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No.19
stract for the 1st International Oyster Symposium).
Smaller quantities of Sydney rock oysters and the
closely related Western rock oyster are grown in
Queensland and Western Australia respectively. At
times there has been some production of native fl at
oysters (Ostrea angasi) and native tropical oyster
species, chiefl y blacklip oysters (Striostrea mytiloi-
des) and milky oysters (Saccostrea cucullata).
Excluding Western Australia, the total value of
Australian edible oyster production was A$71.8
million for the 2003-04 financial year (ABARE,
2005). Most sales are for the high value, half shell
market rather than just as bulk sales of shucked
oyster meat. This total production of over 13,000
tonnes is considerably higher than the 1999-2000
financial year estimate provided by Nell (2001)
who indicated total production of about 9,000
tonnes. The most dramatic growth in production
has occurred in the South Australian industry. Oys-
ter production in NSW has been relatively static
in recent years and has not returned to its peak of
about 8,400 tonnes in the mid 1970s (Nell, 2001)
or 9267 tonnes if production of Sydney rock oys-
ters in Queensland is included (Nell, 1993).
In Australia, oysters are sold by number eg per
dozen, and not by weight although different size
categories attract different prices per dozen. Re-
gardless, the above data imply that Pacifi c oysters
grown in South Australia are more valuable per kg
than Tasmanian Pacifi c oysters. This is not neces-
sarily the case. Industry sources suggest that the
value estimate is a better indicator of the size of the
Tasmanian industry than the tonnage estimate.
SYDNEY ROCK OYSTERS
Taxonomy
At the 1st International Oyster Symposium it was
apparent that there was some confusion over the
appropriate nomenclature for Sydney rock oysters.
The 1st International Oyster Symposium Proceedings
History, Status and Future of Oyster Culture in Australia
Greg B. Maguire1* and John A. Nell2
1. Research Division, Department of Fisheries, Western Australia, PO Box 20, North Beach, WA 6920, Austra-
lia.
2. New South Wales Department of Primary Industries, Port Stephens Fisheries Centre, Private Bag 1, Nelson
Bay, NSW 2315, Australia
* Corresponding author Email: maguirewa@iinet.net.au
INTRODUCTION
Oyster farming is one of the oldest aquacul-
ture industries in Australia, dating back some 120
years (Nell, 2005). While farming methods, par-
ticularly for Sydney rock oysters, changed little
for several decades in the twentieth century, the
Australian industry in recent decades has been a
very dynamic industry with new farming areas and
additional Australian states becoming involved in
oyster production while some traditional farming
areas have experienced long term declines (Smith
and Maguire, 1988). Additional changes include
the commissioning of oyster hatcheries, industries
based on exotic oysters progressively becoming
larger than those based on native oyster species,
new environmental challenges being met, and bet-
ter technology being developed by farmers, compa-
nies and researchers. For earlier reviews of oyster
farming industries in Australia see Holliday et al.
(1988), Maguire et al. (1988), O’Meley (1992),
Nell (1993, 2001, 2002a, 2005), Holliday (1995),
Brown et al. (1997), and Love and Langenkamp
(2003) several of whom provide useful photo-
graphs.
PRODUCTION STATISTICS
The major industries for edible oysters in Aus-
tralia are based on production of native Sydney
rock oysters (Saccostrea glomerata) and introduced
Pacifi c oysters (Crassostrea gigas). The major ar-
eas of production, based on 2003-04 fi nancial year
data (ABARE, 2005), are New South Wales NSW
(approximately 6000 tonnes worth A$37.9 million
predominantly Sydney rock oysters but with 5% of
total value from Pacific oysters), South Australia
(4,382 tonnes worth A$21.2 million, almost all as
Pacifi c oysters) and Tasmania (3,243 tonnes worth
A$12.0 million, almost all as Pacifi c oysters). (1A$
= about 83 Yen at time of preparation of the ab-
Oyster Research Institute News No.19
ing of oysters at harvest (O’Meley, 1992; Nell,
2001, 2002a). These are initially arranged in three-
dimensional bundles of fi ve layers of 20 sticks to
catch spat, with the layers helping to deter preda-
tors, and are then nailed out in single layers of 20
sticks for growout. The appropriate choice of in-
tertidal height also assists with reducing losses due
to winter mortality (Bonamia roughleyi) and some
farmers raise the intertidal growing height in win-
ter (Smith et al., 2000). Oysters, detached from the
sticks but too small for sale, can be grown to larger
sizes in large, intertidal trays. A range of alterna-
tive substrates to tarred sticks and trays were de-
veloped (Holliday et al., 1993; Nell 2001). The use
of tar and tar pits for coating wooden surfaces has
become less acceptable from an environmental per-
spective and many farmers now catch spat on plas-
tic slats (2-3 mm thick, 104 mm wide) (Holliday et
al., 1993). Increasingly, the oysters are detached
as spat, and grown in enclosed mesh trays and then
in baskets or mesh cylinders developed interstate
for Pacifi c oysters (see below).
