Ecomare

Scientists from the NIOZ often do research in the North Sea with a ship. They discovered female whelks with penis-like growth a number of times. The growth blocks the oviduct, whereby the eggs made by the whelk cannot be released. This phenomenon is called imposex and produces major problems for the population. Many whelks have been unable to reproduce. No young whelks are born and the total population is declining rapidly. Infertility caused by imposex was found remarkably often in the area around the busy shipping routes. In fact, during the period 1991-1997 in the Oosterschelde, 90 to 100% of all the whelks had penis-like growths.
Further studies discovered that this phenomenon was being caused by tributyltin (TBT), a toxic material found in paint used to fight the growth of marine organisms on ship hulls. Since 2008, having TBT on ships is banned in all manners. It was first only banned for small ships, but now even remnants on ships are forbidden.
The link between TBT and imposex in whelks is very obvious. Scientists assume that a whelk population in the Wadden Sea will no longer be possible because the concentrations of TBT in the mud is still too high. Whelks are still having problems in the North Sea. A shortage of whelks is also a problem for hermit crabs, since whelk shells are the only shells large enough for adult hermit crabs to live in. Fewer whelks means homeless hermit crabs.

The whelk fisheries used to be an important source of income for dozens of fishermen. The snails were fished using a beam trawl, a net dragged over the bottom. In the first half of the 1920s, whelk fisheries was growing rapidly.
Oyster fishermen had become unemployed when all the oysters in the Wadden Sea died from a disease in 1921. In order to earn money in another way, they switched over to whelks. In 1925 and 1926, a half million kilograms per year were fished in the Wadden Sea and northern Zuiderzee. The whelks were sold primarily to France and England.
After a number of top years, the whelk was not resistant to the great pressure and the nets kept filling up less and less. The closure of the IJsselmeer in 1932 greatly decreased the habitat for the whelk while the intensity of the fisheries kept increasing. The Wadden Sea was prohibited area during the Second World War, which allowed the whelks to recover some. But after the war ended, fishing resumed and it didn't take long to decimated the species.
Despite the fact that whelk fisheries has ended, this snail still suffers from the fisheries in a different way. The egg capsules are easily broken off by beam-trawl tickler chains. Eggs swaying in the water have less chance of finding a suitable place for the larva to grow up in. Adult animals can also be damaged by the chains. They do not necessary die, but recovery costs so much energy that their capacity to reproduce is reduced.