Green-lipped mussels, quinnat salmon and Pacific oysters are the backbone of New Zealand’s aquaculture industry and are significant export items.
With its long coastline bathed in cool ocean waters, New Zealand is ideally suited to a diverse aquaculture. New Zealand aquaculture is not restricted to the farming of fish, but also includes the rearing and cultivation of shellfish (molluscs), prawns, crabs and crayfish (crustaceans), sea cucumbers (echinoderms), sponges, seaweeds (algae) and watercress.
Aquaculture can occur in coastal waters, rivers, lakes, and on land – in excavated pools or specially constructed tanks.
From small beginnings in the 1960s, New Zealand aquaculture has become a multi-million-dollar industry. Since the 1980s it has been the country’s fastest growing rural business. By 2001 aquaculture produce was worth $280 million.
Giant Malaysian river prawns (Macrobrachium rosenbergii) have been commercially farmed in Taupō since 1991. The prawn farm uses waste water from the nearby Wairākei geothermal power plant to heat fresh water to temperatures between 24º and 28º C. Caring for the omnivorous crawlers is labour intensive, as they go through a series of moults before they are harvested at nine months of age. All 17 tonnes of annual harvest is consumed in New Zealand.
Mussels were harvested by hand from intertidal rocks until the 1960s, when a dredge industry attempted to satisfy local demand. However, mussel beds in Tasman Bay (Nelson region) and the Hauraki Gulf (Coromandel region) were quickly dredged out, so a few people turned their attention to mussel culture. The native green-lipped mussel (Perna canaliculus) was used to trial a cultivation technique in which young mussels (mussel spat) were grown on ropes suspended from rafts. The sheltered, clean waters of the Hauraki Gulf and the Marlborough Sounds, rich in nutritious plankton, provided an ideal environment. After 12–18 months the cultured mussels were ready for harvest, and the first went on sale in 1971.
As more growers entered the industry, the labour-intensive raft method of cultivation was dropped in favour of a modified Japanese longline system. Biodegradable stockings full of spat are tied to parallel rows of looped ropes, supported by buoys. The young mussels grow through the stockings and anchor themselves to the ropes with threads formed by a special secretion.
For some years, ropes were reseeded after harvest with spat found growing naturally in coastal waters. This proved risky, however, as the timing and volume of supply was unpredictable. In 1974 a marine scientist discovered abundant mussel spat attached to washed-up seaweed on Ninety Mile Beach, Northland. Local people began to collect the seaweed, pack it into buckets, and air freight it to mussel farmers. Kaitāia spat, as it was called, became the main source of seed mussels in New Zealand.
During the 1970s mussels had been exported to the United States as a powdered health supplement to relieve arthritis symptoms. This market collapsed overnight in 1981, when stringent US drug legislation controls were placed on the powder. Subsequently, extracts from mussels were developed in New Zealand, where they continue to be marketed as health products.
In the mid-1980s fresh green-lipped mussels were cheap and plentiful in New Zealand supermarkets, and the industry turned its attention to developing reliable export markets.
Frozen mussels in half shells became the dominant export item, patented with the trade name NZ Greenshell Mussels. By 2000 the industry was booming: mussels were New Zealand’s second most important seafood export, with sales of $170 million to over 60 countries. About 1,500 people were directly involved with mussel production on marine farms located predominantly in the Marlborough and Coromandel regions.
Between 1901 and 1907, three species of salmon were introduced into New Zealand rivers. Quinnat salmon (Oncorhynchus tschawytscha) was the only one that successfully established sea-running populations, becoming the focus of a successful recreational fishery in the glacier-fed rivers of Canterbury and Otago. For years recreational fishers opposed the development of salmon and trout aquaculture in New Zealand. They feared that disease would spread from fish farms into recreational fisheries, and that poaching of wild fish would increase if their sale was allowed. In 1973 the government declared trout farms illegal, but granted permission for salmon farms.
Koi carp (Cyprinus carpio) and tilapia (Oreochromis species) are amongst the most popular fish to be farmed worldwide, but they are unwelcome in New Zealand. They destroy native plant and fish habitats in freshwater systems, and are classed as noxious. It is illegal to breed, sell or release them into the wild.
