Must see FILM ‘Becoming Visible’ by Janet Solomon

Hullo Sean, thanks for this shout out. FYI: The arrays behind seismic survey vessels are airgun arrays - so they are not 'sonar' but multi beam bathymetric sonar is often used in conjunction with these airguns. I've given you a difference in impacts of both below, otherwise please see the Oceans Not Oil website for loads more info:

Seismic Air Guns are submerged below the water surface, and towed behind a ship. Air gun arrays may consist of up to 48 individual air guns, fired in concert, to create an optimum initial shock wave followed by minimum reverberation of cavitating bubbles.
The blasting schedule of the towed multiple air-gun arrays, which produce this high intensity (215-250 dB) sound, means blasts every 10 seconds for 24 hours a day, for months at a time over large areas. Multi-beam bathymetric sonar is often used concurrently.
Since sound travels more easily under water than through the air, the blasts from a single seismic survey can travel tens of thousands of square kilometres. Scientists have proven that this noise interrupts the communication, reproduction, navigation and eating habits essential to the survival of marine life, including whales, dolphins, turtles, fish, shellfish and even tiny plankton. These waves of energy also damage eggs, larvae and incite fish and other mobile marine species to migrate away from the affected area. Seismic airgun reconnaissance poses an unacceptable risk of serious harm to marine life at the species and population levels, the full extent of which is often not understood until long after the harm occurs.

Ocean depth, multibeam echo sounders (Sonar) sweep a swath up to 7.4 times water depth and so affect a wide area. Potential impacts on marine mammals may range from physical damage, including gross damage to ears and the ‘bends’, temporary and permanent threshold shift (deafness), to perceptual (masking biologically significant noises) and behavioural impacts (temporary or permanent displacement and stress) as well as indirect effects (reduced prey availability) ( Gordon et al., 1998). High intensity, low and mid-frequency sonar has been implicated in some fatal strandings (Frantiz, 1998). Research should be undertaken to determine the effects of bathymetric sonar on beaked whales in areas of steep bathymetry close to an adjacent coastline, when sonar is used seawards (Filadelfo et al, 2010 ).

Keep up the good work and more strength to your bow,
Janet Solomon