Nancy DiMarzio

Beaked Whales Respond to Simulated and Actual Navy Sonar

Beaked whales have mass stranded during some naval sonar exercises, but the cause is unknown. They are difficult to sight but can reliably be detected by listening for echolocation clicks produced during deep foraging dives. Listening for these clicks, we documented Blainvilles beaked whales, Mesoplodon densirostris, in a naval underwater range where sonars are in regular use near Andros Island, Bahamas. An array of bottom-mounted hydrophones can detect beaked whales when they click anywhere within the range. We used two complementary methods to investigate behavioral responses of beaked whales to sonar: an opportunistic approach that monitored whale responses to multi-day naval exercises involving tactical mid-frequency sonars, and an experimental approach using playbacks of simulated sonar and control sounds to whales tagged with a device that records sound, movement, and orientation. Here we show that in both exposure conditions beaked whales stopped echolocating during deep foraging dives and moved away. During actual sonar exercises, beaked whales were primarily detected near the periphery of the range, on average 16 km away from the sonar transmissions. Once the exercise stopped, beaked whales gradually filled in the center of the range over 2–3 days. A satellite tagged whale moved outside the range during an exercise, returning over 2–3 days post-exercise. The experimental approach used tags to measure acoustic exposure and behavioral reactions of beaked whales to one controlled exposure each of simulated military sonar, killer whale calls, and band-limited noise. The beaked whales reacted to these three sound playbacks at sound pressure levels below 142 dB re 1 µPa by stopping echolocation followed by unusually long and slow ascents from their foraging dives. The combined results indicate similar disruption of foraging behavior and avoidance by beaked whales in the two different contexts, at exposures well below those used by regulators to define disturbance.

Estimating cetacean population density using fixed passive acoustic sensors: An example with Blainville’s beaked whales

Methods are developed for estimating the size/density of cetacean populations using data from a set of fixed passive acoustic sensors. The methods convert the number of detected acoustic cues into animal density by accounting for (i) the probability of detecting cues, (ii) the rate at which animals produce cues, and (iii) the proportion of false positive detections. Additional information is often required for estimation of these quantities, for example, from an acoustic tag applied to a sample of animals. Methods are illustrated with a case study: estimation of Blainvilles beaked whale density over a 6 day period in spring 2005, using an 82 hydrophone wide-baseline array located in the Tongue of the Ocean, Bahamas. To estimate the required quantities, additional data are used from digital acoustic tags, attached to five whales over 21 deep dives, where cues recorded on some of the dives are associated with those received on the fixed hydrophones. Estimated density was 25.3 or 22.5 animals/1000 km(2), depending on assumptions about false positive detections, with 95% confidence intervals 17.3-36.9 and 15.4-32.9. These methods are potentially applicable to a wide variety of marine and terrestrial species that are hard to survey using conventional visual methods.

Spatially explicit capture?recapture methods to estimate minke whale density from data collected at bottom-mounted hydrophones

Estimation of cetacean abundance or density using visual methods can be cost-ineffective under many scenarios. Methods based on acoustic data have recently been proposed as an alternative, and could potentially be more effective for visually elusive species that produce loud sounds. Motivated by a dataset of minke whale (Balaenoptera acutorostrata) “boing” sounds detected at multiple hydrophones at the U.S. Navy’s Pacific Missile Range Facility (PMRF), we present an approach to estimate density or abundance based on spatially explicit capture–recapture (SECR) methods. We implement the proposed methods in both a likelihood and a Bayesian framework. The point estimates for abundance and detection parameters from both implementation methods are very similar and agree well with current knowledge about the species. The two implementation approaches are compared in a small simulation study. While the Bayesian approach might be easier to generalize, the likelihood approach is faster to implement (at least in simple cases like the one presented here) and more readily amenable to model selection. SECR methods seem to be a strong candidate for estimating density from acoustic data where recaptures of sound at multiple acoustic sensors are available, and we anticipate further development of related methodologies.

Beaked whale (Mesoplodon densirostris) passive acoustic detection in increasing ambient noise

Passive acoustic detection is being increasingly used to monitor visually cryptic cetaceans such as Blainvilles beaked whales (Mesoplodon densirostris) that may be especially sensitive to underwater sound. The efficacy of passive acoustic detection is traditionally characterized by the probability of detecting the animals sound emissions as a function of signal-to-noise ratio. The probability of detection can be predicted using accepted, but not necessarily accurate, models of the underwater acoustic environment. Recent field studies combining far-field hydrophone arrays with on-animal acoustic recording tags have yielded the location and time of each sound emission from tagged animals, enabling in-situ measurements of the probability of detection. However, tagging studies can only take place in calm seas and so do not reflect the full range of ambient noise conditions under which passive acoustic detection may be used. Increased surface-generated noise from wind and wave interaction degrades the signal-to-noise ratio of animal sound receptions at a given distance leading to a reduction in probability of detection. This paper presents a case study simulating the effect of increasing ambient noise on detection of M. densirostris foraging clicks recorded from a tagged whale swimming in the vicinity of a deep-water, bottom-mounted hydrophone array.

