§ Mr. Viggersasked the Minister of Agriculture, Fisheries and Food if he will list the causes of shell-thickening and other deformities in the Pacific oyster known to his Department.
§ Mr. MacGregorVery low levels of tributyl tin can cause deformities and shell malformation in the Pacific oyster. Other factors such as inherited abnormalities, disease and environmental trauma can reduce growth and may lead to malformation of the shell. However, in surveys and experiments carried out in estuaries in England and Wales which considered such factors, no cause other than tributyl tin has been found for this condition in the Pacific oyster.
§ Mr. Viggersasked the Minister of Agriculture, Fisheries and Food what research his Department has undertaken into the causes of shell thickening and other deformities in the Pacific oyster.
§ Mr. MacGregorSome research was carried out in the mid 1970s on the effect of suspended particulate material in the water on shell thickening of the Pacific oyster, but the results were inconclusive. In 1982, measurements were made of tributyl tin concentrations in estuarine waters and in Pacific oyster, and subsequently a comprehensive laboratory and field investigation has been carried out on the effects of TBT on all stages of the life 369W cycle of this species. Reduced growth and shell malformation was observed in laboratory experiments with concentrations of TBT similar to that found in estuaries where this characteristic deformation of the Pacific oyster occurs. Oysters transferred from clean sites to these contaminated estuaries also developed characteristic thickening; in the reverse transfer, oysters with thickened shells began to grow normally. The results of these experiments have been published in the scientific press.
§ Mr. Viggersasked the Minister of Agriculture, Fisheries and Food if he will give the figure for the total numbers of people employed in the commercial production or fishing of (a) the Pacific oyster and (b) the native British oyster.
§ Mr. MacGregorInformation on levels of employment in the shellfish industry is not collected by my Department.