Improving the yield of cultured parcels is important for the mussel sector and for nature; the improved yield benefits the mussel growers and allows the raw materials to be used more efficiently. As part of PRODUS, research was therefore conducted into factors that affect the yield of the parcels. Besides the influence of natural factors, such as the food supply and predation, this study looked at how the growers manage and maintain the parcels.
Measurements were conducted on mussel parcels to quantify the growth and mortality of the mussels. The results of these measurements were entered into models which can be used to calculate the effects of measures to influence parcel yield. this requires not only knowledge about the food use, behaviour and survival of the mussels, but also about the culture measures that growers can take (such as sowing density, time of sowing, measures to control starfish, etc.) and of course the location of the parcels. The research has shown that the sowing density of mussel seed is an important factor that growers can control directly. The sowing density appears to determine the survival the mussel seed. Sowing mussel seed incorrectly can lead to additional mortality; this is true for both excessively low and excessively high sowing densities. In addition, the survival of mussels is directly related to the parcel location and the predation by crabs and starfish.
The research also looked at the extent to which mussel culture makes a positive or negative contribution to the food availability for birds. The contribution of mussel culture to the total mussel stocks in the Wadden Sea was calculated based on surveys of mussel stocks on wild banks and cultured parcels, and data about the growth and survival of mussels in sections that are open and closed to mussel fishing.