Edmund R. Gerstein

Vocalization characteristics of North Atlantic right whale surface active groups in the calving habitat, southeastern United States

Passive acoustic surveys were conducted to assess the vocal behavior of North Atlantic right whales (Eubalaena glacialis) in the designated critical calving habitat along the shallow coastal waters of southeastern United States. Underwater vocalizations were recorded using autonomous buoys deployed in close proximity to surface active groups (SAGs). Nine main vocalization types were identified with manual inspection of spectrograms, and standard acoustic descriptors were extracted. Classification trees were used to examine the distinguishing characteristics of calls and quantify their variability within the SAG vocal repertoire. The results show that descriptors of frequency, bandwidth, and spectral disorder are the most important parameters for partitioning the SAG repertoire, contrary to duration-related measures. The reported source levels and vocalization statistics provide sound production data vital to inform regional passive acoustic monitoring and conservation for this endangered species.

Comparison of two methods for detection of North Atlantic Right Whale upcalls

In this paper, a study is carried out for detecting North Atlantic Right Whale upcalls with measurements from passive acoustic monitoring devices. Preprocessed spectrograms of upcalls are subjected to two different tasks, one of which is based on extraction of time-frequency features from upcall contours, and the other that employs a Local Binary Pattern operator to extract salient texture features of the upcalls. Then several classifiers are used to evaluate the effectiveness of both the contour-based and texture-based features for upcall detection. Detection results reveal that popular classifiers such as Linear Discriminant Analysis, Support Vector Machine, and TreeBagger can achieve high detection rates. Furthermore, using LBP features for call detection shows improved accuracy of about 3% to 4% over time-frequency features when an identical classifier is used.

Do manatees utilize infrasonic communication or detection

Some researchers speculate Sirenians might utilize infrasonic communication like their distant elephant cousins; however, audiogram measurements and calibrated manatee vocalizations do not support this contention. A comprehensive series of hearing tests conducted with West Indian manatees yielded the first and most definitive audiogram for any Sirenian. The manatee hearing tests were also the first controlled underwater infrasonic psychometric tests with any marine mammal. Auditory thresholds were measured from 0.4 to 46 kHz, but detection thresholds of possible vibrotactile origin were measured as low as 0.015 kHz. Manatees have short hairs on their bodies that may be sensitive vibrotactile receptors capable of detecting particle displacement in the near field. To detect these signals the manatee rotated on axis, exposing the densest portion of hairs toward the projector. Manatees inhabit shallow water where particle motion detection may be more useful near the water’s surface, where sound pressures are ...

Manatee hearing and sound localization can help navigate noisy shallow waters and cocktail events, no Lombard's needed

Simultaneous masking procedures were used to measure the hearing and underwater sound localization abilities of West Indian manatees. Auditory detection thresholds of pulsed, no-pulsed pure tones, and complex sounds were measured against white noise using forced-choice paradigms. Auditory thresholds as a function of intensity, center frequency, bandwidth, pulse rate, and spectral characteristics were measured. Resulting critical ratios for pure tone measurements demonstrated manatees have acute frequency filtering abilities compared with humans and other marine mammals. Signal repetition rate along with amplitude and frequency modulation providing temporal contrasts against aperiodic background noise and lowered detection thresholds. FM signal detection thresholds were measured at or below ambient background levels. Results with species specific calls and boat noise suggested loudness summation across distant critical bands, as well as FM and amplitude modulation reduced the masking effects observed with ...

Female North Atlantic right whales produce gunshot sounds

North Atlantic right whales (Eubalaena glacialis) produce loud, broadband, short duration sounds referred to as gunshots. The sounds have been hypothesized to function in a reproductive context, as sexual advertisement signals produced by solitary adult males to attract females and/or agonistic displays among males in surface active groups. This study provides evidence that gunshot sounds are also produced by adult females and examines the acoustics and behavioral contexts associated with these calls. Results from boat-based observational surveys investigating the early vocal ontogeny and behavior of right whales in the critical southeast calving habitat are presented for a subset of mothers who produced gunshots while in close proximity to their calves. Of 26 different isolated mother-calf pairs, gunshots were recorded from females of varied ages and maternal experience. The signals were recorded when calves separated from their mothers during curious approaches toward objects on the surface. While the s...

Parametric projectors protecting marine mammals from vessel collisions.