Modern subtidal growout systems were also
introduced. Interestingly, given the hosting of the
1st International Oyster Symposium in Japan, these
subtidal systems evolved from initial work using
Japanese techniques (scallop shells with oyster spat
attached were separated by spacers on longlines
(Wisely et al., 1979). Subsequently, in the limited
number of locations that can be used for multi-
layer subtidal culture, a range of cage and stacked
tray systems evolved (Holliday et al., 1988). A sub-
tidal system, called a pontoon, uses long, capped,
PVC pipes for fl otation and supports a single layer
of oysters below. It has become popular in the key
farming area of Wallis Lake about 65 km north of
Port Stephens (Fig. 1). Given the use of intertidal
baskets and cylinders and subtidal cages and trays,
there has been a major shift to single seed culture
(the farming of unattached oysters typically con-
tained within mesh containers).
Other diseases and genetic strategies
Apart from mudworm and winter mortality, the
latter of which usually affects oyster farms in the
southern half of NSW through to the Victorian bor-
der, the major biological problem has been QX dis-
ease (Marteilia sydneyi). This paramyxean proto-
zoan can cause very high losses in warmer months
in the northern half of NSW and further north in
southern Queensland. It appears to affect the host’s
defence mechanisms by inhibiting enzyme (pheno-
It was known for many years as Crassostrea com-
mercialis. In a review of oyster taxonomy in 1971
it was incorrectly considered to be Saccostrea
cucullata, which is in fact the tropical milky
oyster (Nell, 2001) and dual usage of the two sci-
entific names occurred eg Wisely et al. (1979).
Subsequently, the Sydney rock oysters was again
considered to be of the genus Saccostrea and the
name Saccostrea commercialis was used by many
authors eg Holliday et al. (1993). The similarity
between Sydney and New Zealand rock oysters led
to their being considered as subspecies (Buroker
et al., 1979) and Holliday (1995) proposed that the
Sydney rock oyster be called Saccostrea glomerata
commercialis. Because of the genetic similar-
ity of the Sydney and New Zealand rock oysters,
as indicated by DNA sequencing (Anderson and
Adlard, 1994), the name Saccostrea glomerata is
now widely used for both Sydney and New Zea-
land rock oysters eg Nell (2002a). The specific
name glomerata had been used prior to the name
commercialis for Australasian rock oysters and
hence it was, by taxonomic convention, preferred.
The importation of New Zealand rock oyster spat
around 1888 to replenish depleted Sydney rock
oyster stocks (Nell, 2001) may have contributed to
the genetic similarity.
Historical development of production systems
Collecting and farming of Sydney rock oysters
have a long history in Australia (Nell 1993). In-
digenous Australians fi shed for both Sydney rock
oysters or flat oysters, depending on locality, and
middens (collections of old shells presumably ac-
cumulated after removal of meats) for these spe-
cies occur widely along the Australian coastline.
After European settlement, Sydney rock oysters
were collected from rocks and mangroves in NSW
the 19th century and were often just for lime (cal-
cium carbonate) production. Middens were also
excavated for this purpose. Dredging for oysters
occurred and specifi c rock and shell bed areas were
established for oyster production.
