Concern over the issue of acoustic disturbance to marine mammals has led to attention being focussed on seismic surveys as one of a number of potential sources of such disturbance. Seismic surveys use airguns to generate sound at low frequencies for geophysical purposes. These low frequencies overlap with those used by baleen whales. In addition, the airguns incidentally emit higher frequency sounds (Goold and Fish 1998) that overlap with those used by toothed whales and dolphins (odontocetes). Therefore, most species of cetacean may be affected by sounds produced during seismic surveys.

 

To address these concerns, the UK Department for Environment, Food and Rural Affairs (DEFRA) and the Joint Nature Conservation Committee (JNCC) issued the Guidelines for minimising acoustic disturbance to marine mammals from seismic surveys (Appendix 2). Seismic surveys in the UK have been operated in accordance with these guidelines since their first publication in 1995. The guidelines have various requirements at both the planning stage and during the operation of a seismic survey. For example, for at least 30 minutes prior to commencing any use of the seismic sources observers should make a careful check for the presence of marine mammals within 500 m. If any marine mammals are detected then use of the airguns must be delayed until at least 20 minutes have elapsed since the last sighting. Whether marine mammals are detected or not, a soft-start procedure should be employed whenever possible, gradually building up the airgun power over at least 20 minutes from a low energy starting level. There is also a requirement that following the survey a report should be forwarded to JNCC, using standard JNCC recording forms (current versions of these are in Appendix 4). These forms are used to assess the implementation of the guidelines and the effects of seismic activity on marine mammals. Previous analyses of annual sets of data (Stone 1997, 1998a, 2000, 2001, 2003) have been limited by small sample sizes. The present report uses data sets combined over the years 1998 to 2000 to further our understanding of the effects of seismic activity on marine mammals.