From physics to fishing over a shelf sea bank

The research presented in this Special Issue focuses on how seabed topography can drive horizontal patchiness in physical and biogeochemical processes, and organism distributions in a temperate shelf sea during the period of established stratification in summer. The work is based upon data collected during a research cruise aboard the RRS James Cook over Jones Bank in the Celtic Sea in summer 2008. Jones Bank was chosen because of its well-defined topography within an otherwise flat region of shelf. The project arose following observations of patchiness in the chlorophyll concentration within the summer sub-surface chlorophyll maximum (SCM) of the Celtic Sea associated with marked increases in internal turbulent mixing over large bank features such as Jones Bank. These sub-surface chlorophyll patches are not apparent at the sea surface and so cannot be detected in satellite imagery. Similar structures in sub-surface chlorophyll have been found to correlate with the distributions of foraging seabirds in the North Sea (Scott et al., 2010). Our aim was to make measurements from the scale of turbulent microstructure, through the biogeochemical rates and phytoplankton distributions, up to the distributions of fish and seabirds. We were motivated to determine what aspects of the shelf system responded to the bank, and what causitive links there may be between the physical perturbation caused by the bank and the attraction of the bank for marine top predators, including fishing fleets. In this preface to the Special Issue we will describe the physical and biological environment of the Celtic Sea, using earlier data to highlight the likely effects of a bank on shelf sea structure, and set the context and pose the questions addressed by the papers in this issue. We then summarise the findings of the research, and provide a synthesis describing why banks in a stratified shelf sea may attract mobile marine predators.