The first salmon farm was established in 1976 at Waikoropupū Springs, near Tākaka in Golden Bay. Salmon were raised in fresh water, growing to a length of 25 centimetres in two years. The venture was originally set up for ocean ranching, where juvenile salmon are released into the sea in the expectation that some will return as adults. But few did return. The Waikoropupū Springs facility was converted into a hatchery, supplying stock to sea farms. Other ocean-ranching salmon farms were set up in the South Island, but proved uneconomic.
The first sea-cage salmon farm was developed in Big Glory Bay, Stewart Island, in 1983. It was soon followed by farms in the Marlborough Sounds and at Akaroa, Banks Peninsula. These three production areas accounted for 93% of the 8,500 tonnes of salmon produced in 2001. In sea-cage ranching young fish (smolt) are taken from freshwater hatcheries and transferred to net cages about 25 metres across and 15 metres deep, sunk in clean, fast-flowing coastal waters. The salmon remain in the cages all their life, and are fed fishmeal pellets which are high in protein and oil. The fish are harvested at two or three years of age, at weights between 2 and 4 kilograms. Approximately 65% of salmon is exported. Japan is the main market, but smaller quantities go to Australia and Pacific rim countries. Export sales were worth $39 million in 2003.
Farmed salmon are anaesthetised with a herbal extract before being killed by the instant method of brain spiking. The heart continues to beat for a time while the animal is bled from its sliced gills. Because the creature is in a relaxed state when it is killed, a firm, long-keeping flesh is produced.
A unique form of salmon farming developed in the hydroelectric canals of the central South Island in the 1990s. Young salmon were enclosed in net pens in the Ōhau and Tekapo canals, and reared in a similar manner to sea-farmed salmon. The Tekapo site, at 677 metres above sea level, is the highest salmon farm in the world and is fed by fast-flowing cold waters from the Southern Alps.
New Zealanders are partial to oysters and two types are harvested locally: dredge oysters and rock oysters. Both have been commercially harvested since the mid-1800s. Dredge oysters, or Bluff oysters (Ostrea chilensis) have not been farmed in New Zealand. Rock oysters (Saccostrea commercialis) are found naturally in the intertidal zone in the north of the North Island, and were the subject of early cultivation experiments. These trials showed that a marketable product could be farmed within 3½ years – half the time it took an oyster to mature when growing naturally on rocks. During the 1960s the commercial farming of native rock oysters spread throughout the harbours and inlets of the northern North Island. Most farmers grew their oysters on cement-coated sticks laid down in racks.
Oyster spat, the free-swimming larval stage of an oyster, were collected during summer on sticks placed at mid-tide level in Mahurangi estuary, near the Hauraki Gulf. In 1970, farmers noticed another oyster that quickly outgrew the rock oysters. This newcomer was the Pacific oyster (Crassostrea gigas), which had probably been introduced into New Zealand waters from a Japanese source in the 1950s. At first, farmers tried to clear it from their collecting sticks, but each year more and more Pacific oyster spat attached itself until it proved futile to try and get rid of it.
Within a few years most commercial growers wisely began cultivating Pacific oysters. They grow three times faster than native rock oysters, produce a consistent quantity of spat, and have a well-established international market. The Pacific oyster turned up in the Marlborough Sounds in 1977 and farming began there in the 1990s. In contrast to the northern North Island method of racks, Marlborough farmers cultivated their oysters on suspended longlines. By 2001, 100 oyster farms were producing 3,500 tonnes of Pacific oysters; 30% was consumed by the domestic market and the rest was exported, with a value of $13.6 million.
Enhancement is the name given to artificial techniques that boost the recruitment or survival of young animals or seaweeds in the wild. In New Zealand, enhancement of scallops has been very successful in Tasman Bay and Golden Bay. New Zealand scallops (Pecten novaezelandiae) are large fan-shaped shellfish with a flat upper shell and a deeply curved lower shell. They live on the seabed of coastal waters at depths of 30 metres or more.
Scallops are cultivated by suspending spat-collecting bags in coastal waters during summer. Thousands of scallop larvae settle out of the plankton onto the fine feathery surface of the bag. The larvae are left to grow to a suitable size before they are collected and released onto known natural scallop beds at densities of about six per square metre of sea floor. There, they grow for one or two years before the bed is harvested by dredging. This technique resurrected the Tasman scallop fishery, which was near collapse in the 1980s, to a level where 747 tonnes were harvested in 2004.
