A fourth generation farmer on the Clevedon coast, Callum McCallum has diversified into acquaculture in order to stay on the land. These days he produces about 4.8 million oysters a year.

Callum has 95 ha at Kawakawa Bay, on which he runs the oyster operation, and on two smaller farms off Waiheke Island, along with two blocks of farm land, on which he runs sheep and beef.

Callum’s been director and co-owner of Clevedon Coast Oysters for the past 20 years. He’s also chairman of NZ Aquaculture Council, NZ Oyster Association and is a member of the Seafood Industry Council.

The business started in 1986. It is run on about 25ha of mudflats.

Callum says his father was always interested in acquaculture. John McCallum senior and Callum put the first oyster racks down in themselves in the mid 1980s. Callum learnt the business working on an oyster farm at Warkworth.

He says his farming background stood him in good stead. “This is no different from farming sheep…..” They need food, clean water and good paddocks.

Callum says the Clevedon farm can yield up to 17,000 dozen per ha. per year.

Initially they grew oysters and sold them in sacks. There were problems in the industry largely getting out of a seasonal nature of oyster growth – these have largely been overcome.

In 1998 Callum started exporting and an export standard factory was opened in 2001.

Since opening the factory they’ve stayed with local supply but also moved into the export business. They supply half shell oysters in Australia, Asia and the US. About 50% is retained for the domestic trade.

Clevedon Coast also runs a shop on the way to Kawakawa Bay – about 20 minutes out of the Clevedon settlement.

Processes

Water quality is high on the agenda. They need to control run off from the neighbouring farmland. There’s also regular water testing. From weather and water testing they make a contamination prediction. There are occasions where they don’t harvest up to 10 days. For similar reasons they don’t harvest at Waiheke Island in summer.

The water quality monitoring is part of a USFDA audited programme. This programme means that Callum’s product is acceptable to most regulatory health agencies. The company has also pursued organic certification via AGriQuality.

Callum says the ideal farm should be situated at the neap low tide level, with good water flows and minimal urban runoff.

Oyster Farming

Callum farms giant pacific oysters ( Crass Ostrea gigas ). It is said that this variety was probably introduced to NZ accidentally, in all likelihood by spat travelling across the Pacific on the hulls of ships. By mid 1970s pacifics had colonized the native rock oysters.

The spat is collected at Kaipara Harbour on ‘stick bundles” – essentially bundles of wooden batons. These batons are then transported back to Clevedon & Waiheke and nailed on the wooden structures that sit in the inter-tidal zone. The “sticks” are left to grow for about 12 months.

The general idea is that this type of oyster – the Pacific or Rock oyster – needs to be under water some of the time, and out of the water for about five hours a tide. The bluff oyster is under water the whole time. Callum says that they do grow some oysters in full immersion, like the Bluffies, and get much better growing rates, however this does leave them susceptible to predators – in particular an annoying worm that burrows through the shells.

Other predators include the now ubiquitous stingrays and the aptly named oyster catcher.

The biggest challenge to the industry is evening out the growing season through the year. They’ve got around this issue by clustering the spat gathering sticks in bundles with only a small gap between them. These spat bundles can be kept for up to 9 months before laying them out on racks, so the oyster growth is constrained by the space available and the restricted flow of nutrients.

Harvesting and processing

They harvest 4-5 days a week at the low tide. This usually takes about 2 hours. The barge is then taken up the Clevedon river creek to unload.

The oyster are then stripped off the sticks at the back of the factory, washed and separated out. There’s a sophisticated grading machine that sorts according to size – using a flash camera. The grading machine can sort around 240 oysters per minute and was sourced from Tazzie. Currently Callum divides the harvest into 5 different sizes.

Some of these smaller grades are put back out on the farm to grow further. They’re put into on-growing baskets called aqua purses, trays and bags. This has reduced wastage to about 5%.

Callum says one the biggest issues for him is staff. They employ between 30 and 40 people and keeping them in line, trained and ready to work, is a major headache.

Shuckers

The shuckers use a compressed pneumatic drill a bit smaller than a pencil. A good shucker would do 400 dozen per day.

In aquaculture export terms oysters are third on the list after mussels (60%), salmon (30%) and oysters (10%). Oysters earn about $360M per year. Callum reckons there’s heaps of potential to lift production. Callum is already looking at alternative species – including seahorse, paua, whitebait, even goeduck.

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