The changing acoustic environment of the Arctic

Dr. Kate Stafford is a Principal Oceanographer at the Applied Physics Lab and affiliate Associate Professor in the School of Oceanography at the University of Washington in Seattle. She has worked in marine habitats all over the world, from the tropics to the poles, and is fortunate enough to have seen (and recorded) blue whales in every ocean in which they occur. Stafford’s current research focuses on the changing acoustic environment of the Arctic and how changes from declining sea ice to increasing industrial human use may be influencing subarctic and Arctic marine mammals.

Kate Stafford attaching a hydrophone in line with an oceanographic mooring that will be deployed in the Beaufort Sea to monitor bowhead and beluga whales (photographer Jenny Stern).

Richard Bright: Can we begin by you saying something about your background?

Kate Stafford: I am Dr. Kate Stafford, a Senior Principal Oceanographer at the Applied Physics Lab and Associate Professor in the School of Oceanography at the University of Washington in Seattle. I did my undergraduate work in French Literature and Biology from the University of California at Santa Cruz and then moved on to Oregon State University for graduate school. Before going to graduate school, I was lucky enough to have lived as a Fulbright scholar for a year in Paris. My research focuses on using passive acoustic monitoring (recording underwater sounds) to examine migratory movements, geographic variation of marine mammals and how they are influenced by their environments.  My current research focuses on the acoustic behavior of bowhead whales and the changing acoustic environment of the Arctic and how changes, from sea ice declines to increasing industrial human use, may be influencing subarctic and Arctic marine mammals.

A single bowhead whale migrating north in new ice offshore of Utqiagvik, Alaska in May 2011. (photo: Kate Stafford)

The Arctic soundscape can be very noisy but Arctic animals have adapted to an environment that includes ice noise, heard here in the middle of the recording of bowhead whales and walrus.

RB: Have there been any particular influences to your ideas and working practice?

KS: One thing I value the most as a scientist is collaboration – with other scientists, with students, international colleagues, local people, and even artists.  When I was an early career researcher, I thought I had to be entirely self-sufficient and able to do everything on my own without asking for help.  I was incredibly fortunate, though, to have colleagues and mentors who brought me into interdisciplinary projects where it was clear that a fruitful collaboration results in end products (whether that’s a new idea or a scientific study) that are greater than the sum of their parts. Collaboration among people with different skill sets or backgrounds helps me learn more and work more efficiently as part of a team. Because I do research all over the globe, I prioritize capacity-building where I can and always try to be sensitive to not be a ‘parachute scientist’ who drops in, collects data, and leaves. An Inupiat whaling captain that I know always asks me “how does your research benefit my people?” and no matter where I am, I try to keep this in mind.

Deploying a hydrophone off the ice edge to monitor the spring bowhead whale migration. This involves taking snow machines across the frozen Chukchi Sea to the ice edge and then manually lowering weights, the acoustic instruments and flotation to hold it up above the sea floor. The instruments need to be recovered later in the summer to download the data (photographer Leslie Pierce).

RB: Can you say something about your research which focuses on using passive acoustic monitoring and, in particular, how fish and marine mammals use sound and how that sound informs our understanding of marine life behaviour?

KS: Passive acoustic monitoring (or PAM) is a powerful tool that provides a window to the underwater world. Sound travels much further and more efficiently underwater than does light and animals can be monitored 24 hours a day, year-round, even under heavy ice and total darkness. And because sound propagates so well, marine animals rely on sound as the sense that lets them navigate their world. Animals use sound to navigate, find food, defend territories, maintain mother-offspring bonds, keep in contact with each other, and as a reproductive display – essentially sound enables marine animals to navigate a three-dimensional world. And because different species make sounds that are identifiable to species, if not individual, the presence of different species can be determined by their acoustic signatures. PAM allows us to monitor large areas over long time frames even in remote regions. By listening underwater, especially with multiple hydrophones (or underwater microphones) we can track migrations, understand the seasonal occurrence of different species and understand geographic variation to help identify different populations. When combined with environmental data like temperature, sea ice or prey, either from satellites or in situ measurements, we can use PAM to determine what elements of the environment influence the presence of animals.

