To minimize the impact of the SURTASS LFA sonar system on marine mammals and other marine wildlife, the Navy has undertaken a variety of preventive measures that govern how and where the sonar system will be operated during training and testing activities. These include monitoring, both visually and acoustically, of marine wildlife as well as operational and geographic mitigation measures that are implemented when LFA sonar is used during training and testing activities.
Offshore Biologically Important Areas (OBIAs)
Recognizing that certain marine areas of biological importance to marine mammals lie outside the coastal standoff range for SURTASS LFA sonar (i.e., 12 nautical miles / 22 kilometers from any emergent land), NMFS and the Navy developed a systematic process for designating marine mammal “offshore biologically important areas” (OBIAs) as a geographic mitigation measure to minimize impacts and adverse effects to marine mammals associated with use of SURTASS LFA sonar during training and testing activities. OBIAs include migration corridors, breeding and calving grounds, and feeding grounds. OBIAs only pertain to marine mammals since the potential for impacts to other protected marine species (such as sea turtles or marine fishes) from exposure to SURTASS LFA sonar transmissions would be low to moderate, necessitating no additional preventive measures for these taxa beyond those already established for use of SURTASS LFA sonar. Associated with each OBIA is an effective period during which the marine mammal(s) for which the OBIA was designated carry out biologically significant activities in that marine area. During this effective period for each OBIA, the sound field generated by SURTASS LFA sonar cannot exceed received levels of 180 dB re 1 µPa (rms) at a distance of 0.54-nautical mile / 1-kilometer from an OBIA boundary.
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 and geographical criteria for designation as an OBIA. For the marine areas that meet these criteria, a practicability assessment is then conducted by the Navy to determine how practical it is to implement the OBIA and if doing so would impact the effectiveness of SURTASS LFA sonar training and testing activities or personnel safety.
Currently 39 marine mammal OBIAs have been designated worldwide, with 14 of these OBIAs located in the Navy’s current training and testing area of the western and central North Pacific and eastern Indian oceans.
|Marine mammal OBIAs for SURTASS LFA sonar and their annual period of effectiveness.|
|OBIA Name||Period of Effectiveness|
|Roseway Basin Right Whale Conservation Area||June through December|
|Great South Channel, U.S. Gulf of Maine, and Stellwagen Bank National Marine Sanctuary||January 1 to November 14; year-round for Stellwagen Bank NMS|
|Southeastern U.S. Right Whale Critical Habitat||November 15 to April 15|
|Gulf of Alaska||March through September|
|Navidad Bank||December through April|
|Coastal Western Africa (Cameroon to Angola)||June through October|
|Patagonian Shelf Break||Year-round|
|Argentina Southern Right Whale||May through December|
|Central California||June through November|
|Antarctic Convergence Zone||October through March|
|Offshore Piltun and Chayvo||June through November|
|Eastern Madagascar Coastal Waters||July through September for humpback whale breeding; November through December for migrating blue whales|
|Southern Madagascar (Madagascar Plateau, Madagascar Ridge, and Walters Shoal)||November through December|
|Ligurian-Corsican-Provençal Basin and Western Pelagos Sanctuary||July to August|
|Costa Rica Dome||Year-round|
|Great Barrier Reef||May through September|
|Bonney Upwelling||December through May|
|Olympic Coast National Marine Sanctuary, Barkley and Nitinat Canyons, and The Prairie||Olympic National Marine Sanctuary: December, January, March, April, and May;
The Prairie, Barkley and Nitinat Canyons: June through September
|Abrolhos Bank||August through November|
|Grand Manan North Atlantic Right Whale Critical Habitat||June through December|
|Eastern Gulf of Mexico||Year-round|
|Southern Coastal Chile||February to April|
|Perth Canyon||January through May|
|Southwest Australia Canyons||Year-round|
|Main Hawaiian Islands||November to April|
|Northwestern Hawaiian Islands||December to April|
|Marianas Islands||February to April|
|Ryukyu‐Philippines||January to April|
|Ogasawara—Sperm Whale||June to September|
|Ogasawara‐Kazin—Humpback Whale||December to May|
|Honshu||January to May|
|Southeast Kamchatka||June to September|
|Gulf of Thailand||April to November|
|Western Australia—Blue Whale||May to November|
|Western Australia—Humpback Whale||May to December|
|Southern Bali||October to November|
|Sri Lanka||October to April|
Additional Geographic Mitigation Measures During Training and Testing Activities:
- 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 (i.e., coastal standoff range) and within 0.54 nautical miles / 1 kilometer 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 nautical miles / 18.5 kilometers 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 nautical miles / 18.5 kilometers 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.
Mitigation Monitoring Measures
Three methods are used to monitor the LFA mitigation zone during training and testing activities using SURTASS LFA sonar:
- Visual monitoring for marine mammals and sea turtles from the SURTASS LFA sonar vessel during daylight hours
- Passive acoustics using SURTASS to listen for sounds generated by marine mammals as an indicator of their presence
- Active acoustics using the High Frequency Marine Mammal Monitoring (HF/M3) sonar system to detect/locate/track potentially affected marine mammals (and possibly sea turtles).
Visual monitoring includes daytime observations from the bridge of the SURTASS LFA sonar vessel for presence of marine mammals and sea turtles whenever LFA sonar is transmitting during training and testing activities. The visual observers detect and identify marine mammals and sea turtles using standard binoculars (7x) and the naked eye. If a marine mammal or sea turtle is observed in the LFA mitigation zone, then LFA sonar transmissions are immediately suspended or delayed. The visual observers are trained by a qualified marine biologist. An example of the training visual observers receive is the Navy’s Marine Species Awareness Training (MSAT), available on YouTube.
Passive Acoustic Monitoring:
Passive acoustic monitoring using the SURTASS horizontal towed array is conducted when LFA sonar is transmitting during training and testing activities. Passive acoustic monitoring detects the sounds made by 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 during training and testing events. Prior to full-power operations of the HF/M3 sonar, the power level is 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 range: 30 to 40 kHz
- Bandwidth: variable (1.5 to 6 kHz nominal)
- Duty Cycle: 3 to 4 percent (nominal)
- Nominal Source Level: 220 dB re 1 µPa at 1 m
- Pulse Length: variable (10 to 40 msec nominal)
- Pulse Repetition Rate: set by maximum search range (3 to 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 1.08 nautical miles / 2 kilometers
- 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 1.08 nautical miles / 2 kilometers.