§ Mr. Kilroy-Silkasked the Secretary of State for the Environment on which rivers and streams the dipper has been found to have declined because of the relatively high acidity level; and by how many it has declined in each case.
§ Mr. WaldegraveMy Department is aware of two surveys examining the relationship between acidity levels and the dipper population, one carried out by the Welsh water authority on 17 tributaries of the Wye, the other by the Royal Society for the Protection of Birds in conjunction with that authority on 74 sites throughout the Principality.
The findings have not yet been published, but I understand both surveys suggest that higher acidity is associated with a lower dipper population. In only one case, the River Irfon, are historic data available to compare populations over time; a 70 to 80 per cent. decrease in the dipper population has been recorded between the mid-1950s and 1982, during which time the acidity level increased considerably.