Relationships between population density feeding and growth of the roach (Ratilus ratilus, L. 1758) and other coarse fish in a gravel-pit lake in Southern England
Gravel-pit lakes are an increasingly common feature of our landscape, particularly on the flood plains of rivers close to large urban or industrial areas e. g. the Thames Valley (see Fig. 1). When sand and gravel are removed from below the water table, lakes are produced by seepage into the excavation (wet diggings). At least 1600 hectares of land are being excavated in Britain each year for sand and gravel extraction of which ninety per cent are wet diggings (Hartwright, 1974). Filling with town or industrial refuse (back filling) is not common in wet diggings and the majority of the 1400 hectares dug each year remain as lakes.
These lakes provide areas for organised recreation such as sailing, water-skiing, angling and skin-diving. As, open sites, frequently near suburban districts, the lakes and surrounding land can be pleasant amenity areas. Their value is increased if they are landscaped and planted with trees and shrubs (see page 26). Such areas are important for the conservation of a wide range of plants and animals, especially in view of the decline of naturally occurring wetland habitats.
Little is known of the biology of gravel-pit lakes; of their flora and fauna or of how these may change with time. Karim (1967) published a paper on the algae of Thames Valley gravel pits and concluded that the air carried the spores of many of the species of algae that colonised the lakes. Catchpole and Tydeman (1975) studied aspects of the bird faunas of several gravel-pit lakes and Harrison (1972) developed a complex of lakes in Kent as a bird reserve. All stress the value of the lakes as habitats for birds.
At the City of London Polytechnic a group is investigating the biology of gravel-pit lakes with particular reference to their fish faunas with the aim of establishing principles for managing the lakes as fisheries
