The objectives of the investigations comprise three parts: a) an accurate determination of the abundance and biomass of the post-larval Crangon crangon (L.) population in the Belgian coastal waters ; b) a quantitative analysis on a yearly basis of the consumption and production by this population, including a detailed description of the yearly fishery- and predation mortality; c) the formulation of a quantitative consumption-production-model which describes the trophic relationships of the population of postlarval Crangon crangon (L.). Method: The inventory of the biotic and abiotic factors, which influence the abundance and biomass of the population of post larval Crangon crangon (L.), leads to a qualitative model of the interactions between this population and its environment. The seasonal fluctuations in the density of the population are explained by this model. (K1) and egg production, form the starting point for the calculation of total consumption and production by the population. The obtained results lead into a quantitative consumption-production-model of the population and conclude the first part of the investigations. In the second part the production flux is approached from the point of view of the predators of the population (fishery and demersal predators). In the first place the fish species were classified according to their presumed importance as predators of Crangon crangon. This grouping rests on a quantitative inventory of the ichthyofauna in the Belgian coastal area on the one hand, and on bibliographic data on the importance of Crangon crangon (L.) in the food of the various fish species on the other hand. Thereupon the abundance and biomass of the most important predators are estimated. The data of their daily food uptake results into estimates of the total yearly predation mortality of postlarval Crangon crangon. These estimates, completed with estimates of the yearly fishery mortality, are compared with the value of the total production by the population. This comparison ascertains to what extent the model is a reliable representation of the real situation. |
