Temporele patronen in de structuur van de vis- en crustaceagemeenschap in de beneden-Zeeschelde
Maes, J. (1994). Temporele patronen in de structuur van de vis- en crustaceagemeenschap in de beneden-Zeeschelde. MSc Thesis. Katholieke Universiteit Leuven. Faculteit Wetenschappen. Laboratorium voor Ecologie en Aquacultuur: Leuven. 100 pp.
Between September 1991 and August 1992 and during 1993 the lower Zeeschelde was monthly investigated by monitoring fish and crustaceans which were impinged in the cooling circuit of the Nuclear Power Station of Doel. In first instance, a checklist of fish and crustaceans recorded in the lower Zeeschelde has become available. The present checklist of fish contains 31 species. The fish community is composed of 13 marine species, 3 catadromous species, 8 estuarine residents, 1 anadromous species and 6 freshwater species. Six crustacean species were recorded. The obtained checklist of fish is compared with historical and recent data. The comparison shows a remarkable decrease in the total number of fish during the last century. The distribution of diadromous fishes, estuarine residents and freshwater fishes is probably greatly affected by low oxygen levels in the lower Zeeschelde, whereas the disappearance of adventitious marine species is probably due to overfishing in the North Sea. Secondly, densities for each month and for each recorded species were subjected to two classification techniques and one ordination technique in order to study the temporal structure of the community of fish and larger crustaceans. The results show clear seasonal patterns in the distribution of fish. Different species reach their maximal density at different times. High numbers of fish were recorded between September and February. Clupeids and gobies seem to dominate the community. In spring and early summer fish were absent or extremely rare probably due to low oxygen levels. The community of crustaceans is dominated by shrimps. Also for these species, results show clear temporal patterns. Temporal patterns both of fish and crustaceans were discussed.
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