Oyster Production and History
Introduction The Sydney rock oyster (Saccostrea glomerata) is considered a gourmet's delight and is the main focus of oyster production in the State. With a current annual production of over 106 million oysters worth over $35 million, oyster farming has been the most valuable aquaculture industry in New South Wales for over 100 years.
Background Cultivation of oysters is far from a recent innovation, the Japanese were raising oysters as early as 2000 BC and the Romans from about 100 BC. While New South Wales can trace its origins to the 19th century, use of natural stocks of oysters in the State has a much longer history. The Aborigines on the coastal regions feasted on oysters and shell beds can be found in the many kitchen middens along the coast. Some of these middens have been carbon-dated to ten thousand years.
With European settlement of the State and a rapidly increasing population, the demand for oysters grew quickly. The use of oyster shell as a source of lime in cement production resulted in natural oyster stocks being near depletion by the 1860's. Government controls were introduced and this precipitated the introduction of early cultivation practices, the first of which was the establishment of Claires (ponds) based on French cultivation techniques, by Thomas Holt in Gwawley Bay in 1872. Although this technique did not lend itself to local conditions, it demonstrated the potential of the Sydney rock oyster as a commercial species.
Oyster farming now employs many different techniques, all of which take place on selected sites held under about 3200 aquaculture leases, with a total current area of about 4300 hectares, which are administered by NSW DPI. Commercial production in the State occurs in 41 estuaries between Eden in the south to the Tweed River in the north. Wallis Lake and the Hawkesbury River are the main producing areas. Pacific oysters (Crassostrea gigas) have been commercially cultivated in Port Stephens since 1991, but are declared a noxious fish in all other NSW waters.
Biology Most oyster species, including Sydney rock oyster, change sex during their life. The first spawning is usually as a male and subsequent spawnings as a female. During spawning, adult females disperse up to 20 million eggs and males hundreds of millions of sperms into the water when the tide and current are optimal for the widest distribution. Pacific oyster females can produce between 30 to 100 million eggs per spawning. Spawning is so intense during this period that the surrounding water can take on a milky appearance. Fertilisation takes place in the water column and development continues for up to 3-4 weeks as the larval stages of the oyster swim and grow, ultimately settling on a suitable hard clean surface. Survival rates during this phase is less than 0.1%. The surviving oysters are then called "spat" and will grow to maturity in about 3 to 4 years never again leaving their chosen position.
Oysters, which are bivalve molluscs, obtain food by filtering and extracting minute marine plants (algae), bacteria and nutrients from the surrounding water.
Cultivation techniques Three distinct cultivation methods have evolved in New South Wales over the years; rock culture (now seldom practiced), stick culture; and various tray type cultures.
Stick culture This method has been the mainstay of the industry since the 1930's and commences with oyster larvae settling on tarred (and sometimes additionally cemented) hardwood sticks 1.8 metres long and 25 mm square, which are placed in areas of estuaries where spatfall (settling of spat) is most reliable, typically near river mouths. The sticks are then moved to low spatfall areas to reduce "overcatch" (further spatfall on growing oysters) and are grown to maturity on horizontal racks in the inter-tidal zone. The process takes from 3 to 4 years with great care required in the first two years to protect the oysters from excessive heat and predators (bream, octopus and stingray). At maturity, the oysters are removed from the sticks and graded into various sizes prior to marketing. The largest (15 to 25 oysters/kg) are sold as first grade oysters and the next grades (25 to 35 per kg) are sold as "bistro" or "bottle" grade. Oysters too small to meet either of these criteria are usually placed onto trays and returned to the same or other estuaries to develop to a marketable size. While this method has proven to be the most efficient for the industry relying on natural catch, it may be less significant should commercial oyster hatcheries establish and produce single seed oysters.
Tray Culture Oyster trays are usually one metre wide and from 1.8 - 2.7 metres in length, of timber and wire or plastic construction. They have many advantages as a cultivation method over earlier methods and in some cases even stick culture. Trays are more portable, easier to manage and allow precise stocking densities to encourage oysters to grow in a more uniform and marketable shape. Oyster farmers have devised techniques to further exploit these advantages culminating in the "single seed technology".
Single seed culture Increasingly, oyster farmers are removing oyster spat from the catching surface (usually sticks or PVC slats) very soon after settlement when the oysters are still only 3-8 mm in diameter. Spat are then either placed on specially constructed trays or in recently developed plastic mesh cylinders or baskets. These systems provide excellent protection from predators and the early removal of the stick prevents oysters becoming misshapen or clumped together. Faster growth rates have also been reported. Whilst single seed techniques require substantial capital investment, faster growing, better shaped oysters generally allow more precise grading and the oysters generally receive a higher market price. Research into the commercial production of "triploid" oysters which grow fast and hold market condition longer, is aimed at further enhancing the viability of single seed culture.
