Applications of slow-moving autonomous platforms for passive acoustic monitoring and density estimation of marine mammals

Advances in mobile autonomous vehicles for oceanographic sensing provide new opportunities for passive acoustic monitoring of marine mammals. Acoustically equipped mobile autonomous platforms, including gliders, deep-water profiling floats, and drifting surface buoys can survey for a variety of marine mammal species over intermediate spatiotemporal scales. Additionally, such mobile platforms may provide an effective tool for population density estimation of marine mammals. This dissertation advances our understanding of how gliders, deep-water floats, and surface drifters can be used for passive acoustic monitoring and density estimation of two cetacean species, fin whales (Balaenoptera physalus), and Cuvier’s beaked whales (Ziphius cavirostris). One glider and two drifting deep-water floats were simultaneously deployed in the vicinity of a deep-water cabled hydrophone array offshore of San Clemente Island, California, USA. The glider was able to follow a pre-defined track while float movement was somewhat unpredictable. Fin whale 20 Hz pulses were recorded by all recorders throughout the two-week deployment and presence at hourly and daily scales were comparable across all recorders. Performance of an automated template detector did not differ by recorder type. However, the glider data contained up to 78% fewer fin whale detections per hour compared to the floats or stationary hydrophones because of increased low-frequency flow noise present during glider descents. 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. The cabled hydrophone array was also used to estimate fin whale localizations and tracks concurrently with the glider survey. These tracks were used in a trial-based approach to estimate a detection function for six-minute snapshots containing fin whale 20 Hz pulses. Detection probability was strongly dependent on 40 Hz noise levels (flow noise) recorded on the glider. At the median noise level of 97 kHz dB re 1 μPa2/Hz, maximum detection range was nearly 40 km and the estimated effective survey was 870 km2. Density of fin whales was estimated as 2.4 whales per 1000 km2 (coefficient of variation, CV 0.55) using a group size estimate from the tracked whales and an externally derived vocal rate from tagged fin whales. The framework presented here could be applied to other baleen whale species to advance the use of autonomous gliders for density estimation of cetacean species. A second two-week glider and float deployment was conducted concurrently with the deployment of a commonly used deep-water stationary recorder, the High-frequency Acoustic Recording Package (HARP) and an array of drifting near-surface recorders in the Catalina Basin, California, USA. Acoustic recordings were analyzed for the presence of multiple marine mammal species, including beaked whales, delphinids, and minke whales and were compared across the glider, float, and HARPs. Detections of beaked whale echolocation clicks were variable across recorders, likely due to differences in the recording limits of each 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. Minke whale (Balaenoptera acutorostrata) boing sounds were detected almost identically across all recorder types, as was expected given the relatively long detection range of the boing call type. Spatially explicit capture-recapture was used to estimate density of Cuvier’s beaked whales from the near-surface drifting array of acoustic recorders. A snapshot approach was used with presence or absence of echolocation clicks within a 1-minute snapshot acting as the sampling unit. Using external estimates of group size and echolocation probability in a 1-minute snapshot, the density of Cuvier’s beaked whales, from the two best models was estimated at 5.48 animals per 1000 km2 (CV 0.46). This estimate was similar to estimates calculated using trial-based and distance sampling approaches applied to the same data set. Simulation experiments were conducted to investigate potential bias in estimated density caused by the configuration of the drifting array. Bias from the array configuration was found to be negligible, increased array spacing (approximately doubling and tripling between-sensor spacing) decreased bias, and the drifting aspect of the recorders also decreased bias, compared to simulations with stationary sensors. This work provides evidence that animal presence and absence at broad spatial scales such as hours and days are comparable across gliders, deep-water floats, and stationary recorders. The spatial advantage of mobile instruments is most pronounced for species with short acoustic detection ranges, such as beaked whales. Marine mammal density can be estimated from gliders and mobile drifters using either a trial-based or SECR approach examples presented here provide an exciting advance in marine mammal population monitoring

Mobile Autonomous Passive Acoustic Monitoring of Marine Mammals in the Catalina Basin

