What’s that sound? What underwater listening can teach us about the Arctic


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William Halliday
Conservation Scientist/Arctic Acoustics Program Lead

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Whales and seals Arctic

Published

2017-07-04

Large whales can communicate over hundreds of kilometers, something unheard of for a land mammal.

By: William Halliday

Large whales can communicate over hundreds of kilometers, something unheard of for a land mammal. Think of being able to send a signal using only your voice to someone on the other side of your city or even town – impossible. But underwater communication is different: Sound travels more than four times faster underwater than it does in air, which means sound also travels much farther underwater than it does above the surface.

Marine animals, from whales and seals to fish, use sound for both communication and hunting. The ocean is a very dark place, so marine animals must rely less on sight and more on senses like hearing. Many aquatic animals also produce non-vocal sounds during other activities, such as the passage of air through a fish’s swim bladder or the popping sounds that a snapping shrimp’s claw makes when it closes.
The result is that the ocean, even without the contributions of humans, is a noisy place. But all that noise can also be very useful in creating a picture of what is going on beneath the surface. We can listen using underwater microphones called hydrophones (Figure 1).

https://soundcloud.com/rosana-soares-926525576/seaicecracking

Figure 1. A hydrophone used by researchers to record sounds underwater. Photo credit: Steve Insley.

These can be used to constantly record in easily accessible areas or can be left in remote locations in excess of a year before being retrieved. This technique allows us to passively observe the underwater soundscape with minimal disturbance to the animals living there.
Listening to the soundscape provides us with a variety of information. We can identify marine mammals based on the sounds that they make and can even determine how the animals are behaving (i.e. communicating vs. hunting) in species that we know well. We can use this data on acoustics to understand the arrival and departure of migratory species or to monitor seasonal trends in different vocal behaviours of a species.

We currently know much less about sound production in fish and invertebrates, but many fish do actively produce sounds for communication. We can therefore also use sound to study the health of entire ecosystems or even the diversity of a community by listening for sounds made by fish and invertebrates.
But we don’t just hear sounds made by animals when listening underwater -- we also hear other natural sounds and a lot of human-made sounds. From the animal’s perspective, these other sounds represent their acoustic habitat and the sometimes cacophony of noise that they must overcome to effectively communicate and hunt. Natural sounds include waves crashing, rain splashing, underwater volcanic activity and land slides, and even ice cracking and creaking.

In addition, humans make a large variety of sounds underwater, mostly related to transportation, resource exploration and extraction, and military activities. Shipping is a human noise that can be heard across the globe, and it has been getting louder over the past few decades.

Resource exploration includes seismic surveys to assess oil reserves. Military efforts include sonar to search for submarines, and along with seismic surveys, has been central to several incidents where marine mammal deaths have occurred.

Enter the Arctic (Figure 2). Sea ice and available technology has limited human use of arctic waters, which has made the Arctic a quieter place. Sea ice also limits many natural noise sources like waves and rain, while simultaneously creating its own unique noises. However, climate change has caused a drastic loss of sea ice, leading to longer ice-free seasons. This loss of sea ice is going to lead to a louder Arctic soundscape through the combination of increased noise from natural sources and increased access for humans to travel, and explore. How will this changing soundscape affect marine animals living in the Arctic?


Figure2. Sea ice in the Arctic. Photo credit: Steve Insley.


Our team of WCS researchers has been listening to the Arctic soundscape since 2013 to monitor changes brought about by climate change. We started by deploying underwater acoustic recorders in the northern Bering Sea and Bering Strait, and near Sachs Harbour, Northwest Territories, and just deployed our first recorder at Ulukhaktok (Figure 3), NWT, this past autumn. This summer, we will expand our listening zone even further to include the new marine protected area near Cape Parry and will also deploy recorders off the northern end of Banks Island.

Figure3. Map of study site in Western Canadian Arctic, including locations of current and future hydrophone deployments.


Unlike other methods of monitoring marine animals, acoustic data allows us to continuously listen for marine animals -- as long as animals are making sounds, we can detect them. Traditional methods, such as visual surveys or using satellite tags, require much more time in the field, which is very costly in the Arctic. Acoustic data allows for a year-round monitoring program that has the potential to be sustained for years to come (Figure 4).

Figure4. William Halliday prepping the hydrophones before deployment. Photo credit: Steve Insley.


We have heard at least four species of marine mammal at Banks Island: bowhead whales, beluga whales, bearded seals, and ringed seals. Bowhead whales make a low-frequency moan throughout the summer, but in the winter, they also sing complex songs that include low and high frequencies.

Whale songs can be defined as vocalizations that have repeated phrases (or notes). We have not recorded songs with our hydrophones, but have recorded plenty of moans.Beluga whales make a wide variety of sounds, including whistles, more complex sweeping calls, and also echolocation clicks, which are used for navigation, to find food, and to keep in contact with other individuals. (We have not recorded these clicks because they are made at very high frequencies above what we can record with our hydrophones.)

Bearded seals make incredible calls that descend in frequency like a staircase and then rapidly sweep back upwards.

These calls can last more than 60 seconds and in the spring you can hear many of them overlapping each other. Researchers think that they are a type of mating call, advertising underwater territories, but whether they are made only by males or by both sexes is not clear. Ringed seals are much quieter, and make a few different low frequency vocalizations called barks and yelps.

Fish can make a wide range of sounds ranging from incidental sounds from air passing through their swim bladder to more deliberate singing during mating season. At our site, we have recorded sounds called grunts that are likely made by Arctic cod. We did not encounter these fish calls very often, though.

Our data confirm some previously known trends in migration timing for both bowhead and beluga whales: we started hearing both species around Banks Island in late April and stopped hearing beluga whales in late August and bowhead whales in October. Our data also confirm the timing for bearded seal vocalizations, where we heard bearded seals calling 24 hours a day from April through June. Both of these trends are linked to the timing of ice break-up and ice formation. Whales migrate in as the ice breaks up and migrate out before ice forms, while bearded seals only begin vocalizing as ice forms and vocalize all day as ice begins to break-up.

We still do not know the full implications of climate change and sea ice loss for these species. Based on the trends that we have observed so far, it is possible that both whale species will migrate into the area earlier in the year and migrate out later in the year as climate change causes ice to melt earlier and freeze later. Similarly, bearded seals may begin vocalizing later in the fall and will stop vocalizing earlier in the spring.
The decrease in sea ice and longer ice-free season caused by climate change will also lead to increased noise from human activities. Ships may start to use the Northwest Passage through the Canadian Arctic as a shorter route connecting the north Pacific to the north Atlantic. Decreased sea ice has already led to increased cruise ship traffic in the region, including the sailing of the Crystal Serenity through the Bering Sea and Northwest Passage in 2016.

But with increased ship traffic comes increased noise. Ship noise is a pervasive problem in warmer latitudes, where increased ship traffic has caused a doubling of underwater noise levels every decade for the past 40 years. Given that the Arctic is currently such a quiet environment, especially when frozen, and is largely untouched in many areas by ship noise, any increase in noise levels could have drastic effects on Arctic animals. Increased noise levels can diminish the ability of individuals to communicate or hunt using sound, can increase stress levels and affect behaviour, and can even lead to physical hearing damage. We must continue listening to the underwater soundscape in order to monitor any increases in noise that will impact Arctic marine species.
Our research using underwater listening can help inform policy makers and local people. Policy makers can specifically use our data to inform the development of new marine protected areas and to also develop policies for shipping in the changing Arctic. Year-round and long-term data on the presence of marine species that make sound can be used to monitor the impacts of climate change and human activities on these species and their acoustic habitat.

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