Modelling current speed and carrying capacity in long-line blue mussel (Mytilus edulis) farms

The development of the mussel (Mytilus edulis) farming industry in Norway is based on suspended long-line culture, and large areas of the coast are potentially suitable for farming. Norwegian fjords and coastal waters are regarded as oligotrophic environments in comparison with sites where most studies on mussel feeding on natural seston have been carried out. High mussel culture densities in oligotrophic water may cause seston depletion, resulting in low growth or tissue wasting due to reduced feeding and negative net energy balance. In this paper we present a carrying capacity model based on rate conditional processes, balanced against flushing and with emphasis on flow reduction as a function of farm design. The model is based on assumptions that friction forces are a function of geometric shape of the channel made up by the suspended mussel ropes as vertical boundaries and it quantifies carrying capacity according to information of farm length, space between long lines, seston concentration and background current speed and the relative importance of these factors. Estimates of how stocking density in mussel farming can be optimized in relation to the food supply (i.e. carrying capacity) are crucial to production management decisions, and the model may provide predictors for decisions regarding new site selection or expansion of existing operations.