Off-bottom oyster cultivation in the Oosterschelde , the Netherlands, started in 2010 . Off-bottom cultivation typically result in oysters (Crassostrea gigas) with faster growth and a higher meat quality in comparison with the conventional bottom oyster cultivation, due to a higher food quality and availability higher in the water column. Using triploid oysters , which invest more energy in growth , ensures a shorter cultivation process . In off-bottom cultivation oyster spat is placed at a high density (app. 5000 individual pieces) in fine-meshed bags or baskets and will be manually thinned in density during the growth process to consumption size. The starting material, oyster spat, can be of various origins and usually comes from hatcheries, as the Netherlands, Ireland and France.
Currently two di fferent cultivation systems are being used by Dutch oyster farmers in the intertidal area in the Oosterschelde The first system consists of firm plastic bags (available in 4 different mesh sizes) whic h are placed on iron frames. The second system is the so-called BST system which consists of hanging baskets (available in 3 different mesh sizes) attached on longlines or on iron tables . Although t hese systems are widely and successfully used around the world, there seems to be quite some room to optimize this way of farming. Main issue s are i) their labour intensiveness in combination with the relatively high wages in the Netherlands and ii) high losses caused by the variety wave- and flow dynamics in the Oosterschelde . It is questioned if other off- bottom cultivation systems that are also successfully deployed around the world would be a good addition and or alternative to improve efficiency and productivity of Dutch oyster cultivation.
In 2020 the European Marine and Fisheries fund ed project “Oyster yield improvement through knowledge transfer and monitoring” was initiated . The goal of the project is to optimize oyster farming and it should lead to efficiency improvements of sustainable oyster cultivation. In this project a comparative study between current off-bottom oyster cultivation and alternative off-bottom farming systems will be conducted. The effect of the farming systems on the performance of oyster growth, quality and shell shape
will be examined for four different systems in three different off-bottom cultivation locations in the Oosterschelde. In a comparative study between the currently used systems and alternative off-bottom cultivation systems , additionally the following two methods are being tested:
SEAPA - hanging baskets
FlipFlop bags - horizontal hanging bags
For this study T15 triploid oysters, o riginating from the hatchery Roem van Yerseke, the Netherlands., were placed in four bags or baskets at 3 different locations in the Oosterschelde (Prinseplaat-C, Yerseke bank-74/75 and Hooge Kraaijer-46) , see
. The number of oysters per system is calculated according to the total volume of each individual system. All the systems and all the locations are sampled every 10 weeks for the period March 2021 till December 2021 . During sampling, 1 bag or basket of all the systems (and of all three locations) will be collected . Per sample randomly 60 individual oysters are analyzed on - shell shape / growth: length, width, thickness, quality and wet fresh weight. The Condition Index (Rainer and Mann, 1992) is determined for 30 individual oysters per sample.
M onitoring and experiments are ongoing till December 2021. During the presentation the results of the study will be shown and discussed.