Search

Funding: Funding for this work was provided by Living Marine Resources Program Grant No. N39430-14-C-1435 and Office of Naval Research Grant No. N00014-15-1‐2142. S.F. was supported by the Department of Defense National Science and Engineering Graduate Fellowship. This is Pacific Marine Environmental Laboratory (PMEL) Contribution No. 5101. A single-hydrophone ocean glider was deployed within a cabled hydrophone array to demonstrate a framework for estimating population density of fin whales ( Balaenoptera physalus) from a passive acoustic glider. The array was used to estimate tracks of acoustically active whales. These tracks became detection trials to model the detection function for glider-recorded 360-s windows containing fin whale 20-Hz pulses using a generalized additive model. Detection probability was dependent on both horizontal distance and low-frequency glider flow noise. At the median 40-Hz spectral level of 97 dB re 1 μPa2/Hz, detection probability was near one at horizontal distance zero with an effective detection radius of 17.1 km [coefficient of variation (CV) = 0.13]. Using estimates of acoustic availability and acoustically active group size from tagged and tracked fin whales, respectively, density of fin whales was estimated as 1.8 whales per 1000 km2 (CV = 0.55). A plot sampling density estimate for the same area and time, estimated from array data alone, was 1.3 whales per 1000 km2 (CV = 0.51). While the presented density estimates are from a small demonstration experiment and should be used with caution, the framework presented here advances our understanding of the potential use of gliders for cetacean density estimation. Publisher PDF

The population density of Cuvier's beaked whales is estimated acoustically with drifting near-surface hydrophone recorders in the Catalina Basin. Three empirical approaches (trial-based, distance-sampling, and spatially explicit capture-recapture) are used to estimate the probability of detecting the echolocation pulses as a function of range. These detection functions are used with two point-transect methods (snapshot and dive-cue) to estimate density. Measurement errors result in a small range of density estimates (3.9-5.4 whales per 1000 km2). Use of multiple approaches and methods allows comparison of the required information and assumptions of each. The distance-sampling approach with snapshot-based density estimates has the most stringent assumptions but would be the easiest to implement for large scale surveys of beaked whale density. Alternative approaches to estimating detection functions help validate this approach. The dive cue method of density estimation has promise, but additional work is needed to understand the potential bias caused by animal movement during a dive. Empirical methods are a viable alternative to the theoretical acoustic modeling approaches that have been used previously to estimate beaked whale density.

Funding for this work was provided by the Living Marine Resources Program (N39430-14-C-1435 and N39430-14-C-1434), the Office of Naval Research (N00014-15-1-2142, N00014-10-1-0534, and N00014-13-1-0682), and NOAA’s Southwest Fisheries Science Center. SF was supported by the National Science and Engineering Graduate Fellowship. Advances in mobile autonomous platforms for oceanographic sensing, including gliders and deep-water profiling floats, have provided new opportunities for passive acoustic monitoring (PAM) of cetaceans. However, there are few direct comparisons of these mobile autonomous systems to more traditional methods, such as stationary bottom moored recorders. Cross-platform comparisons are necessary to enable interpretation of results across historical and contemporary surveys that use different recorder types, and to identify potential biases introduced by the platform. Understanding tradeoffs across recording platforms informs best practices for future cetacean monitoring efforts. This study directly compares the PAM capabilities of a glider (Seaglider) and a deep-water profiling float (QUEphone) to a stationary seafloor system (High-frequency Acoustic Recording Package, or HARP) deployed simultaneously over a 2 week period in the Catalina Basin, California, United States. Two HARPs were deployed 4 km apart while a glider and deep-water float surveyed within 20 km of the HARPs. Acoustic recordings were analyzed for the presence of multiple cetacean species, including beaked whales, delphinids, and minke whales. Variation in acoustic occurrence at 1-min (beaked whales only), hourly, and daily scales were examined. The number of minutes, hours, and days with beaked whale echolocation clicks were variable across recorders, likely due to differences in the noise floor of each recording system, the spatial distribution of the recorders, and the short detection radius of such a high-frequency, directional signal type. Delphinid whistles and clicks were prevalent across all recorders, and at levels that may have masked beaked whale vocalizations. The number and timing of hours and days with minke whale boing sounds were nearly identical across recorder types, as was expected given the relatively long propagation distance of boings. This comparison provides evidence that gliders and deep-water floats record cetaceans at similar detection rates to traditional stationary recorders at a single point. The spatiotemporal scale over which these single hydrophone systems record sounds is highly dependent on acoustic features of the sound source. Additionally, these mobile platforms provide improved spatial coverage which may be critical for species that produce calls that propagate only over short distances such as beaked whales. Publisher PDF

