The fish disease survey utilising dab was limited to offshore sites. Incidences of skin diseases were low. Generally, there is a low diversity of sediment-dwelling organisms at the head of most estuaries but diversity increases with distance offshore. The low diversity is primarily due to natural physical factors such as widely fluctuating salinity regimes. However, the organisms found in some estuaries are indicative of organic enrichment associated with high inputs of organic matter.
Biological effects associated with chemical contaminants are greatest in estuaries.
A number of industrialised estuaries are polluted to an extent which may be harmful to plankton as shown by the oyster embryo bioassay technique. It is likely that no single contaminant is responsible for this and that the effects are due to several contaminants acting together. This is a phenomenon whereby male characteristics are imposed on the female dogwhelk and is attributed to the presence of organotin compounds usually associated with antifouling paints. New data for Belfast Lough clearly shows the occurrence of Imposex. This is currently being addressed by the regulator.