For 19th-century adventurers like Sir John Franklin, navigating a path through the ice-choked Northwest Passage — the Holy Grail of Arctic exploration — was a treacherous and often deadly undertaking. Today, thanks to climate change, traveling through the passage is quickly becoming another exotic option for cruise ship passengers — and an enticing shortcut for cargo ships.
But an increasingly ice-free Arctic means more than just a chance for a new sightseeing adventure: Significantly increased ship traffic is altering the submarine calm of one of the quietest places on Earth. That could have serious implications for marine mammals and fish that rely on sound for group cohesion, socializing, finding mates, navigating, and detecting threats.
For a study just published in the Marine Pollution Bulletin, my colleagues and I sought to determine just how intrusive ship engines are on the Arctic soundscape and whether or not there are any changes ships can make to improve the aural environment for wildlife there.
Marine mammals and fish make a variety of sounds for a variety of purposes. Bowhead whale songs intended to attract mates are complex and broadband. Other vocalizations (to navigate, for example) fall in a narrower range. Beluga whale vocalizations are highly variable, with tonal sounds and echolocation clicks in different sound ranges. Bearded seals also emit several different call types and fish have their own suite of grunts and pulses.
Audiograms (hearing profiles) of marine mammals and fish show that their hearing ranges often overlap with those of vessel noise, which can “mask” the animal calls from their intended recipients. Think of the difficulty of hearing a friend at a noisy party compared to at the library – except that loud vessel noise can potentially mask vocalizations over a much larger area than your local library.
Unfortunately, routing ships away from areas heavily used by marine mammals is often not an option in the Canadian Arctic. Most traffic there follows fixed southern routes along the mainland.
Vessel transits through Canada’s Northwest Passage have increased from four per year in the 1980s to as many as 30 per year. With ship traffic steadily growing in Arctic waters, our WCS Canada research team, in close collaboration with JASCO Applied Sciences and the University of Victoria, decided to investigate whether reducing vessel speeds could lower the impact of ship noise.
In our study, we chose to focus on “listening space” — essentially, the volume of ocean within which the listener can detect biologically important sounds. We then measured the impact of ship noise on the size (radius) of this space.
Calculating the amount by which ship noise reduces the size of an animal’s listening space requires an understanding of how well a call or sound travels through Arctic waters, the change in masking noise levels (from vessels), and the species’ audiogram. The overlap in sound frequency (perceived as “pitch”) for each of these factors is the key.
Our listening areas were selected based on areas known to attract bowhead and beluga whales, as well as bearded and ringed seals (fish species were assumed to occur at all sites).
We found that vessel speed reductions significantly reduced loss of listening space. Under quiet conditions, beluga whales experienced a 50 percent listening space loss when they were 7 to 14 kilometers (4.3 to 8.7 miles) away from a ship traveling at 25 knots. When ships slowed to 15 knots, whales could get as close as 2 to 4 kilometers before they experienced the same loss of listening space.
In other words, when a ship was going faster, the area over which it cut a beluga’s listening space in half might be more than three times larger. This difference is important because there are many places where whales cannot distance themselves from ships in the Arctic (in the narrow Prince of Wales Strait, animals can maintain a maximum distance of just 7 to 10 kilometers).
We also found that slowing vessels will have even larger benefits when ambient noise is higher and ships are farther away. This finding is especially important since ambient noise from waves and winds is increasing in an Arctic environment that is experiencing ever longer periods without sound-dampening ice.
The Arctic Council has been grappling with the implications of increased shipping operations in the Arctic in areas with high marine mammal densities. Our research finds that vessel slowdowns could indeed be a viable strategy for lowering noise impacts on whales, seals, and fish, with the added benefit of reducing the likelihood of collisions.
While negotiating the Northwest Passage may be less treacherous in the future for cruise ship passengers who thrill at the sight of whales plunging through Arctic waters, melting ice that opens up new sea lanes comes with a new threat for marine life. As we grow sensitive to plastics and other toxins that plague ocean species, we must remember that while noise is the one form of pollution that we cannot see, we can work together to turn down the volume.
Matt Pine is Mitacs Elevate postdoctoral fellow with WCS (Wildlife Conservation Society) Canada, the University of Victoria and JASCO Applied Sciences.
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