Acoustically equipped deep-water mobile autonomous platforms can be used to survey for marine mammals over intermediate spatiotemporal scales. Direct comparisons to fixed recorders are necessary to evaluate these tools as passive acoustic monitoring platforms. One glider and two drifting deep-water floats were simultaneously deployed within a deep-water cabled hydrophone array to quantitatively assess their survey capabilities. The glider was able to follow a pre-defined track while float movement was somewhat unpredictable. Fin whale (Balaenoptera physalus) 20 Hz pulses were recorded by all hydrophones throughout the two-week deployment. Calls were identified using a template detector, which performed similarly across recorder types. The glider data contained up to 78% fewer detections per hour due to increased low-frequency flow noise present during glider descents. The glider performed comparably to the floats and fixed recorders at coarser temporal scales; hourly and daily presence of detections did not vary by recorder type. Flow noise was related to glider speed through water and dive state. Glider speeds through water of 25 cm/s or less are suggested to minimize flow noise and the importance of glider ballasting, detector characterization, and normalization by effort when interpreting glider-collected data and applying it to marine mammal density estimation are discussed.

Primary funding for the SOCAL-BRS project was initially provided by the U.S. Navy’s Chief of Naval Operations Environmental Readiness Division and subsequently by the U.S. Navy's Living Marine Resources Program. This study measured the degree of behavioral responses in blue whales (Balaenoptera musculus) to controlled noise exposure off the southern California coast. High-resolution movement and passive acoustic data were obtained from non-invasive archival tags (n=42) whereas surface positions were obtained with visual focal follows. Controlled exposure experiments (CEEs) were used to obtain direct behavioral measurements before, during and after simulated and operational military mid-frequency active sonar (MFAS), pseudorandom noise (PRN) and controls (no noise exposure). For a subset of deep-feeding animals (n=21), active acoustic measurements of prey were obtained and used as contextual covariates in response analyses. To investigate potential behavioral changes within individuals as a function of controlled noise exposure conditions, two parallel analyses of time-series data for selected behavioral parameters (e.g. diving, horizontal movement and feeding) were conducted. This included expert scoring of responses according to a specified behavioral severity rating paradigm and quantitative change-point analyses using Mahalanobis distance statistics. Both methods identified clear changes in some conditions. More than 50% of blue whales in deep-feeding states responded during CEEs, whereas no changes in behavior were identified in shallow-feeding blue whales. Overall, responses were generally brief, of low to moderate severity, and highly dependent on exposure context such as behavioral state, source-to-whale horizontal range and prey availability. Response probability did not follow a simple exposure–response model based on received exposure level. These results, in combination with additional analytical methods to investigate different aspects of potential responses within and among individuals, provide a comprehensive evaluation of how free-ranging blue whales responded to mid-frequency military sonar. Postprint

Sympatric short- and long-beaked common dolphins in the Southern California Bight (Delphinus delphis and D. delphis bairdii) are challenging to identify acoustically because their whistles overlap in many time-frequency characteristics. We therefore asked whether frequency modulation patterns can help with species identification. Whistle contours from single-species encounters (short-beaked = 902 whistles, 14 schools, long-beaked = 872 whistles, 10 schools) were extracted and categorized based on frequency content and shape using dynamic time warping and artificial neural networks. This analysis resulted in 447 whistle types with 38% being produced by both species. Of the remaining species-specific whistle types, 22% (n = 60) were recorded from more than one school. Thirty-two of these were specific to short-beaked common dolphins and 28 were specific to long-beaked common dolphins. Almost half of the short-beaked common dolphin species-specific whistle types (47%) were oscillatory (contour shape containing at least two cycles with the maximum and minimum of each cycle separated by at least 1 kHz), while only 3% of long-beaked common dolphin species-specific types were oscillatory. Thus, oscillatory whistles appear to be diagnostic of short-beaked common dolphins in this area. More broadly, our findings suggest that repertoire-wide comparisons of acoustic features may overlook possible species recognition via specific signals.

In fall 2014 and spring 2015, passive acoustic data were collected via autonomous gliders east of Guam in an area that included the Mariana Trench Marine National Monument. A short (2-4 s), complex sound was recorded that features a ∼38 Hz moan with both harmonics and amplitude modulation, followed by broad-frequency metallic-sounding sweeps up to 7.5 kHz. This sound was recorded regularly during both fall and spring surveys. Aurally, the sound is quite unusual and most resembles the minke whale "Star Wars" call. It is likely this sound is biological and produced by a baleen whale.

