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Zoölogy. — “The unfavourable condition of which complain the 
oyster cultivators on the Kastern-Schelde.” By Dr. P. P.C. Hoek. 
(Communicated in the meeting of December 28, 1901.) 
Dr. Hoek discusses the unfavourable condition of which the oyster- 
cultivators on the Kastern-Schelde complain and explains that the 
reason of this is; 1. that for some years the oysters have not 
thriven so well nor so quickly, 2. because of great mortality in certain 
years, 3. of a much greater mortality than formerly in all the 
later years. The speaker was commissioned to investigate this matter. 
A detailed report on the results of these researches was now in the 
press. With the permission of the Minister of Public Works, by whose 
order the investigation had taken place, the following summary 
was given of what these researches had brought to light. 
There were three possibilities, which were successively taken under 
consideration, viz. 
Ist that the physical circumstances under which the cultivation 
takes place, had undergone changes; 
2nd that the oyster itself had altered ; 
rd that the less favourable condition, in which the oyster-culture 
finds itself at present, was to be imputed to that culture itself. 
As regards the physical circumstances, it would not seem probable 
a priort that meteorological factors have played a prominent part 
in this decline, considering the period of 1870-85 as a time of 
high prosperity of the oyster-culture in Zeeland and the years 
1885—1900 as a period of decline. Some of those interested in the 
culture, are of opinion, that the laying of the dyke at Woensdrecht 
has raised the salinity of the water in the eastern part of the 
Western-Schelde and that the consequences have become fatal for 
the oysters, which are cultivated there. 
Considering however that this dyke has been built in 1867, that 
the oysterculture only began after 1870 and from the Hoen 
attained to a period of prosperity, this supposition must also be rejected 
as extremely improbable. From investigations made in ’81—82 and 
from a comparison of those with similar ones of later years, it is 
moreover evident that the salinity has not been raised in any way 
in the last twenty years. 
It would appear from informations supplied by the “ Waterstaat” that 
the quantity of seawater, which at every tide restocks the Wastern- 
- Schelde-basin, has not diminished to any amount, since the oyster-culture 
there has appeared to bein a less favourable condition. And in regard 
to the nature of the soil the hydrographic survey has indeed brought 
to light that here and there, locally, shallow places have lately 
