Wind energy in the Dutch North Sea is rapidly expanding. These areas create trawling- and shipping-free zones that can possibly be used for food production and nature enhancement. Shellfish aquaculture has the potential to contribute to both of these goals. The North Sea Foundation (NSF) is a Dutch NGO that works towards achieving “a clean and healthy North Sea that is used sustainably” (North Sea Foundation, 2016). They are interested in whether shellfish aquaculture within wind farms can truly be sustainable and if so, what steps are needed to implement multi-use. Therefore the main research question of this advisory report is, “What is the optimal method for implementing shellfish aquaculture amidst offshore wind farms that safely combines sustainable food production and enhancement of wild shellfish beds, and what can the North Sea Foundation do to help achieve this?”
There are two native species of reef-building shellfish that are currently cultivated in the Dutch North Sea: Blue mussels and European flat oysters. Both species can be cultivated offshore using variations of a longline system where mussel ropes or oyster cages are suspended vertically from a central horizontal line. The main horizontal line should be submerged in the water column to prevent gear from breaking loose and hitting wind turbines or cables. Ideally, shellfish aquaculture can help with nature enhancement by creating structural complexity and hard substrate. As a result, shellfish farms may serve as a foraging ground, nursery, and shelter for a diverse community of marine organisms. Aquaculture can also aid in the enhancement of wild shellfish beds by increasing the local population density of breeding shellfish and consequently the number of larvae in the North Sea. These wild shellfish beds provide their own ecosystem services including habitat provision, coastal protection, and increased biodiversity. Certain best practices are required, however, to ensure that shellfish aquaculture can meet these nature-enhancement goals and act as part of a healthy ecosystem.
This study resulted in suggested best practices for sustainable, nature-enhancing offshore shellfish aquaculture and actions that the North Sea Foundation can take to ensure sustainability going forward. The suggested best practices include:
● Use diploid flat oysters and blue mussels.
● Don’t harvest an entire farm at once in order to maintain more consistent habitat provision.
● The scale of the farm should not exceed the local carrying capacity.
● Use seed capture installations or hatchery seed instead of seed dredging.