Selective decline in imposex levels in the dogwhelk Lepsiella scobina following a ban on the use of TBT antifoulants in New Zealand

The level of imposex, the imposition of male characters in female gastropods, was compared in populations of dogwhelks before and after restrictions were introduced on the use of organotin antifouling paints in New Zealand. In one area subject only to pleasure craft there has been a significant decline in the percentage of imposex and in the relative penis size index (RPSI) in female dogwhelks. In a harbour area subject to both pleasure craft and commercial vessels there has been no decline in the percentage of imposex, but a significant decline in the RPSI.