Mariculture offers growth potential

By Sue Matthews. Published in Fishing Industry News Southern Africa (April 2001)

As many of the world’s fisheries reach a state of maximal or over-exploitation, mariculture is seen as increasingly important in providing food security, creating employment opportunities and generating income. Indeed, the Food and Agriculture Organisation (FAO) estimates that mariculture production worldwide totaled 13 million tons in 1999, and predicts that its relative contribution to seafood supply will continue growing over the next three decades.

In South Africa, the Marine Fisheries Policy document clearly identifies mariculture as a sector requiring special attention, particularly with regard to promoting expansion and diversification of activities. The Marine Living Resources Act introduced the first South African legislation dealing specifically with mariculture, and delegated Marine and Coastal Management (M&CM) as the lead agency for mariculture in South Africa.

However, many stakeholders in the sector accuse the government of merely paying lip-service to the promotion of mariculture.

“It’s a crying shame that we have the policy, in which mariculture is punted strongly, yet very little money is being made available by government for R&D work”, says Prof Tom Hecht, head of the Department of Ichthyology and Fisheries Science at Rhodes University. “If the State is serious, it should put its money where its mouth is!”

Others claim that the permitting process is obstructive, and highlight the need for a comprehensive shellfish monitoring programme. M&CM’s Dr Jeannie Bailey acknowledges the criticism, but feels positive that the situation is improving.

“To date most government research relating to mariculture has focussed on the environmental impact of mussel farms and on red tides,” she says. Scientists of the ex-Sea Fisheries Research Institute also played an instrumental role in experimental studies on seaweed culture, while much of the early work on abalone culture was conducted by postgraduate students using the SFRI’s old aquarium facilities in Sea Point.

“As part of the M&CM restructuring exercise in 1999 a dedicated mariculture section was formed for the first time,” continues Dr Bailey. “Initially we operated in a state of crisis management as we struggled to sort out application procedures, but we are now initiating new research projects, such as the culture potential of the clam Mactra glabatra. We’re also trying to address permit problems, and aim to have drafted a sector planning document for the Minister’s endorsement by the end of 2002.”

At present mariculture production in South Africa is in the region of 4 000 tons per annum, and much of this is attributable to mussel production, which peaked in 1998 at 2 600 tons. In the same year production of the Pacific oyster reached 480 tons, while cultivation of the Indian white prawn comprised 104 tons. At that stage abalone culture contributed only 25 tons to the total, but this figure has since doubled.

In this special report Fishing Industry News profiles the mussel and oyster mariculture sectors, as well as a variety of sectors still at the experimental stage. See the October 2000 issue for a feature on abalone farming.

Production down at mussels farms

Despite the fact that mussel farming has been the mainstay of the local mariculture industry, its track record has been far from stable, perhaps reflecting the high-risk nature of the industry.

“A lot of people have got into mussel farming and out again over the last 15 years,” remarks Vossie Pienaar, manager of Blue Bay Aquafarms’ mussel operation in Saldanha Bay.

The country’s first mussel farm was started here in 1981 by enterprising engineer, Philip Steyn, who now runs an oyster farm on the other side of the bay. He sold out to Atlas Sea Farms, who were in turn taken over by Sea Harvest. In July 1999 Sea Harvest sold off the mussel-farming rafts to Blue Bay Aquafarms, which currently leases 50 ha of water area in “Small Bay” from Portnet. Lusitania runs another 15 ha operation nearby, while 50 ha on the sea side of the causeway have been set aside for new entrants, and a further 1000 ha have been zoned for mariculture in “Big Bay”. Great interest has been shown in the potential for community-based mussel-farming projects, but to date none have been initiated.

Both of the existing mussel farms culture the fast-growing Mediterranean mussel Mytilus galloprovincialis, which has become the dominant intertidal organism on the West Coast since its accidental introduction from Europe. The mussels are grown on ropes hanging from large wooden rafts at intervals of 1 sq m – any closer together and the mussels in the centre of the raft would be starved of planktonic food. Indeed, the raft system is considered an unsuitable method of mussel farming in most parts of the world.

“When mussel farming first started in Saldanha Bay, the raft design was being used worldwide, except for a few farms who were experimenting with longlines,” says Mr Pienaar. Before long the rest of the world had converted to the longline system - 100 m long ropes buoyed up along the surface, with the mussel ropes suspended from them at regular intervals. The system has the dual advantages of better growth rates and opportunities for mechanical harvesting, but it might not be ideal for the shallow waters of Saldanha Bay.

