Neogastropod imposex for monitoring recovery from marine TBT contamination

Imposex, the imposition of male sexual characters on female snails, was used as a bioindicator of recovery from tributyltin (TBT) pollution in the Pacific Northwest. Whelks surveyed before TBT use was regulated had shown a high frequency of affected females in the Strait of Juan de Fuca and the Strait of Georgia; and lower frequency on the west coast of Vancouver Island. A reduction in imposer is now evident on the west coast of Vancouver Island and in some locations in the Strait of Georgia. There is no clear evidence of recovery near Victoria, and Vancouver Harbour still does not have whelks in any abundance, if at all. Of the four species studied, Nucella emarginata is the most suitable bioindicator species because it is abundantly distributed and has the shortest lifespan (1-2 years). When frequency of imposer remains at 100%, the FPL (female penis length) is still available as a useful bioindicator.