Abstract
Knowledge of the needs of shellfish eating birds is crucial for developing and maintaining a fisheries/nature protection management strategy in the Wadden Sea. Potentially conflicting demands exist between the fishery and the birds. Remarkably, the needs and intake of the main species in this respect, the Eider, are poorly known. From the differences in the life history of the shellfish eating birds and their shellfish prey one would expect that the long-term exploitation of the shellfish stocks by the shellfish eating birds will be adjusted to the years with the poor shellfish stocks, instead of the average stocks. To test this hypothesis we propose an ambitious study, including cage experiments, field studies and large-scale surveys to further develop and calibrate two coupled models for the Eider. The first model, to which we will refer as DEPLETE, describes for a given initial prey distribution and Eider population how these prey will be exploited (depleted) by the birds in the course of the winter and how many ducks will survive. This survival rate of the birds is input to the second model, to which we will refer as LARGEPOP, which yields the long-term changes in the large-scale population of the birds from the assembled demographic parameters. Once properly calibrated these models provide input to the socio-economical models of the fishery that must take the needs of the protected species of birds into account.
Netherlands