Construction phase of the Centrica Renewable Energy Ltd’s (CREL) Inner Dowsing and Lynn offshore wind farms began in April 2007. As underwater noise generated during construction of wind farms - principally through pile driving - has previously been shown to be of physical risk to marine mammals in close proximity, and the area is known to be utilised by marine mammals, Natural England and DEFRA requested a procedure of mitigation measures against this potential damage. In response CREL commissioned and adopted a project specific marine mammal monitoring protocol (MMMP) for implementation during foundation installation. The basic principle of the MMMP was to ensure that no marine mammals were within 500 metres of the pile during the 30 minute period preceding the start of piling. To confirm their absence two marine mammal observers (MMOs), one of whom operated a passive acoustic monitoring (PAM) system, were to be stationed onboard a crew boat prior to all pile-driving operations. By conducting radial transect surveys around the point of piling the MMO’s could ensure that piling would not commence should marine mammals be detected in the 500 metres exclusion zone in the critical pre-piling period. In addition, a soft start was to be implemented for all piling events.