Common scoters Melanitta nigra are diving birds that feed on benthic prey,
primarily bivalves, at depths down to 20 m and are a species of conservation
importance in Europe and the UK where Liverpool Bay is the most important
over-wintering site for the species. However, Liverpool Bay is subject to extensive development of inshore waters for windfarms that are known to exclude common scoter from the associated area of the sea. The research presented in this thesis was undertaken to i) understand the spatial distribution and quality of benthic communities and prey resources for common scoter in Liverpool Bay, ii) to identify important underlying physical mechanisms that might be used as predictors of habitats that could provide suitable prey resources for common scoter, and iii) to improve our understanding of the relationship between common scoter, their physical environment and their food supply.
A large scale intensive benthic survey of Liverpool Bay, extending from Blackpool (Lancashire) to Red Wharf Bay (Anglesey), revealed five macrobenthic community types. Of these, the Abra-Lagis and the Tellina communities provided the best foraging habitat for the birds and were visited more consistently by them.
Wave generated seabed stress was identified as the key determinant of the
distribution of bivalve biomass through a Gaussian, depth-mediated relationship,
attributed to optimal conditions for sediment resuspension and food availability
to the benthos. Accordingly, zones of potential maximum biomass can be mapped. As a result, it is possible to infer a possible zone shift under a future
changing wave regime.
The spatial structure of the common scoter population, bivalve prey availability and the aggregative response of predators to their prey were studied. The interaction between social foraging, prey dispersal and information flow led to two different patterns of resource exploitation: strong spatial concordance with
high and consistent bivalve biomass over rich, medium size patches or aggregation over medium/low but more predictable prey densities in areas where
the grain of resource heterogeneity was finer.
A hierarchical design was utilised to examine multiple nested spatial scales of variability of macrobenthic communities and individual taxa at scales commonly employed during benthic surveys. The scale of kilometres proved to be the most important for spatial variability patterns. A subsequent cost-benefit analysis led to the proposal of a grid sampling design with station intervals at the scale of 2 kilometres with possible replicates spaced 100-500 metres apart for future surveys of the area.
The combined results of the present thesis strongly suggest that it is possible to determine habitat characteristics (such as fetch, erosion, depth etc.) that are most likely to provide valuable foraging habitats for common scoter at suitable scales. Such a combination of physical and biological information can identify and advise effectively on areas of the seabed of conservation importance that should be avoided for development in the context of spatial management.