An oceanographic mooring about to be dropped into the Beaufort Sea. Hydrophone (underwater microphone) packages are often incorporated into moorings with other oceanographic instrumentation so that in situ environmental data can be collected at the same time as the passive acoustic data to better understand environmental drivers of marine mammal behavior. (photo: Kate Stafford)

What has been revelatory about PAM in the Arctic is the ability to listen during the polar night, in frigid temperatures and heavy sea ice and hear how much life is going on in such a harsh environment. By simply listening underwater, we’ve discovered that bowhead whales, the only Arctic endemic baleen whale, sings complex and varied songs and that these songs change daily and weekly throughout the winter. This behaviour rivals the most complex bird song and was only discovered because we could listen under the ice for months at a time. We can hear the migrations of beluga whales in the spring and the onset of bearded seal males trilling to impress females in the winter. The downsweeps of ribbon seals and knocks and bells of walrus signal the presence of these iconic species in high Arctic regions. We humans are such visual creatures- we navigate our world largely by sight, but marine animals use sound instead. And we, as scientists, can use this to better study these animals that spend the vast majority of their time underwater and away from the prying eyes of humans.

Five adult beluga whales (two surfacing, three still underwater) migrating into the Beaufort Sea. Beluga whales migrate in loose groups that use whistles and buzzes to keep in contact with each other underwater. (photo: Kate Stafford)

Belugas are sometimes called “canaries of the sea” for their remarkable repertoire of cries and whistles. They also echolocate, like bats, but their echolocation clicks are well above human hearing.

Five bowhead whales milling at the surface in the ice covered Chukchi Sea in April 2018. (photo: Kate Stafford)

Only two species of baleen whales make complex songs – humpback whales and bowhead whales. Bowhead whales sing throughout the winter during the polar night under heavy sea ice. Their songs change by week and month and year.

A ribbon seal hauled out (resting) on ice in the Beaufort Sea, September 2018. (photo: Kate Stafford).

Ribbon seals produce a remarkable variety of sounds, including the almost artificial-sounding downsweeps heard in this recording from the Bering Sea in 2012.


RB: Your current research focusses on the changing acoustic environment of the Arctic. Can you say something about the soundscape of the Arctic and how ambient sound levels inform our understanding of climate change?

KS: If we think about using PAM to listen to climate change in the Arctic, we can think of it as hearing changes that come from the sky, the sea and the land. The soundscape of the Arctic includes naturally occurring sounds that are atmospherically-driven like winds and waves and the myriad sounds of sea ice and also underwater sounds made by animals (marine mammals and fish). Increasingly, though, there are also anthropogenic (or human-caused) sounds like the noise from ships, including commercial tankers, cruise ships and tug and barges, and oil and gas extraction. If we listen underwater over long time periods (months to years) we can hear changes in the acoustic environment be it changes in wind speed, the migration of marine mammals, or the passage of a large ship.

As sea ice extent, thickness and seasonal presence declines throughout the Arctic, changes largely driven by sea ice decline can be heard in the Arctic soundscape. For instance, when the ocean is covered by sea ice, although wind can move ice around and cause it to rub and groan and crack, wind-driven waves cannot form on the surface of the ocean. The ice insulates the ocean from waves and wave noise. With less sea ice cover, and climate-driven changes in the atmosphere that are resulting in increasing wind speeds, the Arctic is becoming noisier. We know that increasing wind speeds results in increasing noise levels over open water, especially in shallow waters such as those found in much of the nearshore Arctic. A rough land analogy for increases in wind noise underwater might be living next to a freeway with the background fuzzy-static of traffic noise that may increase during rush hour and decrease at other times, and that you don’t notice until it stops – and your shoulders drop, and you relax in the quiet.

Jumbled sea ice on the frozen Chukchi Sea. Although this appears to be a deserted expanse of ice, dropping a hydrophone under the ice makes it immediately clear that there is a lot going on underwater. In the spring, the sounds of bowhead and beluga whales and bearded seals are often the loudest contributors to ambient noise.

The sounds of sea ice rubbing and cracking and breaking are some of the most variable and loud sounds heard in the Arctic in winter.

Another, perhaps more obvious way in which the Arctic acoustic environment is changing is in the introduction of the relatively novel noises from shipping and oil and gas extraction. Declines in sea ice have opened up trade routes from the Pacific to the Atlantic along the northern coast of Russia, through the famed Northwest Passage and even right across the North Pole. The sounds of commercial ships and ice breakers increase noise levels in the Arctic in the frequency range used by many marine mammals. The opening of the Arctic to oil and gas exploration is not new, seismic air gun surveys (injecting loud bubbles into the water column to image the bottom in the quest for oil and gas deposits) and drilling have occurred over the past several decades but always during very limited time periods, not for many months at a time. The loud impulsive sounds from air guns, which occur every 10-20 seconds for days and weeks at a time raise low-frequency noise levels and the air gun pulses can be heard for 100 seconds to 1000 seconds of kilometers. And by listening to the Arctic we can hear the increase in shipping and the expansion of oil and gas exploration.