Marine mammals are vulnerable to ship collisions. Measurements of controlled ship passages through vertical hydrophone arrays demonstrate a confluence of propagation factors and near surface effects that obscure the sounds of approaching vessels which then pose serious detection challenges for marine mammals. Joe Blue, who first identified these challenges, later conceived of a parametric method to mitigate them. A highly directional, dual‐frequency parametric array has been developed to reduce collision risks by selectively alerting only those animals in the direct path of approaching vessels. The system projector is comprised of multiple elements, band‐centered to transmit a high carrier frequency along with a lower side band signal. A single‐side band modulation and phase‐shift method are employed. The non‐linearity of water then demodulates the mixed high frequency carrier into a lower frequency waveform audible to both manatees and whales. The bow mounted array projects a narrow beam directly ahead o...

Underwater noise and zones of masking with respect to hopper dredging and manatees in the St. Johns River in Jacksonville, FL

Underwater noise radiating from dredging can effectively obscure or mask biological and other important sounds. This study recorded underwater acoustic characteristics of hopper dredging in the St. Johns River, Jacksonville, FL, to evaluate noise impacts in the waterway with respect to the endangered West Indian manatee. Of particular interest was the extent and range that dredging noise may mask the sounds of approaching commercial and recreational vessels. Vertical hydrophone arrays and a multi‐channel PC‐based recording system were used to measure dredging noise at various distances. Ambient noise surveys, active propagation of calibrated sources, and controlled boat noise measurements were conducted along the waterway. These data were integrated with behavioral hearing data to estimate zones of masking surrounding dredging. Three discernable noise sources that masked boat noise were (1) cavitation from dredge propellers, (2) draghead vacuuming, and (3) noise from submerged slurry pipelines. Sustained ...

Ship strikes and whales: Shadows, mirrors and paradoxes

Ship collisions with whales and other marine animals occur near the surface. Here Snells law applies and can play a crucial role in the survival and behavioral ecology of marine mammals. In this study we investigated some theoretical constructs of near surface sound propagation that can render whales vulnerable to collisions. Empirical measurements support predictions and demonstrate that propeller noise directly ahead of many large vessels can become indistinguishable from the ambient noise. Large acoustic shadows in front of approaching ships and the confluence of near surface acoustic propagation effects seriously challenge the whales’ ability to detect and locate approaching ships. At the surface, ship noise profiles are loudest at the stern and off the port and starboard sides while remaining remarkably quiet at the bow. Whales with calves swimming near the surface alerted to ship sounds may seek refuge by actively swimming into the quieter shadow zones directly ahead of vessels. Once here, hydrodyna...

Ship strike acoustics: It is all just shadows and mirrors

Whales are vulnerable to collisions when near the surface and in shallow water. Here the physics of near‐surface sound propagation may play a crucial role in their survival. Ships sufficient in size to mortally injury whales generate acoustic spectra dominated by very low frequencies. Since the ocean’s pressure‐release surface severely attenuates frequencies that are generated at distances less than a wavelength from the surface, whales may not detect low‐frequency sounds generated by approaching ships. The Lloyd Mirror Effect predicts sound pressure levels at the surface approximate zero and empirical acoustic measurements support the prediction, while quantifying another important phenomenon associated with large ships, Acoustical Shadowing. The confluence of these acoustic propagation effects pose significant ecological consequences for marine mammals at the surface. While aerial and shipboard monitoring networks help navigate ships away from whales sighted on the surface, these programs are not reliab...

Vocal behavior and ontogeny of Northern right whales in the southeast critical habitat

North Atlantic right whales are one of the most endangered of the great whales. A remnant population of ~500 inhabits the eastern seaboard of North America. A small fraction (2%) travels south to their critical calving habitat along the Florida and Georgia coast. By late November and through the winter, right whales give birth and nurse their calves in these shallow waters before departing in early spring to their northern habitats. In the southeast critical habitat mother-calf pairs remain generally isolated from other whales, presenting a unique platform to study vocal development and learning in large whales. Using small boats, GPS-instrumented, free-drifting autonomous acoustic buoys were deployed in close proximity to 44 photo-identified mother-calf pairs over 7 calving seasons. Surface video and synchronized underwater recordings documented their social and vocal behavior. With the exception of some low-energy gunshot sounds, mothers, and their calves, remained predominantly silent during the first ...