ACOUSTICS:
SOUND IN THE WATER
ACOUSTICS
Acoustics pertains to the properties or qualities of sound and how it is transmitted in the marine
environment.
Some sounds are from natural sources, such as storms, earthquakes, waves, and marine animals
that produce and use sound to communicate and learn about their environment. Other sounds come
from a wide variety of man-made sources, including vessels, oil and gas activity, renewable energy
development, and national defense activities.
Sound in the water has the potential to affect marine species such as invertebrates, fish, marine
mammals, and sea turtles. This Draft Programmatic EIS evaluates and discloses potential impacts of
man-made sound sources related to leasing activities for oil and gas exploration and development.
ANALYSES OF ACOUSTICS AND ENVIRONMENTAL EFFECTS
The following components of the potential impacts of sound are examined in the Draft Programmatic EIS:
• Acoustic Sources (Section 4.2.2.5): Acoustic sources are natural phenomena or man-made equipment/
objects that produce sound. They are described by the sound characteristics they produce, and they are
generally considered to be impulsive (e.g. lightning strikes, explosions, airguns, impact pile drivers) or
non-impulsive (e.g. sonars, engines).
• Acoustic Sound Propagation (4.2.2.6): “Propagation” refers to how sound is transmitted through the
water from the source;
• Marine Animal Characteristics (4.2.2.9): These are the things about the animals in the water that may
be affected by sound. This includes the local abundance and distribution of the animals and their habitats, as well as their hearing capabilities, movement patterns, and the activities they are involved in;
• Acoustic Thresholds (4.2.2.10): These are numeric values, established by NOAA Fisheries, that identify the received acoustic level above which an animal is presumed to have been impacted by sound; and
• Risk Analysis Approaches: These techniques are used to assess what the modeled and predicted
acoustic exposures mean to marine life and the environment and any analyses used to assess which
alternative should be pursued.
More information on acoustic terminology, basic concepts, and characterization can be found in the Section
4.2.2 of the Draft Programmatic EIS.
SUMMARY OF FINDINGS:
Evaluating the potential impacts of underwater noise on the environment can be extremely complex, difficult,
expensive, and time consuming. The Draft Programmatic EIS is national in scope and looks at the potential
for impacts from a very high level. It discloses the complete range of possible impacts. Impacts may range
from negligible to significant in nature, depending on the location, time of the year, animal species, and
activity discussed. Before an actual lease sale occurs, BOEM does additional analyses to evaluate impacts
with much more specificity than is possible at the programmatic level (e.g., NEPA analysis for individual
lease sales or environmental review of post-lease plans).
POTENTIAL BIOLOGICAL IMPACTS (SECTION 4.2.2.11)
Many species of marine animals produce and use sound to
communicate as well as to orient, locate, and capture prey
and to detect and avoid predators. When man-made noise
occurs within animal hearing ranges and is at a high enough
intensity or duration, research has shown that exposures
can, in some instances, lead to adverse effects, including:
• Mortality (death);
• Injury such as permanent or temporary hearing loss and
physiological stress responses;
• Masking of important sound signals;
• Behavioral responses such as fright, avoidance, and
changes in physical or vocal behavior; and
• Indirectly altering prey availability
It is generally believed that the greatest potential for impact
of sound on marine life is through behavioral changes and
auditory masking, rather than direct physical injury or death.
Of the sound sources that may be used under the Proposed
Action, seismic surveys, decommissioning using explosives,
drilling and associated vessels are believed to have the
greater potential for effects.
Relationship Among Sound Levels and Potential Effects on Animals
Responses of animals to acoustic stimuli vary widely depending on the species, the individual, hearing
ability, context of animal and source activities (e.g., how close is the animal to the source, how is the source
operating, and how is the animal behaving when it receives the acoustic signal), properties of the stimuli,
and prior exposure of the animals. Large baleen whales, such as the blue whale, may be more susceptible
to low-frequency sounds associated with Alternative A (the Proposed Action). Less is known about sea turtle
and fish hearing or impacts to individual fish and catch rates. Very little is known about whether and how
invertebrate species may hear and if other aspects of sound, such as particle motion, may be of concern to
these species.
Sound has the potential to impact marine life depending on a variety of factors. It can range from not being
an issue at all to causing potentially significant impacts. For example, sounds can interrupt important
biological behaviors (courtship, nursing, feeding, and migration) and mask communication between animals
(prevent them from hearing one another, for example). In more extreme instances, exposures to high levels
or extended periods of sound can lead to physiological effects, including hearing loss and death. Research
shows that the same level of sound may have different levels of impact on marine life depending where
in the ocean the sound occurs. Further, individuals of the same species can react to sound differently in
different situations. Given scientific uncertainty surrounding potential effects from sound sources under the
Proposed Action, and whether they may rise to the level of biological significance, it is assumed that impacts
can range from negligible to significant in nature.
SUMMARY OF FINDINGS: MITIGATIONS / ALTERNATIVES
Alternative B, the Reduced Proposed Action, includes some considerations that may reduce acoustic
impacts. For example, the exclusion of an entire Program Area would mean that the animals in that area
would not experience any impacts from noise related to activities stemming from the 2017-2022 Oil and
Gas Leasing Program. Similarly, exclusion of Environmentally Important Areas within a given Program Area
may result in less exposure to some species. Regardless of the alternative, all BOEM activities that may
result in impacts to marine mammals from sound require the use of Protected Species Observers and other
mitigations such as ramping up the intensity of seismic survey airguns.
For more information, please visit www.BOEMOceanInfo.com.