Aaron Thode | University of California, San Diego (original) (raw)

Papers by Aaron Thode

PloS one, 2017

During summer 2012 Shell performed exploratory drilling at Sivulliq, a lease holding located in t... more During summer 2012 Shell performed exploratory drilling at Sivulliq, a lease holding located in the autumn migration corridor of bowhead whales (Balaena mysticetus), northwest of Camden Bay in the Beaufort Sea. The drilling operation involved a number of vessels performing various activities, such as towing the drill rig, anchor handling, and drilling. Acoustic data were collected with six arrays of directional recorders (DASARs) deployed on the seafloor over ~7 weeks in Aug-Oct. Whale calls produced within 2 km of each DASAR were identified and localized using triangulation. A "tone index" was defined to quantify the presence and amplitude of tonal sounds from industrial machinery. The presence of airgun pulses originating from distant seismic operations was also quantified. For each 10-min period at each of the 40 recorders, the number of whale calls localized was matched with the "dose" of industrial sound received, and the relationship between calling rates a...

The Journal of the Acoustical Society of America, 2017

Automated and manual acoustic localizations of bowhead whale calls in the Beaufort Sea were used ... more Automated and manual acoustic localizations of bowhead whale calls in the Beaufort Sea were used to estimate the minimum frequency attained by their highly variable FM-modulated call repertoire during seven westerly fall migrations. Analyses of 13 355 manual and 100 009 automated call localizations found that between 2008 and 2014 the proportion of calls that dipped below 75 Hz increased from 27% to 41%, shifting the mean value of the minimum frequency distribution from 94 to 84 Hz. Multivariate regression analyses using both generalized linear models and generalized estimating equations found that this frequency shift persisted even when accounting for ten other factors, including calling depth, call range, call type, noise level, signal-to-noise ratio, local water depth (site), airgun activity, and call spatial density. No single call type was responsible for the observed shift, but so-called "complex" calls experienced larger percentage downward shifts. By contrast, the call source level distribution remained stable over the same period. The observed frequency shift also could not be explained by migration corridor shifts, relative changes in call detectability between different frequency bands, long-term degradation in the automated airgun detector, physiological growth in the population, or behavioral responses to increasing population density (estimated via call density). V

The Journal of the Acoustical Society of America, 2015

Each winter gray whales (Eschrichtius robustus) breed and calve in Laguna San Ignacio, Mexico, wh... more Each winter gray whales (Eschrichtius robustus) breed and calve in Laguna San Ignacio, Mexico, where a robust, yet regulated, whale-watching industry exists. Baseline acoustic environments in LSI's three zones were monitored between 2008 and 2013, in anticipation of a new road being paved that will potentially increase tourist activity to this relatively isolated location. These zones differ in levels of both gray whale usage and tourist activity. Ambient sound level distributions were computed in terms of percentiles of power spectral densities. While these distributions are consistent across years within each zone, inter-zone differences are substantial. The acoustic environment in the upper zone is dominated by snapping shrimp that display a crepuscular cycle. Snapping shrimp also affect the middle zone, but tourist boat transits contribute to noise distributions during daylight hours. The lower zone has three source contributors to its acoustic environment: snapping shrimp, ...

ICES Journal of Marine Science, 2015

Since 2003, a collaborative effort (SEASWAP) between fishers, scientists, and managers has resear... more Since 2003, a collaborative effort (SEASWAP) between fishers, scientists, and managers has researched how Alaskan sperm whales locate demersal longline fishing activity and then depredate sablefish from gear. Sperm whales constantly produce relatively low-frequency biosonar signals whenever foraging; therefore, over the past decade, passive acoustic monitoring (PAM) has become a basic tool, used for both measuring depredation activity and accelerating field tests of potential depredation countermeasures. This paper reviews and summarizes past published PAM research on SEASWAP, and then provides a detailed example of how PAM methods are currently being used to test countermeasures. The review covers two major research thrusts: (i) identifying acoustic outputs of fishing vessels that provide long-distance “cues” that attract whales to fishing activity; and (ii) validating whether distinctive “creak” sounds can be used to quantify and measure depredation rates, using both bioacoustic t...

The Journal of the Acoustical Society of America, 2014

ABSTRACT Underwater acoustic vertical arrays can localize sounds by measuring the vertical elevat... more ABSTRACT Underwater acoustic vertical arrays can localize sounds by measuring the vertical elevation angles of various multipath arrivals generated by reflections from the ocean surface and bottom. This information, along with measurements of the relative arrival times of the multipath, can be sufficient for obtaining the range and depth of an acoustic source. At ranges beyond a few kilometers ray refraction effects add additional multipath possibilities; in particular, the existence of a sound-speed minimum in deeper waters permits purely refracted ray arrivals to be detected and distinguished on an array, greatly extending the tracking range for short-aperture systems. Here, two experimental vertical array deployments are presented. The first is a simple two-element system, deployed using longline fishing gear off Sitka, AK. By tracking a tagged sperm whale, this system demonstrated an ability to localize this species out to 35 km range, and provide estimates of the detection range of these animals as a function of sea state. The second deployment—a field trial of an 128-element, mid-frequency vertical array system off Southern California—illustrates how multi-element array gain can further extend the detection and tracking ranges of sperm and humpback whales in deep-water environments. [Work supported by NPRB, NOAA, and ONR.]

