In the last couple of weeks evidence has come forth associating seismic airgun surveys with catastrophic strandings of marine mammals. The Falkland Islands are the site of two mass strandings of pilot whales, one in March 2011 of 400 whales, and another this this last February 2013 with 52 whales.
The fact that both incidents involved pilot whales ambiguates the situation a bit because accounts of pilot whale strandings go back hundreds of years – prior to the introduction of industrialized noise events in the ocean. A popular theory is that these animals form really tight social bonds and when one falls ill or gets confused and hits the shore the rest will follow. This is an interesting conjecture but is not too strongly associated with common survival behaviors. For 400 animals to throw themselves onto shore for the illness or confusion of one or a few individuals rings more like the lemmings myth than an adaptive situational response.
Coincident to both stranding events though were seismic surveys – looking for oil in the South Atlantic. Heretofore there have been only a few strandings correlated with seismic surveys. Towed airgun array operations try to limit their operating bandwidth to lower frequencies which while they can be really loud, tend not to be as damaging to hearing or animal tissues as equally loud higher frequency signals.
But a high concentration of dolphin strandings along the coast of Peru last March concurrent to seismic operations raised a lot of eyebrows. Necropsies indicated that the animals were subject to acoustic trauma, and there was no evidence of any marine earthquakes at that time large enough to have caused the damage.
It could be that in addition to the typical airgun arrays that there is a new technology being deployed such as an echo sounder or a marine acoustic data channel that is transmitting in a higher frequency range that may be damaging the hearing of these animals.
If a new technology is the case I don’t anticipate the survey operators to come forth with any explanations. Hopefully someone gets a hunch about the causes of these seismic survey-associated strandings and helps bring about a less damaging way to proceed.