Stephen W. Martin

Echolocation characteristics of free-swimming bottlenose dolphins during object detection and identification.

A biosonar measurement tool (BMT) was created to investigate dolphin echolocation search strategies by recording echolocation clicks, returning echoes, and three-dimensional angular motion, velocity, and depth of free-swimming dolphins performing open-water target detections. Trial start and stop times, locations determined from a differential global positioning system (DGPS), and BMT motion and acoustic data were used to produce spatial and acoustic representations of the searches. Two dolphins (LUT, FLP) searched for targets lying on the seafloor of a bay environment while carrying the BMT. LUT searched rapidly (< 10 s), produced few clicks, and varied click-peak frequency (20-120 kHz); FLP searched relatively slowly (tens of seconds) and produced many hundreds of clicks with stereotypical frequency-dependent energy distributions dominating from 30-60 kHz. Dolphins amplified target echo returns by either increasing the click source level or reducing distance to the target but without reducing source level. The distribution of echolocation click-peak frequencies suggested a bias in the dominant frequency components of clicks, possibly due to mechanical constraints of the click generator. Prior training and hearing loss accommodation potentially explain differences in the search strategies of the two dolphins.

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.

Instrumenting free-swimming dolphins echolocating in open water

Dolphins within the Navy Marine Mammal Program use echolocation to effectively locate underwater mines. They currently outperform manmade systems at similar tasks, particularly in cluttered environments and on buried targets. In hopes of improving manmade mine-hunting sonar systems, two instrumentation packages were developed to monitor free-swimming dolphin motion and echolocation during open-water target detection tasks. The biosonar measurement tool (BMT) is carried by a dolphin and monitors underwater position and attitude while simultaneously recording echolocation clicks and returning echoes through high-gain binaural receivers. The instrumented mine simulator (IMS) is a modified bottom target that monitors echolocation signals arriving at the target during ensonification. Dolphin subjects were trained to carry the BMT in open-bay bottom-object target searches in which the IMS could serve as a bottom object. The instrumentation provides detailed data that reveal hereto-unavailable information on the search strategies of free-swimming dolphins conducting open-water, bottom-object search tasks with echolocation.

Automated acoustic localization and call association for vocalizing humpback whales on the Navy's Pacific Missile Range Facility

Time difference of arrival (TDOA) methods for acoustically localizing multiple marine mammals have been applied to recorded data from the Navys Pacific Missile Range Facility in order to localize and track humpback whales. Modifications to established methods were necessary in order to simultaneously track multiple animals on the range faster than real-time and in a fully automated way, while minimizing the number of incorrect localizations. The resulting algorithms were run with no human intervention at computational speeds faster than the data recording speed on over forty days of acoustic recordings from the range, spanning multiple years. Spatial localizations based on correlating sequences of units originating from within the range produce estimates having a standard deviation typically 10 m or less (due primarily to TDOA measurement errors), and a bias of 20 m or less (due primarily to sound speed mismatch). An automated method for associating units to individual whales is presented, enabling automated humpback song analyses to be performed.

Behavioral responses of California sea lions to mid-frequency (3250-3450 Hz) sonar signals.

Military sonar has the potential to negatively impact marine mammals. To investigate factors affecting behavioral disruption in California sea lions (Zalophus californianus), fifteen sea lions participated in a controlled exposure study using a simulated tactical sonar signal (1 s duration, 3250-3450 Hz) as a stimulus. Subjects were placed into groups of three and each group received a stimulus exposure of 125, 140, 155, 170, or 185 dB re: 1 μPa (rms). Each subject was trained to swim across an enclosure, touch a paddle, and return to the start location. Sound exposures occurred at the mid-point of the enclosure. Control and exposure sessions were run consecutively and each consisted of ten, 30-s trials. The occurrence and severity of behavioral responses were used to create acoustic dose-response and dose-severity functions. Age of the subject significantly affected the dose-response relationship, but not the dose-severity relationship. Repetitive exposures did not affect the dose-response relationship.

