Why is the Navy considering a new sonar system?
A: The new Surveillance Towed Array Sensor System
(SURTASS) Low Frequency Active (LFA) system is essential to
the Navy’s anti-submarine warfare efforts. The passive part
of the system (SURTASS) uses a string of underwater hydrophones
that are towed behind a ship to listen for sounds in the ocean
produced by submarines. The system also uses active low frequency
(LFA) transmissions to listen for reflections of sounds off
submarines that are too quiet to hear with a passive system
alone. By using specialized signals and echo detection, the
system increases the distance at which submarines can be detected
and tracked. Only low frequency active sonar can provide this
kind of long-range submarine detection.
Q-2: What is the Navy doing to protect marine life?
A: The Navy has made a tremendous effort to ensure
that the low frequency active (LFA) system does not pose a
risk to marine life. Here are some of the steps that have
been taken to mitigate biological risk and keep the potential
for harmful effects at a negligible level:
system is being developed in compliance with the National
Policy Act and Presidential Executive Order 12114.
independent Scientific Working Group was established
in 1997 to recommend research priorities and to assess
the research for environmental implications.
- A $10 million,
three-phase Scientific Research Program (SRP) studied
behavioral responses to low frequency sound (LFS) by baleen
whales off California and Hawaii. The principal investigators
had two decades of experience with this kind of research,
and had published authoritative studies documenting whale
responses to noise.
modeling of animal movements and acoustical exposure was
conducted to estimate the environmental impact of deployment
of the low frequency active system.
studies and research were conducted to ensure that the
system would not harm humans who were diving in the ocean.
- An independent
scientific team reviewed and edited the Environmental
and mitigation programs have been put in place to minimize
the risk of harm to any marine mammal from the proposed
low frequency active system.
How did the Navy decide that the deployment of SURTASS LFA
sonar will not significantly affect the marine environment?
A: This question addresses two issues. What facts
and logical deductions were used to reach this conclusion
(see Question 11), and what was the public process that led
to the decision.
Under the National Environmental Policy Act (NEPA) the Navy
is required to prepare an environmental impact statement (EIS)
for actions that may significantly affect the quality of the
human and natural environment.
The EIS must provide full disclosure of significant environmental
impacts and inform decision-makers and the public of reasonable
alternatives, including the No Action Alternative. The EIS
must identify all potential direct and indirect effects that
are known, and make a good faith effort to explain the effects
that are not known but are “reasonably foreseeable.” This
includes the Navy’s responsibility to make informed judgments,
and to estimate the potential for future impacts on that basis,
especially if trends are ascertainable. However, the Navy
is not required to engage in speculation or contemplation
about future plans that could influence the EIS’s analysis
of potential direct and indirect effects.
The Navy’s Draft and Final Environmental Impact Statements
(EIS) for Surveillance Towed Array Sensor System Low Frequency
Active (SURTASS LFA) Sonar were filed with the US Environmental
Protection Agency and made available to the public in July
1999 and January 2001, respectively.
23 July 2002, the Navy published the notice of Record of Decision
(ROD) for Surveillance Towed Array Sensor System Low Frequency
Active (SURTASS LFA) Sonar in the Federal Register (Vol. 67,
No. 141) (Click
Here to link to the ROD in the Federal Register). The
ROD is a concise public record in which the Navy states what
the decision is, identifies the alternatives considered, specifies
the most environmentally preferable alternative, and states
whether all practical means were adopted to avoid or minimize
environmental harm. Based upon review of the comparative analysis
of the potential for environmental and socioeconomic effects
from the three alternatives presented in the Final OEIS/EIS
and public comments received during the NEPA process, the
Deputy Assistant Secretary of the Navy (Environment) decided
to implement Alternative 1 of the Final OEIS/EIS, which requires
certain geographical restrictions and monitoring mitigation
designed to reduce potential adverse effects on the marine
environment. This decision completed the NEPA process.
Has the Navy responded to concerns of citizens that SURTASS
LFA sonar may be harmful to marine life?
A: The Navy organized nine public outreach meetings
and ensured that experts on Navy operations, marine mammals,
and diver safety were present to answer questions. The Navy
also participated in three public hearings on the National
Marine Fisheries Service (NMFS) Proposed Rule and participated
in three public scoping meetings and three public hearings
on the EIS.
Every public comment was scrutinized by a group of scientists
to determine if it raised an issue that had not been considered
in the development of the EIS. One citizen’s comment precipitated
the development of the High Frequency Marine Mammal Monitoring
(HF/M3) sonar to detect marine mammals before they got close
enough to the LFA array to risk injury. Concerns raised by
scuba divers were addressed by an extensive study of human
reactions to the LFA signal.
