacks each
containing about 800 oysters was set. This has dropped steadily over
the years and from 1992 to 1995 the beds were closed completely
because of bonamia. Today the dredged Bluff oyster quota is
14,950,000 units and there is an another smaller quota of 505,000
kgs from the Nelson/Marlborough region at the north of the South
Island.
At this stage there in no commercial
aquacultural production of flat oysters and this is why this
annoucement and others by NIWA have been greeted with such
excitement.
Professor Rufus Wells, who is in
charge of the university research, says that after two years of
experimentation in an area north of the Auckland the results have
been remarkable. "The growth rate is much higher than expected given
the origins of the species in the cold southern waters of Foveaux
Strait. Bluff oysters are growing to the size of a fifty-cent coin
in less than four months, which compares well with the Pacific
Oyster.
"Just as importantly, we are able to
grow the species in the north without the major disease problems
that plague the wild stock at Bluff.
"Farmed Bluff oysters would also
overcome another practical problem. Wild Bluff oysters are always
marketed without their shells because the shells are unattractive
and infested with parasites and overgrowth. International gourmands
insist on oysters being sold in the shell. Therefore aquaculture of
the Bluff oyster will allow the sale of intact oysters."
"The first step has been to develop
new spat collecting methods for the Bluff oyster," Professor Wells
said. "Spat has been collected from Bluff oysters that have drifted
north on oceanic currents during the larval phase and settled on the
mudflats of the Manukau Harbour. Unlike Pacific oysters, the mother
Bluff oyster retains eggs and broods them throughout larval
development prior to release and settlement."
Niwa under the leadership of Dr
Andrew Jeffs has been developing a flat oyster hatchery at a new
facility at Bream Bay. According to Dr Jeffs. "The difficulty with
the New Zealand flat oyster is its breeding cycle which is far from
predictable. It was very difficult to get males and females to spawn
at the same time. Also only a small proportion of the adult female
population produces larvae each season. They fertilise their egg
with sperm found in the seawater they draw into their shell." The
female parent then retains the larvae to an advanced state in the
shell."
From work done in Europe, Dr Jeffs
knew that temperature and diet were the main ways that you could
manipulate the breeding cycle and get the males and females to be
sexually active at the same time.
"We knew how to feed the oyster but
finding the right temperature for the water proved far more
difficult. In Europe, if you wanted to make the oysters breed, you
put them in warm water. For the Bluff oyster the breakthrough came
when we found that if we put them into colder water then we
encouraged the shellfish to perform. Success came when we lowered
the water temperature to 10-11 degrees for a two to three month
period."
Professor Wells said that the Bluff
oyster looks like a good candidate for aquaculture in the North.
"The future work will come in securing an artificial supply of spat
for growing, determining the cultivation methods for on-growing
oysters at optimum rate and quality, finding a suitable location on
west Kaipara or east Mahurangi, and testing the market."
Professor Wells and Brendon Dunphy, a
postgraduate student funded by a Technology New Zealand scholarship,
have developed new technologies to enable the development of the
fishery with assistance from BioMarine Ltd, Warkworth, Pakahi Marine
Farms in Clevedon and Kia Ora Seafoods from Manakau City.
So far as the aquaculture of oysters
is concerned New Zealand has approximately 2,200 hectares in farmed
Pacific oysters worth NZD 45 million. |