Acoustic Sensing Techniques for the Shallow Water Environment, 2006

Matched-field processing (MFP) is a technique for tracking an acoustic source in range and depth ... more Matched-field processing (MFP) is a technique for tracking an acoustic source in range and depth by comparing the output of an ocean acoustic propagation model with measured acoustic data collected across multiple hydrophones. In October 2003 a MFP experiment was conducted using humpback whale sounds recorded during the spring migration off the Sunshine Coast in Queensland, in conjunction with a larger experiment conducted by the Humpback Acoustic Research Collaboration (HARC). Humpback whale sounds with frequency content between 50 Hz to 1 kHz were recorded on a fivehydrophone vertical array deployed in 24 m deep water near Noosa, Queensland. The vertical array consisted of a set of flash-memory autonomous recorders attached to rope with an anchor at one end, and a subsurface float at the other. Acoustic data were simultaneously collected and monitored on five sonobuoys deployed over approximately 2 km range. The azimuth and range of the whale could be estimated via relative time-of-arrival measurements on the buoys. Using the range estimates as bounds on the matched-field processing, a inversion using the calls was performed on the vertical array data using a genetic algorithm. Inversion parameters included animal range, depth, and array geometry. Preliminary results of the inversion and resultant 3-D position fixes are presented.

The Journal of the Acoustical Society of America, 2009

ABSTRACT

The Journal of the Acoustical Society of America, 2008

In July 2007 bioacoustic tags were attached to adult sperm whales in the Gulf of Alaska under bot... more In July 2007 bioacoustic tags were attached to adult sperm whales in the Gulf of Alaska under both natural foraging conditions, and situations wherein the animals were depredating sablefish from commercial longlining vessels. A small Rigid-Hull Inflatable was used to approach and attach a suction-cup acoustic recording tag on 13 occasions and stayed on animals for a total of 168 hours, yielding 80 hours of depth, orientation, and acoustic data. These results, combined with passive acoustic tracking and underwater video-camera data, indicate that sperm whales depredate at depths shallower than 50 m, compared to natural foraging depths of 300-400 m in the area. During depredation the animals demonstrate changes in pitch and roll that are greater when compared with normal foraging behavior. Observations on the acoustic behavior of the animals are noted as well. The fact that these normally deep-diving animals depredate so close to the surface has interesting implications for both depredation-reduction strategies and biosonar research.

The Journal of the Acoustical Society of America, 2009

ABSTRACT The detection and identification of repetitive or stereotyped bioacoustic signals in raw... more ABSTRACT The detection and identification of repetitive or stereotyped bioacoustic signals in raw acoustic data are typically accomplished via matched filtering or spectrogram correlation techniques. However, the detection of FM-modulated sweeps that have variable frequency-modulated contours or bandwidths is still an active challenge. The problem is made more complex by the possible presence of other frequency-modulated signals such as airguns or other biologics. To provide a specific example, in 2007 and 2008 directional autonomous recording packages (DASARs) were deployed in the Beaufort Sea to monitor the annual migration of the bowhead whale (Balaena mysticetus) population during seismic exploration activities. A portion of these data sets has been manually analyzed, providing an opportunity to characterize the miss and false alarm rates of various FM-modulated detection and classification methods. Here literature and software on bioacoustic FM-contour tracing and classification are reviewed, with a particular emphasis on the use of contour tracing, image segmentation, feature extraction, and neural networks for identifying species-distinctive sounds. A combination of these methods, when applied to the Arctic data set, has been found to reduce the false alarm rate by a factor of 5, while preserving a miss rate of less than 20%. [Work supported by Shell Oil Co.].

The Journal of the Acoustical Society of America, 2010

In 2008 the Louis S. St-Laurent (LSSL) surveyed deep Arctic waters using a three-airgun seismic s... more In 2008 the Louis S. St-Laurent (LSSL) surveyed deep Arctic waters using a three-airgun seismic source. Signals from the seismic survey were detected between 400 km and 1300 km range on a directional autonomous acoustic recorder deployed in water 53 m deep off the Alaskan North Slope. Observations of received signal levels between 10-450 Hz versus LSSL range roughly fit a cylindrical transmission loss model plus 0.01 dB/km attenuation in deep ice-free waters, and fit previous empirical models in icecovered waters. The transition between ice-free and ice-covered propagation conditions shifted 200 km closer to the recorder during the survey.

The Journal of the Acoustical Society of America, 2010

ABSTRACT A group of software tools has been developed for automated detection and localization of... more ABSTRACT A group of software tools has been developed for automated detection and localization of bowhead whale sounds with arbitrary frequency-modulated tones. The software is a mixture of JAVA, UNIX C-shell scripts, and MATLAB components, and consists of six sequential components: an incoherent spectral band event detector that yields time and bearings of transient events; an interval estimator to remove weak airgun signals; a feature extractor that processes an input spectrogram to yield a 23-element feature vector; two feed-forward neural network classifiers that sequentially winnow non-biologic signals and pinnipeds; a linking procedure to combine signals detected on sensors several kilometers apart; and a localization method that uses a maximum-likelihood procedure for estimating a position from a series of bearings. The software has been applied to data collected between 2007 and 2009 from at least 35 vector sensor autonomous recorders deployed over a 280-km swath in the Beaufort Sea. The largest dataset (2008) logged 1.35 × 10(6) calls at 386 000 locations over 54 days across 40 recorders and took 24 days to compute using a single 2.66-GHz processor. Seven recorders consumed over 50% of the processing time. [Work supported by Shell Exploration and Production Company.].