New Zealand aquaculture has been built around a few low-value and easily cultured species, and is concentrated in two small regions. In 2004, the Marlborough Sounds and the Coromandel area accounted for over 70% of the country’s aquaculture production. Such concentration makes the industry extremely vulnerable to downturns in export demand or hazards such as sudden growths of toxic algae (toxic algal blooms).
Two toxic bloom disasters have struck the industry, highlighting the unpredictable nature of the marine environment. In 1989, a bloom of poisonous plankton contaminated salmon farms in Big Glory Bay, Stewart Island. Another widespread bloom developed in the summer of 1992–93, and people became sick from eating contaminated shellfish. The government closed all harvesting from mussel farms for a number of months, and growers placed a voluntary ban on the transport of young mussels from Northland beaches.
As a consequence, a nation-wide programme was developed to monitor coastal waters and shellfish for the presence of poisons from plankton. The New Zealand Food Safety Authority manages the programme and ensures that water and shellfish samples are tested weekly.
In an attempt to diversify the aquacultural industry, scientists have looked at a variety of organisms – from seaweeds to seahorses – that could be farmed in New Zealand. The native pāua (abalone) is one that shows potential as a high-value species. Although pāua aquaculture started in 1980, it has been slow to move out of the development phase. New Zealand blackfoot pāua (Haliotis iris) is a large, single-shelled marine snail which has been commercially harvested from the wild since 1944. Unlike mussels, oysters or salmon, pāua are slow growers and have very exacting requirements for their development. Separate cultivation systems are needed for larval pāua and juveniles.
Most farming is done in small land-based operations. Farmers receive juvenile pāua from specialised hatcheries and grow them in flat tanks or tubs, where they are fed fresh kelp. One farmer raised wild pāua in plastic barrels suspended from buoys in Akaroa Harbour. Five tonnes of cultured pāua meat were harvested in 2002, achieving sales of $400,000.
One of New Zealand’s pioneer pāua farmers cultivates pearls. He inserts a fleck of grit between the pāua body and its shell. The pāua secretes nacre or mother-of-pearl over the irritant, and a blue pearl develops. After two to three years the shellfish is harvested for its meat and the pearl is cut from the shell.
A number of other species are suitable for aquaculture in New Zealand. The commercial farming of rock lobsters, kingfish and giant kelp is under consideration. Dredge or Bluff oysters breed more prolifically in Northland waters than they do in Foveaux Strait, where they are commercially harvested from the wild, and their potential for aquaculture was being considered by National Institute of Water and Atmospheric Research scientists in 2004. Other prospects which are being trialled include the common New Zealand bath sponge (Spongia manipulatus), the sea urchin, and the native seahorse (Hippocampus abdominalis). Seahorses are highly valued as aquarium fish and are used in traditional Asian medicines. Around the world, seahorses have been over-harvested in the wild; aquaculture offers an alternative source.
Aquaculture in New Zealand developed in a haphazard fashion, with regional councils initially giving little thought to the cumulative impact of marine farms on the coastal environment. By 2001, marine farms occupied 4,000 hectares of coastal waters – about the size of a large sheep farm. Some councils had become inundated by applications for marine farms, and it was evident that guidelines were needed to manage the coast in a sustainable manner.
On 21 March 2002 the government imposed a ban on new farms in coastal marine areas while they carried out a major reform of aquaculture legislation. The aim of the reform was to streamline application processes for marine and freshwater farms, which operated under a dual licensing system overseen by regional councils and the Ministry of Fisheries. Established farmers objected to the ban – they believed that delaying expansion and diversification would jeopardise the industry. Māori groups felt that they were disproportionately affected, as they were major applicants for new marine farms. Since the moratorium was announced, the New Zealand government has also had to consider Māori claims for ownership of the seabed and foreshore.
There is a great demand for seafood worldwide, and New Zealand is well placed to satisfy some of this. However, the industry relies on low-value filter-feeding shellfish (mussels and Pacific oysters). There is potential for the industry to diversify into farming high-value species such as pāua, kingfish and crayfish. These species require a special food supply and are more expensive to farm, but they can be sold at a higher price.
With new legislative reforms to safeguard the environment, New Zealand aquaculture should continue to flourish.
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