Dog whelk and common whelk, and environmentally hazardous substances
The dog whelk and common whelk are declining, probably because of the use of anti-fouling paints on ships' hulls.
Trends
Since 1965 the number of large populations of dog whelk has fallen by two-thirds. And since 1980-1984 the numbers of common whelks have fallen by 40%. These changes have been linked to the use of paints containing tributyltin (TBT) on ships' hulls to reduce fouling from acorn barnacles and other organisms. TBT has been shown to have undesirable side-effects, however. In laboratory tests it has been found that in certain molluscs, including dog whelk and common whelk, it causes females to develop male reproductive organs (a phenomenon known as imposex), which results in some or all of the population becoming sterile. Other factors also contribute to the species' decline: the asphalting of dikes affects the dog whelk in particular, whereas beam trawling adversely affects the whelk.
A ban on the use of TBT has resulted in the amount of TBT measured in marinas declining since 1990. The concentrations are not yet below the hazard threshold, however, and neither species has rallied.