The Journal of the Acoustical Society of America, 2005

ABSTRACT In 1996 matched-field processing (MFP) and geoacoustic inversion methods were used to in... more ABSTRACT In 1996 matched-field processing (MFP) and geoacoustic inversion methods were used to invert for range, depth, and source levels of blue whale vocalizations. [A. M. Thode, G. L. D'Spain, and W. A. Kuperman, J. Acoust. Soc. Am. 107, 1286-1300 (2000)]. Humpback whales also produce broadband sequences of sounds that contain significant energy between 50 Hz to over 1 kHz. In Oct. 2003 and 2004 samples of humpback whale song were collected on vertical and titled arrays in 24-m-deep water in conjunction with the Humpback Acoustic Research Collaboration (HARC). The arrays consisted of autonomous recorders attached to a rope, and were time synchronized by extending standard geoacoustic inversion methods to invert for clock offset as well as whale location. The diffuse ambient noise background field was then used to correct for subsequent clock drift. Independent measurements of the local bathymetry and transmission loss were also obtained in the area. Preliminary results are presented for geoacoustic inversions of the ocean floor composition and humpback whale locations and source levels. [Work supported by ONR Ocean Acoustic Entry Level Faculty Award and Marine Mammals Program.]

The Journal of the Acoustical Society of America, 2009

Sperm whales have learned to depredate black cod ͑Anoplopoma fimbria͒ from longline deployments i... more Sperm whales have learned to depredate black cod ͑Anoplopoma fimbria͒ from longline deployments in the Gulf of Alaska. On May 31, 2006, simultaneous acoustic and visual recordings were made of a depredation attempt by a sperm whale at 108 m depth. Because the whale was oriented perpendicularly to the camera as it contacted the longline at a known distance from the camera, the distance from the nose to the hinge of the jaw could be estimated. Allometric relationships obtained from whaling data and skeleton measurements could then be used to estimate both the spermaceti organ length and total length of the animal. An acoustic estimate of animal length was obtained by measuring the inter-pulse interval ͑IPI͒ of clicks detected from the animal and using empirical formulas to convert this interval into a length estimate. Two distinct IPIs were extracted from the clicks, one yielding a length estimate that matches the visually-derived length to within experimental error. However, acoustic estimates of spermaceti organ size, derived from standard sound production theories, are inconsistent with the visual estimates, and the derived size of the junk is smaller than that of the spermaceti organ, in contradiction with known anatomical relationships.

The Journal of the Acoustical Society of America, 2007

Sperm whales ͑Physeter macrocephalus͒ have learned to remove fish from demersal longline gear dep... more Sperm whales ͑Physeter macrocephalus͒ have learned to remove fish from demersal longline gear deployments off the eastern Gulf of Alaska, and are often observed to arrive at a site after a haul begins, suggesting a response to potential acoustic cues like fishing-gear strum, hydraulic winch tones, and propeller cavitation. Passive acoustic recorders attached to anchorlines have permitted continuous monitoring of the ambient noise environment before and during fishing hauls. Timing and tracking analyses of sperm whale acoustic activity during three encounters indicate that cavitation arising from changes in ship propeller speeds is associated with interruptions in nearby sperm whale dive cycles and changes in acoustically derived positions. This conclusion has been tested by cycling a vessel engine and noting the arrival of whales by the vessel, even when the vessel is not next to fishing gear. No evidence of response from activation of ship hydraulics or fishing gear strum has been found to date.

The Journal of the Acoustical Society of America, 2013

ABSTRACT Sperm whales have been depredating black cod (Anoplopoma fimbria) from demersal longline... more ABSTRACT Sperm whales have been depredating black cod (Anoplopoma fimbria) from demersal longlines in the Gulf of Alaska for decades, but the behavior has now become pervasive enough that it may be affecting government estimates of the sustainable catch, motivating further studies of this behavior. Over a three-year period, 11 B-Probe bioacoustic tags have been attached to seven adult sperm whales off Southeast Alaska, permitting observations of the animals' dive profiles and acoustic behavior during natural and depredation foraging conditions. Two rough categories of depredation were identified: "deep" and "shallow." "Deep depredating" whales consistently surface within 500 m of a hauling fishing vessel, have maximum dive depths greater than 200m, and display significantly different acoustic behavior than naturally foraging whales, with shorter inter-click intervals, occasional bouts of high "creak" rates, and fewer dives without creaks. "Shallow depredating" whales conduct dives that are much shorter, shallower, and more acoustically active than both the natural and deep depredating behaviors, with median creak rates three times that of natural levels. Occurrence of slow clicks and the behavioral context in which these vocalizations are produced were also investigated. These results provide insight into the energetic benefits of depredation behavior to sperm whales. [Work conducted under the SEASWAP program, supported by the North Pacific Research Board and the National Geographic Society.].

