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From Rodney Coates

The presumption mentioned in Tam Dalyell’s column that acoustic pingers may be employed to discourage cetaceans from approaching the airguns used in seismic surveys is very dangerous, since it offers the offshore industry yet another excuse to continue using these devices (24 January, p 45).

Airgun arrays, which are the most common energy source used in seismic surveying, discharge every 7 seconds. They operate hour upon hour, day upon day, for a season that lasts at least six months. The energy released per discharge by the airgun array is vastly greater than that produced by a pinger. It has to be – the job of the airgun is to whack sound energy many kilometres through the Earth’s crust and back again, and was previously done with dynamite. In energy terms, such arrays “dynamite” everything in their vicinity.

From observation and underwater recordings we know that airgun arrays do not discourage cetaceans from approaching. We, and others, have recordings taken during seismic surveys in which, intermingled with the airgun detonations, dolphins and killer whales can be heard calling. This means they had to be close to the survey. So I pose the question: why should pingers keep them away?

Assertions that pingers will “alert” the cetaceans to danger are most unfortunate, since they carry with them the assumption that cetaceans have a human awareness of what is happening to them. We can read the health warning on the packet, yet no small number of us still smoke. Cetaceans never get to see the packet, let alone read and understand the health warning.

Trefor, Anglesey, UK