Moored shellfish cages for pollution monitoring: Design and operational experience

Environmental bioassay utilizing bivalve molluscs moored in floating cages is a well accepted monitoring tool. Cages built from existing designs proved unsuitable even in relatively sheltered waters. The need to monitor long sea outfalls in the comparatively exposed outer Firth of Clyde led to the development of a more robust construction based on a fibreglass spar buoy. This new design has now been tested for two seasons and has proved to be a useful compromise between a size large enough to dissuade casual pilfering and small enough to keep costs down while allowing ready handling by ship's booms and hydraulic cranes.