One area of ecological benefit not yet fully evaluated in European waters is the utilisation of restored saltmarsh habitats by fish species. This study examines the utilisation of managed realignments and relic saltmarsh by fish species. Factors affecting habitat heterogeneity and fish populations are discussed, and recommendations are made with respect to scheme design and management that will maximise the biological and socio-economic values. Fish populations in the high intertidal areas were assessed using a suite of techniques, including observations on feeding behaviour. Each microhabitat was discussed as a function of the extent of fish colonisation. A positive relationship between the degree of fish utilisation and habitat heterogeneity was ascertained using species richness, abundance and behavioural observations. This study will aid habitat valuation for economic justification of managed realignments, over and above existing drivers, such as compensatory habitat for encroachment, flood defence and the European Union Habitats Directive. The work now forms part of a wider European Interreg IIIb project, COMCOAST.K E Y W O R D S : fish, habitat, intertidal, managed realignment, saltmarsh.

Managed realignment often involves the construction of new sea walls at a location behind existing sea walls to create parcels of land that can be flooded to create new inter-tidal environments. It is employed in the UK to improve flood risk management within the context of flood risk management strategies, but so far most emphasis has focused upon creation of new wildlife habitat because this has been where the opportunities and funding have been found. Initial projects were relatively small in scale, but recent projects have been much larger. Scaling up the size of realignments introduces a variety of additional engineering and social challenges and the realignment of Wallasea Island in 2006 is one of the largest. There were a variety of issues encountered during the development of the Wallasea Island realignment that make it a good platform for exploring the issues and some of the solutions that have been found to date. This account describes the project and some of the measures taken to give it as high a level of social acceptability as possible. Such measures include design features for fish nurseries, provision of public access and careful liaison with affected communities.

The diets of 0-group bass Dicentrarchus labrax were investigated in SE England in the Blackwater Estuary: three managed realignment sites at Tollesbury, Abbotts Hall and Orplands; and two established saltmarshes at Tollesbury and Abbotts Hall. In Summer, small 0-group (15-30 mm) bass consumed calanoid and harpacticoid copepods predominantly and left the sites significantly fuller than on entering them (Mann-Whitney, W = 5837, P \ 0.001). In Summer, large 0-group (30-59 mm) bass consumed benthic prey, predominantly Carcinus maenas, Nereis spp. and amphipods. These larger bass left Tollesbury managed realignment site, and the established saltmarshes at Tollesbury and AbbottsHall, significantly fuller than on entry (MannWhitney, W = 1116, 372 and 229, respectively, all P \ 0.05), unlike at the Abbotts Hall and Orplands managed realignment sites where they had less time to feed. Early site access and soft sediments for macroinvertebrates improved bass feeding opportunities. A wider range of prey was exploited by large 0-group bass in Autumn than in Summer (ANOSIM, R = 0.093, P \ 0.05) including organisms associated with the vegetation such as chironomids and fulgoromorphs. Microhabitat differences influence the feeding of this recreationally and commercially important species during one of its most vulnerable life stages, however by Autumn, these site differences are mitigated by the opportunistic feeding of 0-group bass.

In recent decades, following the cleanup in the 1960s, the Thames Estuary has become a major nursery ground for economic and conservation species, and has seen the development of substantial commercial and recreational fisheries. The Environment Agency has both sea fisheries and freshwater fisheries statutory powers in the estuary. A unique and focussed survey programme has been developed to inform management policies. A Fisheries Management Action Plan has been developed to promote integrated salmonid, eel Anguilla anguilla and sea fisheries management, promote nurseries, sustainable exploitation and habitat protection and enhancement. Data are used to influence water quality, water resources and flood defence management regimes and in the planning field to influence development proposals. Consensus and collaboration have been built through the Thames Estuary Partnership. Research aims identified through the Thames Estuary Research Forum are described together with future pressures on key species. The survey rationales being developed will contribute to new standard sampling strategies and classification scheme to meet the requirements of the E.U. Water Framework Directive.

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