Q-5: Is the Navy proposing to waive environmental laws
in order to deploy this new sonar system?
A: On the contrary, under the National Environmental
Policy Act (NEPA) the Navy undertook a five-year Environmental
Impact Statement (EIS) process (the first for a sea-based
operational system). It included an at-sea Scientific Research
Program (SRP) to fill data gaps on how low frequency sound
(LFS) affected free-ranging marine mammals. Some of the country's
top marine mammalogists and bioacousticians planned and executed
this $10 million, three-phase SRP off California and Hawaii.
The Navy will operate the SURTASS LFA system under a permit
issued by the National Marine Fisheries Service (NMFS), and
will regularly consult with NMFS to review the data collected
as part of the mitigation protocol and Long Term Monitoring
Q-6: What about the deaths of whales in the Bahamas in
A: The SURTASS LFA sonar has not been used since April
1998, and no other low frequency sources were in use in the
Bahamas in March 2000. An extensive review of the Smithsonian
marine mammal stranding database has shown that no stranding
can be associated with any of the early development or training
exercises in which LFA was used.
NOAA Fisheries and the Navy are continuing to investigate
the cause of this stranding. This response will be updated
as soon as those investigations are completed.
to read the Joint Interim Report - Bahamas Marine Mammal Stranding
Event of 15-16 March 2000.
What about reports that this system will affect 80 percent
of the world’s ocean area?
A: The total ocean area that would be available for
LFA training operations includes about 75 percent of the world's
oceans. But this does not mean that 75 percent of the world's
ocean area will be affected. The current plan is for two vessels
to have this sonar system, one in the Atlantic, the other
in the Pacific. Each vessel would be underway at sea for up
to 270 days per year, each moving at only 3 knots, transmitting
less than 20 percent of the time.
The EIS covers up to four systems, but even if all four were
operational, rarely would more than two be at sea at once.
If the Navy were to deploy more than four systems, another
EIS process would be required.
Q-8: Are there still “secret” aspects to the proposed system?
A: Almost all technical aspects of the SURTASS LFA
sonar system have been declassified. The Navy is striving
to comply with all environmental laws and make the EIS process
as open as possible within the bounds of national security.
Q-9: Is it true that the proposed system will generate
sound in the range of 235 dB, which could cause hearing loss,
serious injury, or even death to whales and other marine mammals?
A: The LFA system has 18 projectors, or sound sources,
each capable of transmitting sound at a level of approximately
215 dB between 100 and 500 Hz. Because it is an array, if
one looks at LFA from a distance, it will appear to have an
“effective source level” on the order of 230 to 240 dB. However,
in the actual water column, no portion of the ocean will experience
sound levels greater than 215 dB.
Q-10: What are the potential effects that low frequency
sound may have on marine mammals?
A: Marine mammals may change their behavior whenever
they perceive any type of underwater low frequency sound and
injury can occur at very high levels. Some changes in behavior
may be too short or subtle for our best observations to detect.
Other changes can be detected, but they may have no significant
impact on the behavior of the animals. For the purposes of
the EIS, behavioral risk was assessed in terms of its likely
impact on survival or reproduction. The potential for injury
exists at very high received levels. This risk is confined
to a relatively small area very close to the LFA vessel.
What has been done to evaluate the potential effects that
the proposed sonar system will have on marine mammals?
A: To determine the potential effects of the system,
the Navy funded several projects:
operational restrictions (mitigation measures) will be implemented
to protect marine animals?
- A thorough
review of the scientific literature to summarize present
knowledge and identify gaps in the data
screening of marine animal species for potential sensitivity
to low frequency sound
research into the effects of low frequency sound on the
species of marine mammals believed to be most at risk
of a model that relates acoustic exposure to risk of biologically
acoustic modeling of acoustic propagation and animal movements
in relation to plausible deployments of SURTASS LFA sonar
of marine mammal stocks potentially affected
of mitigation to minimize impact and monitoring to measure
the potential effects of operations.