Air gun blasts recorded in the Beaufort Sea in September 2018. These signals are produced by the release of compressed air into the water column to image the ocean’s bottom for oil and gas deposits. These signals are repeated every 10-20 s for days and weeks at a time and are in the same frequency band as signals of many marine mammals.

One of the final ways we can hear climate change in the Arctic by listening underwater is by listening to changes in the acoustic behavior, seasonal presence, and distribution of vocal marine mammals. By recording the spring mating signals of bearded and ribbon seals and correlating that with sea ice concentration we can hear that when sea ice declines in a region in the spring, the bearded seals either stop trilling or move north where there is ice. We can hear changes in the migratory patterns of bowhead and beluga whales who are delaying their southbound migrations until late fall or early winter and moving northwards again earlier in the spring under thinner, less extensive sea ice. And we can also hear the signals of subarctic species, like fin, minke, humpback and killer whales, as they move northwards in the summer and stay high in the Arctic until the sea ice eventually pushes them out.  In particular, we can hear the rise of a novel predator in the Arctic, the killer whale, which is expanding further and further north in both the Pacific and Atlantic Arctic.

A killer whale surfaces in the Chukchi Sea in 2016. Mammal eating killer whales are on the increase in the Alaskan and Canadian Arctic where they are potentially becoming major, novel, predators.

Killer whales recorded in the northern Bering Sea in fall 2017. Killer whales are increasingly heard in Arctic waters both later in the year and further and further north.

Ice bergs that have calved off from glaciers in Melville Bay, far northwest Greenland in August 2019 when air temperatures at 78 N reached 20 C. (photo: Kate Stafford)

RB: How is climate change having an effect on the decrease in seasonal sea ice and the behaviour of marine mammals?

KS: The most obvious impact of climate change in the Arctic is the dramatic decrease in sea ice cover, thickness, and seasonality. The Arctic is warming twice as fast as other areas of the globe. For many Arctic endemic marine mammals, such as the ice seals, walrus and polar bears, the reduction in sea ice has essentially eliminated critical habitat for them. Sea ice is used as a platform on which to give birth and shelter young, as a means to move about over shallow feeding grounds, for hauling out to rest, and as a platform for hunting prey for polar bears. As a result of reduced sea ice, we are regularly seeing thousands of walrus haul out on land, and increased sightings of polar bears scavenging on land instead of hunting ringed seals, their preferred prey, on sea ice. For the Arctic endemics that are ice associated (bowhead, beluga and narwhals) throughout their lives, it is less clear how climate change is impacting them although we know that both belugas and bowheads are changing their migratory seasonality. More critically, narwhals seem especially susceptible to increases in underwater noise and to decreases in sea ice.  If we consider seasonal visitors to the Arctic, like humpback and killer whales, we can hear that they are spending more time in the Arctic and moving further and further north as sea ice declines. In this way, one might consider some subarctic species to be Arctic climate change winners as decreases in sea ice are allowing these species to expand into new habitat created by lack of sea ice. What isn’t yet clear is whether these “invasive species” will be in competition with Arctic endemic species for food or habitat.

Humpback whales feeding in front of icebergs that have calved off Jakobshavn Glacier in Ilulissat Greenland. Increasing numbers of subarctic species are spending more time in the Arctic than in times past possibly because of changes in seasonal sea ice but also because many subarctic populations are recovering from previous declines due to commercial whaling. Humpback whales are being heard singing in the Arctic, which may introduce novel “noise” into a soundscape dominated previously by the songs of bowhead whales. (photo: Kate Stafford)

Humpback whales are moving further north in the Arctic and spending more time there with decreasing sea ice. Increasingly, humpback whale songs are being recorded in the early winter well to the north of their tropical breeding grounds.  An open question is, given that both humpback and bowhead whales are prolific singers capable of learning new songs, will the overlapping presence of these species singing in the Arctic influence the songs they sing?

A polar bear on the beach in the fall in Utqiagvik, Alaska digging up an old gray whale carcass for food. (photo: Kate Stafford)

RB: How does human noise affect ocean habitats?

