Tsunami reveals human noise pollution in Hawaiian waters

October 30, 2017, Duke University
One of the seafloor data loggers used to record underwater sound in a new study of human interactions with spinner dolphins in Hawaii. Credit: Duke University

A tsunami that struck Hawaii in 2011 and caused a temporary halt to boat traffic has provided scientists a rare glimpse into what the bays might sound like without human activities.

The tsunami, triggered by the same earthquake that caused the Fukushima nuclear disaster in Japan, reached waters along the island of Hawaii's Kona Coast while a Duke University-lead team was recording underwater sound in four bays there.

"On the tsunami day, underwater sound levels during the loudest part of the day measured 98.8 decibels (re 1 uPa). On days when human activities in and near the bays weren't halted, we recorded sound pulses more than 16 times louder than that," said Heather L. Heenehan, a postdoctoral scientist at NOAA's Northeast Fisheries Science Center, who led the study as part of her doctoral dissertation at Duke's Nicholas School of the Environment.

Because sound waves travel and are amplified differently in water than in air, scientists use the reference "(re 1 uPa)" to express the relative loudness of sounds recorded underwater.

Noise from boat traffic in the four bays reached up to 125 decibels (re 1 uPa), while pulses from nearby sonar exercises reached 143 decibels (re 1 uPa). "Keep in mind that every increase of 10 decibels is perceived as a doubling in loudness," Heenehan said.

The new peer-reviewed paper was published online Oct. 24 in the journal Marine Pollution Bulletin.

One of Hawaii's many tourist attractions is the opportunity to see and interact with spinner dolphins, but we're noisy about it, bothering the marine mammals. Credit: Duke University

Using passive acoustic recorders, Heenehan and her colleagues measured and identified the sources of sound pollution in four shallow bays along the Kona Coast that are home to populations of spinner dolphins, a major eco-tourism draw. Conservationists have long feared that interactions caused by dolphin-encounter boat tours and other human activities disrupt the sleeping behaviors of the dolphins, who rest in the bays during the day to gain energy to hunt for food in offshore waters at night.

The new study validated these concerns by showing that humans create the loudest disruptions in each of the four bays. Boat traffic and sonar were significant causes of noise in all four bays. Sounds from boats involved in recreational activities in the bays and nearby fish farms also contributed to the daytime din to varying degrees.

Because different combinations of human noises affected each bay's soundscape differently, policy solutions will have to be tailored to individual situations, said David W. Johnston, a co-author on the study and associate professor of the practice of marine conservation ecology at Duke's Nicholas School.

"No one-size-fits-all approach will work," he said.

The new tsunami-enabled benchmark of what the bays sound like without human disruptions gives policymakers, conservationists and local communities an aspirational target to aim for when implementing future measures to reduce underwater levels, Heenehan said.

"This shows just how much human activities interrupt the acoustic environment of these animals at a critical resting time," she said.

Explore further: Policy action urgently needed to protect Hawaii's dolphins

More information: Heather L. Heenehan et al, Natural and anthropogenic events influence the soundscapes of four bays on Hawaii Island, Marine Pollution Bulletin (2017). DOI: 10.1016/j.marpolbul.2017.06.065

Related Stories

Policy action urgently needed to protect Hawaii's dolphins

December 17, 2014

The best way to protect wild spinner dolphins in Hawaii while also maintaining the local tourism industry that depends on them is through a combination of federal regulations and community-based conservation measures, finds ...

The underwater jungles of the sea give clearer water

August 30, 2017

The new study, that has been conducted in 32 archipelago bays along the Baltic Sea coast shows that underwater plants can contribute to a better water quality, thus improving their own living environment. The water becomes ...

Assessing threats to Hawai'i's spinner dolphins

January 23, 2014

(Phys.org) —Researchers have completed the most extensive study of the Hawai'i Island spinner dolphin population to date, with the data to be used to inform the local management agency.

New maps may reduce tourism impacts on Hawaiian dolphins

August 27, 2012

Over-eager eco-tourists intent on seeing spinner dolphins up close may inadvertently be disturbing the charismatic animals' daytime rest periods and driving them out of safe habitats in bays along Hawaii's coast.

Boat noise stops fish finding home

June 28, 2013

(Phys.org) —Boat noise disrupts orientation behaviour in larval coral reef fish, according to new research from the Universities of Bristol, Exeter and Liège. Reef fish are normally attracted by reef sound but the study, ...

Recommended for you

Individual lichens can have up to three fungi, study shows

January 17, 2019

Individual lichens may contain up to three different fungi, according to new research from an international team of researchers. This evidence provides new insight into another recent discovery that showed lichen are made ...

Sea slug study illuminates how mitochondria move

January 17, 2019

Your cells have an amazing ability—they can build their own energy factories, called mitochondria. Once built, mitochondria must move where needed in the cell. Defects in mitochondrial transport are a suspected cause of ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.