The combined effects of siltation and mudworm
commensals (spionid polychaetes especially Poly-
dora websteri – see Skeel, 1979) forced farmers to
develop off-bottom, timber post and horizontal rail
intertidal systems (racks). These supported vari-
ous types of horizontal timber oyster sticks with
tarred hardwood sticks (25 mm x 25 mm x 1.8 m)
becoming the preferred material. The tar inhibits
shipworm (Toredo spp.) and assists with detach-
No.19
induction in bivalves become available.
It is important to note that that Pacific oysters
have become established in NSW but it was not
through introductions approved by the NSW gov-
ernment. While they have the advantage of grow-
ing much faster than Sydney rock oysters and are
resistant to some of the above diseases, spatfall
of this exotic species is considered undesirable in
NSW estuaries from a conservation perspective.
High levels of spatfall on farmed oysters are also
undesirable from husbandry and marketing per-
spectives and, while techniques are available for
killing the overcatch, they increase labour costs
(Nell, 2005).
While triploid, or selectively bred, or triploid,
selectively bred Sydney rock oysters may be use-
ful in helping to restore oyster industries around
Sydney, farmers in these areas will further evalu-
ate “natural triploid” Pacific oysters as supplies
from Tasmania increase. An additional advantage
of “natural triploid” oysters is the minimal risk of
spatfall because of greatly reduced gonad produc-
tion and likelihood of viable offspring when all of
the oysters are triploids (Nell, 2002b).
Profi tability
While Pacifi c oyster farming can be very profi t-
able (see below for Tasmania), some less widely
available economic analyses have cast doubt on
the profitability of more traditional Sydney rock
oyster farming methods (Holliday et al., 1988;
Maguire et al., 1988). Clearly, losses due to disease
are a serious problem, as is the slow growth rate of
this species (3.5 years to 50 g size for unselected,
diploid Sydney rock oysters in intertidal culture
in NSW (Nell, 2001) compared to 17-18 months
from spawning for diploid Pacifi c oysters in inter-
tidal culture in Tasmania (Maguire et al., 1994)).
The choice of production system may also be in-
fluential. Growing Sydney rock oyster on sticks
is a relatively low yielding farming system, partly
because of variable coverage of sticks by oysters,
whereas standing crop may be at least double with
the use of single seed Pacific oysters in baskets,
at least in Tasmania. This estimated difference is
based on data in Maguire et al. (1994) and also
from Holliday et al. (1988) who estimated yields
for a range of production systems including culture
of Sydney rock oysters on hardwood sticks, i.e.
5-8 kg of whole oysters per m2 of oyster rack area
in two years. Because single seed techniques allow
adjustment of density through the production cycle,
loxidase) activity (Peters and Raftos, 2003). Unfor-
tunately, its impact has spread further south in re-
cent years and has contributed to a severe reduction
in oyster farming in areas around Sydney (120-180
km south of Port Stephens). (Note that the oyster
diseases discussed above do not affect consumers
of oysters.) Predators can cause signifi cant losses
of Sydney rock oysters grown in systems that are
not fully enclosed by mesh that can exclude preda-
tors such as fl atworms, fi sh and crabs (Nell, 1993).
Most Sydney rock farms have relied on wild
caught spat, traditionally from Port Stephens, al-
though hatchery produced oysters have allowed
for lines of Sydney rock oysters that are selective
bred for growth rate and resistance to QX disease
(Nell and Hand, 2003). This breeding program
has been based on mass selection and fortunately
genetic diversity has been conserved well through
the use of large numbers of broodstock initially
used to create the mass selected line (English et al.,
2001). Growth rate has continued to improve with
successive generations and growout time has been
reduced by 11 months (Nell and Perkins, 2005a).
Survival rate, in response to exposure to QX dis-
ease, has also improved greatly with each genera-
tion (Nell and Perkins, 2006).
