De rol van de Afsluitdijk bij de achteruitgang van de wulk in de Waddenzee

The whelk Buccinum undatum was very frequent in the Dutch Wadden Sea the first half of this century. Its decline started in the 1920’s, mainly due to overfishing but also dike construction probably had a negative influence. The construction in 1932 of the ”Afsluitdijk”, the dike that separates the former ”Zuiderzee”, now IJssel Lake, from the Wadden Sea, diminished the area preferred by the whelk: waters over 4 to 5 m deep. One of the main fishing areas for whelks in former times, south of Wieringen became land and freshwater after 1932. Some of the deeper gullies in the Wadden Sea silted up after closure of the dam and became too shallow for whelks. Next to the main cause of whelk decrease in the Wadden Sea in the 1930s and 1940s viz. overfishing, the construction of the Afsluitdijk will also have had a negative effect on the whelk population. After fishing was no longer profitable in 1970, TBT-based antifouling paints gave the final blow to the whelks in the Wadden Sea. The proposed subsidised fishery on whelks in the German Bight of the North Sea will decrease possibilities for a reappearance of the whelk in the Wadden Sea.