Can new farming techniques restore oyster production?
The oyster sector is currently facing twin threats. As a result, oyster farmers are looking for new cultivation methods. Since 2010, there has been an oyster herpes virus in the Oosterschelde which is causing high mortality, particularly among young Pacific oysters. In addition, there is a problem with Japanese oyster drills that were introduced in the Oosterschelde. The Japanese oyster drill is a snail that bores a hole in the shell of the oyster and then eats the flesh. The first reports of the Japanese oyster drill date from 2007 (Faase & Ligthart, 2009). Oyster farmers encounter many Japanese oyster drills and also regularly find their egg cases on and near the oysters on the oyster beds. In addition, many shells are found with bore holes in them. Few of the young animals which survive the herpes virus reach maturity due to predation by the drills. The combination of the two enemies is now having a severe impact on oyster farming (Strietman et al., 2016).
In order to restore oyster production, the Dutch Oyster Association (NOV) and the Ministry of Economic Affairs have formulated an 'Action Plan for Oyster measures 2016-2018' to bring the problem under control, inter alia with the help of new techniques (NOV, 2016; Smaal et al., 2016). The new techniques consist of off-bottom culture. This is a new technique to the Netherlands which involves oysters being cultivated in bags and baskets. These bags and baskets lie on tables or in cages, or are suspended from long lines. The benefit compared to traditional bottom cultivation is that there is no longer any contact with the sea floor. This means that the primary predator, the Pacific oyster drill, has virtually no chance of reaching its prey. The multi-year project Begeleiding OesterKweek eXperimenten ('support for oyster farming experiments' – BOKX) is aimed at bringing together questions from practice with knowledge and research.
Oyster farming takes place in the Oosterschelde and Lake Grevelingen. These are Natura 2000 areas, which means that permits have to be requested for all trials. The application must be accompanied by an Appropriate Assessment. If a permit is obtained, it is often accompanied by monitoring requirements. The BOKX project provides the Appropriate Assessment and monitoring of off-bottom experiments. In addition, the project management is exploring whether it is possible to expand the area where fishing is permitted under the permit for free oyster fisheries. This is also part of the 'Action Plan for Oyster measures 2016-2018’.
A number of oyster farmers are currently experimenting with off-bottom techniques. These involve bags and baskets, but machine factories are also working on new designs. By pooling knowledge, the development of these new techniques can be accelerated. The project involves meetings between oyster farmers and the BOKX research team. They also discuss how the monitoring can be carried out in the most effective manner, for example in partnership with HZ University of Applied Sciences.
The project is financed with the help of contributions from Reimerswaal municipality and Zeeland province.
Faasse, M., & Ligthart, M. (2009). American (Urosalpinx cinerea) and Japanese oyster drill (Ocinebrellus inornatus)(Gastropoda: Muricidae) flourish near shellfish culture plots in The Netherlands. Aquatic Invasions, 4(2), 321-326.
NOV (2016) Plan van Aanpak ‘Oester-maatregelen’ 2016 – 2018.
Smaal A.C., P. Kamermans & WJ Strietman (2016) Kennis en onderzoeksagenda voor de Nederlandse oestersector. IMARES Rapport C057/16
Strietman, WJ, A. Smaal & B. Bolman, 2016. Economische situatie van de oestersector. Potentiele impact van herpesvirus in oesters en Japanse oesterboorder op de oestersector. Quickscan, LEI.