A: The Navy has developed complex and costly measures
to minimize risks to marine mammals. These measures are intended
to detect animals within a range of approximately two kilometers
of the source vessel. These reduce the chances that any animal
would experience received levels greater than 180 dB to close
to zero. The mitigation measures include:
monitoring - daytime observations for marine mammals and
other protected species, such as sea turtles, from the
vessel by personnel trained in detecting and identifying
acoustic monitoring - the SURTASS towed horizontal line
array (the passive or “listening” part of the system)
will be used whenever the low frequency active system
is transmitting to detect vocalizing marine mammals
- Use of
a high frequency (HF) active sonar - operating like a
“fish finder.” This high frequency sonar will help detect
marine mammals that approach the system prior to and during
geographic restrictions to operations apply to areas within
22 kilometers (12 nautical miles) of any coastline, designated
offshore biologically important areas, and known recreational
and commercial dive sites.
Is it true that the Scientific Research Program (SRP) was
not a representative scientific study of the impact on marine
mammals because the sound levels of testing were below those
of actual planned system use?
A: A guiding principle for the SRP was that no experimental
animal would be exposed to sounds in excess of 155 dB. This
was agreed upon after consultation with the National Marine
Fisheries Service, which issued the permits for the experiments.
In practice, it proved difficult to realize a received level
of 155 dB for the experimental animals, even when the full
source power of the LFA system was used (as it was during
portions of Phase I). Subsequent modeling has proven that
the overwhelming majority of animals would never be exposed
to LFA received levels in excess of 155 dB even during full-power
Q-14: Is it true that the SRP did not study impacts from
received levels from 155 to 180 dB?
A: None of the experiments with free-ranging animals
during the SRP generated exposure levels in excess of 155
dB. In order to account for this data gap, the Navy has
assumed that risk increases quite rapidly at exposed levels
above 155 dB, reaching a value near 100% at 180 dB.
Q-15: Why did the SRP only study four species of whales?
A: It is impossible to conduct studies on all marine
animal species. Four mysticete species of whales (blue,
fin, gray, and humpback whales) were selected for study
are considered to have the best hearing in the low frequency
band of all marine mammals
These species have protected status under the law
is prior evidence that these species react to low frequency
The SRP was
designed such that responses of these representative species
to low frequency sound signals would serve as indicators
for responses of other potentially low frequency-sensitive
species, which should be less vulnerable to low frequency
active system signals.
During SRP Phases I and III, all other marine mammal species
in the study area were observed from the LFA vessel. During
Phase I, aerial surveys were also used to monitor all marine
mammal species. Protocols were in place to suspend the experiments
if any dramatic responses were detected. These data have
been analyzed to look for changes in the numbers and distribution
of these species during the course of the experiments.
Is it true that during Phase III of the SRP conducted off
Hawaii, whale-watch boat captains reported humpback whales
disappearing from the testing area as soon as the broadcast
A: Some whale watch captains did assert that they observed
a premature decrease in the number of humpback whales. This
assertion was tested by comparing the quantitative measures
of abundance from the SRP shore station with identical measures
made during previous years of study. The pattern of abundance
observed during LFA Phase III was completely consistent with
the historical record. The decline in humpback numbers reflected
the normal seasonal pattern of migration.
Q-17: What about theories that the new sonar system will
affect migration of whales?
A: SRP Phase II and prior studies of migrating gray
whales indicate that whales avoid a low frequency sound source
that is in their path, and resume migrating on their historical
route within a few kilometers.
During SRP Phase II, a significant new result was that this
deviation only occurred when the source was located in the
middle of their migration route (source at 2 km from shore).
Gray whales in the same migration corridor did not appear
to react to the LFA source transmission when it was outside
the corridor (4 km from shore), even though the source level
was adjusted so that the migrating whales’ received sound
levels were the same.
Whales tend to swim closer to the surface during migration
than during other activities. This diminishes their exposure
to LFA, because low frequency sounds are attenuated near the
ocean surface. These facts suggest that whales migrating in
the open ocean would not be adversely affected by LFA operations.
LFA will never be operated within 22 km of the coast and,
therefore, not in the path of whales that migrate near shore.
Are there potential long-term impacts from the Navy’s SURTASS
LFA sonar system that could affect the behavior and viability
of entire populations of marine mammals and push endangered
species into extinction?
A: Exposure to LFA is intermittent because of the short
duration of each mission and the low duty cycle of the transmissions.
It is unlikely that many LFA missions would be scheduled in
exactly the same place. Therefore, the potential for cumulative
impact seems modest.
The SRP analyses looked for cumulative effects during the
three phases of experiments, which were approximately the
same duration as a normal LFA operation. No evidence of cumulative
effects was found. Nonetheless, the Navy and NMFS have agreed
on monitoring protocols and have planned long-term research
to investigate this issue further.
Q-19: What will be done to protect human divers?