The Journal of the Acoustical Society of America, 2008

ABSTRACT In 2007, directional autonomous seafloor acoustic recorders (DASARs) were deployed at 35... more ABSTRACT In 2007, directional autonomous seafloor acoustic recorders (DASARs) were deployed at 35 locations over a 280 km swath in the Beaufort Sea in order to monitor potential changes in bowhead whale (Balaena mysticetus) locations andor acoustic activity during seismic exploration activities. The large amount of acoustic data generated motivated the development of computer-aided methods to assist in detecting and classifying bowhead whale calls. In the classification stage, bowhead whale calls were divided into six categories: (1) upsweeps, (2) downsweeps, (3) constant calls, (4) u-shaped and (5) n-shaped undulated calls, and (6) complex calls. The frequency range, duration, and fine structure of individual calls vary considerably, creating difficulties when using match-filtering or spectrogram correlation methods. A manually reviewed test data set was assembled, containing examples from each call category, arranged by signal-to-noise ratio. The data set was then used to test several methods (based on image segmentation techniques) for extracting relevant parameters from the signal for subsequent classification. An optimization procedure was then used to generate receiver operating characteristic curves and thus determine appropriate decision boundaries for optimum statistical classifiers. [Work supported by Shell Exploration and Production Company.].

The Journal of the Acoustical Society of America, 2005

ABSTRACT In 2004, the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) introduced the use... more ABSTRACT In 2004, the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) introduced the use of passive acoustics to help monitor the behavior of sperm whales depredating longline fishing operations. Acoustic data from autonomous recorders mounted on longlines provide the opportunity to demonstrate a tracking algorithm based on acoustic propagation modeling while providing insight into whales' foraging behavior. With knowledge of azimuthally dependent bathymetry, a 3D track of whale motion can be obtained using data from just one hydrophone by exploiting multipath arrival information from recorded sperm whale clicks. The evolution of multipath arrival patterns is matched to range-, depth-, and azimuth-dependent modeled arrival patterns to generate an estimate of whale motion. This technique does not require acoustic ray identification (i.e., direct path, surface reflected, etc.) while still utilizing individual ray arrival information, and it can also account for all waveguide propagation physics such as interaction with range-dependent bathymetry and ray refraction.

The Journal of the Acoustical Society of America, 2004

Sperm whales have learned to take sablefish off longline gear in the Gulf of Alaska. Over the pas... more Sperm whales have learned to take sablefish off longline gear in the Gulf of Alaska. Over the past two years the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) has collected biopsy and photo‐ID data concerning longline depredation, via collaboration with local fishermen in Sitka, AK. In 2004, in collaboration with SEASWAP, sets of autonomous acoustic recorders were attached to the anchor lines of several longline deployments, effectively converting the fishing gear into a vertical acoustic array deployed 200 m beneath the surface. The fishing vessels then left the area, leaving the acoustic instruments behind to monitor the region. Several hours later, typically the next morning, each vessel would return and begin hauling in the gear, a procedure that was also recorded by the instruments. In May 2004 an interaction of two sperm whales with the F/V Cobra was recorded. It was found that the animals started producing sounds within 20 min of the longline recovery and continued being extremely vocall...

The Journal of the Acoustical Society of America, 2012

An automated procedure has been developed for detecting and localizing frequency-modulated bowhea... more An automated procedure has been developed for detecting and localizing frequency-modulated bowhead whale sounds in the presence of seismic airgun surveys. The procedure was applied to four years of data, collected from over 30 directional autonomous recording packages deployed over a 280 km span of continental shelf in the Alaskan Beaufort Sea. The procedure has six sequential stages that begin by extracting 25-element feature vectors from spectrograms of potential call candidates. Two cascaded neural networks then classify some feature vectors as bowhead calls, and the procedure then matches calls between recorders to triangulate locations. To train the networks, manual analysts flagged 219 471 bowhead call examples from 2008 and 2009. Manual analyses were also used to identify 1.17 million transient signals that were not whale calls. The network output thresholds were adjusted to reject 20% of whale calls in the training data. Validation runs using 2007 and 2010 data found that the procedure missed 30%-40% of manually detected calls. Furthermore, 20%-40% of the sounds flagged as calls are not present in the manual analyses; however, these extra detections incorporate legitimate whale calls overlooked by human analysts. Both manual and automated methods produce similar spatial and temporal call distributions.

The Journal of the Acoustical Society of America, 2011

ABSTRACT A two-element vertical array was deployed between August, 15 and 17 2010, on the contine... more ABSTRACT A two-element vertical array was deployed between August, 15 and 17 2010, on the continental slope off Southeast Alaska, in 1200 m water depth. The instruments were attached to a longline fishing anchorline, deployed at 300 m depth, close to the sound-speed minimum of the deep water profile. The anchorline also served as a decoy, attracting seven depredating sperm whales to the area. Three animals were tagged with a satellite tag and one of them was tagged with both a satellite and bioacoustic "BProbe" tag. Both tags recorded dive depth information. Relative arrival times of surface- and bottom-reflected paths are used to estimate animal range and depth on a single hydrophone, and compared with tagging results. The two-element array is then used to estimate vertical arrival angles of the direct and surface-reflected paths to determine whether range and depth localization can occur without the use of bottom multipath. This data will be useful in determining whether long-range tracking of sperm whales is possible using a single compact instrument deployment. Potential applications include observing what ranges whales are willing to travel to depredate. [Work conducted under the SEASWAP program, supported by the National Oceanic and Atmospheric Administration and the North Pacific Research Board.].

