CHANGES IN THE FISH FAUNA OF THE OOSTERSCHELDE ESTUARY - A 10-YEAR TIME-SERIES OF FYKE CATCHES

Frequency of occurrence of fish species was monitored on a fortnightly basis in four fykes and a weir in the Oosterschelde estuary from 1979 through 1988. This was done in order to record changes in the fish fa una that may have occurred as a response to the construction of a stor m-surge barrier in the mouth of the Oosterschelde (1984-1986) and the concomitant building of compartmentalization dams in the landward part . These compartmentalization dams reduced the freshwater inflow into t he system. Principal component analysis using the annual averages in f requency of occurrence suggests a slight shift occurred in the fish co mmunity separating a cluster of years 1979-1984 from the cluster 1985- 1988. Many of the changes in individual species could be attributed to fluctuations in yearclass strength or were part of changes occurring on a wider geographical scale. The only impact of the construction wor ks seems to be the decrease in a number of anadromous fish. Fish traps seem to be useful as a monitoring tool for a number of species. The v alue of the data collected could be improved if catch size and length- frequency data are recorded.