A detailed investigation into a highly unusual mass stranding in May-June 2008 in which about 100 melon-headed whales washed up around the Loza Lagoon, northwest Madagascar has concluded that the cause was likely to have been high levels of underwater noise from sonar used by an oil exploration company to map the seabed.
The report says that noise from a high-power 12kHz multibeam echosounder system operated by a survey vessel contracted by ExxonMobil Exploration and Production (Northern Madagascar) Limited was determined to be the most likely cause of the mass stranding.
While aspects of this tragic event will remain unknown, the Independent Scientific Review Panel systematically excluded or deemed highly unlikely nearly all potential reasons for the animals leaving their typical offshore habitat and entering the Loza Lagoon. Seismic airguns, used in an offshore seismic survey several days after the whales were already in the lagoon system, were ruled out.
The multibeam echosounder system operated intermittently about 65km offshore by a survey vessel the day before the first known stranding.
Evidence of the widespread impacts of intense noise pollution continues to be felt by an increasing number of whale and dolphin species throughout the worlds’ oceans. Regulators, and marine users that generate intense noise pollution, need to reassess how we manage and mitigate these disruptive and sometimes fatal sources of pollution. Noise-reducing alternatives to noisy sound sources should be advanced wherever possible”.
The full report can be found here: http://iwc.int/2008-mass-stranding-in-madagascar