Chemically induced, triploid Sydney rock oys-
ters (3N; three sets of chromosomes per cell in-
stead of two), also produced in hatcheries, confer
improved resistance to winter mortality (Hand et
al., 1998) and grow faster than diploids, although
this advantage varies with farming site (Nell,
2002b). However, as with triploid Pacific oysters
(Nell and Perkins, 2005b), there can be meat disco-
louration problems at times (Hand and Nell, 1999;
Nell 2002b). In contrast to Pacifi c oysters, “natural
triploid” Sydney rock oyster production, achieved
by obtaining sperm (2N) and eggs (1N from fe-
male after meiosis) from tetraploid (4N) and dip-
loid (2N) lines respectively (Guo et al., 1996), has
not been successful because of the lack of success
with producing tetraploid lines. This is despite the
wide range of techniques that were assessed with
Sydney rock oysters (Nell et al., 1998). One of the
problems is the low number of high quality eggs
produced by chemically induced triploid Sydney
rock oysters. “Natural” triploids are almost all trip-
loids, as opposed to a mixture of triploid and dip-
loid individuals as occurs with batches of chemi-
cally induced triploids. This is a major advantage
and further work should be undertaken with Syd-
ney rock oysters as new techniques for tetraploidy
Oyster Research Institute News No.19
has involved classification of waterways and not
just reliance on land-based oyster depuration tech-
nology (Nell 2002a). Oysters can also be relocated
to “cleaner” fi nishing sites within estuaries but this
increases costs. These developments should en-
gender greater public health confi dence in the con-
sumption of Sydney rock oysters produced in NSW
and promote exports. In a major literature review
by C. Burke and G. Maguire in 1998, which was
further developed by Jackson and Ogburn (1999),
the key conclusion was that bacterial indicators
eg E. coli, are not necessarily good indicators of
viruses that are pathogenic to humans. While viral
monitoring is carried out in NSW, the development
of more cost-effective techniques for monitoring
specifi c viruses, including Nowalk virus and hepa-
titis A viruses, is a worldwide challenge.
Environmental issues
The Sydney rock oyster is a robust species in
terms of environmental tolerance but can be vul-
nerable to extended exposure to very low salinities
(to less than 10 ppt for 2 weeks) and acute expo-
sure to high air temperatures when out of water
(Nell, 1993). As such, Sydney rock oyster farms
could be vulnerable to climate change although
some researchers consider that the natural range
of this species extends north through tropical areas
of Australia (Nell, 2005). Changes in rainfall pat-
terns could also affect nutrient input into estuaries.
Urbanisation of coastal areas can lead to a range
of other environmental changes including eutro-
phication and the associated risks of algal blooms.
Fortunately, toxic algal blooms that impact on
the health of consumers have been much less of
a problem for bivalve industries in Australia than
in many other countries. Unfortunately, not all
members relocating to coastal areas are favourably
disposed to the perceived visual and navigational
impacts of oyster farms and sea-based aquaculture
in general.
PACIFIC OYSTERS
Origin of stocks
Pacific oysters were introduced Tasmania from
1947-52 (from Sendai, Hiroshima and Kumamoto
regions of Japan). Such introductions were unsuc-
cessful in other Australian states and the industry
expanded in northern Tasmania, based on natu-
ral spatfall. There are still locations in Tasmania
where Pacific oysters have become naturalised,
periodically setting on rock structures even though
lease space can be more efficiently utilised than
with growout on sticks. The latter technique re-
quires relatively little labour input, after the sticks
are rearranged as single layers on intertidal leases,
until harvest. However, processing clumps of oys-
ters into marketable individual oysters as whole
oysters or in the half-shell is labour intensive.
There is an ongoing need to promote this small
oyster as a gourmet product and to maintain high
product standards. However, the tendency towards
sales of smaller size grades of Sydney rock oysters
is of concern to the NSW industry because it can
reduce profi tability (Nell, 2005).
Hatchery issues
Some of the technical innovations (triploidy and
selective breeding) should help greatly with profi t-
ability however they rely on hatchery production.
The Sydney rock oyster industry in NSW is still
heavily reliant on natural spatfall and the hatchery
sector has struggled to produce this species reli-
ably because of anorexia in 2-8 day old larvae
and sudden gaping and death of spat below 2 mm
(Heasman, 2004). There has been some success
with producing Sydney rock oysters in a hatchery
in Queensland and the very closely related West-
ern rock oyster in Western Australia (WA) can be
produced reliably in a hatchery near Albany on the
south coast of WA. Fortunately, there has been re-
cent success with large-scale hatchery production
of Sydney rock spat in NSW. The use of single
seed culture systems for Sydney rock oysters may
also improve profi tability and this is not necessar-
ily reliant on hatcheries.
