Scientific Research
Monitoring/Research to Increase Understanding of the Potential Effects
of SURTASS LFA Sonar Transmissions on Beaked Whales and/or Harbor
Porpoises
A monitoring and research provision was included in the 2012 MMPA Final
Rule and subsequent annual LOAs for SURTASS LFA sonar that required the
Navy to consider research or monitoring strategies that would increase
the understanding of the potential effects of SURTASS LFA sonar
transmissions on beaked whales and/or harbor porpoises. The Navy’s first
step in this effort was to convene a group of recognized scientific
subject matter experts in the fields of marine bio-acoustics, marine
mammal biology and hearing, and marine behavioral sciences to evaluate
and recommend possible research or monitoring efforts. The goal of this
Scientific Advisory Group (SAG) was to specifically evaluate and
recommend a practical strategy for the Navy on the possible monitoring
and research efforts it could undertake to provide information on how
exposure to SURTASS LFA sonar might affect the behavior of beaked whales
and/or harbor porpoises.
The Navy organized a group of renowned marine scientists and
bio-acousticians to form the SAG, which included:
- Dr. Christopher W. Clark
- Dr. Daniel P. Costa
- Dr. William T. Ellison
- Dr. Jason Gedamke
- Dr. Ronald A. Kastelein
- Dr. Brandon L. Southall (chair)
The SAG convened twice during 2012 to 2013 and developed a strategic,
iterative, parallel research approach for beaked whales (primarily
involving field work with existing methods) and harbor porpoises
(primarily involving laboratory studies with existing methods) that
could be implemented to address specific information gaps, if deemed
necessary. The
LFA SAG Report
of their recommended research approach was submitted to the National
Marine Fisheries Service in August 2013.
In their report, the SAG concluded that the available data suggest that
the potential for adverse effects to beaked whales and harbor porpoises
from exposure to SURTASS LFA sonar appears limited. They also concluded
that the potential effects of SURTASS LFA sonar on marine mammal species
within these two odontocete taxa would depend largely on the frequencies
of the transmissions relative to the species’ hearing sensitivity, the
species’ responsiveness to underwater sounds, and the spatial overlap
between SURTASS LFA sonar mission areas and the species’ distributions.
However, the SAG concluded that a number of research questions should be
addressed to verify this conclusion and provided several specific
recommendations to address the research questions.
Effects of Low Frequency Sonar on Fishes
The Navy sponsored a $3 million series of controlled exposure
experiments that were 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 led by Dr. Arthur Popper. During this research, even
after exposure to relatively high levels (up to 193 dB re 1 µPa [rms]
RL, a sound level found only within about 200 m (656 ft) of the LFA
source array) of LFA sonar sound and even after 96 hours of exposure,
only minimal impacts resulted on the fish species that were studied.
None of the fish experienced damage to their ear’s sensory hair cells
or any damage to their tissues, either at the gross or cellular
levels, and no fish died as a result of the exposure. Some behavioral
responses and hearing loss resulted from exposure to LFA sonar during
the experiments, but only a very small level of hearing loss was shown
in two of three fish species studied. Several papers were published in
peer-reviewed journals to document the results of these research
efforts; click
here
to read Popper et al. 2007.
Low Frequency Sound Scientific Research Program (LFS SRP)
When the use of SURTASS LFA sonar was first proposed in the mid
1990’s, very little data existed upon which an assessment of the
potential effects could be based. Therefore, the Navy convened the Low
Frequency Sound Scientific Research Program (LFS SRP) to investigate
the reaction of species engaged in critical, biologically-important
behaviors to the low-frequency transmissions produced by the LFA
system. Species were selected that were believed to be sensitive to
low-frequency sound. If the prevailing hypothesis was confirmed that
received sound levels of approximately 140 dB would cause avoidance
behaviors by marine mammals, then LFA probably would not have been
deployed or its use would have been severely restricted.
The LFS SRP was conducted in three phases. The chart shows the
location of each phase.
Low Frequency Sound Scientific Research Program Phases
Phase |
Dates |
Location |
Species |
Phase I |
September–October 1997 |
Southern California Offshore, West of San Nicolas Island
|
Blue and Fin Whales |
Phase II |
January 1998 |
Central California Offshore |
Gray Whales |
Phase III |
February–March 1998 |
Hawaii Offshore |
Humpback Whales |
LFS SRP Phase I
Objectives
The primary objective of Phase I was to determine whether exposure
to low-frequency sounds elicited disturbance reactions from feeding
blue or fin whales. The goal was to characterize how whale reactions
vary to the sounds depending on: (1) the received level of the
sound, (2) changes in the received level, and (3) whether the system
was operating at a relatively constant distance or approaching a
whale.
