Ship sounds causing dirty hulls - research

Niwa biosecurity scientist Serena Wilkens says two-thirds of all of New Zealand's marine-invasive species have come in as bio-fouling on vessels. Photo / supplied

Barnacles, mussels and other sea creatures which cling to ships' hulls - costing the shipping industry millions of dollars each year - are attracted by the underwater sounds the vessels generate, research has found.

Marine fouling increases the drag on ships' hulls, is costly to clean and has biosecurity implications because it allows unwanted organisms to hitchhike around the world.

Scientists from the National Institute of Water and Atmospheric Research (Niwa) recorded the noise generated by a range of vessels -including log transport, container and cruise ships - and then played it to mussel larvae in a controlled environment at the Leigh Marine Laboratory.

The larvae were at a pre-settlement stage, which means they were swimming in the water, looking for something to latch on to.

Another group of larvae was kept in silent tanks.

Niwa biosecurity scientist Serena Wilkens said the larvae exposed to the high-intensity vessel sound settled and metamorphosed within a few hours - significantly quicker than those in the silent tanks.

This is within the timeframe that the larvae would be exposed to the noise from a vessel's generator in port.

"About two-thirds of all of our marine-invasive species have come in as bio-fouling on vessels, so that's a big problem, Dr Wilkens said.

"Also, marine fouling covers the surfaces of boats, clogs up intake pipes and destroys paint surfaces and that sort of thing, so it's a nightmare for the shipping industry, too."

Researchers were hoping to find ways of reducing the underwater noise produced by ships, such as dampening or eliminating sound production or, where possible, switching to shore-based electrical supply while berthed.