Changes in the composition of fish assemblages collected on two closely located power stations' intake screens over nearly four decades in the middle Forth Estuary, Scotland were examined. There were no significant differences in fish assemblages from Kincardine in 1979 and 1961–1962 or between Longannet in 1979 and 1994. Otherwise, the 1979 assemblages from both locations were significantly different from the 1999 and 2000 Longannet assemblages and from each other. The long-term differences may have reflected local environmental changes, notably a considerable increase in smelt (Osmerus eperlanus) abundance due to improved water quality, and declines in some species (eelpout (Zoarces viviparous) and cod (Gadus morhua)) because of regional environmental influences such as increases in water temperature and overfishing.