KS: Increasing ocean noise reduces the communication space over which marine animals interact acoustically. To overcome increased noise, animals must call more loudly, more often, change the pitch at which they communicate, or just go silent and wait until they can be heard again. In the Arctic although the levels of shipping are unlikely to reach those of major international ports south of the Arctic circle, the animals of the Arctic have only recently been exposed to these noise increases and have not had time to adapt to seasonal changes in noise. We know that seismic air gun pulses change the acoustic behavior of bowhead whales. When the seismic ship is distant, but still audible, bowhead whales increase how often they call. But when the ship is close and the signals much louder (think the booms of nearby fireworks every 10 seconds), bowhead whales clam up and stop calling. Whether this disrupts daily life and interactions over longer time periods is currently unknown. We do know, however, from a number of studies, that increased noise increases levels of stress hormones in large whales, in the same way that it does in humans. And of course, marine animals cannot just shut out the noise the way we might be able to by closing our windows or using noise-cancelling headphones. So we are making it harder for marine animals to hear each other and to hear cues from their environment and we don’t yet know, if we ever will, what the cumulative impact of all this sound will be on marine populations.

Increasing ship noise in the Arctic is occurring as decreasing sea ice permits commercial shipping to shortcut across the Arctic between the Pacific and Atlantic Oceans.

RB: What can we do to reduce human-caused underwater noise?

KS: We know that sound is vitally important for marine animals as noted above. The sounds different animals use change with location and season and behavioural state. Some signals are used for long-distance communication and others for close neighbours. Because of this, changes in the acoustic environment risk disrupting important life-history events for animals. To reduce the impact of human noise on marine life, we can try to reduce human-caused underwater noise or at the very least, mitigate its impacts on marine life.

Mitigation measures for shipping and resource exploration and extraction might include closing regions of the Arctic, either seasonally or permanently, that have high ecological value or where species are most vulnerable. For instance, requiring that seismic and development activities take place when high concentrations of marine mammals are unlikely to be present in an area. Another possibility would be to impose a sound “budget” to limit the cumulative amount of sound from industrial activities in regions or seasons like calving areas or times of year when animals are actively migrating. Mitigation that is most commonly used involves modifying or shutting down a sound source (like an air gun) when marine mammals are detected within a specified distance from the course, or slowly increasing the volume of the sound source to provide animals the opportunity to leave the area before the loudest noises begin. Really though, to reduce the sounds of seismic surveys for oil and gas in the Arctic, and elsewhere, we need to reduce our dependence on fossil fuels and leave them in the ground. This would be a win for the climate and reduce underwater noise in most of the world’s oceans.

Because we know that fast ships are louder than slow ships, the shipping industry and vessel traffic in general might need to have seasonal speed limits imposed, and implementation of quieting technologies on vessels to reduce sound in the environment. Additionally, with international cooperation, changing the location of shipping lanes and the timing of transits could reduce ship strikes of marine mammals. Some of these efforts are being undertaken outside of the Arctic and are being used in the North Atlantic to protect critically endangered North Atlantic right whales, off southern California to protect blue and fin whales, and off Vancouver Island, Canada to reduce noise levels for killer whales.

A large tanker transiting the Arctic in summer 2017. With decreases in seasonal sea ice, the “open water season” (when the Arctic is navigable by vessels) is extending by weeks to months in the Arctic allowing large commercial vessels to move between the Atlantic and Pacific Oceans via the Arctic. (photo: Kate Stafford)

A group of walrus jammed together on a small ice floe. Walrus are very social animals and even if there are empty ice floes nearby, the walrus will all congregate on the same floe, even if means crawling over and lying on top of one another.

RB: Are you optimistic about the future of the Arctic and its marine life?

KS: I am not as optimistic about the future of the Arctic, as it existed 20 or 30 years ago. The tipping point for saving multi-year Arctic sea ice appears to have passed because we humans, as a species, have not been willing to make the hard choices to reduce our dependence on fossil fuels and bring global temperatures changes in line with the Paris accords. I think the Arctic in 20 years will look very different than even the Arctic of today. As noted above, there will be winners and losers in climate change where subarctic species may benefit while Arctic endemic species may change their migratory patterns by no longer moving southward in the winter. Ice seals may have to adapt to give birth and rest on land which will lead to new challenges and exposure to new predators. And novel fish species, including salmon and pollock will continue to move north, potentially displacing or otherwise outcompeting Arctic species. Essentially, we will see ecosystem-wide changes cascading through Arctic food webs and the extent of these is difficult to predict. What gives me some hope is that we know marine systems, and the people who rely on them, can be very resilient in the face of change so perhaps instead of an Arctic ecosystem collapse, we may witness an ecosystem adapt.

A juvenile walrus attracted to the USCGC Healy in high Arctic 2017
in July 2016. This animal was all by itself with no ice nor other walrus around.
(photo: Kate Stafford)

Bearded seal trills (with walrus knocks and bowhead moans in the background). Bearded seal males trill throughout the winter and spring to attract mates and these trills can dominate the underwater soundscape, especially in spring when many males trill at the same time.





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