A passive acoustic survey off Southern California is being conducted in summer–fall 2019 to estimate the distribution of beaked whale species. Two gliders are being flown to estimate the occurrence of Cuvier's, Blainville's, Stejneger's, Hubbs', and Baird's beaked whales in several regions: (1) near the Navy's Southern California Offshore Range (SCORE), in particular near fixed passive recorders there; (2) over the farther reaches of the continental shelf and shelf slope; and (3) over deep (>3000 m) waters offshore of the shelf slope up to 350 km from shore. The gliders collect passive acoustic data up to ca. 90 kHz, which should enable differentiation of these species of beaked whales in situations of reasonably high signal-to-noise ratios. Preliminary results of the glider flights and data analysis will be presented. [Funding from Navy NAVFAC.]

There is a variety of evidence that increased anthropogenic noise (e.g., shipping, explosions, sonar) has a measureable effect on marine mammal species. Observed impacts range in severity from brief interruptions of basic life functions to physiological changes, acute injury, and even death. New research tools are needed to better measure and understand the potential effects of anthropogenic noise on marine mammals. Current behavioral response studies typically utilize ship-based sound sources to study potential acute behavioral responses in tagged animals experimentally exposed to noise. Integrating the sound source within animal-mounted passive acoustic and motion-sensing tags provides a novel tool for conducting additional highly controlled response studies. We developed and conducted pilot field trials of a prototype tag on five juvenile northern elephant seals, Mirounga angustirostris, using experimental exposures to both natural and anthropogenic noise stimuli. Results indicate behavioral responses were elicited in tagged individuals. However, no pattern was found in the occurrence and types of response compared to stimulus type. Responses during the ascending dive phase consisted of a dive inversion, or sustained reversal from ascending to descending (8 of 9 exposures). Dive inversions following exposure were 4–11 times larger than non-exposure inversions. Exposures received during the descending dive phase resulted in increased descent rates in 9 of 10 exposures. All 8 exposures during dives in which maximum dive depth was limited by bathymetry were characterized by increased flow noise in the audio recordings following exposure, indicating increased swim speed. Results of this study demonstrate the ability of an animal-mounted sound source to elicit behavioral responses in free-ranging individuals. Behavioral responses varied by seal, dive state at time of exposure, and bathymetry, but followed an overall trend of diving deeper and steeper and swimming faster. Responses did not consistently differ based on stimulus type, which may be attributable to the unique exposure context of the very close proximity of the sound source. Further technological development and focused field efforts are needed to advance and apply these tools and methods in subsequent behavioral response studies to address specific questions.

Work is being conducted to estimate marine mammal density and abundance from slow-moving, passive acoustically equipped underwater gliders and deep-water floats. We deployed five drifting acoustic spar buoy recorders (DASBRs) simultaneously with a seaglider and QUEphone float in the Catalina Basin of Southern California in 2016 to estimate the probability of detecting Cuvier’s beaked whale echolocation clicks from the glider and float. The DASBRs successfully localized and tracked individual whales, though a limited number of encounters prohibited estimation of detection probability through a trial-based method. We explored using a spatially explicit capture recapture (SECR) approach. The SECR analysis was modified to account for the non-static array and we explored sample size requirements for SECR using simulations. During tracked dives, over 200 one-minute time bins contained echolocation clicks on at least one DASBR. Of these, 10 and 34 bins contained clicks recorded on the glider and float, respectively, and were used to make preliminary estimates of detection probability as a function of range. Detection probability estimation is a key step towards animal density estimation; other information such as encounter rate and click production rates are required to estimate animal density, which will form the next part of this work.

Increased human activities in coastal and offshore waters, including renewable energy efforts such as the deployment and operation of wind, wave, and tidal energy converters, leads to potential negative impacts on marine ecosystems. Efficient monitoring of marine mammals in these areas using stationary passive-acoustic technologies is challenging. Many recreational and commercial activities (e.g., fishing) can hinder long-term operation of moored listening devices. Further, these waters are often utilized by cetaceans such as porpoise species which produce high-frequency echolocation clicks (peak frequency ~130 kHz) for navigation, communication, and prey detection. Because these ultrasonic signals are strongly absorbed during propagation, the acoustic detection range is limited to a few 100 m, and therefore the spatial coverage of stationary recorders is relatively limited. In contrast, mobile passive-acoustic platforms could potentially be used to survey areas of concern for high-frequency cetacean vocalizations and provide increased temporal coverage and spatial resolution. In a pilot study, a commercially available acoustic recorder featuring sampling rates of up to 384 kHz was customized and implemented on an autonomous underwater vehicle (AUV) and an unmanned surface vehicle (USV) and tested in the field. Preliminary results indicate that these systems (a) are effective at detecting the acoustic presence of high-frequency cetaceans such as porpoises, and (b) could be a valuable tool to monitor potential negative impacts of renewable energy and other anthropogenic disturbances in the marine environment.