Here the ropes are initially seeded with 20 mm mussels, held in place by a cotton stocking. Within a fortnight the cotton mesh has rotted away, and the mussels have adhered to the rope and to each other with their strong byssal threads. After six months the mussels are harvested, and any natural settlement that has taken place during the grow-out period is used to re-seed the ropes.

Market size is between 55 and 100 mm length, the larger mussels commonly being served on the shell as hors d’oeuvres, while the smaller ones might be used as an ingredient in soups or sauces. When Sea Harvest owned the farm up to 80% of annual mussel yield was marketed as frozen product, but Blue Bay Aquafarms can currently only market live, fresh mussels.

“We want to put up a processing plant as soon as possible, but for now all sorting and size-grading is done on-board our vessel, the Musselcat,” says Mr Pienaar. “Mussels destined for Western Cape restaurants are simply packed into an onion bag for road distribution; for air-freighting up-country the bag is dropped into a plastic-lined carton to prevent leakage.”

Lately, though, the mussel farms have been struggling to meet market demand.

“We’ve been plagued by slow growth rates in recent years, possibly a response to some strange weather patterns,” says Mr Pienaar. “Under normal conditions we’d expect a yield of 50 to 60 kg per rope at each harvest, but it hasn’t been above 20 kg for the last 18 months.”

Researchers from Marine and Coastal Management attribute the slow growth rates to a reoccurring bloom of a planktonic algal species, Aureococcus anophagefferens, which was first noticed in Saldanha Bay in early 1997. The algal cells are so small that they clog the filter-feeding apparatus and inhibit grazing of mussels and other bivalves. During the bloom period, cultured mussels developed a characteristic ridge on the shell, indicative of growth arrest. The bloom is apparently non-toxic, and is referred to as a ‘brown tide’ because the high concentration of pigmented cells causes a brown discoloration of the water.

Then there’s the problem of red tides, many of which are toxic, causing various types of shellfish poisoning. In Saldanha Bay, blooms of the toxic species Alexandrium catanella and Dinophysis have become a regular seasonal occurrence since 1994, and frequently disrupt mussel-farming operations. Plankton samples are routinely tested twice a week for the presence of these species, and mussels are not harvested after a toxic red tide until they have been given the ‘all clear’ again.

Another factor impacting mussel farming is that the rafts are being colonised by a resurgence of the indigenous black mussel Choromytilus meridionalis, which may be better suited to the prevailing environmental conditions. This species not only has slower growth rates, but is unsuitable for marketing.

“The female has chocolate-brown gonad tissue, which creates a negative perception among consumers,” explains Mr Pienaar. “In the Mediterranean mussel the female has orange gonads, while those of the male are cream-coloured. Consumers are accustomed to their appearance, so they treat the indigenous species with great suspicion.”

Saldanha oysters rally

On the other side of the bay, Philip Steyn runs an oyster farm – the Saldanha Bay Oyster Company – in a tidal dam created by an artificial embankment.

"The embankment was built as a route for a pipeline to the oil storage facility," Mr Steyn explains. "It completely encloses a 20 ha area of water apart from a small tidal opening, which means we have excellent storm shelter and the ability to seal off the farm if necessary."

Apart from the ever-present threat of oil spills, Saldanha Bay is frequently affected by red tides. To date production at the farm has never had to be stopped because of a red tide, as the oysters have not reached toxic levels. Instead it is a non-toxic brown tide that is threatening the farm's future. The algal species responsible, Aureococcus anophagefferens, was probably introduced to Saldanha Bay in the ballast water of a visiting ship. In the 1980s, the same species almost wiped out the scallop industry on the Atlantic Coast of the United States.

"Two years ago the bloom in the dam was so dense – about 2 to 3 million cells per litre – that you couldn't see 20 cm below the surface, " says Mr Steyn.

The bloom has gone for now, but it's likely that the cells are lying dormant on the dam floor, so Mr Steyn is experimenting with a treatment option involving bacterial inoculation of the sediments. Oyster mortality is back down to about 20% and growth rates are good, attributable to a combination of favourable factors. Whereas the oyster racks in Knysna lagoon are exposed at low tide, here in the dam the tidal difference is only half a metre and the water is up to 9 m deep. Because the oysters are permanently submerged they can filter-feed all day on nutritious algae, which grow rapidly in the dam's sun-warmed waters. The depth and absence of wave action also ensures that the oysters do not come into contact with sediments, so they taste better, according to Mr Steyn.

The culture cycle at the farm starts with the importation of oyster spat from Chile. For the first two months the 5 mm spat are reared in a nursery facility built on the shore of the dam. Then they are seeded out into the dam, where they are housed in crates stacked on suspended frames. About 10 000 of these seed oysters can be accommodated on each frame, which drops to 4 000 once they're approaching market size. Every day, seven of the 130 frames are towed to the shore and defouled of redbait (this "bycatch" is sold as bait), while the oysters are washed, size-graded and returned to the crates. This means that every oyster on the farm receives individual attention once a month.

