|Densiteit van demersale vissoorten in de Oosterschelde periode 1983-1990|
Maandag, H. (Ed.) (1999). Densiteit van demersale vissoorten in de Oosterschelde periode 1983-1990. Graduate Thesis. Hogeschool Zeeland: Yerseke. 34 pp.
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VLIZ: Non-open access 118819
|Document type: Dissertation|
Brackishwater fish; Population density; Pisces [WoRMS]; ANE, Netherlands, Oosterschelde [Marine Regions]; Brackish water
Sport-fishermen have stated that there aren’t as many fishes in the Oosterschelde as before the construction of the storm surge. For NIOO-CEMO this was the motive to re-analyse the data of their catches from the period 1983 - 1990.In the period 1983 - 1990 NIOO-CEMO has sampled 1 - 4 times a year (every season) for demersal fish at 36 stations in the Oosterschelde. The net was a beam trawl with an effective width of 2.7 m and a mesh size of 10 mm. The estimated efficiency is 20%. When possible the haul was 1000m.During the entire research period 42 different fish-species have been caught. Most of them were demersal fish pelagic fish were caught as well. Many species had preferences, for example for season, depth or a certain type of sediment. Not every fish-species is caught with the same efficiency. For example Gasterosteiformes have small diameters and will easy slip trough the net. Only when seaweed is slightly blocking the meshes the net will hold more Gasterosteiformes.In spring the density was lower (approximately 100 fish per 1000m²) than in the autumn (350 fishes per 1000m²). The number of species was highest in June and lower in spring and winter. Cluster analysis proved an apparent summer - winter change in densities and species. Two groups of species were in anti-phase with each other.Flatfish mainly fixed the trend. Gobiidae and Clupaeidae (only in November) also had an important share in the autumn. Gadidae mainly appeared in summer.Density was highest in 1987, approximately 4 times higher then in the other years. In this year there were more flatfish, Gobidiidae and Clupaeidae then in most other years. The number of species was the same throughout the entire period.Further into the Oosterschelde the density decreased, in the ‘Kom’ the density was again higher. In the ‘Kom’ there were many flatfishes, Gobidiidae, Clupaeidae and Gadidae. Gadidae hardly appeared at the other locations. The number of species was the same at every station.Clupaeidae preferred depths between 11 and 15 m. For the other species the density was at every depth approximately equal.The period is not long enough to recognise the natural strong population dynamics. This is why it is important to restart the research and keep up with it for a longer period.
- Fishstocks in the Oosterschelde (The Netherlands), period 1983-1990 & August 1999, more