PloS one, 2017

During summer 2012 Shell performed exploratory drilling at Sivulliq, a lease holding located in t... more During summer 2012 Shell performed exploratory drilling at Sivulliq, a lease holding located in the autumn migration corridor of bowhead whales (Balaena mysticetus), northwest of Camden Bay in the Beaufort Sea. The drilling operation involved a number of vessels performing various activities, such as towing the drill rig, anchor handling, and drilling. Acoustic data were collected with six arrays of directional recorders (DASARs) deployed on the seafloor over ~7 weeks in Aug-Oct. Whale calls produced within 2 km of each DASAR were identified and localized using triangulation. A "tone index" was defined to quantify the presence and amplitude of tonal sounds from industrial machinery. The presence of airgun pulses originating from distant seismic operations was also quantified. For each 10-min period at each of the 40 recorders, the number of whale calls localized was matched with the "dose" of industrial sound received, and the relationship between calling rates a...

The Journal of the Acoustical Society of America, 2017

Automated and manual acoustic localizations of bowhead whale calls in the Beaufort Sea were used ... more Automated and manual acoustic localizations of bowhead whale calls in the Beaufort Sea were used to estimate the minimum frequency attained by their highly variable FM-modulated call repertoire during seven westerly fall migrations. Analyses of 13 355 manual and 100 009 automated call localizations found that between 2008 and 2014 the proportion of calls that dipped below 75 Hz increased from 27% to 41%, shifting the mean value of the minimum frequency distribution from 94 to 84 Hz. Multivariate regression analyses using both generalized linear models and generalized estimating equations found that this frequency shift persisted even when accounting for ten other factors, including calling depth, call range, call type, noise level, signal-to-noise ratio, local water depth (site), airgun activity, and call spatial density. No single call type was responsible for the observed shift, but so-called "complex" calls experienced larger percentage downward shifts. By contrast, the call source level distribution remained stable over the same period. The observed frequency shift also could not be explained by migration corridor shifts, relative changes in call detectability between different frequency bands, long-term degradation in the automated airgun detector, physiological growth in the population, or behavioral responses to increasing population density (estimated via call density). V

The Journal of the Acoustical Society of America, 2015

Each winter gray whales (Eschrichtius robustus) breed and calve in Laguna San Ignacio, Mexico, wh... more Each winter gray whales (Eschrichtius robustus) breed and calve in Laguna San Ignacio, Mexico, where a robust, yet regulated, whale-watching industry exists. Baseline acoustic environments in LSI's three zones were monitored between 2008 and 2013, in anticipation of a new road being paved that will potentially increase tourist activity to this relatively isolated location. These zones differ in levels of both gray whale usage and tourist activity. Ambient sound level distributions were computed in terms of percentiles of power spectral densities. While these distributions are consistent across years within each zone, inter-zone differences are substantial. The acoustic environment in the upper zone is dominated by snapping shrimp that display a crepuscular cycle. Snapping shrimp also affect the middle zone, but tourist boat transits contribute to noise distributions during daylight hours. The lower zone has three source contributors to its acoustic environment: snapping shrimp, ...

ICES Journal of Marine Science, 2015

Since 2003, a collaborative effort (SEASWAP) between fishers, scientists, and managers has resear... more Since 2003, a collaborative effort (SEASWAP) between fishers, scientists, and managers has researched how Alaskan sperm whales locate demersal longline fishing activity and then depredate sablefish from gear. Sperm whales constantly produce relatively low-frequency biosonar signals whenever foraging; therefore, over the past decade, passive acoustic monitoring (PAM) has become a basic tool, used for both measuring depredation activity and accelerating field tests of potential depredation countermeasures. This paper reviews and summarizes past published PAM research on SEASWAP, and then provides a detailed example of how PAM methods are currently being used to test countermeasures. The review covers two major research thrusts: (i) identifying acoustic outputs of fishing vessels that provide long-distance “cues” that attract whales to fishing activity; and (ii) validating whether distinctive “creak” sounds can be used to quantify and measure depredation rates, using both bioacoustic t...

The Journal of the Acoustical Society of America, 2014

ABSTRACT Underwater acoustic vertical arrays can localize sounds by measuring the vertical elevat... more ABSTRACT Underwater acoustic vertical arrays can localize sounds by measuring the vertical elevation angles of various multipath arrivals generated by reflections from the ocean surface and bottom. This information, along with measurements of the relative arrival times of the multipath, can be sufficient for obtaining the range and depth of an acoustic source. At ranges beyond a few kilometers ray refraction effects add additional multipath possibilities; in particular, the existence of a sound-speed minimum in deeper waters permits purely refracted ray arrivals to be detected and distinguished on an array, greatly extending the tracking range for short-aperture systems. Here, two experimental vertical array deployments are presented. The first is a simple two-element system, deployed using longline fishing gear off Sitka, AK. By tracking a tagged sperm whale, this system demonstrated an ability to localize this species out to 35 km range, and provide estimates of the detection range of these animals as a function of sea state. The second deployment—a field trial of an 128-element, mid-frequency vertical array system off Southern California—illustrates how multi-element array gain can further extend the detection and tracking ranges of sperm and humpback whales in deep-water environments. [Work supported by NPRB, NOAA, and ONR.]

