Sound is a way of life for marine species
17 July 2018
In an underwater environment where light is often limited, the acoustic soundscape holds key information for many marine organisms, including those who migrate over great distances in search of food and mates. But as Henriette Schack notes, with human activities increasing in the Arctic, the soundscape is changing—and the effects could be substantial for animals and humans alike.
Close your eyes and try to imagine the sounds of the Arctic: Ice creaking as it moves with the wind and the currents. Continuous fizzing of bubbles released from melting ice. Sudden, loud cracks from breaking icebergs. And in the background, the whistles and calls of belugas and narwhals, the songs of bowhead and fin whales, and the barks, yelps, chirps, knocks, trills, moans and grunts of ringed seals, bearded seals and walruses.
All of these diverse sounds have long combined to form the Arctic orchestra. Newer to the auditory scene are man-made sounds—many of which directly interfere with naturally occurring sounds, in both frequency and intensity.
Marine mammals depend on acoustic information to survive. Precisely what information they use, and how they use it, is still a mystery—but our understanding of their senses has been developing steadily through decades of research. For example, we now know that toothed whales, like belugas and narwhals, emit intense high-frequency clicks and use the echoes reflected by prey to locate and eventually capture it. They also use echoes to avoid obstacles. This is known as echolocation. Baleen whales, such as bowhead and fin whales—as well as pinnipeds—use their hearing to communicate with each other and most likely also for orientation and navigation.
How do various species of marine mammals respond to anthropogenic noise?
Scientific studies have shown that noise from human activities can affect marine mammals in various ways:
- Some whale species have been observed compensating for noise by calling or singing more loudly, shifting their signals up in frequency, calling more often or simply going quiet until the noise has passed.
- Many studies have found that noise can cause behavioural changes, such as flight and avoidance.
- Narwhals and belugas have both been observed reacting to noise from icebreakers at long ranges—but where belugas would flee and call to each other in alarm, narwhals seemed to stop calling and sink down in the water column instead.
How and when animals change their behaviours to cope with noise depends on a wide variety of factors. Existing ambient noise levels and the animal’s proximity to a sound source are two important ones. With greater levels of ambient noise, animals must be closer to other members of their species to hear them. Ice conditions can also change how animals react. Factors such as age and sex—and what the animal is currently doing, like foraging—can also play a role.
As ice-free periods in the Arctic become longer and more frequent, shipping and exploration for oil and gas are increasing. Shipping is expected to expand considerably in the coming decades. The consequence could be a substantially altered Arctic soundscape. Noises from container ships, cruise ships and icebreakers overlap in frequency with the known or presumed hearing range of many marine mammals, as well as with sounds produced by these animals, interfering with their ability to communicate, navigate, forage, mate and defend themselves. As well, the high-intensity noise of oil and gas exploration has the potential to cause hearing loss in marine mammals. Exposure to intense noise, like that from seismic surveys, or longer exposure to lower levels of noise, can cause temporary or permanent hearing loss in animals and may cause changes in stress hormone levels.
Precisely what acoustic information marine mammals use, and how they use it, is still a mystery—but we know they depend on it to survive.
Underwater noise has long been a concern regarding marine mammals. New studies are constantly contributing pieces of the puzzle, but exactly how changes in the Arctic soundscape will affect marine mammal populations is still just guesswork.
What is clear is that the time for preventive action is now. With human activities still at relatively low levels in the Arctic, we have a unique opportunity, through careful marine spatial and temporal planning, to shape how we utilize the area. If we make the right decisions now, we can preserve the harmony of the Arctic’s underwater orchestra in a way that benefits animals and humans alike.
Henriette Schack is a freelance environmental consultant in Denmark who specializes in risk and impact assessments of underwater noise and marine organisms.
A report from WWF details the problems increasingly noisy oceans are creating for whales.
This predominantly Arctic species is associated with ice floes. Its movement patterns are therefore influenced by the melting and freezing of the ice. The bowhead has suffered from severe over-exploitation that has seen its range shrink considerably since the 17th century.