06 March

Invasive Oysters in the LImfjord.


For more than 10 years the pacific oyster (Crassostrea gigas) has been found in the Limfjord. The pacific oysters is not a native species, but after being imported to farms in France, Netherlands and Germany, they are now spreading all over Europe.

The pacific oyster is very strong and takes over both mussel beds and oysters beds of the native flat oyster (Ostrea edulis). This problem has been discussed in Denmark for several years but up until now little has been done. The pacific oyster needs to be limited in it's spreading or the natural bivalves will disappear.

At present the Danish legislation limits the possibilities of fighting the spread.

1) In Natura 2000 areas the fishing of the pacific oysters is limited because of rules limiting the fishing to maximum 15 % of the area over a period 4 years period, which means that removing the pacific oysters would mean that fishing of mussels would be reduced. So at present the oysters are not removed in Natura 2000 areas through fishing.

2) Fishing of oysters with dredges is only allowed a depths of more than 2 meters. But the main part of the oysters are at shallower grounds.

3) on the shallower grounds the pacific oysters beds have now turned in to reefs where the oysters stick to each other , making it impossible to separate them by hand.

The Danish Fishing Ministery is aware of the problem, but until now only scientific investigations have been initiated. In my opinion there is no longer need for investigations but instead action is called for.

How to fight pacific oysters

To make the pacific oyster go away from Danish waters is not realistic, but to stop them from spreading is possible. The pacific oysters should be fought in the following way.

1) Allow a targeted fishing in the Natura 2000 areas of pacific oysters, which does not limit the other existing fisheries.

2) On shallower grounds start removing the oyster reefs. This would probably have to be done with excavators and other construction machinery. Such an action should only be started in areas where the oysters have already made reefs. By doing this the oyster breeding grounds are removed and the spreading is effectively limited. After this first hard action is should be allowed to collect pacific oysters on shallower grounds for commercial purposes.

I hope and actually also expect that these actions can be started within the next year and we at Vilsund Blue will do our outmost to get the process on it's way.