Dispersal of TBT from a Fishing Port Determined Using the Dogwhelk Nucella Lapillus as an Indicator

Abstract

Ireland was the first country to introduce a legislative ban in April 1987 on the usage of organotin antifouling paints, this included tri-butyl-tin (TBT). Vessels under 25 metres were not permitted to use these substances because of harmful effects to shallow water sea inlets. The ban prevented use of organotins on most fishing vessels and pleasure craft. TBT causes a condition, imposex, resulting in sexual impairment in neogastropods. This condition was examined in the dogwhelk Nucella lapillus at 66 stations in Bantry Bay, SW Ireland, to determine dispersal from source from the main input areas. Highest imposex levels were recorded in the harbour of the fishing port Castletownbearhaven. High levels of TBT in sediments and use of TBT antifouling paints by the fishing fleet have resulted in reductions of dogwhelk abundance at the harbour entrance. Nearby, dogwhelks had high levels of imposex, which declined with distance from source. The lower frequency of imposex observed elsewhere within Bantry Bay may be due to residual flow of water through the Bay and periodic exchanges with shelf water from an area of upwelling off the bay entrance. A gradual recovery of the area would be expected if the ban on TBT usage were applied to vessels of less than 50m.