New algorithms for open ocean marine mammal monitoring

The Naval Undersea Warfare Center has been funded by the Office of Naval Research Environmental Requirements Advanced Technology (ERAT) program to create a multi-disciplinary program to conduct Marine Mammal Monitoring on Navy Undersea Ranges (M/sup 3/R). The objective is to supplement extensive undersea range and signal processing hardware with state of the art passive marine mammal detection, localization and tracking algorithms. This system will provide the opportunity to determine the number of acoustically active species within an instrumented, open ocean area and to evaluate baseline behavior. The initial system will be demonstrated at the Atlantic Undersea Test and Evaluation Center (AUTEC), Andros Island, Bahamas. Many of the existing assets at AUTEC will be leveraged, including the data collected by the ongoing marine mammal monitoring program. Undersea range coverage at AUTEC includes a steep island slope feature that may serve as a feeding habitat for several cetaceans including the sperm whale (Physter macrocephalus), short-finned pilot whale (Globicephala macrorhynchus), minke whale (Balaenoptera acutorostrata), and several species of dolphins. The development of a database of marine mammal recordings at AUTEC is currently underway using five-minute recordings taken once every half hour. The M/sup 3/R program is increasing the rate of acoustic data collection at AUTEC and evaluating the ability to passively track the location of various species based on features of the transient acoustic marine mammal calls. Acoustic characteristics of species recorded at the AUTEC as well as developmental marine mammal monitoring algorithms are presented.

Verified passive acoustic detection of beaked whales (Mesoplodon densirostris) using distributed bottom‐mounted hydrophones in the tongue of the ocean, Bahamas

Passive detection of beaked whales has become increasingly important as at least two species, Blainville’s beaked whales (Mesoplodon densirostris) and Cuvier’s beaked whales (Ziphius cavorostris) have stranded in events associated with sonar. Passive acoustic detection and localization algorithms develop as part of the Office of Naval Research (ONR) Marine Mammal Monitoring on Navy Range (M3R) program will be presented along with results from a series of tests that demonstrate the efficacy of passive acoustic detection of vocalizing M. densirostris. Ninety‐two bottom‐mounted sensors at the Atlantic Undersea Test and Evaluation Center (AUTEC) were monitored for vocalizations. M3R systems were used to detect and localize vocalizing animals. Based on these real‐time data, trained observers were vectored to the animals and verified the species. Focal follows coordinated with passive acoustics were completed. Observer photos along with raw sensor, detection and localization data were collected.

Passive monitoring and localization of marine mammals in open ocean environments using widely spaced bottom mounted hydrophones

The Marine Mammal Monitoring on Navy Ranges (M3R) project has developed a toolset for passive detection and localization of marine mammals using the existing infrastructure of Navy’s undersea ranges. The Office of Naval Research funded the M3R project as part of the Navy’s effort to determine the effects of acoustic and other emissions on marine mammals and threatened/endangered species. A necessary first step in this effort is the creation of a baseline of behavior, which requires long‐term monitoring of marine mammals. Such monitoring, in turn, requires the ability to detect and localize the animals. This paper will present the passive acoustic monitoring and localization tools developed under M3R. It will also present results of the deployment of the M3R tools at the Atlantic Undersea Test and Evaluation Center (AUTEC), Andros Island, Bahamas from June through November 2003. Finally, it will discuss current work to improve automated species classification.

Automated Classification of Beaked Whales and Other Small Odontocetes in the Tongue of the Ocean, Bahamas

Navy sonar has recently been associated with a number of marine mammal stranding events. Beaked whales have been the predominant species involved in a number of these strandings. Monitoring and mitigating the effects of anthropogenic noise on marine mammals are active areas of research. Key to both monitoring and mitigation is the ability to automatically detect and classify the animals, especially beaked whales. This paper presents a novel support vector machine based methodology for automated species level classification of small odontocetes. To date, the algorithm presented has been trained to differentiate the click vocalizations of Blainvilles beaked whales (Mesoplodon densirostris) from the clicks produced by delphinids and from man-made sounds. The automated classification capability compliments the detection and tracking tools already developed through ONR funding for the monitoring and localization of whales at the Atlantic Undersea Test and Evaluation Center, Andros Island, Bahamas

Passive detection, data association, and localization of marine mammal calls using traditional 3D hyperbolic tracking algorithms

The Office of Naval Research Marine Mammal Monitoring on Navy Ranges (M3R) project has developed a toolset for passive detection and localization of marine mammals using the existing infrastructure of Navy undersea ranges. The tools are designed to work across a broad class of calls including clicks, sweeps, and whistles. Using vocalizations received by widely spaced omni‐directional hydrophones, the M3R tools can detect and localize marine mammals in real‐time. Signal detection algorithms, data association algorithm, and tracking algorithm have been developed, and demonstrated. The tools have also been successfully fielded to conduct extended monitoring of a 500 square nautical mile area located in the Tongue of the Ocean. This presentation will present the passive acoustic monitoring and localization tools developed under M3R. It will also present results of the application of these tools to the real‐time detection and tracking as well as extended monitoring of various toothed whale species at the Atlan...

Mesoplodon densirostris transmission beam pattern estimated from passive acoustic bottom mounted hydrophones and a DTag recording

The transmission beam pattern of a female Mesoplodon densirostris tagged on October 23, 2006 in the Tongue of the Ocean, Bahamas is estimated using data from a Woods Hole Oceanographic Institution DTag and simultaneous recordings from broadband, bottom mounted hydrophones at the Atlantic Undersea Test and Evaluation Center, Andros Island, Bahamas. The bottom mounted hydrophones are used to localize the tagged animal and measure the received level of each click. Pitch, roll and heading from the DTag are used to determine the horizontal and vertical aspect angles relative to the hydrophone. An estimate of the M. densirostris horizontal and vertical transmission beam pattern based on four dives will be presented.