Acoustic Ecology and Behavior of Minke Whales in the Hawaiian and Marianas Islands: Localization, Abundance Estimation, and Characterization of Minke Whale “Boings”

Balaenoptera acutorostrata (minke whale) is a small and elusive baleen whale that is rarely sighted in the tropical waters of the North Pacific Ocean. During winter and spring, complex sounds called ”boings” are frequently detected around the Hawaiian Islands and other Pacific island regions (Norris et al. 2009; Thompson and Friedl 1982). Although boings were described over 45 years ago (Wenz 1964), they were not attributed to minke whales until very recently (Rankin and Barlow 2005). Sightings of Balaenoptera acutorostrata are uncommon in tropical and subtropical waters; however, boings are frequently detected around the Hawaiian Islands using seafloor hydrophones and from hydrophone arrays towed from research vessels. Even today, very little is known about acoustic behaviors and ecology of Balaenoptera acutorostrata. The long-term objective of this research effort is to improve our understanding of the acoustic ecology and behavior of Balaenoptera acutorostrata in their breeding habitat.

Minke whales (Balaenoptera acutorostrata) respond to navy training.

Minke whales (Balaenoptera acutorostrata) were acoustically detected and localized via their boing calls using 766 h of recorded data from 24 hydrophones at the U.S. Navys Pacific Missile Range Facility located off Kauai, Hawaii. Data were collected before, during, and after naval undersea warfare training events, which occurred in February over three consecutive years (2011-2013). Data collection in the during periods were further categorized as phase A and phase B with the latter being the only period with naval surface ship activities (e.g., frigate and destroyer maneuvers including the use of mid-frequency active sonar). Minimum minke whale densities were estimated for all data periods based upon the numbers of whales acoustically localized within the 3780 km(2) study area. The 2011 minimum densities in the study area were: 3.64 whales [confidence interval (CI) 3.31-4.01] before the training activity, 2.81 whales (CI 2.31-3.42) for phase A, 0.69 whales (CI 0.27-1.8) for phase B and 4.44 whales (CI 4.04-4.88) after. The minimum densities for the phase B periods were highly statistically significantly lower (p < 0.001) from all other periods within each year, suggesting a clear response to the phase B training. The phase A period results were mixed when compared to other non-training periods.

Analysis of melon‐headed whale aggregation in Hanalei Bay, July 2004

On 3 July 2004, an aggregation of ca. 150–200 melon‐headed whales (Peponocephala electra) appeared in the shallow waters of Hanalei Bay, Kauai and congregated there for over 27 h. Preceding the whales’ appearance and partially coincident with their time in the Bay, midrange (3.5–5 kHz) tactical sonars were intermittently deployed during the Rim of the Pacific 2004 (RIMPAC) joint military exercises being conducted in waters near Kauai by the U.S., Japan, and Australia Navies. An NOAA report (Southall et al., 2006) attributed the active sonar usage as a plausible, if not likely, contributing factor. A detailed timeline and reconstruction of the RIMPAC activities is presented showing the worst‐case estimates of the sonar sound levels in the waters surrounding Kauai. A re‐examination of available evidence combined with a new report of a simultaneous and similar aggregation in Sasanhaya Bay, Rota, Commonwealth of the Northern Mariana Islands, brings the plausibility conclusion into question. [This work was spo...

Swim track kinematics and calling behavior attributed to Bryde's whales on the Navy's Pacific Missile Range Facility

Time difference of arrival methods for acoustically localizing multiple marine mammals have been applied to recorded data from the Navys Pacific Missile Range Facility in order to localize and track calls attributed to Brydes whales. Data were recorded during the months of August-October 2014, and 17 individual tracks were identified. Call characteristics were compared to other Brydes whale vocalizations from the Pacific Ocean, and locations of the recorded signals were compared to published visual sightings of Brydes whales in the Hawaiian archipelago. Track kinematic information, such as swim speeds, bearing information, track duration, and directivity, was recorded for the species. The intercall interval was also established for most of the tracks, providing cue rate information for this species that may be useful for future acoustic density estimate calculations.

Simultaneous recordings of marine mammal calls by a glider, float, and cabled hydrophone array

Recent advances in passive acoustic monitoring (PAM) technologies have led to development of mobile autonomous platforms for recording marine mammals. These instruments may allow greater spatial and temporal sampling than traditional towed or bottom moored systems. However, comparison of recording abilities of these instruments to traditional methods has yet to be performed. We deployed two types of commercially available platforms at the Southern California Offshore Range (SCORE) complex in late December 2015 through early January 2016. The QUEphone, based on the APEX float (Teledyne Webb Research, Falmouth, MA, USA), is a buoyancy driven device capable of descending to 2000 m where it drifts horizontally with the currents. The Seaglider (Kongsberg Underwater Technology, Lynwood, WA, USA) is also buoyancy driven, but dives repeatedly up to 1000 m following a flight path controlled via satellite. We deployed one glider and two floats, each equipped with identical acoustic sensors developed by Oregon State...