Phase I Research Approach
Bottom Bounce Acoustic Field
-
Sound is refracted (bent) downward and reflects upward off the
seafloor
-
Simulated the type of sound field that whales could experience
from a distant source
Direct Path Acoustic Field
-
Omni-directional sound field (sound levels are same throughout
the water column)
-
Simulated the type of sound field that whales could experience
from an approaching source
Phase I Research Assets
Research Vessel Cory Chouest
-
Source Ship (played LFA acoustic transmissions)
-
Collected acoustic recordings with SURTASS towed array,
especially of whale vocalizations
Research Vessel Dariabar
-
Independent observation vessel
-
Marine mammal experts observed fin and blue whale behavior
-
Collected acoustic recordings, especially of whale
vocalizations
Research Vessel John Martin
-
Surveyed prey fields (whale food)
-
Tagged blue and fin whales with time/depth recorders to assess
dive behavior
Aerial Surveys
-
Documented the distribution and density of marine mammals
Pop-Ups
-
Autonomous seafloor acoustic recording units
SOSUS
-
Acoustic recordings from Navy seafloor passive hydrophone
arrays
Phase I Results
-
Full and reduced LFA source power transmissions were used.
-
Highest received levels at animals estimated to be 148-155 dB
rms.
-
In 19 focal animal observations (4 blue whales and 15 fin
whales), no overt behavioral responses were observed. Note: A
“focal animal” is an individual animal selected for intensive
observation during an experiment.
-
No changes in whale distribution could be related to LFA
operations; whale distributions closely tracked the distribution
of food.
-
One preliminary analysis of whale sound detections indicated a
slight decrease in whale calling activity during LFA operations,
but this was not confirmed by a second analysis.
SRP Phase II
Objectives
-
Quantify responses of migrating gray whales to low-frequency
sound signals.
-
Compare whale responses to different received levels (RL).
-
Determine whether whales respond more strongly to RL, sound
gradient, or range to the source.
-
Compare whale avoidance responses to the low-frequency source
when located in the center of the migration corridor versus in
the offshore portion of the migration corridor.
Phase II Research Assets
For this phase of the Scientific Research Program, a sound source
was moored offshore of the central California coast, near Point
Buchon. Shore-based observers tracked whales using methods that
provided highly sensitive measures of avoidance responses.
Observers on the playback vessel (100 ft work boat) also carefully
monitored marine mammals to stop broadcasting in case of worrisome
behavioral reactions or if any marine mammals were sighted at
close enough range that the sound level to which they were exposed
might exceed the maximum planned exposure level (155 dB).
SRP Phase III
Objectives
Assess potential effects of LFA signals on behavior, vocalization
and movement of humpback whales off the Kona coast.
Phase III Research Approach
-
Shipboard visual and acoustic observation
- Shore-based visual observation
-
Controlled exposure of whales to LFA transmissions from SURTASS
LFA source
-
SURTASS ship (passive only) available for better localization
and additional observations
-
Additional R/V collected visual, acoustic and sound field data
-
Applicable mitigation measures employed during all operations
Phase III Research Assets
For this phase of the SRP, the Research Vessel Cory Chouest
operated off the west coast of the big island of Hawaii. A passive
SURTASS ship also participated to listen for whale songs.
Shore-based observers tracked whales. Calibrated hydrophones were
deployed from a small vessel to measure received levels (RL),
verify the transmission loss (TL) models, and improve
determination of the sound field to which the whales were exposed.
This vessel also followed individual humpback whales and described
in detail their surface behaviors before, during, and after LFA
transmissions. Visual and acoustic observers on the playback
vessel (R/V Cory Chouest) carefully monitored marine mammals in
order to stop broadcasting in case of worrisome behavioral
reactions or if any marine mammals were sighted at close enough
range that the sound level to which they were exposed might exceed
the maximum planned exposure level.
Phase III Summary
-
33 LFA playback (acoustic transmission) experiments
-
More than 950 humpback sightings
-
500 hours of passive acoustic data collected
-
Whale exposure levels of 115 dB to 152 dB
-
Variety of responses to playbacks, including temporary cessation
of song and apparent temporary avoidance response
-
Many whales continued to sing and interact with other whales
during playbacks
-
Three aerial surveys conducted as part of separate research
project but included Phase III study area during playbacks
-
Whale distributions and abundances compared with similar survey
data from 1993 and 1995
Phase III Results
-
Maximum exposure levels were as high as 152 dB.
-
Roughly half of the whales that were visually observed ceased
their song during transmissions, but many of these did so while
joining a group of whales (when singers usually stop their
songs).
-
All singers who interrupted their songs were observed to resume
singing within tens of minutes.
-
Analysis of one data set showed that whales increased their song
lengths during LFA transmissions, but a second analysis
indicated that song length changes were more complicated, and
depended on the portion of the song that was overlapped by LFA
transmissions.
-
A delayed response to LFA transmissions was observed, in the
form of an increase in song length that occurred 1-2 hours after
the last transmission.
-
Overall patterns of singer and cow-calf abundance were the same
throughout the experiment as they were during several years of
prior study.