Acoustic Sensing Techniques for the Shallow Water Environment, 2006

Matched-field processing (MFP) is a technique for tracking an acoustic source in range and depth ... more Matched-field processing (MFP) is a technique for tracking an acoustic source in range and depth by comparing the output of an ocean acoustic propagation model with measured acoustic data collected across multiple hydrophones. In October 2003 a MFP experiment was conducted using humpback whale sounds recorded during the spring migration off the Sunshine Coast in Queensland, in conjunction with a larger experiment conducted by the Humpback Acoustic Research Collaboration (HARC). Humpback whale sounds with frequency content between 50 Hz to 1 kHz were recorded on a fivehydrophone vertical array deployed in 24 m deep water near Noosa, Queensland. The vertical array consisted of a set of flash-memory autonomous recorders attached to rope with an anchor at one end, and a subsurface float at the other. Acoustic data were simultaneously collected and monitored on five sonobuoys deployed over approximately 2 km range. The azimuth and range of the whale could be estimated via relative time-of-arrival measurements on the buoys. Using the range estimates as bounds on the matched-field processing, a inversion using the calls was performed on the vertical array data using a genetic algorithm. Inversion parameters included animal range, depth, and array geometry. Preliminary results of the inversion and resultant 3-D position fixes are presented.

The Journal of the Acoustical Society of America, 2009

ABSTRACT

The Journal of the Acoustical Society of America, 2008

In July 2007 bioacoustic tags were attached to adult sperm whales in the Gulf of Alaska under bot... more In July 2007 bioacoustic tags were attached to adult sperm whales in the Gulf of Alaska under both natural foraging conditions, and situations wherein the animals were depredating sablefish from commercial longlining vessels. A small Rigid-Hull Inflatable was used to approach and attach a suction-cup acoustic recording tag on 13 occasions and stayed on animals for a total of 168 hours, yielding 80 hours of depth, orientation, and acoustic data. These results, combined with passive acoustic tracking and underwater video-camera data, indicate that sperm whales depredate at depths shallower than 50 m, compared to natural foraging depths of 300-400 m in the area. During depredation the animals demonstrate changes in pitch and roll that are greater when compared with normal foraging behavior. Observations on the acoustic behavior of the animals are noted as well. The fact that these normally deep-diving animals depredate so close to the surface has interesting implications for both depredation-reduction strategies and biosonar research.

The Journal of the Acoustical Society of America, 2009

ABSTRACT The detection and identification of repetitive or stereotyped bioacoustic signals in raw... more ABSTRACT The detection and identification of repetitive or stereotyped bioacoustic signals in raw acoustic data are typically accomplished via matched filtering or spectrogram correlation techniques. However, the detection of FM-modulated sweeps that have variable frequency-modulated contours or bandwidths is still an active challenge. The problem is made more complex by the possible presence of other frequency-modulated signals such as airguns or other biologics. To provide a specific example, in 2007 and 2008 directional autonomous recording packages (DASARs) were deployed in the Beaufort Sea to monitor the annual migration of the bowhead whale (Balaena mysticetus) population during seismic exploration activities. A portion of these data sets has been manually analyzed, providing an opportunity to characterize the miss and false alarm rates of various FM-modulated detection and classification methods. Here literature and software on bioacoustic FM-contour tracing and classification are reviewed, with a particular emphasis on the use of contour tracing, image segmentation, feature extraction, and neural networks for identifying species-distinctive sounds. A combination of these methods, when applied to the Arctic data set, has been found to reduce the false alarm rate by a factor of 5, while preserving a miss rate of less than 20%. [Work supported by Shell Oil Co.].

The Journal of the Acoustical Society of America, 2010

In 2008 the Louis S. St-Laurent (LSSL) surveyed deep Arctic waters using a three-airgun seismic s... more In 2008 the Louis S. St-Laurent (LSSL) surveyed deep Arctic waters using a three-airgun seismic source. Signals from the seismic survey were detected between 400 km and 1300 km range on a directional autonomous acoustic recorder deployed in water 53 m deep off the Alaskan North Slope. Observations of received signal levels between 10-450 Hz versus LSSL range roughly fit a cylindrical transmission loss model plus 0.01 dB/km attenuation in deep ice-free waters, and fit previous empirical models in icecovered waters. The transition between ice-free and ice-covered propagation conditions shifted 200 km closer to the recorder during the survey.

The Journal of the Acoustical Society of America, 2010

ABSTRACT A group of software tools has been developed for automated detection and localization of... more ABSTRACT A group of software tools has been developed for automated detection and localization of bowhead whale sounds with arbitrary frequency-modulated tones. The software is a mixture of JAVA, UNIX C-shell scripts, and MATLAB components, and consists of six sequential components: an incoherent spectral band event detector that yields time and bearings of transient events; an interval estimator to remove weak airgun signals; a feature extractor that processes an input spectrogram to yield a 23-element feature vector; two feed-forward neural network classifiers that sequentially winnow non-biologic signals and pinnipeds; a linking procedure to combine signals detected on sensors several kilometers apart; and a localization method that uses a maximum-likelihood procedure for estimating a position from a series of bearings. The software has been applied to data collected between 2007 and 2009 from at least 35 vector sensor autonomous recorders deployed over a 280-km swath in the Beaufort Sea. The largest dataset (2008) logged 1.35 × 10(6) calls at 386 000 locations over 54 days across 40 recorders and took 24 days to compute using a single 2.66-GHz processor. Seven recorders consumed over 50% of the processing time. [Work supported by Shell Exploration and Production Company.].