Background Cultivation of oysters is far from a recent innovation, the Japanese were raising oysters as early as 2000 BC and the Romans from about 100 BC. While New South Wales can trace its origins to the 19th century, use of natural stocks of oysters in the State has a much longer history. The Aborigines on the coastal regions feasted on oysters and shell beds can be found in the many kitchen middens along the coast. Some of these middens have been carbon-dated to ten thousand years.
With European settlement of the State and a rapidly increasing population, the demand for oysters grew quickly. The use of oyster shell as a source of lime in cement production resulted in natural oyster stocks being near depletion by the 1860's. Government controls were introduced and this precipitated the introduction of early cultivation practices, the first of which was the establishment of Claires (ponds) based on French cultivation techniques, by Thomas Holt in Gwawley Bay in 1872. Although this technique did not lend itself to local conditions, it demonstrated the potential of the Sydney rock oyster as a commercial species.
Oyster farming now employs many different techniques, all of which take place on selected sites held under about 3200 aquaculture leases, with a total current area of about 4300 hectares, which are administered by NSW DPI. Commercial production in the State occurs in 41 estuaries between Eden in the south to the Tweed River in the north. Wallis Lake and the Hawkesbury River are the main producing areas. Pacific oysters (Crassostrea gigas) have been commercially cultivated in Port Stephens since 1991, but are declared a noxious fish in all other NSW waters.
Biology Most oyster species, including Sydney rock oyster, change sex during their life. The first spawning is usually as a male and subsequent spawnings as a female. During spawning, adult females disperse up to 20 million eggs and males hundreds of millions of sperms into the water when the tide and current are optimal for the widest distribution. Pacific oyster females can produce between 30 to 100 million eggs per spawning. Spawning is so intense during this period that the surrounding water can take on a milky appearance. Fertilisation takes place in the water column and development continues for up to 3-4 weeks as the larval stages of the oyster swim and grow, ultimately settling on a suitable hard clean surface. Survival rates during this phase is less than 0.1%. The surviving oysters are then called "spat" and will grow to maturity in about 3 to 4 years never again leaving their chosen position.
Oysters, which are bivalve molluscs, obtain food by filtering and extracting minute marine plants (algae), bacteria and nutrients from the surrounding water.
Cultivation techniques Three distinct cultivation methods have evolved in New South Wales over the years; rock culture (now seldom practiced), stick culture; and various tray type cultures.
Stick culture This method has been the mainstay of the industry since the 1930's and commences with oyster larvae settling on tarred (and sometimes additionally cemented) hardwood sticks 1.8 metres long and 25 mm square, which are placed in areas of estuaries where spatfall (settling of spat) is most reliable, typically near river mouths. The sticks are then moved to low spatfall areas to reduce "overcatch" (further spatfall on growing oysters) and are grown to maturity on horizontal racks in the inter-tidal zone. The process takes from 3 to 4 years with great care required in the first two years to protect the oysters from excessive heat and predators (bream, octopus and stingray). At maturity, the oysters are removed from the sticks and graded into various sizes prior to marketing. The largest (15 to 25 oysters/kg) are sold as first grade oysters and the next grades (25 to 35 per kg) are sold as "bistro" or "bottle" grade. Oysters too small to meet either of these criteria are usually placed onto trays and returned to the same or other estuaries to develop to a marketable size. While this method has proven to be the most efficient for the industry relying on natural catch, it may be less significant should commercial oyster hatcheries establish and produce single seed oysters.
Tray Culture Oyster trays are usually one metre wide and from 1.8 - 2.7 metres in length, of timber and wire or plastic construction. They have many advantages as a cultivation method over earlier methods and in some cases even stick culture. Trays are more portable, easier to manage and allow precise stocking densities to encourage oysters to grow in a more uniform and marketable shape. Oyster farmers have devised techniques to further exploit these advantages culminating in the "single seed technology".
Single seed culture Increasingly, oyster farmers are removing oyster spat from the catching surface (usually sticks or PVC slats) very soon after settlement when the oysters are still only 3-8 mm in diameter. Spat are then either placed on specially constructed trays or in recently developed plastic mesh cylinders or baskets. These systems provide excellent protection from predators and the early removal of the stick prevents oysters becoming misshapen or clumped together. Faster growth rates have also been reported. Whilst single seed techniques require substantial capital investment, faster growing, better shaped oysters generally allow more precise grading and the oysters generally receive a higher market price. Research into the commercial production of "triploid" oysters which grow fast and hold market condition longer, is aimed at further enhancing the viability of single seed culture.