Production statistics

Global production has increased from about 150 tonnes in 1950 to 750 tonnes in 1980.[8] By 2003, global

production had increased to 4.38 million tonnes.[8] The majority was in China, which produced 84% of the

global production.[8] Japan, France and the Republic of Korea also contributed, producing 261 000, 238

000 and 115 000 tonnes produce, respectively.[8] The other two major producers are the United States (43

000 tonnes) and Taiwan (23 000 tonnes).[8] In 2003, global Pacific oyster production was worth $ 3.69

billion, with Asia contributing over half of this amount.[8]

Global aquaculture production ofCrassostrea gigas

[edit]Current issues

[edit]Virus management

Pacific oysters are nonspecific filter feeders, which means they ingest any particulate matter in the water

column.[9] This presents major issues for virusmanagement of open water shellfish farms, as shellfish like

the Pacific oyster have been found to contain norovirus strains which can be harmful to humans.[9] Globally, noroviruses are the most common cause of nonbacterial gastroenteritis, and are introduced

into the water column by faecal matter, either from sewage discharge or land runoff from nearby farmland.[9] Numerous gastroenteritis outbreaks in the world have been directly caused by the consumption

of shellfish from polluted areas.[10]

[edit]Heavy metal pollution

Pacific oysters, like other shellfish, are able to remove heavy metals, such as zinc and copper, as well

as biotoxins (microscopic toxic phytoplankton), from the surrounding water.[5] These can accumulate in

the tissues of the animal and leave it unharmed (bioaccumulation).[5] However, when the concentrations of

the metals or biotoxins are high enough, shellfish poisoning can result when they are consumed by

humans. High copper concentration in Pacific oyster can be recognised by the meat turning a grass-green

colour.[5] Most countries have strict water regulations and legislation to minimise the occurrence of such

poisoning cases.[11][12][13]

[edit]Diseases

Disease Agent Type Measures

Denman Island disease Mikrocytos Protozoan Restricted modified culture

mackini parasite practices

NocardiosisNorcardia

crassoteaeBacterium Modified culture practices

Oyster velar virus disease (OVVD) Unknown Virus None known

Herpes-type virus disease

of C.gigas larvaeUnknown Virus None

[8]

[edit]Predators

Numerous predators are known to damage Pacific oyster stocks.[14] Several crab species (Metacarcinus

magister, Cancer productus, Metacarcinus gracilis ), oyster drills and starfish species (Pisater

ochraceus, P. brevispinus, Evasterias troschelii and Pycnopodia helianthoides ) can cause severe impacts

to oyster culture.[14]

[edit]Productivity

Productivity of the Pacific oyster can be discussed as the amount of meat produced in relation to the

amount of seed planted on cultch.[5] The productivity of a farm also depends on the interaction

of biotic factors, such as mortality, growth, and oyster size, as well as the quality of the seed and the

growing technique used (off bottom, bottom, suspended or floating culture).[5] The main causes of

mortality in the Pacific oystere are: natural mortality (age), predators, disease, environmental conditions

(ice, freak winds), competition for space (crowding of cultch), silting (sediment runoff from land) and

cluster separation (process of breaking up clusters of oysters to into as many individual oysters as

possible).