International audience; Northern elephant seals ( Mirounga angustirostris ) have a polygynous breeding system in which adult males establish dominance hierarchies that determine access to females. Acoustic signaling plays an important role in settling fights between males, as stereotyped displays elicit appropriate behavioral responses from individuals without contact during an energetically demanding breeding season. To determine whether reliable differences exist in the acoustic displays of individuals and whether these differences function to convey identity, we behaviorally and acoustically sampled male seals during the breeding season. Vocalizations were recorded during competitive interactions and analyzed for spectral, temporal, and amplitude characteristics. A cross-validated discriminant function analysis revealed small differences within—and significant differences between—the calls produced by 17 adult males of known dominance status. To determine whether acoustic displays serve as individual signatures that males learn to recognize during the breeding season, we conducted playback experiments to test if having prior experience with a particular caller would influence the approach or avoidance response of the listener. Our findings reveal that these unique acoustic signals serve as individual vocal signatures, and males likely remember the identity of their rivals based on call features that have been associated with the outcome of previous competitive interactions.

Without a means of studying large whales in a controlled experimental environment, less is understood about their sound production mechanisms than is understood about those of smaller odontocetes. To describe call production behavior in fin whales, we used a recent technique that correlates fast-sampling accelerometer signals from tags with concurrently recorded acoustic signals to identify calls produced by the tagged animal. We tagged 18 fin whales as part of the Southern California Behavioral Response Study (SOCAL BRS), of which four were confirmed to be calling. We were then able to describe their kinematic and social behavior in relation to call production. Behaviors associated with elevated call rates included shallow maximum dive depths, little body movement, and negative pitch in body orientation, similar to some other calling baleen whale species. These are the first descriptions of body orientation and dive depths at which fin whales are most likely to call. We also describe calling responses (or lack thereof) from blue and fin whales exposed to simulated mid-frequency active sonar. The call behavior characterizations presented here will help with predicting calling behavior from surface behavior, informing interpretation of passive acoustic data, and further investigating effects of anthropogenic sound on baleen whales.

A pilot study was conducted to evaluate the potential of animal-borne active and passive acoustic tags for conducting minimally-invasive behavioral response studies on pinnipeds. A prototype tag was developed and tested on juvenile northern elephant seals (Mirounga angustirostris) using translocation experiments at Ano Nuevo State Park, CA, USA, in spring 2012. The principal scientific questions of this pilot study were (1) do low-intensity sounds emitted by an animal-borne tag elicit behavioral responses, and (2) are potential animal responses related to signal content (e.g., threatening vs non-threatening)? Preliminary results indicate that (1) low-intensity sounds emitted by animal-borne tags elicit distinct behavioral responses, (2) these responses appear related to signal content, and (3) the responses may differ based on depth, bathymetry, and location. The results of the study show the promise of this approach as a minimally invasive and cost-effective method to investigate animal responses to underwater sounds, as well as a method to develop mitigation strategies. We are currently in the process of improving the tag design for future field efforts with the goal to increase the sample size, range of acoustic stimuli, and age/sex classes of tagged seals. [Funding from NOAA/NMFS Ocean Acoustics Program.]

In 2011 a pilot study was begun to evaluate the potential of animal-borne active acoustic tags for conducting minimally-invasive behavioral response studies on pinnipeds. A basic prototype tag was developed and tested on juvenile northern elephant seals (Mirounga angustirostris) during translocation experiments at Ano Nuevo State Park, CA, USA in spring 2012. The principal scientific questions of this pilot study were these: (1) do sounds emitted from an animal-borne low acoustic intensity tag elicit behavioral responses, and (2) are potential animal responses related to signal content (e.g., threatening vs. non-threatening). Although the sample size was small, preliminary results indicate that (1) low-intensity sounds emitted by animal-borne tags elicit distinct behavioral responses, (2) these responses appear related to signal content, and (3) the responses may differ based on depth, bathymetry, and location. The results of the conducted study show the promise of this approach as a minimally-invasive an...