Environmental factors and interactions affecting the temporal abundance of juvenile flatfish in the Thames Estuary

Abstract

Samples taken regularly from the intake screens of West Thurrock power station between January 1977 and November 1992 were used to investigate the factors controlling flatfish abundance (flounder: Platichthys flesus; dab: Limanda limanda; plaice: Pleuronectes platessa; sole: Solea solea) in the middle Thames estuary. Most sampled fish were age-0. All species followed regular patterns of seasonal occurrence, had distinctive seasonal abundance peaks and demonstrated only minimal temporal overlap. Multiple-regression models were used to study the relationship between physico-chemical variables, physico-chemical variable interactions, trends and seasonal factors on fluctuations in flatfish sample abundance. Flounder abundance was significantly influenced by temperature, suspended solids, oxygen-flow and oxygen-temperature interactions, trend and seasonal variables. Dab abundance was significantly related to suspended solids, oxygen-flow, oxygen-temperature and flow-chlorinity interactions, Crangon crangon abundance and seasonal variables. Sole abundance was controlled only by seasonal variables, whilst plaice abundance could not be adequately explained by the available physico-chemical data. The combination of variables affecting flatfish abundance indicates species using the estuary were affected by a complex set of events within the estuary. The interactions between routinely measured environmental variables further suggest that estuarine monitoring studies must attempt to understand the nature of possible interactions between variables if an improved understanding of the changes in estuarine fish communities resulting from human activity is to be gained.