Susan E. Parks

Evidence that ship noise increases stress in right whales

Baleen whales (Mysticeti) communicate using low-frequency acoustic signals. These long-wavelength sounds can be detected over hundreds of kilometres, potentially allowing contact over large distances. Low-frequency noise from large ships (20–200 Hz) overlaps acoustic signals used by baleen whales, and increased levels of underwater noise have been documented in areas with high shipping traffic. Reported responses of whales to increased noise include: habitat displacement, behavioural changes and alterations in the intensity, frequency and intervals of calls. However, it has been unclear whether exposure to noise results in physiological responses that may lead to significant consequences for individuals or populations. Here, we show that reduced ship traffic in the Bay of Fundy, Canada, following the events of 11 September 2001, resulted in a 6 dB decrease in underwater noise with a significant reduction below 150 Hz. This noise reduction was associated with decreased baseline levels of stress-related faecal hormone metabolites (glucocorticoids) in North Atlantic right whales (Eubalaena glacialis). This is the first evidence that exposure to low-frequency ship noise may be associated with chronic stress in whales, and has implications for all baleen whales in heavy ship traffic areas, and for recovery of this endangered right whale population.

Short- and long-term changes in right whale calling behavior: The potential effects of noise on acoustic communication

The impact of anthropogenic noise on marine mammals has been an area of increasing concern over the past two decades. Most low-frequency anthropogenic noise in the ocean comes from commercial shipping which has contributed to an increase in ocean background noise over the past 150 years. The long-term impacts of these changes on marine mammals are not well understood. This paper describes both short- and long-term behavioral changes in calls produced by the endangered North Atlantic right whale (Eubalaena glacialis) and South Atlantic right whale (Eubalaena australis) in the presence of increased low-frequency noise. Right whales produce calls with a higher average fundamental frequency and they call at a lower rate in high noise conditions, possibly in response to masking from low-frequency noise. The long-term changes have occurred within the known lifespan of individual whales, indicating that a behavioral change, rather than selective pressure, has resulted in the observed differences. This study provides evidence of a behavioral change in sound production of right whales that is correlated with increased noise levels and indicates that right whales may shift call frequency to compensate for increased band-limited background noise.

Individual right whales call louder in increased environmental noise

The ability to modify vocalizations to compensate for environmental noise is critical for successful communication in a dynamic acoustic environment. Many marine species rely on sound for vital life functions including communication, navigation and feeding. The impacts of significant increases in ocean noise levels from human activities are a current area of concern for the conservation of marine mammals. Here, we document changes in calling behaviour by individual endangered North Atlantic right whales (Eubalaena glacialis) in increased background noise. Right whales, like several bird and primate species, respond to periods of increased noise by increasing the amplitude of their calls. This behaviour may help maintain the communication range with conspecifics during periods of increased noise. These call modifications have implications for conservation efforts for right whales, affecting both the way whales use sound to communicate and our ability to detect them with passive acoustic monitoring systems.

Measuring acoustic habitats

1. Many organisms depend on sound for communication, predator/prey detection and navigation. The acoustic environment can therefore play an important role in ecosystem dynamics and evolution. A growing number of studies are documenting acoustic habitats and their influences on animal development, behaviour, physiology and spatial ecology, which has led to increasing demand for passive acoustic monitoring (PAM) expertise in the life sciences. However, as yet, there has been no synthesis of data processing methods for acoustic habitat monitoring, which presents an unnecessary obstacle to would-be PAM analysts. 2. Here, we review the signal processing techniques needed to produce calibrated measurements of terrestrial and aquatic acoustic habitats. We include a supplemental tutorial and template computer codes in matlab and r, which give detailed guidance on how to produce calibrated spectrograms and statistical analyses of sound levels. Key metrics and terminology for the characterisation of biotic, abiotic and anthropogenic sound are covered, and their application to relevant monitoring scenarios is illustrated through example data sets. To inform study design and hardware selection, we also include an up-to-date overview of terrestrial and aquatic PAM instruments. 3. Monitoring of acoustic habitats at large spatiotemporal scales is becoming possible through recent advances in PAM technology. This will enhance our understanding of the role of sound in the spatial ecology of acoustically sensitive species and inform spatial planning to mitigate the rising influence of anthropogenic noise in these ecosystems. As we demonstrate in this work, progress in these areas will depend upon the application of consistent and appropriate PAM methodologies.

Variability in ambient noise levels and call parameters of North Atlantic right whales in three habitat areas

The North Atlantic right whale inhabits the coastal waters off the east coasts of the United States and Canada, areas characterized by high levels of shipping and fishing activities. Acoustic communication plays an important role in the social behavior of these whales and increases in low-frequency noise may be leading to changes in their calling behavior. This study characterizes the ambient noise levels, including both natural and anthropogenic sources, and right whale upcall parameters in three right whale habitat areas. Continuous recordings were made seasonally using autonomous bottom-mounted recorders in the Bay of Fundy, Canada (2004, 2005), Cape Cod Bay, (2005, 2006), and off the coast of Georgia (2004-2005, 2006-2007). Consistent interannual trends in noise parameters were found for each habitat area, with both the band level and spectrum level measurements higher in the Bay of Fundy than in the other areas. Measured call parameters varied between habitats and between years within the same habitat area, indicating that habitat area and noise levels alone are not sufficient to predict variability in call parameters. These results suggest that right whales may be responding to the peak frequency of noise, rather than the absolute noise level in their environment.

