STRAIT OF GEORGIA — A science team deployed a 450-kilogram “underwater listening station” on the floor of the Strait of Georgia on Friday, in an attempt to further unlock the secrets of ocean noise.
Tom Dakin, a researcher with the University of Victoria’s Ocean Networks Canada, said the station is made up of an array of hydrophones — “microphones that work under water” — that monitors undersea ambient noise, as well as sounds from shipping and marine life such as orcas and humpback whales.
“We can monitor sound waves coming in and tell which direction they are coming from — the exact direction of the ship or whale that made the noise,” he said in an on-board interview.
The $500,000-per-year initiative also involves Transport Canada, the Vancouver Fraser Port Authority and Jasco Applied Sciences working aboard the John P. Tully, a 226-foot-long Canadian Coast Guard research ship.
The project began a year ago with two hydrophone arrays.
Those two have been pulled for maintenance and replaced with a new array, deployed at a depth of 170 metres about 11 kilometres offshore, midway between the Fraser River and Tsawwassen ferry terminal.
“This one unit is more than enough to do everything we need,” Dakin said.
Carrie Brown, the port’s director of environmental programs, said more than 2,200 underwater noise measurements from ships have been recorded during the initiative’s first year, making it “one of the most comprehensive vessel noise datasets in the world.”
A summary of the data is still underway, although the study shows orcas are most common in the area in June to October.
As more information is compiled on the loudest ships, port officials may contact the owners in hopes of reducing sound levels, which can disrupt whales’ ability to feed and communicate. Incentives such as reduced port fees are being considered.
Dakin said the hydrophones can tell if there are maintenance problems creating excessive noise, such as rope wrapped around a propeller shaft.
“In some cases, we can tell them specifically what maintenance to do. There’s a lot of variability in the ships.”
The Oceanic Explorer, a remotely operated vehicle, helped deploy the hydrophone array and connect it to a subsea cable leading to a shore-based observatory, which will allow scientists to continuously receive data from ships, whales and other ocean sounds.
The loudest ocean-going ships measure up to about 195 decibels underwater, Dakin said. (Even whales are noisy: The moan of a grey whale or humpback song can exceed 140 decibels.)
“I’ve been in the water in Active Pass when two vessels went by, generating about 180 decibels, ” he said.
“It felt like someone was hitting me in the chest with a two-by-four. Thump, thump, thump. A lot of energy in the water.”
Sound travels an immense distance in the ocean, he noted, with blue whales capable of communicating across a distance of 1,000 kilometres.
“The energy emitted by ships affects a long range, especially at the lower frequencies,” Dakin said.
Two B.C. Ferries ships, Queen of Alberni and Coastal Inspiration, produce much of the underwater noise in the area because they regularly move passengers between Tsawwassen and Duke Point, near Nanaimo, he said.
“They’re the two most measured vessels in the world right now,” he said. “How does the noise vary with their load, speed, weather conditions and currents? All that plays into how much noise the ship generates.”
With greater study, officials might be able to recommend, say, a slower speed under certain conditions to reduce noise. “This next year will provide a lot more information,” Dakin added.
Natural Resources Canada is also deploying instrumentation at Sand Heads off the Fraser River designed to measure underwater avalanches off the mouth of the Fraser River. It’s the third in a series of such initiatives since 2008.
Scientist Gwyn Lintern said information on underwater avalanches can be useful during the laying of subsea cables and pipelines, providing information on their frequency and times of the year when they are most likely to occur.
In some areas of the world, underwater avalanches have even caused tsunamis, Lintern noted.
“This is the only place in the world, I think, where there is an observatory to try to understand these things,” he said.