Killer whales call louder as vessel noise increases

This clipping from the NOAA/NWFSC Marine Mammal Program shows that southern residents are increasing the source level of their S1 calls by about 1dB for every decibel increase of the ambient noise level. Counts of vessels within 1km of the hydrophone correlate with the ambient noise levels.

While the ecological consequences of this behavioral change are up for debate and further study, these results could motivate owners of vessels that operate near the whales to reduce their underwater noise production. They could also lead to the development of new regulations regarding how vessels interact with the endangered killer whales.

The peer-reviewed article is expected to be published in the next couple months. Similar results have been acquired by a Beam Reach student in fall 2007 (Elise Chapman, ) and by Val Veirs in spring 2005 ( ).

clipped from

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Speaking up: killer whales compensate for vessel noise

A photograph of a woman looking at a group of killer whale from a boat.
NWFSC postdoctoral researcher Marla Holt measuring the sound levels of killer whale
calls near San Juan Island.

A study by NRC postdoctoral researcher, Dr. Marla Holt, and collaborators including NWFSC, Colorado College and Beamreach researchers have found that Southern Residents compensate for the masking effects of vessel noise by calling louder. In a new article (in press) in JASA Express Letters, “Speaking up: killer whales compensate for vessel noise,” these researchers show that whales increase their call level by one decibel for every decibel increase in background noise levels.
The researchers also report that noise levels increase as the number of motorized vessels around the whales increases, illustrating the contribution vessel traffic has to background noise levels in the whales’ underwater environment.
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