Are noisy oceans to blame for beached whales?

Posted by Fiona Nicholls — 23 May 2016 at 12:36pm - Comments
Sperm whales beached on the Dutch Island of Texel, Jan 2016
All rights reserved. Credit: Greenpeace
Sperm whales beached on the Dutch Island of Texel, Jan 2016.

Noise is the most invisible of all the man-made threats to the ocean, but to whales who ‘see’ by hearing, they simply cannot escape it.

Water is an excellent medium for relaying sound, enabling some species of whale to communicate across entire oceans. However, during the last century, things have started to get loud in the ocean. Increasingly industrialised, the seas can be an inescapable aural assault for marine life; noise is created by ship engines, seabed drilling, seismic blasting, military sonar use, and bomb testing.

Hearing and navigational abilities are one and the same for whales, and so if deafened by, say, a bomb going off underwater, their ability to steer away from unsafe shallow waters is hindered, and they may beach.

Last week, 27 pilot whales were beached on Mexico's Baja California Peninsula , and while 3 of the whales survived (including a calf), 24 of them died. Why were they there?

Pilot whales are highly sociable and move in pods, but their all-for-one nature can serve them badly when it comes to a misguided (possibly sick) member of the family leading the whole pod off course.  As a result of their tight bonds, whole pods of cetaceans can end up in river systems, bays, and on beaches.There are also more sinister reasons for beachings...

In 2011, four bombs were detonated underwater by the Royal Navy off the north coast of Scotland , within 24 hours, a mass stranding of 19 pilot whales took place on Kyle of Durness. A scientific report of the incident explains that the whales were likely left “functionally deaf”, due to the noise from the blast. In a world where every aspect of life and communication relies on sound (many species of whale have poor eyesight), once deafened, things can head south pretty quickly.

IB Image

Mass strandings have happened before - so what’s new?

In the Canary Islands in 2002, a mass stranding of beaked whales (the deepest diving whale known) enabled scientists to study the pathological effects of sonar use (by the US Navy at the time) on whales. What they found changed the way we think of these deep divers. Gas bubbles found in the fat and veins of the beaked whales indicated the deadly plight of scuba divers: the bends.

But why would these whales, who are physiologically perfect for diving, develop decompression sickness? Theories focus on man-made noises in the ocean, which startle the whales and cause them to flee to shallow waters. Dr. Paul Jepson of IoZ suggests that the mid-frequency noise mimics the calls of predatory killer whales. The whales are so spooked by this sudden ‘attack’, that they flee to the surface far too quickly, develop the bends and strand ashore.

IB ImageAnd let’s not forget the sperm whale mass stranding earlier this year, also deep diving whales - these incidents are not isolated.

Sound is unlike most pollution in the ocean, in that once it has stopped, it leaves no oil, nor islands made of plastic. Once sound stops, it’s gone. 

It’s time we all made some noise about making less noise in the ocean.

P.S.   What should you do if you come across a sea mammal on the beach? If they are alive – contact your local Wildlife Trust, or British Divers Marine Life Rescue. If you find a dead whale, dolphin or porpoise on a beach, then get in touch with the UK strandings network.

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