Public health issues
As with many bivalve industries worldwide,
the Sydney rock oyster industry in NSW operated
in many estuaries that experienced little human
impact but which subsequently were subject to
coastal urbanisation. After serious cases of gastro-
enteritus occurred near Sydney that were linked
with oyster consumption, land-based oyster depu-
ration technology was introduced in the late 1970s.
In the 1980s and 1990s there were several episodes
of gastroenteritus caused by Nowalk virus associ-
ated with oysters. In 1997 another major outbreak
of gastroenteritus occurred which was linked to
hepatitis A and often was associated with con-
sumption of Sydney rock oysters. A shellfi sh qual-
ity assurance program was formally implemented
later that year (Jackson and Ogburn, 1999). This
No.19
inder design have emerged and the technology has
been introduced to most Australian oyster produc-
ing states. These Tasmanian and South Australian
systems are lightweight and allow oyster boats to
be loaded with large numbers of baskets or cylin-
ders for grading or sale of oysters on-shore.
Diseases and genetic strategies
Pacifi c oyster farming has been particularly suc-
cessful in Tasmania and South Australia largely
because of the absence of significant diseases.
Apart from sacrificial sampling, overall mortality
of diploid and triploid Pacifi c oysters at two good
farming in Tasmania were <1% during the 22-23
months the oysters were held in intertidal mesh
baskets (Maguire et al., 1994). Losses can occur in
nursery systems if overcrowded or if food levels in
the seawater supply are severely limiting. (Saxby,
2002 reviewed food availability at bivalve farm-
ing sites internationally, including at Pacifi c oyster
farms in Tasmania and South Australia.) Losses, by
displacement or to predators, can be minimised by
placing a cover over the top of open baskets or by
complete enclosure of oysters within the cylinders
or tubes.
Pacifi c oyster farming in Australia have benefi ted
from selective breeding programs involving mass
selection for faster growth and use of family lines
(Maguire, 1997a; Ward et al., 2000; Thompson and
Ward, 2004). Progress has also been made with full
sib crosses (to remove deleterious recessives) and
with using microsatellites to help interpret perfor-
mance of family lines (McGoldrick et al., 2000).
The results of much of this research program have
been commercialised and while initial demand was
highest for mass selected oysters, farmers are now
more inclined to purchase specifi c family lines (R.
Pugh, pers. comm. 2004).
Research on triploid Pacifi c oysters in Tasmania
and South Australia was aimed primarily at inhibit-
ing spawning so that the oysters remained saleable
in summer months. This was achieved with chemi-
cally induced triploids although the more rapid
shell growth of triploid oysters after they reach
about 60 mm in Tasmania can reduce meat weight
to shell cavity volume ratio (condition index)
(Maguire et al., 1994). There have been examples
of large growth rate advantages of triploid oysters
of various species (31-81%), often commencing at
sizes much less than 60 mm (Nell, 2002b). How-
ever, the growth advantages at the two better sites
in Tasmania were only 23.4%, on a whole weight
commercial farms are not operating in those ar-
eas. Deupree (1993) concluded that deep-cupped
Pacifi c oysters in Tasmania were not derived from
Kumamoto strain oysters (C. sikamea). However,
English et al. (2000) showed using allozyme tech-
niques that nine groups were very similar geneti-
cally. These included four naturalised groups,
three of which were Tasmanian and one was from
Port Stephens, three hatchery-derived groups from
Tasmanian farms and two groups obtained from
Sendai and Hiroshima in Japan. These results were
confirmed by English (2001) using microsatel-
lite techniques. Overall, the results confirmed the
origin of the Tasmanian stocks and indicated that
sound hatchery practices had allowed the Tas-
manian industry to avoid major losses in genetic
diversity. It is likely that the deep-cupped shape of
many Tasmanian Pacifi c oysters partly refl ects the
high degree of shell abrasion that occurs during
grading of oysters on vibrating or rotating screens
during routine stock management of single seed
oysters (O’Meley, 1995).
