FARMERS ARE CHANGING COURSE on tables

To outwit a destructive predator snail and a virus, igh in the Oosterschelde, and the oyster ship C’est la vie is setting oyster farmers in the Oosterschelde are Hcourse for Yerseke harbour. Captain raising their game. The oysters are being lifted off and oyster farmer Danny Nelis (50) delivers his guests – on a works outing – safely the seabed to be farmed on tables. ‘Without inter­ ashore. ‘My father was a fisherman. I started farming oysters in 1992,’ says Nelis. He vention, the whole oyster industry will go under.’ farms some of the oysters in the traditional fashion, on beds on the sea floor. But since TEXT MARION DE BOO PHOTOGRAPHY HARMEN DE JONG 2015, Nelis has also been trying out a new method. He farms the oysters in large bags

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Oysters on tables

Oyster farmer Danny Nelis checks his sacks of oysters at low tide in the Oosterschelde.

on about 800 specially constructed tables doesn’t leave many oysters and without disentangle after a storm. But farming which become dry at low tide. This system intervention the whole oyster industry would oysters on tables is working well for him, protects the oysters better against predators go under,’ says shellfish expert Pauline and the method is effective in stopping the that live on the sea floor, such as crabs, Kamermans of Wageningen Marine oyster drill. Switching methods is quite a starfish and the infamous oyster drill. This Research. In recent years, Kamermans has job, however. Nelis has had a new ship built, predatory snail, which originated from , studied the effectiveness and the a flat-bottomed oyster boat in the French has rapidly spread around the world, first environmental impact of alternative farming style. At high tide, he sails to the oyster appearing in the Oosterschelde in 2007. It methods, using bags on tables or plastic tables. At low tide, the boat runs aground drills a pinprick-like hole in the oyster’s baskets floating in the water on longlines. and the men wade to the tables, cleaning shell and sucks it empty. ‘One oyster drill Nelis’s experiences with longlines were not things up, sorting and shaking the young eats two or three oysters a week. That good, as they were impossible to oysters and transferring the largest to new >

WAGENINGENWORLD | 2 | 2019 27 Breeding algae and oyster larvae in the hatchery at Roem van Yerseke, a fish and shellfish wholesaler.

cannot eat during that time but on the other hand, they are not attacked so much by the ‘If the oysters spend some time out oyster herpes virus that is in the waters of the Oosterschelde. We also looked at how of the water, they are not attacked well the oysters grow. We thought they would grow more slowly in the middle of so much by the herpes virus’ the area, because their neighbours would already have filtered the water. But they actually grow faster, probably because the water in the middle bags in which they have more space. When Japanese oysters were imported, and that is of the area is calmer.’ the tide comes in, the tables disappear now the main species of oyster farmed in underwater again and the boat sails back to the . In 2017, harvested MALE BECOMES FEMALE Yerseke with the ripe oysters. This method 28 million oysters, 73 per cent of which Oysters are bivalve, hermaphroditic has been in use in for some time. were Japanese oysters, also known as molluscs. They start out as males and turn Nelis harvested the first of his ‘off-bottom Zeeland creuses. The other 27 per cent were into females after a couple of years. oysters’ in the summer of 2018. ‘These flat oysters and the overall turnover was Spawning entails the male oysters summer oysters are very good quality. They about five million euros. Most of the oysters depositing their sperm in the seawater, are milder in taste and meatier. But the new are destined for export. One hundred after which females capture them. The approach is labour-intensive. We work people work in the sector. Besides the fertilized egg cells then develop into oyster longer hours and those full bags are heavy, Oosterschelde­ (1500 hectares), oyster larvae. weighing 20 to 30 kilos. We try and get farming also takes place in Lake At first the larvae swim freely in the water, most of the work done between September Grevelingen, a closed-off part of the Rhine- looking for a place to settle. Larvae develop and June. In the summer months we run Maas estuary (500 hectares). a foot at 10 days old. At that point, the sightseeing trips to our oyster farm with Kamermans and HZ University of Applied oyster farmer in the Oosterschelde scatters our tour company The Oyster Baron.’ Sciences studied the effectiveness of new shells on the bed for the larvae to oyster farming methods. ‘Oysters live off attach themselves to. Later, these mussel ZEELAND CREUSES algae, which they filter out of the water with shells with the little oysters growing on Zeeland oysters have been popular for their gills. Traditionally, they live on the them are fished up and brought to the hundreds of years. At first indigenous flat seabed and can feed around the clock. With farming locations. oysters were farmed here, but they were the new techniques, they are out of the ‘This is a roundabout method. You have to wiped out in the harsh winter of 1963. Then water for 20 to 30 per cent of the time. They sow tons of mussel shells and often you

