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National Defense Exemption (NDE)

What is an NDE? What is the process for requesting one?

A National Defense Exemption (NDE) is a provision within Section 101(f) of the Marine Mammal Protection Act (MMPA) that allows the Secretary of Defense, after conferring with the Secretary of Commerce, Secretary of Interior, or both, as appropriate, to exempt any action or category of actions undertaken by the Department of Defense or its components from compliance with any requirement of the MMPA, if the Secretary of Defense determines that it is necessary for national defense.

How long does the NDE last?

The Secretary has invoked the exemption for up to two years, or until the National Marine Fisheries Service issues Regulations and Letters of Authorization for SURTASS LFA sonar military readiness activities, whichever is earlier.

When will a new MMPA permit be issued by NMFS?

NMFS intends to authorize a new MMPA Rule and 7-year Letter of Authorization for SURTASS LFA sonar before August 13, 2019.

Will the Navy continue to use SURTASS LFA sonar during the exemption period?

Yes. During the period of the NDE, the Navy will continue to employ SURTASS LFA sonar due to its critical importance to the security of the United States and will continue to comply with all marine mammal protection requirements of the previous permit as well as additional restrictions agreed to during the ongoing rule making process.

Will the NDE result in diminished protections for marine mammals?

No. During the period of the NDE, the Navy has committed to complying with all of the existing mitigation and monitoring requirements that are required under its previous MMPA permit. The Navy has also agreed to implement additional mitigations that were agreed to during the ongoing rulemaking process.


Why does the Navy need the SURTASS LFA sonar system?

The 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 vessel to listen for sounds in the ocean produced by submarines. The system also uses low frequency active (LFA) sonar transmissions to would bounce 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.

What is the Navy doing to protect marine life?

The Navy has made a tremendous effort to ensure that the low frequency active (LFA) system does not pose a risk to marine life. Some of the steps that have been taken to minimize or prevent risk to marine mammals, sea turtles, and marine fishes include:

  • A $10 million, three-phase Scientific Research Program (SRP) studied behavioral responses to SURTASS LFA sonar signals by baleen whales off California and Hawaii to determine if exposure to LFA sonar caused the whales to change their behavior. Baleen whales are low-frequency hearing specialists, so scientists believed they would be most affected by the proposed SURTASS LFA sonar signals. This research was independently conducted by recognized experts in the fields of marine bioacoustics, marine mammal biology, and underwater acoustics.
  • An independent Scientific Working Group was established in 1997 to recommend research priorities and to assess the research for environmental implications.
  • Quantitative 4D (3D space plus time) modeling of animal movements and acoustical exposure is conducted to estimate the potential impacts on marine mammals from exposure to SURTASS LFA sonar. Scientific research and publications are continuously monitored to ensure that the best available information is used in all analyses the Navy conducts.
  • Monitoring and mitigation procedures are implemented onboard the LFA sonar vessels any time LFA sonar is transmitting. These procedures minimize or prevent risk of harm to marine mammals and sea turtles from exposure to LFA sonar transmissions.
  • Research was conducted on the potential impact of SURTASS LFA sonar on human divers.
  • A $3 million set of controlled exposure experiments was conducted to determine the effects of SURTASS LFA sonar signals on fishes. This independent research was conducted by eminent scientists in the fields of fish biology and fish bioacoustics.
  • The Navy recognizes 39 offshore biologically important areas (OBIAs) globally in which marine mammals conduct vital activities such as calving, feeding, mating, or migrating during specified season(s); 14 OBIAs have been designated in the western and central North Pacific and eastern Indian oceans where SURTASS LFA sonar is currently used. To protect marine mammals during these important times of the year, SURTASS LFA sonar is currently limited to transmitting such that the received level of sound will not exceed 180 dB re 1 µPa (rms) within 1 kilometer (0.54 nautical miles) of any OBIA boundary.

Is the Navy proposing to waive environmental laws to deploy the SURTASS LFA sonar system?

Absolutely not. The Navy considers all environmental laws relevant to SURTASS LFA sonar through the National Environmental Policy Act (NEPA) process, which is documented in Environmental Impact Statements (EISs).

What about the deaths of whales in the Bahamas in March 2000?

SURTASS LFA sonar was not used, nor were any other low-frequency active acoustic sources, in the Bahamas in March 2000. A Joint Interim Report was published regarding the Bahamas Marine Mammal Stranding Event of 15-16 March 2000.

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?

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.

What are the potential effects that low frequency sound may have on marine mammals?

Marine mammals may change their behavior whenever they perceive any type of unusual, underwater sound. Injury could occur at very high exposure levels, but this risk is confined to a relatively small area very close to the LFA vessel. Most impacts to marine mammals are behavioral responses that do not lead to population-level effects.

What operational restrictions (mitigation measures) will be implemented to protect marine animals?

The Navy has developed and implements comprehensive measures to minimize or prevent risks to marine mammals and sea turtles. The monitoring measures are intended to detect marine mammals and sea turtles within a 2,000 yard radius around the SURTASS LFA sonar vessel. The mitigation monitoring actions effectively reduce to near-zero the chance that any marine mammal or sea turtle would be exposed to SURTASS LFA sonar at high enough sound levels to potentially cause injury. The mitigation monitoring measures include:

  • Visual monitoring – daytime observations for marine mammals or sea turtles from the SURTASS LFA sonar vessel by personnel trained in detecting and identifying these species
  • Passive acoustic monitoring – the SURTASS towed horizontal line array (the passive or “listening” part of the system) receives sounds of vocalizing marine mammals that indicate their presence
  • Active acoustic monitoring – Use of the high frequency (HF) active sonar to detect marine mammals (and possibly sea turtles) within 2,000 yards of the vessel

If marine mammals or sea turtles are detected within 2,000 yards of the LFA sonar vessel, the transmitting LFA sonar will be stopped or delayed from transmitting until the animals are no longer detected to ensure that no marine mammals or sea turtles are exposed to potentially injurious sound levels.

Additionally, geographic restrictions to transmissions 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 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 operations.

Is it true that the SRP did not study impacts from received levels from 155 to 180 dB?

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.

Why did the SRP only study four species of whales?

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 because:

  • They are considered to have the best hearing in the low frequency band of all marine mammals
  • These species have protected status under the law
  • There is prior evidence that these species react to low frequency sounds

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 began?

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.

What about theories that the new sonar system will affect migration of whales?

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?

Exposure to LFA sonar is intermittent because of the short duration of each mission and the low duty cycle of the transmissions. It is unlikely that LFA sonar would be used repeatedly 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.

What will be done to protect human divers?

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 the ocean?

When deployed and transmitting, SURTASS LFA sonar would add to the ambient noise levels of the ocean, but the benefit to national security that SURTASS LFA sonar provides far outweighs the intermittent addition of sound to the ambient noise environment.

Commercial shipping is the dominant source of man-made, low frequency noise in the sea. Seismic survey efforts also contribute more noise to the ocean than LFA sonar, as do many natural sources of low frequency sound, including lightning strikes, earthquakes, volcanic eruptions, and baleen whales. Currently, only four SURTASS LFA sonar systems are in use compared to millions of commercial ships that operate worldwide.

Is the Navy working on another system of submarine detection, other than the use of low frequency active sonar?

As analyzed in the 2001 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 has developed other passive sonar technologies, such as Advanced Deployable System (ADS) and Twin Line SURTASS, but even with these upgrades, passive sonar systems are not sufficient to meet the needed long-range detection that only LFA sonar 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 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 HERE 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.

Therefore, 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.