Long time-series data showing recent recovery of gastropod populations from the effects of tributyl tin at the Shetland Oil Terminal

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Surveys of gastropod (dogwhelk, Nucella lapillus) populations at the Shetland Oil Terminal in Sullom Voe for the effects of tributyl tin (TBT) from shipping have been commissioned by the terminal’s Environmental Advisory Group (SOTEAG) and now represent one of the longest time-series of biological effects data available (1987–2009). These data from 20 shoreline sites around the oil terminal in the Voe and less affected waters of Yell Sound, show a substantial recovery of TBT-induced imposex as measured by vas deferens sequence index (VDSI), relative penis size index (RPSI), and female sterility associated with decreasing shipping traffic, reduced usage of free-association antifoulants and now the complete ban imposed by the International Maritime Organization (IMO) on TBT usage on large vessels in 2008. Data are presented that show in 2009, for the first time and following the IMO ban, no incidence of imposex-induced female sterility at any of the surveyed sites. At some of the most affected sites, some metrics of imposex are now at or close to zero (sterility, RPSI) and the rate of recovery of VDSI is greater than previously recorded. Data are assessed using OSPAR statistical methodologies and assessment criteria and presented alongside data showing associated changes in dogwhelk population structure in the area.