The Journal of the Acoustical Society of America, 2005

ABSTRACT In 1996 matched-field processing (MFP) and geoacoustic inversion methods were used to in... more ABSTRACT In 1996 matched-field processing (MFP) and geoacoustic inversion methods were used to invert for range, depth, and source levels of blue whale vocalizations. [A. M. Thode, G. L. D'Spain, and W. A. Kuperman, J. Acoust. Soc. Am. 107, 1286-1300 (2000)]. Humpback whales also produce broadband sequences of sounds that contain significant energy between 50 Hz to over 1 kHz. In Oct. 2003 and 2004 samples of humpback whale song were collected on vertical and titled arrays in 24-m-deep water in conjunction with the Humpback Acoustic Research Collaboration (HARC). The arrays consisted of autonomous recorders attached to a rope, and were time synchronized by extending standard geoacoustic inversion methods to invert for clock offset as well as whale location. The diffuse ambient noise background field was then used to correct for subsequent clock drift. Independent measurements of the local bathymetry and transmission loss were also obtained in the area. Preliminary results are presented for geoacoustic inversions of the ocean floor composition and humpback whale locations and source levels. [Work supported by ONR Ocean Acoustic Entry Level Faculty Award and Marine Mammals Program.]

The Journal of the Acoustical Society of America, 2009

Sperm whales have learned to depredate black cod ͑Anoplopoma fimbria͒ from longline deployments i... more Sperm whales have learned to depredate black cod ͑Anoplopoma fimbria͒ from longline deployments in the Gulf of Alaska. On May 31, 2006, simultaneous acoustic and visual recordings were made of a depredation attempt by a sperm whale at 108 m depth. Because the whale was oriented perpendicularly to the camera as it contacted the longline at a known distance from the camera, the distance from the nose to the hinge of the jaw could be estimated. Allometric relationships obtained from whaling data and skeleton measurements could then be used to estimate both the spermaceti organ length and total length of the animal. An acoustic estimate of animal length was obtained by measuring the inter-pulse interval ͑IPI͒ of clicks detected from the animal and using empirical formulas to convert this interval into a length estimate. Two distinct IPIs were extracted from the clicks, one yielding a length estimate that matches the visually-derived length to within experimental error. However, acoustic estimates of spermaceti organ size, derived from standard sound production theories, are inconsistent with the visual estimates, and the derived size of the junk is smaller than that of the spermaceti organ, in contradiction with known anatomical relationships.

The Journal of the Acoustical Society of America, 2007

Sperm whales ͑Physeter macrocephalus͒ have learned to remove fish from demersal longline gear dep... more Sperm whales ͑Physeter macrocephalus͒ have learned to remove fish from demersal longline gear deployments off the eastern Gulf of Alaska, and are often observed to arrive at a site after a haul begins, suggesting a response to potential acoustic cues like fishing-gear strum, hydraulic winch tones, and propeller cavitation. Passive acoustic recorders attached to anchorlines have permitted continuous monitoring of the ambient noise environment before and during fishing hauls. Timing and tracking analyses of sperm whale acoustic activity during three encounters indicate that cavitation arising from changes in ship propeller speeds is associated with interruptions in nearby sperm whale dive cycles and changes in acoustically derived positions. This conclusion has been tested by cycling a vessel engine and noting the arrival of whales by the vessel, even when the vessel is not next to fishing gear. No evidence of response from activation of ship hydraulics or fishing gear strum has been found to date.

The Journal of the Acoustical Society of America, 2013

ABSTRACT Sperm whales have been depredating black cod (Anoplopoma fimbria) from demersal longline... more ABSTRACT Sperm whales have been depredating black cod (Anoplopoma fimbria) from demersal longlines in the Gulf of Alaska for decades, but the behavior has now become pervasive enough that it may be affecting government estimates of the sustainable catch, motivating further studies of this behavior. Over a three-year period, 11 B-Probe bioacoustic tags have been attached to seven adult sperm whales off Southeast Alaska, permitting observations of the animals' dive profiles and acoustic behavior during natural and depredation foraging conditions. Two rough categories of depredation were identified: "deep" and "shallow." "Deep depredating" whales consistently surface within 500 m of a hauling fishing vessel, have maximum dive depths greater than 200m, and display significantly different acoustic behavior than naturally foraging whales, with shorter inter-click intervals, occasional bouts of high "creak" rates, and fewer dives without creaks. "Shallow depredating" whales conduct dives that are much shorter, shallower, and more acoustically active than both the natural and deep depredating behaviors, with median creak rates three times that of natural levels. Occurrence of slow clicks and the behavioral context in which these vocalizations are produced were also investigated. These results provide insight into the energetic benefits of depredation behavior to sperm whales. [Work conducted under the SEASWAP program, supported by the North Pacific Research Board and the National Geographic Society.].

