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

Samples taken regularly from the intake screens of West Thurrock power stat ion between January 1977 and November 1992 were used to investigate the fac tors controlling flatfish abundance (flounder: Platichthys flesus; dab: Lim anda limanda; plaice: Pleuronectes platessa; sole: Solen solea) in the midd le Thames estuary. Most sampled fish were age-0, All species followed regul ar patterns of seasonal occurrence, had distinctive seasonal abundance peak s and demonstrated only minimal temporal overlap. Multiple-regression model s were used to study the relationship between physico-chemical variables: p hysico-chemical variable interactions, trends and seasonal factors on fluct uations in flatfish sample abundance. Flounder abundance was significantly influenced by temperature, suspended solids, oxygen-flow and oxygen-tempera ture interactions, trend and seasonal variables. Dab abundance was signific antly related to suspended solids, oxygen-Bow, oxygen-temperature and How-c hlorinity interactions, Crangon crangon abundance and seasonal variables. S ole abundance was controlled only by seasonal variables, whilst plaice abun dance could not be adequately explained by the available physico-chemical d ata. The combination of variables affecting flatfish abundance indicates sp ecies using the estuary were affected by a complex set of events within the estuary, The interactions between routinely measured environmental variabl es further suggest that estuarine monitoring studies must attempt to unders tand the nature of possible interactions between variables if an improved u nderstanding of the changes in estuarine fish communities resulting from hu man activity is to be gained. (C) 2000 Elsevier Science B.V. All rights res erved.