A: The Navy has conducted a comprehensive, scientifically-based
research program on the potential effects of low frequency
sound on human divers. Medical doctors and clinical researchers
have carried out extensive computer modeling and testing of
human and animal subjects. (All testing was done within the
guidelines for the protection of human subjects and standard
ethical procedures for animal experiments).
Based on the data obtained from these studies, the Navy Bureau
of Medicine and Surgery (BUMED) incorporated a safety margin
and established a conservative limit of 145 dB for low frequency
received sound level for recreational and commercial divers.
The mitigation measures proposed in the EIS will ensure that
no recreational or commercial diver, or known dive site, will
be exposed to levels of sound above 145 dB.
Will the Navy’s new sonar system create additional noise in
A: When deployed and transmitting, SURTASS LFA sonar
will add to the ambient noise levels of the ocean, but the
benefit to national security that SURTASS LFA sonar provides
far outweighs the infinitesimal and intermittent addition
of oceanic sound from the system’s operation.
Currently, commercial shipping is the dominant source of man-made,
low frequency noise in the sea. If two LFA systems were fully
deployed, maximum transmission time would be 864 hours, or
36 ship-days per year, compared with 22 million ship-days
per year for commercial shipping.
Seismic survey efforts also contribute more noise to the ocean
than LFA, as do many natural sources of low frequency sound,
including lightning strikes, earthquakes, volcanic eruptions,
and baleen whales.
Q-21: Won’t whales be at risk from this new form of low
A: It is unlikely that the LFA sounds will ever be
the loudest low frequency sounds any whale will experience
in its lifetime. Each year the earth’s oceans experience numerous
lightning strikes at levels up to 260 dB. There are billions
of lightning strikes hitting the ocean per year. Seafloor
volcanic eruptions have source levels of 255 dB. Many baleen
whales can create sounds at levels above 180 dB. These low
frequency sounds have been present during the entire evolutionary
history of marine mammals, and their physiological and behavioral
systems have adapted to function in this environment.
The Scientific Research Program (SRP) investigated the possibility
that there could be something in the structure of the LFA
signal that posed a special risk for behavioral disruption
in marine mammals. Although some responses were measured,
none of the responses indicated a potential for the disruption
of biologically important activities.
Is the Navy working on another system of submarine detection,
other than the use of low frequency active sonar?
A: As analyzed in the EIS, the only technology (acoustic
or non-acoustic) capable of providing reliable, long-range
detection of today’s quieter, harder-to-find submarines is
low frequency active sonar. The Navy is developing new passive
sonar technology, such as Advanced Deployable System (ADS)
and Twin Line SURTASS; but even with these upgrades, passive
sonar systems will not be sufficient to meet the needed long-range
detection requirements that only LFA can provide.
When the Navy is attempting to locate submarines, the priority
is to detect the target passively at distances far enough
away so that the submarine is outside of its effective weapons
range. When a ship uses active sonar, the active “ping” gives
away the ship's position, which can be lethal if an enemy
submarine is lurking within its weapon's range when it hears
the ping. So, the Navy will only use active sonar when passive
alone will not meet its ASW needs. This can occur when the
acoustic “signature” of the target cannot be heard over the
din of the surrounding noise in the ocean. In this circumstance,
the use of active sonar is the only viable alternative.
Can air space resonance produced by SURTASS LFA sonar cause
tissue damage and inflict injury on marine mammals?
The concept that resonance will increase stress on tissue
to the point of damage is in reality two separate concepts:
resonance and tissue damage. Cudahy and Ellison (2002) (Click
to read the paper) state that resonance does not equal damage
and damage is not always linked to resonance. So the issue
is not resonance in air/gas cavities, but tissue damage,
whether it is caused by resonance or by other means. The
potential for in vivo tissue damage to marine mammals from
exposure to underwater LF sound will not occur at a level
less than 180 to 190 dB (Cudahy and Ellison, 2002).
This includes: (1) Transluminal (hydraulic) damage to tissues
at intensities on the order of 190 dB or greater; (2) Vascular
damage thresholds from cavitation at intensities in the
240-dB regime; (3) Tissue shear damage at intensities on
the order of 190 dB or greater; and (4) Tissue damage in
air-filled spaces at intensities above 180 dB.
unless an animal is within the 180-dB SURTASS LFA sonar
mitigation zone, there should be no physical damage to body
systems or tissues, either with or without resonance. Because
of the mitigation measures, the probability that a marine
mammal will be detected in the 180-dB LFA mitigation zone
is close to 100 percent. Consequently, the potential impact
to any marine mammal stock from injury is considered negligible.