Whelk

You have probably never seen a living whelk. Nevertheless, the whelk is a large sea snail belonging to the normal benthic fauna of the North Sea. You usually only find the empty shells on the beach or occupied by a hermit crab. This snail is very sensitive to overfishing, churning up of the sea floor and toxins, such as tributyltin. Due to a combination of all these factors, the whelk has practically disappeared from the Dutch coastal region and the Wadden Sea. Just like common wentletraps, whelks can close off the opening of the shell with a flap to keep out enemies.

Features

size:	maximum 15 centimeters, usually smaller
color:	shell usually greyish brown, snail yellowish-white to light brown
age:	maximum 30 years old
food:	particularly worms, but also small crustaceans, bivalves and carrion
enemies:	flatfish, benthic fisheries, people, toxic materials such as TBT
reproduction:	sexually

Clusters of eggs

The strange clump of transparent bubbles found on the beach, resembling plastic blisters, is regularly found by beach strollers. This is a clump of whelk eggs. The whelk lays its eggs on stones or other hard material on the sea floor. What one finds on the beach has broken away, sometimes due to water movements but more often from fishing gear pulled over the bottom.

Distribution and habitat

The whelk lives in deeper parts of the North Sea. They have practically disappeared along the coast and in the Wadden Sea, the fisheries being one of the causes. They live on sandy or muddy bottoms, as well as hard substrate such as rocks. Normally speaking, they live around 100 meters deep, although whelks are also found at 1200 meters deep.

Whelk and toxins

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.

Whelk fisheries in the Wadden Sea

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.

Names:
Dut: Wulk
Lat: Buccinum undatum
Eng: Common whelk (Buckie)
Ger: Wellhornschnecke
Fren: Buccin
Dan: Konk

Source: de Vleet, Ecomare