ASA Lay Language Papers
161st Acoustical Society of America Meeting

Studying the effects of man-made noise on marine animals

Christine Erbe
JASCO Applied Sciences
Brisbane Technology Park
1 Clunies Ross Ct.
Eight Mile Plains, Queensland 4113

Popular version of papers 2aUWb1 and 3pED3
Sessions: Tuesday Morning, May 24; 8:30 am and Thursday Afternoon, May 26

Ocean water conducts light very poorly, but sound very well. As a result, marine animals rely heavily on acoustics to support many of their life functions. Underwater man-made noise can interfere with these life functions (Erbe, 2011). At low levels, the noise would be merely detectable. At somewhat higher levels, it could impact the animals’ hearing of communication signals emitted by fellow animals. It might hinder the hearing of environmental sounds—like the sound of surf—which animals might listen to while migrating along coasts. Noise could mask the sounds emitted by predators or prey, altering the “normal” predator-prey relationship. Noise can alter animal behavior. The sudden onset of noise may lead to a fright-and-flight response. Animals might stop their current behavior (resting, feeding, mating, nursing etc.).  Migration routes might be deflected; animals might be driven away from their preferred habitat. Noise further can affect the auditory system and induce a shift in hearing threshold, similar to the “disco-effect” in humans. Other systems potentially affected by noise include the vestibular, reproductive, and nervous systems. Noise might cause concussive effects, physical damage to tissues and organs (in particular gas-filled ones), and cavitation (bubble formation). Stress is a physiological response, aimed at surviving an immediate threat. Prolonged stress can cause serious health problems.
The effects of noise and the ranges over which they happen depend on the acoustic characteristics of the source (e.g., noise level, duration, duty cycle, rise time, spectrum), the sound propagation characteristics of the medium (hydro- and geoacoustic parameters of the environment, bathymetry), and certain characteristics of the receiving animal (species, age, size, behavioral state, auditory capabilities, prior exposure etc.).

In the same way as we would do any controlled scientific experiment: We choose a control group of animals and an experimental group of animals. The control group and the experimental group live in the same environment, in which we keep all the factors that could affect the animals constant, except for one factor: noise. The experimental group is exposed to a controlled sound source, the control group is not. We observe both groups and determine any differences that might be a result of the introduced noise.
The problem with studies done on wild animals is that the control group also experiences noise: ambient noise as well as man-made noise. There is hardly a place on Earth which is free from man-made noise. So we end up studying the relative effects of a bit of additional noise in an already noisy environment, instead of what we actually want to know: what the absolute effects of noise are compared to a historically quiet environment.

Prior to the era of industrialization, man-made sound in the ocean was absent, apart from the slapping of oars and the wake of sailing ships.  Nowadays, you hear ship engines, propellers, airguns, sonars, explosions, construction, drilling, pile driving etc. underwater. Some of these sounds no longer affect only local regions, but rather contribute to natural ambient sound on ocean-wide, even global scales. Acoustic energy at low frequencies traverses entire ocean basins. Ambient levels at low frequencies have increased by about 3 dB / decade in certain Northern Hemisphere regions since the 1960s, believed due to shipping (McDonald et al., 2006). The number of commercial vessels doubled, and their gross tonnage quadrupled during this time (McDonald et al., 2006). The combined sound from ships distributed over entire ocean basins contributes to ambient “background” noise, in which individual ships are not discernible. Similarly, offshore oil and gas exploration can contribute to ambient levels on ocean-basin scales, as seismic survey sounds have been recorded more than 5000 km from the source (Hildebrand, 2009). Man-made noise in the ocean is expected to keep increasing.

How can we measure the effects of increasing ambient noise? How much have animals already been affected by the ambient noise increase from pre-industrialization to now? Rather than adding experimental sound sources to already noisy baseline conditions, what if we could quiet the ocean temporarily? The control group in this experiment would be the same as discussed in Section B: wild animals in their normal habitat. But the experimental group would be treated not with additional noise but with silence. This idea was suggested by Jesse Ausubel in 2009 and has led to a series of workshops organized by the Scientific Committee on Oceanic Research (SCOR) and the Partnership for Observation of the Global Oceans (POGO) with financial support from the Alfred P. Sloan Foundation.

There are a lot of potential problems (economical, political, logistical, etc.) with this idea. How do we get all the contributors to ambient noise to agree to shut down? What is the cost of shutting industries down temporarily? If we conduct the experiment in a small region, how do we select this region, and how do we select the timing of this experiment? Rather than shutting industries down, could we perhaps temporarily divert shipping lanes?
A lot of scientific questions remain and need to be answered in order to design the quieting experiment.

A series of workshops has identified a number of knowledge gaps and first steps needed. We need to characterize ocean soundscapes. The marine soundscape is made up of natural ambient sounds, biological sounds and anthropogenic sounds. We need to identify the sources, characterize their sound, and identify temporal and geographic variability. We also need to improve our understanding of acoustic ecology. Acoustic ecology encompasses the relationships—mediated through sound—between organisms and their environment. Noise effects on marine animals are part of acoustic ecology.

As a first step, a website ( was developed that contains a searchable literature database of man-made underwater noise, noise effects on marine animals and sounds made by marine animals. There are links to online databases of underwater sounds and to ocean acoustic observatories. The public is encouraged to submit any missing articles or links. While the peer-reviewed literature is easy to find, a need to capture the “grey” literature was identified. The grey literature, in particular consulting reports, often undergoes a much more rigorous review than the peer-reviewed literature. Much of the valuable information remains with industry and either never gets published or gets published after a substantial delay in time. Users are encouraged to submit their own reports. The website further contains an events calendar. The series of workshops has led to an international open science meeting, to be held at the UNESCO Headquarters in Paris, 30 Aug – 1 Sep 2011 (

Erbe, C. (2011). The effects of underwater noise on marine mammals. In A. N. Popper & A. D. Hawkins (Eds.), Proceedings of the 2nd International Conferecne on the Effects of Noise on Aquatic Life, August 15-20, 2010, Cork, Ireland (pp. in press). Berlin: Springer Verlag.
Hildebrand, J. A. (2009). Anthropogenic and natural sources of ambient noise in the ocean. Marine Ecology-Progress Series, 395, 5-20.
McDonald, M. A., Hildebrand, J. A., & Wiggins, S. M. (2006). Increases in deep ocean ambient noise in the Northeast Pacific west of San Nicolas Island, California. Journal of the Acoustical Society of America, 120(2), 711-718.