Traditional visual survey methods for marine mammals can only detect a fraction of the animals present. Even if the animal can be observed from the surface, visual limitations such as time of day and weather conditions can impede this ability. Recent advances in passive acoustic monitoring technologies have led to the development of mobile autonomous platforms for recording marine mammals. These instruments may allow for improved monitoring of species presence through greater spatial and temporal sampling capabilities. We deployed two types of commercially available platforms in the Catalina Basin in late July through early August 2016. The QUEphone, based on the APEX float (Teledyne Webb Research, Falmouth, MA, USA), is a buoyancy-driven device that dove to 1,000 m where it drifted horizontally with the currents. The Seaglider (Kongsberg Underwater Technology, Lynwood, WA, USA) is also buoyancy-driven, but repeatedly dove down to 1000 m and traversed back and forth across the survey area. Using MATLAB based software Triton, (Scripps Whale Acoustics Laboratory, La Jolla, CA), and Raven (Cornell Lab of Ornithology, Ithaca, NY) programs, I analyzed the acoustic data both visually and aurally using long term spectrogram analysis. The most prevalent species were unidentified delphinids, with 240 of 313 hours containing calls. Marine mammal detections also included unidentified otariid, Risso’s dolphins, and blue, humpback, minke, and Cuvier’s beaked whales. These data will be used to compare the detection capabilities of the QUEphone and Seaglider, contributing to the advancement of the use of these instruments in marine mammal surveys

Species information in whistle frequency modulation patterns of common dolphins

Funding for this project was generously provided by the Office of Naval Research Marine Mammals and Biology program.The most flexible communication systems are those of open-ended vocal learners that can acquire new signals throughout their lifetimes. While acoustic signals carry information in general voice features that affect all of an individual's vocalizations, vocal learners can also introduce novel call types to their repertoires. Delphinids are known for using such learned call types in individual recognition, but their role in other contexts is less clear. We investigated the whistles of two closely related, sympatric common dolphin species, Delphinus delphis and Delphinus bairdii, to evaluate species differences in whistle contours. Acoustic recordings of single-species groups were obtained from the Southern California Bight. We used an unsupervised neural network to categorize whistles and compared the resulting whistle types between species. Of the whistle types recorded in more than one encounter, 169 were shared between species and 60 were species-specific (32 D. delphis types, 28 D. bairdii types). Delphinus delphis used 15 whistle types with an oscillatory frequency contour while only one such type was found in D. bairdii. Given the role of vocal learning in delphinid vocalizations, we argue that these differences in whistle production are probably culturally driven and could help facilitate species recognition between Delphinus species.Publisher PDFPeer reviewe

Detections of whale vocalizations by simultaneously deployed bottom-moored and deep-water mobile autonomous hydrophones

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 PDFPeer reviewe

Behavioral responses of fin whales to military mid-frequency active sonar

Funding. Primary funding for the SOCAL-BRS project was initially provided by the US Navy’s Chief of Naval Operations Environmental Readiness Division and subsequently by the US Navy’s Living Marine Resources (LMR) Program. Additional support for environmental sampling and logistics was also provided by the Office of Naval Research, Marine Mammal Program.The effect of active sonars on marine mammal behavior is a topic of considerable interest and scientific investigation. Some whales, including the largest species (blue whales, Balaenoptera musculus), can be impacted by mid-frequency (1-10 kHz) military sonars. Here we apply complementary experimental methods to provide the first experimentally controlled measurements of behavioral responses to military sonar and similar stimuli for a related endangered species, fin whales (Balaenoptera physalus). Analytical methods include: (1) Principal Component Analysis paired with Generalized Additive Mixed Models; (2) Hidden Markov Models; and (3) structured expert elicitation using response severity metrics. These approaches provide complementary perspectives on the nature of potential changes within and across individuals. Behavioral changes were detected in five of 15 whales during controlled exposure experiments (CEEs) using mid-frequency active sonar (MFAS) or pseudorandom noise (PRN) of similar frequency, duration, and source and received level. No changes were detected during six control (no noise) sequences. Overall responses were more limited in occurrence, severity, and duration than in blue whales and were less dependent upon contextual aspects of exposure and more contingent upon exposure received level. Quantifying the factors influencing marine mammal responses to sonar is critical in assessing and mitigating future impacts.Publisher PDFPeer reviewe

Behavioral responses of individual blue whales (Balaenoptera musculus) to mid-frequency military sonar

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.PostprintPeer reviewe