On average it takes a year for an oyster to reach market size of 60 g, and the farm currently has 2,6 million oysters in production. Taking natural mortality into account and assuming no disasters, this translates to 1,5-2 million oysters ready for marketing in a year's time. Mr Steyn also hopes to increase production by 30% per year for the next three years, and is investigating options for expansion.

"The middle of an industrial harbour is not an ideal location for a mariculture operation, and with the West Coast's harmful algal blooms it would be better from a risk management point of view to expand elsewhere. There are a limited number of sheltered bays along the South African coast, so at the moment we're looking at the Gansbaai area," he says.

"We would probably go for a bottom-culture system, which has the dual advantage of being protected from rough seas at the surface and being out of sight. There's often quite a bit of public pressure against mariculture operations because nobody wants the view from their holiday home spoiled! All in all, you have to be a real desparado to start a mariculture farm these days!”

South Cape oysters expand from Knysna

Unfavourable environmental conditions have also brought about a change in oyster-culture operations in Knysna Lagoon. South Cape Oyster’s Tony Tonin explains that the farm has been hit by two major mortality events in the last four years, with about 60% of stock being lost on each occasion.

The first mortality event, at the end of 1996, was associated with a 1:50 year flood that resulted in low salinity levels and a high sediment load in the lagoon. The reason for the second event, in October 1998, is less clear, but may have been related to some abnormal weather patterns at the time.

Even without these catastrophic events, oysters living in the lagoon face a harsh existence. Exposure to the sun at low tide results in high mortality rates during the hot summer months, and like all estuaries, the lagoon’s food web is based on detritus, which has low nutrient value compared to algae.

“The oysters here are usually in a starved state, so it’s not an ideal place for a farm,” says Mr Tonin, who took over South Cape Oysters in 1994. He is currently in the process of rebuilding the entire farm, replacing the old rotting racks and at the same time changing the design in an attempt to reduce mortality and improve growth rates.

“The old system involved placing the oyster bags on top of 100 m-long racks, which obstructed water flow and hence the oysters’ food supply. We’re now rebuilding with smaller blocks of racks and more cross-channels to improve circulation. We’re also lowering the racks and suspending the bags below them, so that the oysters are exposed for a shorter period at low tide. This means that they can filter-feed for longer and the risk of overheating is reduced.”

However, daily exposure does have its advantages: it prevents contamination by the flatworm Polydora, which attacks permanently submerged oysters, and minimises fouling by barnacles and redbait.

“Our start-to-finish mortality is still about 60-70%,” says Mr Tonin. “This means that for every spat we buy, only one oyster gets to market. To date our best harvest has been 1,75 million oysters in a year.

Mr Tonin imports his spat from Normandy, and aims to seed out a consignment every spring tide during the cooler months from March to September. For their first three months on the racks the spat are grown in a bag of 6 mm mesh. Then they’re brought back to land to be mechanically size-graded and sorted into new bags with the appropriate mesh size - small enough to contain the oysters, but large enough to maximise water flow. After another four to five months the bags are graded again. Previously they were returned to the lagoon for a further five to six months, but now they are just allowed a bit of recovery time before being moved to South Cape Oyster’s new farm in Algoa Bay.

The new farm is a longline system moored in 10 m of water about two miles north of the Port Elizabeth harbour. Each 150 m long rope has a stack of five bags hanging from it at 1 m intervals, which totals 750 bags per longline. So far eight longlines have been set, but this will be increased to 22 during 2001.

“It’s a very robust system that can withstand sea swells,” says Mr Tonin. “We switched to the PE site in December, and the oysters are growing at an incredible speed. They’re ready to market after three to four months in the sea, and the meat quality is better than those grown in the lagoon. Mortality is very low because temperatures in the sea are more stable.”

Mr Tonin stresses, however, that South Cape Oysters are by no means giving up on Knysna lagoon.

“The Knysna farm will now act as a nursery area, and it’s vital to our operation. Apart from the physical constraints against growing oysters in the sea from spat, they would just get smothered by fouling organisms. Knysna is good for producing clean seed with a hard shell.”

This year the Knysna operation is expected to produce about 6 million seed oysters for the PE site. Taking into account a mortality of 20%, the marketable harvest will be 5 million oysters - almost three times their previous best.

“We’re starting to run at a profit at last,” says Mr Tonin. “It’s quite exciting – I think we’re on the threshold of becoming a really significant oyster producer.”

