Underwater Pile Driving Harmful to Dolphins

LONDON, UK, May 4, 2006 (ENS) - Pile driving and industrial noise can adversely impact dolphin behavior, communication, and breeding as the noise is detectable up to 40 kilometers (25 miles) from the source, new research reveals.

Bottlenose dolphins that live in designated Special Areas of Conservation throughout the United Kingdom, including Dorset, Anglesey and Cornwall, are at significant risk from pile driving noise, writes the study's author, J.A. David, a member of the Chartered Institution of Water and Environmental Management.

Long used to place docks, bulkheads and bridges, and more recently to site off-shore oil platforms, pile drivers now are being used ever more frequently as countries place wind turbines in off-shore waters to generate electricity with strong coastal winds.

The frequency range of pile driving noise can interfere with dolphins' ability to communicate, find food and avoid predators. This can affect their behavior, health and their ability to breed successfully. Lactating females and young calves are particularly vulnerable, suffering from impaired hearing and temporary displacement, David writes.

Dolphins play in UK waters. (Photo courtesy University of Dundee)

At 9 kHz, pile driving noise is capable of masking strong vocalizations within 10–15 kilometers and weak vocalizations up to 40 kilometers, David documents in a scientific paper published in the latest issue of "Water and Environment Journal," a peer-reviewed quarterly publication of the Chartered Institution of Water and Environmental Management.

The impacts of masking are expected to be limited by the intermittent nature of pile driver noise, the dolphin's directional hearing, their ability to adjust vocalization amplitude and frequency, and the structured content of their signals.

Still, David suggests that mitigation measures should be put in place to help prevent the effects of pile driving on dolphins.

Operations should be restricted to low tide and suspended during calving season, David advises. An exclusion zone should be monitored before any activity starts, and marine work should cease if a dolphin enters the work area.

David calls for further research into the reactions of marine mammals to industrial noise to help mitigate future effects in relation to the increase in off-shore industry, such as the construction of wind farms.

He proposes creating an air bubble curtain and issuing a ramped warning signal to give dolphins time to leave the area before work commences.

The sound blocking capabilities of an underwater air bubble curtain were tested in 2000 by scientists with the Marine Mammal Research Program at Texas A&M University.

A team led by Texas A&M Professor of Marine Biology Bernd Würsig found that underwater bubbles can inhibit sound transmission through water due to density mismatch and concomitant reflection and absorption of sound waves.

A perforated rubber hose was used to produce a bubble curtain, or screen, around pile-driving activity in six to eight meter deep waters of western Hong Kong.

Texas A&M Professor of Marine Biology Bernd Würsig co-edited the "Encyclopedia of Marine Mammals." (Photo courtesy Texas A&M)

Wursig's team found that Indo-Pacific hump-backed dolphins, Sousa chinensis, occurred in the immediate area of the industrial activity before and during pile driving, but with a lower abundance immediately after it.

While hump-backed dolphins generally showed no overt behavioral changes with and without pile driving, their speeds of travel increased during pile driving, indicating that bubble screening did not eliminate all behavioral responses to the loud noise, Wursig's team reported.

Because the bubble curtain effectively lowered sound levels within kilometer of the activity, the experiment and its application during construction represented a success, Wursig said, suggesting that this measure should be considered for other areas with high industrial noises and resident or migrating sound-sensitive animals.