How is NIWA research helping sustainable Pacific oyster farming? Subtidal oysters can have issues with fouling, pests and parasites, and can be moved for a time in an intertidal area to “harden-off” to increase their value. Single-seed oysters are grown in several different systems including trays, baskets, long-line and cages in subtidal or intertidal areas. Single-seed oysters require more labour and mechanisation but produce a more even-shaped product and can benefit from breeding programs. Thus, some growers have recently moved to growing ‘single-seed’ oysters by either stripping wild-caught spat off the sticks at an early age and reseeding, or by growing spat that have been produced in a hatchery. The ultimate quality (size and uniformity) of the oyster crop is strongly influenced by the initial density and evenness of the settled spat – which are difficult to regulate in this traditional growing system. Once grown, the oysters are then simply harvested for processing. The wooden sticks are then nailed onto wooden racks, set out at the correct intertidal level to minimise fouling, parasites and pests. Oyster farmers catch the spat on bundles of wooden sticks at preferred sites. Pacific oysters ‘broadcast’ spawn and their larvae drift in the sea for several weeks before settling. In the 1960s, the faster growing Japanese or Pacific oyster ( Crassostrea gigas) became introduced - some say with shipments of sections of the Auckland Harbour bridge.

Rock oysters were revered and ‘gardened’ by early Māori and hand-picked to unsustainable levels by the early European fishery. The New Zealand oyster industry historically started outgrowing the native rock oyster ( Saccostrea commercialis) 1. Oyster farms can also provide habitat for some fishes when the tide is in. Shellfish production imposes a relatively small burden upon the local environment and the industry’s carbon and freshwater footprints are small in comparison with many other protein crops 2, 3. Shellfish are a nutritious food: high in trace elements, protein and poly-unsaturated fatty-acids, but low in cholesterol, saturated fats, and trans-fats 3, 4, 5. Once settled, oyster spat cannot re-attach and will continue to grow on their chosen settlement surface. Newly settled individuals (spat) are small (0.5 mm shell length). They will drift in the sea for approximately three weeks and prefer to settle on horizontal surfaces. Eggs, sperm and subsequent larval stages are planktonic. Adults release their gametes into the open water.

In the wild, they can live for several years and grow to 20 cm or more (shell length) but most have become reproductively active by the time they reach 6-8 cm in 12-20 months. Pacific oysters were introduced in New Zealand and have a moderately complex life-cycle. How is NIWA research helping sustainable Pacific Oyster aquaculture?.

Oyster spat settlement