Development of production systems
Because natural spatfall did not prove to be reli-
able, the Tasmanian industry moved to a hatchery-
derived spat supply and new growout areas about
25 years ago (Ward et al., 2000). Modern produc-
tion in Tasmania is based on single seed oysters
produced, by relatively standard international
techniques, in indoor larval tanks and then in land-
based upwellers before being moved into intertidal,
plastic mesh nursery trays. Growout is typically
within units of two plastic mesh, open baskets
supported by two timber stakes that pass through
the length of both baskets. The sticks are then ar-
ranged across intertidal post and rail systems (Nell,
2002a) and are secured with strong rubber ties than
can be easily detached for stock management. Sig-
nificant quantities are also grown out in subtidal
cage systems. Subsequently, spat were provided
to South Australian farmers and a Pacific oyster
industry was established in South Australian with
government approval, and has outgrown the indus-
try in Tasmania. A significant innovation was the
“horizontal longline” system in which tensioned
wire replaced timber rails on intertidal leases and
enclosed individual plastic mesh tubes or cylinders
were hung from a single wire with two simple,
detachable clips (see Nell, 2002a). This allowed
farming in areas where wave action was excessive
for more traditional systems. Variations to the cyl-
Oyster Research Institute News No.19
O’Meley (1992) indicated that Pacifi c oysters may
be graded 5-7 times during growout in Tasma-
nia (excluding grading operations in the nursery
phase). Reducing the frequency of size grading
should lower production costs for Pacific oysters
as grading operations, including moving oysters
to and from leases, are labour intensive and labour
costs are highly significant to the economics of
oyster farming in Tasmania (Treadwell et al., 1991;
Maguire, 1993). While selectively bred or triploid
spat attract a price premium, better performance of
these oysters should also assist with maintaining
profi tability.
Hatchery issues
In contrast to NSW, Tasmania now has more
than adequate hatchery capacity particularly with
the move towards smaller, high density, flow
through larval rearing systems. Increased demand
will largely be for genetically selected lines and
natural triploids. In contrast to some Pacifi c oyster
hatcheries overseas, it has not been necessary to
rely on antibiotics in Tasmanian hatcheries.
Public health issues
In contrast to NSW, the relevant coastlines of
Tasmania and South Australia are not very heav-
ily urbanised and these states have had few public
health problems due to oyster consumption. They
rely on oyster growing area classifi cation and ap-
propriate closures after substantial rainfall rather
than land-based depuration systems.
Environmental issues
In terms of impacts of the environment on oys-
ters, “heat kill” can occur particularly on South
Australian leases if hot weather coincides with
very low tides. Some leases in Tasmania had to be
relocated because of extended exposure to fresh-
water after heavy rainfall.
The environmental impact of oyster farming in
Tasmania and South Australia has not been a major
problem although not all community members are
comfortable with perceived visual and navigational
impacts of oyster farms (Maguire, 1992). Pacific
oyster spatfall has at times been contentious in Tas-
mania but in general the degree of “overspatting”
in much lower than in NSW. While some spat do
develop on oyster cylinders in South Australia, it is
generally a very minor problem in these hypersa-
line areas. Intertidal culture in Tasmania does lead
to biodeposition of organic wastes on the seabed.
basis, at age 27-28 months (Maguire et al., 1994).
Subsequently, no growth advantage was recorded
at one site in South Australia (Ward et al., 2000).
Meat discolouration can be an occasional problem
with triploids in Tasmania.
The development of “natural triploids” has led
to increasing demand for triploid Pacific oysters.
Tetraploids produced by the first author, using
techniques developed by Guo and Allen (1994),
have been used for several years in Tasmania to
produce “natural triploids” but fortunately a new
tetraploid line has now been produced there, using
eggs from “natural triploids”, to help replace this
ageing line of tetraploids. Moreover, there has also
been success in Tasmania with a tetraploid x tetra-
ploid cross to produce another tetraploid line (G.
