COMMENT

Most people think of our oceans as quiet places where they can go to relax, swim and enjoy glimpses of our diverse marine life.

Contrary to this belief, our oceans are actually loud and getting louder due to renewable energy harvesting, seismic blasts for oil and gas surveys, and container ships. These man-made sounds are affecting our marine life and new research shows that whales respond with silence while dolphins try to shout over the din.

Cargo ships are the lifeblood of New Zealand business with our sea ports responsible for moving 99 per cent by weight of all our physical exports. Shipping products in and out of New Zealand has had a negative effect on our marine life, specifically the endangered Bryde's whale, which spends most of its time within the top 10m of the water's surface.

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Although the voluntary 10-knot speed limit for ships travelling in the Hauraki Gulf seems to have reduced the number of whale deaths caused by ship strike, local research published in the journal Global Change Biology showed that even with this speed reduction, the noise created by passing ships reduced the space that Bryde's whales can communicate in by up to 87 per cent.

Powered by large diesel engines, cargo ships can create low frequency sounds as high as 188 decibels when travelling at 20 knots - much louder than a jet engine taking off.

Male humpback whales, known for their beautiful and complex songs, are thought to sing for mating opportunities, as a migratory beacon and even possibly as a biosonar to help them navigate.

The rumble of tankers and container ships caused humpback whales in Japan to fall silent. Research published in PLOS One this week found the whales stopped singing when a ship was 1200m away and didn't resume singing again until 30 minutes after the ship had passed.

Although the reasons for the whale silence are not known, one theory is that the humpbacks may be confused by the ships sounds as they emit at the same frequency as whale song.

Banning noisy ships from our oceans is not an easy or practical thing to do, however, immediately after the 9/11 tragedy in the US, Governments halted a lot of commercial transportation which dramatically reduced movement in the shipping industry.

At the same time, a study was being carried out on North Atlantic right whales in their summer feeding ground of the Bay of Fundy. As a busy shipping route in Canada, the researchers found that the 6-decibel reduction in shipping noise from the reduced marine traffic resulted in a huge drop in the level of stress hormones measured from the whales.

Twelve months later, when the commercial shipping traffic had resumed, the researchers found that the stress levels of the whales had also increased up to much higher levels.

While the whales respond with stress and silence, bottlenose dolphins go the other way, according to research published in the journal Biology Letters this week.

Dolphins use sound to help them navigate, locate food and communicate with other dolphins and the researchers found that when encountering shipping noise, the dolphins raised the pitch of their whistles and reduced the complexity of their sounds, likely simplifying their messages while making them louder to get them across.

While the specific effects of this human-made cacophony are still being put together, what is obvious is that shipping sounds are causing the whales and the dolphins to change their natural behaviour.

Being an island nation reliant on cargo ships, our noisy seas might eventually drive away the nature that we take for granted on our shores.

Dr Michelle Dickinson, creator of Nanogirl, is a nanotechnologist who is passionate about getting Kiwis hooked on science and engineering. Tweet her your science questions @medickinson