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catch just one little oyster on each shell, it is when you use those sacks, which you birds look for food. We are still at the data and sometimes not even that,’ says aquatic have to turn over regularly,’ says Bakker. analysis stage, but in Ireland it has been technologist Nienke Bakker of Roem van Together with the Worldwide Fund for found that the disturbance to foraging birds Yerseke, a fish and seafood wholesaler. The Nature (WWF), Stichting Ark and is very limited. The birds get used to the company sells millions of oysters per year Wageningen Marine research, the company new situation. We look at the formation of and since 2005, has had its own shellfish is also breeding young flat oysters to release new silt too. A lot of silt is not only hatchery: a large hall with several nurseries at new wind farms on the North Sea. dangerous for the oysters, which need clear for young shellfish. Wageningen was The oyster drill is not the only threat to the water, but also for all the worms and other engaged in 2005 to help start up this oyster industry. They oyster herpes virus has animals that live in the sandy Oosterschelde hatchery, which is unique in the done a lot of damage in recent years too. seabed. No accumulation of silt has been Netherlands. There are several such This virus from Japan came to the Ooster­ noted so far.’ W hatcheries in France. schelde in cargo in 2010. It penetrates to the blood of young oysters and in some www.wur.eu/shellfish-farming FOOTBATH years can kill 80 to 95 per cent of them. We step through a disinfecting footbath Working with Roem van Yerseke, and reach the parent oysters: adult Japanese Wageningen has set up a programme to oysters from the Oosterschelde, which are breed herpes-resistant oysters. Oysters that WHAT DOES YERSEKE now in large white tanks. ‘With good looked healthy were removed from the REGIONAL CENTRE DO? nutrition and warming water, we get them Oosterschelde and brought to the hatchery. spawning. In other words, releasing seed There, the offspring of each individual Yerseke Regional Centre is part of and egg cells,’ explains Bakker. The oyster were raised separately. The hatchery Wageningen University & Research microscopically small larvae are caught on has space to breed 40 separate oyster and carries out research assign- very fine sieves and raised to become young families, each of which gets its own basket ments for third parties, focused on oysters. Every few days they are sorted by in the Oosterschelde. Of those 40 families, the sustainable use and manage- size using sieves, and the largest are there were just two that were totally ment of the Zeeland delta. Other transferred to new tanks each time. resistant to the virus. They were cross-bred participants include the province of Everything in the nursery chambers fizzes and new families were bred from those Zeeland, Reimerswaal , and bubbles. In the algae breeding space offspring. The hope is to end up with the Mussel Producers Organization, there are tall glass columns full of all kinds resistant oysters. The oysters are also being the Dutch Oyster Association and of brown, green and yellow algae from the selected for fast growth, homogeneity and the nature conservation organization Oosterschelde, which are tested here for shape. Nienke Bakker: ‘Survival rates are Staatsbosbeheer. They buy a stake their nutritional value. The smallest larvae steadily improving. It takes time but I think in the centre and can then submit eat the smallest algae, and so on. After 10 we will succeed.’ research requests. days to three weeks, the larvae are ready to About a quarter of the research settle on hard substrate as oyster spat. They EXPANDING carried out by Wageningen Marine must then be filtered out of the water The 16 oyster farmers in the Oosterschelde Research in Yerseke is work for the quickly, otherwise they have to be scraped want to expand from seven to 50 hectares of Regional Centre. Pauline Kamermans off the walls, getting damaged in the off-bottom oyster farming, but the monitors the effects of oyster farm- process. After about three months, the licensing process is slow, partly because the ing on nature in the context of licens- oysters are taken off to the outdoor farms Oosterschelde is part of the protected ing. Other research topics include and after three years, they reach adulthood, Natura 2000 network. Pauline Kamermans annual quantities of mussel spat, Bakker explains. is monitoring the impact of oyster farming the reintroduction of oysters in wind Just like Nelis’s oyster fishery, Roem van on nature in the Oosterschelde. ‘We farms on the North Sea, the creation Yerseke farms oysters in sacks on tables, compare the new methods with the of artificial oyster banks, and the but this company also makes use of plastic traditional ones. We have installed four cultivation of seaweed as a source baskets hanging in the water on poles. The cameras to analyse the behaviour of of protein. The Regional Centre also oyster drill cannot reach them there. ‘In foraging birds. With the off-bottom has a help desk for the shellfish those baskets you have more control over farming, the farmers are busier doing farmers. the process and the work is not as heavy as things at low water, which is also when the

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