Imposex in populations of dogwhelks Thais spp. in relation to shipping intensity and mariculture activity in east Asia

Imposex was recorded in samples of dogwhelks Thais spp. from each of the si tes surveyed in Hong Kong and Singapore, and the majority of those in Phuke t and Penang. There was no imposex in samples from Langkawi. The most advan ced symptoms were those from shores close to commercial harbours, marinas a nd mariculture sites, suggesting that tributyltin (TBT) is a primary cause of the condition. All females were categorised as sterile from four sites o n Hong Kong. In these cases recruitment has probably occurred as a result o f the dispersal of larvae from fecund populations elsewhere. However, sever e imposex was surprisingly localised, even in Hong Kong. There was evidence of decreasing symptoms of imposex with increasing distance from centres of shipping activity.