Preventive Measures

In order to minimize the impact of the SURTASS LFA system on marine mammals and other wildlife, the Navy has undertaken a variety of measures to restrict how and where the system will be operated. These include careful monitoring, both visual and acoustic, of marine wildlife during the operation of the system and strict geographic limitations on the areas where the system will be used.

Offshore Biologically Important Areas (OBIAs)

To meet the least practicable adverse impacts to marine mammals under the MMPA, NMFS and the Navy developed a systematic process for designating marine mammal “offshore biologically important areas” (OBIA) for SURTASS LFA sonar. These areas include migration corridors, breeding and calving grounds, and feeding grounds. OBIAs are part of a comprehensive suite of mitigation measures used to minimize impacts and adverse effects of SURTASS LFA sonar to marine mammals and are not intended to apply to other Navy activities or sonar operations.

The process of identifying potential marine mammal OBIAs involves an assessment by both NMFS and the Navy to identify marine areas that meet the biological, geographical, and hearing criteria for designation as an OBIA. For those marine areas that are determined to meet these criteria, a practicability assessment is then conducted by the Navy to determine if implementing the OBIAs would have any effect on SURTASS LFA sonar training and testing activities or personnel safety and would be practicable to implement.

Prior to 2017, 22 marine mammal OBIAs had been designated by NMFS and Navy for SURTASS LFA sonar. In 2017, Navy and NMFS concluded that there was an adequate basis to expand the areal extent of 6 of the existing OBIAs and to create 6 new OBIAs. During the development of regulations for SURTASS LFA sonar, the Navy and NMFS agreed to the designation of a 7th new OBIA, bringing the total number of OBIAs to 29 worldwide.

Four of these OBIAs are located in the Navy’s current study area of the western and central North Pacific Ocean and eastern Indian Ocean. As part of the analysis for the 2019 SEIS/SOEIS and MMPA Rule, the Navy and NMFS expanded these four OBIAs and added an additional 10 OBIAs to the study area.

Additional Geographic Mitigation Measures

• SURTASS LFA sonar-generated sound field will be transmitted such that received levels are equal to or below 180 dB re 1 µPa (rms) (SPL) within 12 nautical miles (22 kilometers) of any emergent land and within 0.54 nmi (1 km) of any OBIA boundary during biologically important seasons
• No more than 25 percent of the authorized amount of SURTASS LFA sonar would be used for training and testing activities within 10 nmi (18.5 km) of any single OBIA during any year unless the following condition is met: should national security present a requirement to conduct more than 25 percent of the authorized hours of SURTASS LFA sonar within 10 nmi (18.5 km) of any single OBIA during any year, naval units would obtain permission from the appropriate designated Command authority prior to commencement of the activity. The Navy would provide NMFS with notification as soon as is practicable and include the information (e.g., sonar hours) in its annual activity reports submitted to NMFS
• When in the vicinity of known recreational or commercial dive sites, SURTASS LFA sonar will be transmitted such that the received sound levels would not exceed 145 dB re 1 µPa (rms) (SPL) unless the following conditions are met: should national security present a requirement to transmit SURTASS LFA sonar during training or testing activities such that exposure at known recreational or commercial dive sites may exceed RLs =145 dB re 1 µPa (rms) (SPL), naval units would obtain permission from the appropriate designated Command authority prior to commencement of the activity. Prior to conducting training or testing activities, the designated Command authority shall conduct a risk assessment, taking into account the potential for exposure to SURTASS LFA sonar by divers
• SURTASS LFA sonar would not be used in the waters over Penguin Bank, Hawaii, to a water depth of 600 feet (183 meters) and would be operated such that the sound fields would not exceed RLs of 145 dB re 1 µPa (rms) (SPL) in Hawaii State waters

Monitoring Techniques

Three monitoring techniques will be implemented during SURTASS LFA sonar training and testing activities:

• Visual monitoring for marine mammals and sea turtles from the SURTASS LFA sonar vessel during daylight hours
• Passive (low frequency) SURTASS array to listen for sounds generated by marine mammals as an indicator of their presence
• High frequency (HF) active sonar to detect/locate/track potentially affected marine mammals (and possibly sea turtles) near the SURTASS LFA sonar vessel and the sound field produced by the SURTASS LFA sonar source array

Visual Monitoring

Visual monitoring will include daytime observations from the bridge of the SURTASS LFA sonar vessel for presence of marine mammals and sea turtles whenever LFA sonar is transmitting. The visual observers detect and identify marine mammals and sea turtles using standard binoculars (7x) and the naked eye.

• Delay/suspend transmission if marine mammal or sea turtle sighted within LFA mitigation zone
• Restricted to daylight
• Formal record logging
• Trained by marine biologist. Example of the Navy’s Marine Species Awareness Training (MSAT) is available on YouTube

Passive Acoustic Monitoring

Passive acoustic monitoring using the SURTASS towed array would be conducted when LFA sonar is transmitting. Passive monitoring listens for vocalizing marine mammals as an indicator of their presence. If a detected sound were estimated to be from a vocalizing marine mammal, the sonar technician would notify the senior military member-in-charge, who would alert the HF/M3 sonar operator and visual observers (during daylight). Delay or suspension of SURTASS LFA sonar transmissions would be ordered when the HF/M3 sonar and/or visual observers verify the presence of a marine mammal to be within the LFA mitigation zone.

Active Acoustic Monitoring

Active acoustic monitoring uses the high frequency marine mammal monitoring (HF/M3) sonar system to detect, locate, and track marine mammals that enter the LFA mitigation zone whenever LFA sonar is transmitting. Prior to full-power operations of the HF/M3 sonar, the power level would be ramped up over a period of 5 minutes from the source level of 180 dB re 1 µPa @ 1 m (rms) (SPL) in 10 dB increments until full power is attained. If a marine mammal or sea turtle were detected within the LFA mitigation zone by HF/M3 monitoring, the immediate delay or suspension of LFA sonar transmissions would occur.

The general characteristics of the HF/M3 sonar are:

• Frequency: 30 to 40 kHz
• Bandwidth: variable (1.5 to 6 kHz nominal)
• Duty Cycle: 3-4 percent (nominal)
• Nominal Source Level: 220 dB re 1 microPascal at 1 m
• Pulse Length: variable (10-40 msec nominal)
• Pulse Repetition Rate: set by maximum search range (3-4 sec nominal)
• Source Ramp-Up: five-minute period
• Detection Volume: 4 equally spaced swept 8º (horizontal) x 10º (vertical) beams making up a 10º (vertical) sector sweep through full 360º (horizontal) around the source (i.e., omnidirectional in the horizontal, 10º vertical beamwidth); nominal time for full 360º sweep 45 to 60 seconds
• Maximum Detection Range: nominally 2 km (1.08 nm)
• Operational Depth Capability: compatible with maximum deployed depth of SURTASS LFA sonar source array
• Vertical Steering: ±10o
• Receiver Gain: 23 dB (nominal vs. omnidirectional noise)

Analysis and testing of the HF/M3 sonar operating capabilities indicates that this system substantially increases the probability of detecting marine mammals within the LFA mitigation zone, and provides an excellent monitoring capability (particularly for medium-large marine mammals) out to approximately 2 km (1.08 nm).