Kent, pers. comm. 2005). Interviews with oyster
farmers in Tasmania and South Australia indicate
that they prefer the natural triploids because of
the almost 100% triploidy level and ongoing suc-
cess with avoiding spawning in summer but again
growth rate advantages with triploids were con-
sidered to be relatively small. In contrast, Nell and
Perkins (2005b) obtained “natural triploid” Pacifi c
spat from Tasmania and achieved high growth and
survival rate advantages in Port Stephens. These
spat reached 55 g whole weight in 13 months in-
stead of 20 months with unrelated diploid Pacifi c
oysters. It seems likely that a combination of warm
water temperatures and adequate food supplies
is necessary to achieve a large growth advantage
with triploid Pacific. Meat discolouration again
occurred but the “natural triploid” Pacific oysters
reached market size before this was evident (Nell
and Perkins, 2005b).
Profi tability
Pacific oyster farming can provide an excel-
lent and highly predictable return on capital (27%
per annum) at good farming sites in Tasmania
(Treadwell et al., 1991). Subsequently, marketing
pressures have been placed on Tasmanian farmers
because of the rapid growth in production of Pacif-
ic oysters in South Australia. Increased exports of
Australian oysters would assist the domestic mar-
ket and South Australian Pacifi c oysters are being
exported to Japan during the northern hemisphere
summer.
Earlier research by the fi rst author showed that it
was not necessary to grade oysters so often to pre-
vent excessive size variation (Maguire, 1997b) and
this is being adopted by some farmers in Tasmania.
No.19
Attempts to grow venerid clams below the oyster
racks, as a way of minimising organic buildup,
were unsuccessful (Maguire, 2005). To meet Aus-
tralian government requirements for export, both
Pacific oyster industries have to demonstrate that
they meet sustainability principles (Fletcher et al.,
2004).
OTHER ISSUES FOR OYSTER FARMING IN
AUSTRALIA
Forms of aquaculture that use inshore coastal
waters do attract criticism from communities and it
is important that these industries minimise environ-
mental impact. For example, quality assurance pro-
grams for bivalve aquaculture industries in Western
Australia require shoreline surveys to ensure that
farming debris, such as displaced oyster baskets, is
not evident.
Conversely, it is also appropriate to highlight the
benefi ts associated with these industries. Typically,
these are economic and social benefi ts that accrue
from increased employment and investment. In the
case of oyster farms there are additional environ-
mental benefi ts. At least in Australia, where quality
assurance programs require monitoring of oyster
growing areas for a range of attributes including
water quality and types of phytoplankton, oyster
leases represent one of the most signifi cant sources
of estuarine water quality monitoring. This can be
augmented by periodic checks on any heavy metal
or pesticide contamination in seafood (not a sig-
nifi cant problem so far with oysters in Australia).
As bioaccumulators of contaminants, oysters are
sentinels for any estuarine pollution. Moreover,
oyster farmers visually inspect their oysters quite
regularly and poor growth or unexpected mortality
can be observed and investigated. Some years ago
in NSW, chambering in oyster shells highlighted a
problem with tributyl tin from antifouling paints on
boats (Batley et al., 1989). This led to restrictions,
on the use of such paints, that probably also ben-
efited non-commercial bivalve species. It is clear
that oyster farmers can be effective lobby groups
for environmental protection (Maguire, 1991). In
the absence of oyster farms, oysters, which are
not subsequently released for human consump-
tion, have been deployed in NSW specifi cally for
environmental monitoring purposes (Avery et al.,
1998).
Given the environmental protection role that
oyster leases can have, it is important that where
oyster industries have declined in waterways
around Sydney, efforts be made to rejuvenate them.
Finally, the ongoing commitment to public
health and product quality standards with Aus-
tralian oysters is important both for promoting
exports and for encouraging younger consumers in
Australia to purchase oysters so that the domestic
market remains strong.
ACKNOWLEDGMENTS
The authors are grateful for information supplied
by oyster industry staff in Australia. Mr Kunio
Shirasu kindly arranged access to information from
oyster buyers at the Tokyo Fish Market.
DEDICATION
This paper is dedicated to the outstanding con-
tributions made by the late Drs Baughan Wisely
and John Holliday. They and several other key
researchers played major roles in making the re-
search facility, currently known as the Port Ste-
phens Fisheries Centre, one of the world’s major
oyster husbandry research centres for over 30
years.
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Fig. 1
Map of Australia showing some of the individual oyster growing areas where triploid oyster
research has been undertaken by the authors.
