No abstract

The environmental quality objective and standards (EQO/EQS) approach to controlling and assessing estuarine pollution is described together with details of the information necessary to assess the health of the fish populations and determine whether the EQO/EQS are being met in an estuary. These concepts are illustrated by examples from the Forth estuary, Scotland, involving studies of the ecology, pathology, biochemistry and contaminant bioaccumulation of fish in relation to the benthos, water quality and anthropogenic influences.

The fish community of the Forth estuary, Scotland, has several components -estuarine resident species, diadromus migratory species, marine and freshwater adventitious species, marine juvenile migrants using the area as a nursery, and adults of marine species with seasonal migrations. The population changes during the period 1981-88 in six species representative of the last two categories are described here. The species are the juvenile gadoids, whiting, Merlangius merlangus (L.) and cod, Gadus morhua L., juvenile flatfish, plaice, Pleuronectes platessa L. and common dab, Limanda limanda (L.), and the adult clupeids, sprat, Sprattus sprattus (L.) and herring, Clupea harengus L.The species' population changes are described in relation to aspects of wider significance such as commercial fishing for these species in North Sea areas. In particular, the underlying decline of the juvenile cod populations since 1981 in the Forth Estuary is discussed in relation to the recent reduction in commercial fishing quotas.

Regular samples at nine stations ranging from fresh water to fully marine conditions in the Forth Estuary and Firth, on the East coast of Scotland, allow a description of the community structure, composition and distribution of the zooplankton over an eighteen month period. A transition gradient in the occurrence of species along the length of the estuary was clearly identified that could be linked to salinity and hydrographic features using both traditional and nonparametric techniques. The fauna included both resident estuarine and incursive marine populations, having strong seasonal components of variation.Calanoid copepods dominated the estuary, with Eurytemora and several Acarfia species present, independent from analogous populations to seaward. The data reflected distinct seasonal episodes of predatory dominance, resulting in the temporary but complete absence of grazers in the lower estuary. In the middle and upper estuaries there was an apparent complete dislinkage between the phytoplankton levels and the zooplankton. It is hypothesised that the zooplankton of the upper and middle estuaries were dependant not upon phytoplankton but upon either anthropogenic inputs of distillery waste and sewage, or the microphytobenthos.

SynopsisA description of the community structure of the Forth estuary's zooplankton was obtained by sampling monthly at nine stations ranging from fresh water to fully marine conditions for an eighteen-month period. The variation in species abundance and distribution is related to environmental variables. The apparent spatial and temporal successions of members of the Acartia species complex are described, as are the episodes of predation spreading from the firth and the domination of the upper estuary by Eurytemora. It is observed that the estuary of the Forth is rare among British estuaries in its ability to support a truly pelagic self-maintaining assemblage of species.