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. OBIAs are part of a comprehensive suite of mitigation measures used to minimize impacts and adverse effects to marine mammals. These areas include migration corridors, breeding and calving grounds, and feeding grounds.
The process of identifying potential marine mammal OBIAs involved an assessment by both NMFS and the Navy to identify the areas that met the biological, geographical, and hearing criteria for an OBIA. For those marine areas that were determined to meet these criteria, a practicability assessment was conducted by the Navy.
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. These OBIAs, as part of the overall mitigation measures, will reduce incidental takings by SURTASS LFA sonar and are not intended to apply to other Navy activities and sonar operations.
|Marine mammal OBIAs for SURTASS LFA sonar and their period of effectiveness.|
|OBIA Name||Period of Effectiveness|
|Roseway Basin Right Whale Conservation Area||June through December, annually|
|Great South Channel, U.S. Gulf of Maine, and Stellwagen Bank National Marine Sanctuary||January 1 to November 14, annually; year-round for Stellwagen Bank NMS|
|Southeastern U.S. Right Whale Critical Habitat||November 15 to April 15, annually|
|Gulf of Alaska||March through September, annually|
|Navidad Bank||December through April, annually|
|Coastal Western Africa (Cameroon to Angola)||June through October, annually|
|Patagonian Shelf Break||Year-round|
|Argentina Southern Right Whale||May through December, annually|
|Central California||June through November, annually|
|Antarctic Convergence Zone||October through March, annually|
|Offshore Piltun and Chayvo||June through November, annually|
|Eastern Madagascar Coastal Waters||July through September, annually for humpback whale breeding; November through December for migrating blue whales|
|Southern Madagascar (Madagascar Plateau, Madagascar Ridge, and Walters Shoal)||November through December, annually|
|Ligurian-Corsican-Provençal Basin and Western Pelagos Sanctuary||July to August, annually|
|Penguin Bank, Hawaiian Islands Humpback Whale National Marine Sanctuary||November through April, annually|
|Costa Rica Dome||Year-round|
|Great Barrier Reef||May through September, annually|
|Bonney Upwelling||December through May, annually|
|Northern Bay of Bengal and Head of Swatch-of-No- Ground (SoNG)||Year-round|
|Olympic Coast National Marine Sanctuary, Barkley and Nitinat Canyons, and The Prairie||Olympic National Marine Sanctuary: December, January, March, April, and May, annually;
The Prairie, Barkley and Nitinat Canyons: June through September, annually
|Abrolhos Bank||August through November, annually|
|Grand Manan North Atlantic Right Whale Critical Habitat||June through December, annually|
|Eastern Gulf of Mexico||Year-round|
|Southern Coastal Chile||February to April, annually|
|Offshore Sri Lanka||December through April, annually|
|Camden Sound/Kimberly Region||June through September, annually|
|Perth Canyon||January through May, annually|
|Southwest Australia Canyons||Year-round|
Additional Geographic Mitigation Measures
- SURTASS LFA sonar-generated sound field will be below 180 dB within 22 km (12 nm) of any coastlines, and in offshore areas outside this zone that have been determined by NMFS and the Navy to be biologically important
- When in the vicinity of known recreational or commercial dive sites, SURTASS LFA sonar will be operated such that the sound fields at those sites will not exceed 145 dB
- SURTASS LFA sonar operators will estimate sound pressure levels (SPL) prior to and during operations to provide the information necessary to modify operations, including the delay or suspension of transmissions, in order not to exceed the 180-dB and 145-dB sound field criteria cited above.
The system will use three monitoring techniques:
- 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 will include daytime observations from the SURTASS LFA sonar vessel for potentially affected species.
- Formal record logging
- Delay/suspend transmission if marine mammal sighted within LFA mitigation zone
- Restricted to daylight
- Formal training by marine biologist
Passive Acoustic Monitoring
Passive acoustic monitoring for low frequency sounds generated by marine mammals will be conducted when SURTASS is deployed.
High Frequency Active Acoustic Monitoring
The Navy will conduct high frequency (HF) active acoustic monitoring (through the use of an enhanced HF commercial-type sonar) to detect, locate, and track marine mammals (and possibly sea turtles) that pass close enough to the SURTASS LFA sonar transmit array to exceed the 180-dB mitigation criterion. This HF Marine Mammal Monitoring (HF/M3) sonar operates with a similar power level, signal type and frequency as HF “fish finder” type sonars used worldwide by both commercial and recreational fishermen.
HF/M3 Sonar, LFA Mitigation Zone, and Sound Propagation
The extent of the LFA mitigation zone (i.e., within the 180-dB sound field) is based on onboard acoustic modeling and environmental data collected in situ. Factored into this calculation are SURTASS LFA sonar source physical parameters of tow speed, depth, vertical steering, signal waveform/wavetrain selection, and peak transmit source level (SL).
The HF/M3 sonar is located near the top of the SURTASS LFA sonar vertical line array. The HF/M3 sonar computer terminal for data acquisition/processing/display is located in the SURTASS Operations Center (SOC). 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)
The HF/M3 sonar will operate 30 minutes prior to commencement of LFA transmissions and continuously while the SURTASS LFA sonar is deployed. Detection of a marine animal by the HF/M3 sonar automatically triggers an alert to the SURTASS Operations Center Watch Supervisor, who has the HF/M3 tracking team immediately evaluate the detection.
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) beyond the LFA mitigation zone, out to approximately 2 km (1.08 nm).
There are two potential visual monitoring scenarios.
First, if a potentially affected marine mammal or sea turtle is sighted outside of the LFA mitigation zone (approximately a 1 kilometer radius around the transmit array), the observer will notify the Officer-in-Charge (OIC). The OIC will then notify the HF/M3 sonar operator to determine the range and projected track of the animal. If it is determined that the animal will pass within the LFA mitigation zone, the OIC will order the delay or suspension of SURTASS LFA sonar transmissions when the animal enters the LFA mitigation zone. If the animal is visually observed within 2 km (1.08 nm), the OIC will order the delay or suspension of SURTASS LFA sonar transmissions. The observer will continue visual monitoring/recording until the animal is no longer seen.
Second, if the potentially affected animal is sighted within the LFA mitigation zone, the observer will notify the OIC who will order the immediate delay or suspension of SURTASS LFA sonar transmissions.
Passive Acoustic Monitoring
Passive acoustic monitoring will be conducted when SURTASS is deployed, using the SURTASS towed array to listen for vocalizing marine mammals as an indicator of their presence. If the sound is estimated to be from a marine mammal that may be potentially affected by SURTASS LFA sonar, the technician will notify the OIC who will alert the HF/M3 sonar operator and visual observers. If prior to or during transmissions, the OIC will then order the delay or suspension of the SURTASS LFA sonar transmissions when the animal enters the LFA mitigation zone.
Active Acoustic Monitoring
There are two potential scenarios for mitigation via active acoustic monitoring.
First, if a contact is detected outside of the LFA mitigation zone, the HF/M3 sonar operator will determine the range and projected track of the animal. If it is determined that the animal will pass within the LFA mitigation zone, the sonar operator will notify the OIC. The OIC will then order the delay or suspension of transmissions when the animal is predicted to enter the LFA mitigation zone.
Second, if a contact is detected by the HF/M3 sonar within the LFA mitigation zone, the observer will notify the OIC who will order the immediate delay or suspension of transmissions.
Resumption of Transmissions
SURTASS LFA sonar transmissions can commence/resume 15 minutes after there is no further detection by the HF/M3 sonar and there is no further visual observation of the animal within the LFA mitigation zone.