Traffic noise causes physiological stress and impairs breeding migration behaviour in frogs

Noise from human activities is increasing globally. We provide evidence that traffic noise increases glucocorticoid concentrations and impairs reproductive behavior in frogs. Since prolonged stress can compromise health, survival and reproduction, and because impaired reproductive behavior can reduce mating opportunities, these results suggest noise may contribute to amphibian declines.

Detection and Recognition of North Atlantic Right Whale Contact Calls in the Presence of Ambient Noise

In this paper, the problem of detecting and recognizing North Atlantic right whale (NARW), Eubalaena glacialis, contact calls in the presence of ambient noise is considered. A proposed solution is based on a multistage, hypothesis-testing technique that involves the generalized likelihood ratio test (GLRT) detector, spectrogram testing, and feature vector testing algorithms. The main contributions of this paper are the inclusion of noise kernels for signals likely to produce false alarms and a second stage classification algorithm which extracts parameters from candidate contact calls and constructs a scaled squared error statistic for parameters which lie outside the range of expected calls. Closed-form representations of the algorithms are derived and realizable detection schemes are developed. Test results show that the proposed technique is able to detect approximately 80% of the contact calls detected by the human operator with about 26 false alarms per 24 h of observation. Testing data set included 44 227 right whale contact calls detected by eight human operators who performed visual and aural inspection of the data spectrogram. Data were collected in different periods from March 2001 to February 2007, in Cape Cod Bay, Great South Channel, and in the coastal waters of Georgia.

Assessing marine ecosystem acoustic diversity across ocean basins

Abstract Concurrent with the elevation of the concern over the state of sound in the ocean, advances in terrestrial acoustic monitoring techniques have produced concepts and tools that may be applicable to the underwater world. Several index values that convey information related to acoustic diversity with a single numeric measurement made from acoustic recordings have been proposed for rapidly assessing community biodiversity. Here we apply the acoustic biodiversity index method to low frequency recordings made from three different ocean basins to assess its appropriateness for characterizing species richness in the marine environment. Initial results indicated that raw acoustic entropy (H) values did not correspond to biological patterns identified from individual signal detections and classification. Noise from seismic airgun activity masked the weaker biological signals and confounded the entropy calculation. A simple background removal technique that subtracted an average complex spectrum characteristic of seismic exploration signals from the average spectra of each analysis period that contained seismic signals was applied to compensate for salient seismic airgun signals present in all locations. The noise compensated (HN) entropy index was more reflective of biological patterns and holds promise for the use of rapid acoustic biodiversity in the marine environment as an indicator of habitat biodiversity and health.

The Lombard effect and other noise-induced vocal modifications: Insight from mammalian communication systems

Humans and non‐human mammals exhibit fundamentally similar vocal responses to increased noise, including increases in vocalization amplitude (the Lombard effect) and changes to spectral and temporal properties of vocalizations. Different research focuses have resulted in significant discrepancies in study methodologies and hypotheses among fields, leading to particular knowledge gaps and techniques specific to each field. This review compares and contrasts noise‐induced vocal modifications observed from human and non‐human mammals with reference to experimental design and the history of each field. Topics include the effects of communication motivation and subject‐specific characteristics on the acoustic parameters of vocalizations, examination of evidence for a proposed biomechanical linkage between the Lombard effect and other spectral and temporal modifications, and effects of noise on self‐communication signals (echolocation). Standardized terminology, cross‐taxa tests of hypotheses, and open areas for future research in each field are recommended. Findings indicate that more research is needed to evaluate linkages among vocal modifications, context dependencies, and the finer details of the Lombard effect during natural communication. Studies of non‐human mammals could benefit from applying the tightly controlled experimental designs developed in human research, while studies of human speech in noise should be expanded to include natural communicative contexts. The effects of experimental design and behavioural context on vocalizations should not be neglected as they may impact the magnitude and type of noise‐induced vocal modifications.

Anatomical predictions of hearing in the North Atlantic right whale

Some knowledge of the hearing abilities of right whales is important for understanding their acoustic communication system and possible impacts of anthropogenic noise. Traditional behavioral or physiological techniques to test hearing are not feasible with right whales. Previous research on the hearing of marine mammals has shown that functional models are reliable estimators of hearing sensitivity in marine species. Fundamental to these models is a comprehensive analysis of inner ear anatomy. Morphometric analyses of 18 inner ears from 13 stranded North Atlantic right whales (Eubalaena glacialis) were used for development of a preliminary model of the frequency range of hearing. Computerized tomography was used to create two‐dimensional (2D) and 3D images of the cochlea. Four ears were decalcified and sectioned for histologic measurements of the basilar membrane. Basilar membrane length averaged 55.7 mm (range, 50.5 mm–61.7 mm). The ganglion cell density/mm averaged 1,842 ganglion cells/mm. The thickness/width measurements of the basilar membrane from slides resulted in an estimated hearing range of 10 Hz–22 kHz based on established marine mammal models. Additional measurements from more specimens will be necessary to develop a more robust model of the right whale hearing range. Anat Rec, 290:734–744, 2007.