The Journal of the Acoustical Society of America, 2008

ABSTRACT In 2007, directional autonomous seafloor acoustic recorders (DASARs) were deployed at 35... more ABSTRACT In 2007, directional autonomous seafloor acoustic recorders (DASARs) were deployed at 35 locations over a 280 km swath in the Beaufort Sea in order to monitor potential changes in bowhead whale (Balaena mysticetus) locations andor acoustic activity during seismic exploration activities. The large amount of acoustic data generated motivated the development of computer-aided methods to assist in detecting and classifying bowhead whale calls. In the classification stage, bowhead whale calls were divided into six categories: (1) upsweeps, (2) downsweeps, (3) constant calls, (4) u-shaped and (5) n-shaped undulated calls, and (6) complex calls. The frequency range, duration, and fine structure of individual calls vary considerably, creating difficulties when using match-filtering or spectrogram correlation methods. A manually reviewed test data set was assembled, containing examples from each call category, arranged by signal-to-noise ratio. The data set was then used to test several methods (based on image segmentation techniques) for extracting relevant parameters from the signal for subsequent classification. An optimization procedure was then used to generate receiver operating characteristic curves and thus determine appropriate decision boundaries for optimum statistical classifiers. [Work supported by Shell Exploration and Production Company.].

The Journal of the Acoustical Society of America, 2005

ABSTRACT In 2004, the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) introduced the use... more ABSTRACT In 2004, the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) introduced the use of passive acoustics to help monitor the behavior of sperm whales depredating longline fishing operations. Acoustic data from autonomous recorders mounted on longlines provide the opportunity to demonstrate a tracking algorithm based on acoustic propagation modeling while providing insight into whales' foraging behavior. With knowledge of azimuthally dependent bathymetry, a 3D track of whale motion can be obtained using data from just one hydrophone by exploiting multipath arrival information from recorded sperm whale clicks. The evolution of multipath arrival patterns is matched to range-, depth-, and azimuth-dependent modeled arrival patterns to generate an estimate of whale motion. This technique does not require acoustic ray identification (i.e., direct path, surface reflected, etc.) while still utilizing individual ray arrival information, and it can also account for all waveguide propagation physics such as interaction with range-dependent bathymetry and ray refraction.

The Journal of the Acoustical Society of America, 2004

Sperm whales have learned to take sablefish off longline gear in the Gulf of Alaska. Over the pas... more Sperm whales have learned to take sablefish off longline gear in the Gulf of Alaska. Over the past two years the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) has collected biopsy and photo‐ID data concerning longline depredation, via collaboration with local fishermen in Sitka, AK. In 2004, in collaboration with SEASWAP, sets of autonomous acoustic recorders were attached to the anchor lines of several longline deployments, effectively converting the fishing gear into a vertical acoustic array deployed 200 m beneath the surface. The fishing vessels then left the area, leaving the acoustic instruments behind to monitor the region. Several hours later, typically the next morning, each vessel would return and begin hauling in the gear, a procedure that was also recorded by the instruments. In May 2004 an interaction of two sperm whales with the F/V Cobra was recorded. It was found that the animals started producing sounds within 20 min of the longline recovery and continued being extremely vocall...

The Journal of the Acoustical Society of America, 2012

An automated procedure has been developed for detecting and localizing frequency-modulated bowhea... more An automated procedure has been developed for detecting and localizing frequency-modulated bowhead whale sounds in the presence of seismic airgun surveys. The procedure was applied to four years of data, collected from over 30 directional autonomous recording packages deployed over a 280 km span of continental shelf in the Alaskan Beaufort Sea. The procedure has six sequential stages that begin by extracting 25-element feature vectors from spectrograms of potential call candidates. Two cascaded neural networks then classify some feature vectors as bowhead calls, and the procedure then matches calls between recorders to triangulate locations. To train the networks, manual analysts flagged 219 471 bowhead call examples from 2008 and 2009. Manual analyses were also used to identify 1.17 million transient signals that were not whale calls. The network output thresholds were adjusted to reject 20% of whale calls in the training data. Validation runs using 2007 and 2010 data found that the procedure missed 30%-40% of manually detected calls. Furthermore, 20%-40% of the sounds flagged as calls are not present in the manual analyses; however, these extra detections incorporate legitimate whale calls overlooked by human analysts. Both manual and automated methods produce similar spatial and temporal call distributions.

The Journal of the Acoustical Society of America, 2011

ABSTRACT A two-element vertical array was deployed between August, 15 and 17 2010, on the contine... more ABSTRACT A two-element vertical array was deployed between August, 15 and 17 2010, on the continental slope off Southeast Alaska, in 1200 m water depth. The instruments were attached to a longline fishing anchorline, deployed at 300 m depth, close to the sound-speed minimum of the deep water profile. The anchorline also served as a decoy, attracting seven depredating sperm whales to the area. Three animals were tagged with a satellite tag and one of them was tagged with both a satellite and bioacoustic "BProbe" tag. Both tags recorded dive depth information. Relative arrival times of surface- and bottom-reflected paths are used to estimate animal range and depth on a single hydrophone, and compared with tagging results. The two-element array is then used to estimate vertical arrival angles of the direct and surface-reflected paths to determine whether range and depth localization can occur without the use of bottom multipath. This data will be useful in determining whether long-range tracking of sperm whales is possible using a single compact instrument deployment. Potential applications include observing what ranges whales are willing to travel to depredate. [Work conducted under the SEASWAP program, supported by the National Oceanic and Atmospheric Administration and the North Pacific Research Board.].