New candidates

Apart from the existing four commercial mariculture sectors – mussels, oysters, prawns and abalone – the cultivation potential of a variety of other marine organisms is being investigated.


During the 1990s, experimental projects on the suspended cultivation of the red seaweed Gracilaria were conducted in both Saldanha Bay and St Helena Bay. A small-scale commercial operation started in November 1998 has since been discontinued, but a number of other groups have shown interest in developing this sector.

The International Ocean Institute (IOI), based at the University of the Western Cape, is assisting Maribus Industries, made up of shareholders from the St Helena Bay community, in getting the go-ahead for a farm.

“We’ve applied for a water lease from M&CM for a 5 ha experimental farm, which would be increased to 20-25 ha at a later stage,” says IOI’s Dr Neville Sweijd. “The commercial viability of seaweed farming is marginal, but it’s a labour-intensive operation, so it’s important from a job-creation point of view.”

The initial motivation for cultivating Gracilaria was its value as a source of agar, which is used as a culture medium for bacteria and fungi. But with the recent proliferation of shore-based abalone farms, the seaweed is also in demand as feed for cultured abalone. Connie Muller of Marine Growers abalone farm outside Port Elizabeth was the first to start cultivating his own Gracilaria, as well as the green seaweed Ulva, using nutrient-rich effluent from the farm to enhance growth. By stripping nutrients from the effluent before it is returned to the sea, the system has the added advantage of being environmentally friendly. Other abalone farms are following his lead, and M&CM is keen to make it a permit condition for abalone culture.

Abalone ranching

While shore-based abalone farms have graduated to commercial production, abalone ranching – the stocking of natural waters with juvenile abalone for grow-out and subsequent harvesting – is still at the experimental stage. Port Nolloth Sea Farms on the northern Cape coast initiated this concept, and others have since applied for permits. The operation has yet to prove its viability, however, as seeding experiments with different size abalone have yielded inconclusive results.


To date much of the northern Cape coast has been off-limits to mariculture ventures because of the diamond-mining there, but now that these operations are drawing to a close, mariculture is being investigated as an alternative source of income and employment opportunities.

The mines’ large pump-ashore ponds, which are exposed to high levels of solar radiation, might prove ideal for the cultivation of warm-water fish such as turbot. A number of other companies also hold experimental permits for the cultivation of turbot, which does not occur naturally in South African waters.

Several applications have also been made to import Atlantic salmon for culture, and M&CM has requested one applicant – Norwegian-based Salmon Salar Sea Farming – to undertake an Environmental Impact Assessment and feasibility study before a decision is made on the matter.

The EIA revealed that there is no danger that this alien species would become invasive, as the fingerlings would not be able to survive in the Cape’s warm rivers. The salmon would be imported from Norway as fertilised eggs - certified disease-free – and reared in a freshwater shore-based facility to the smolt stage. They would then be transferred to net cages in the sea and grown to marketable size. A production of 200 tons would be expected during the pilot phase, comprising only four cages, increasing to 350-400 tons at full production.

“The local RDP Forum is very keen for the farm to be approved, because the community needs it,” says Doug Jeffery, the environmental consultant who conducted the EIA. “It’s estimated that the project would create 20-30 jobs in the short-term.”

Indigenous fish species are also being investigated for their mariculture potential; for example, research on spotted grunter and kob has been conducted at the Department of Ichthyology at Rhodes University.

“Our conclusion is that both species are ideal candidates for mariculture,” says Professor Tom Hecht. “Cob grew to 2 kg after 16 months in the cages, which is a phenomenal growth rate, while grunter reached 600 g in 18 months. That means it beats species like sea bass and sea bream, which are cultivated overseas, hands down!”

Prof Hecht stresses that a dedicated hatchery is needed if this work is to be taken further. He is currently approaching various companies and organisations for funding, and the Centre of Investment Marketing of the Eastern Cape has already agreed to provide a third of the required R3 million.

Marine worms

Many finfish farms overseas use marine worms as feed for broodstock. A UK-based company, Seabait, which cultures the ragworm Nereis virens for broodstock feed and angling bait, recently visited South Africa. The IOI at UWC hopes to collaborate with Seabait while setting up a community-based project for marine worm culture in Saldanha Bay. Dr Sweijd explains how the project came about.

“The Bergrivier Vissersvrou Vereeniging were awarded an anchovy quota, and to qualify as a community organisation the funds generated have to be ploughed back into the community. They approached us to help them develop a number of job-creation projects for their Saldanha branch, and the marine worm project is one of these.”

“The project will have a three-year lead-in phase for market and biological research. Marine worms have a complex biology, so we hope to draw on Seabait’s experience. We’ll be investigating a few different indigenous species."

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