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.