Effects of vibratory pile driver noise on echolocation and vigilance in bottlenose dolphins (Tursiops truncatus)

Males miss and females forgo: Auditory masking from vessel noise impairs foraging efficiency and success in killer whales

Understanding how the environment mediates an organism's ability to meet basic survival requirements is a fundamental goal of ecology. Vessel noise is a global threat to marine ecosystems and is increasing in intensity and spatiotemporal extent due to growth in shipping coupled with physical changes to ocean soundscapes from ocean warming and acidification. Odontocetes rely on biosonar to forage, yet determining the consequences of vessel noise on foraging has been limited by the challenges of observing underwater foraging outcomes and measuring noise levels received by individuals. To address these challenges, we leveraged a unique acoustic and movement dataset from 25 animal-borne biologging tags temporarily attached to individuals from two populations of fish-eating killer whales (Orcinus orca) in highly transited coastal waters to (1) test for the effects of vessel noise on foraging behaviors-searching (slow-click echolocation), pursuit (buzzes), and capture and (2) investigate the mechanism of interference. For every 1 dB increase in maximum noise level, there was a 4% increase in the odds of searching for prey by both sexes, a 58% decrease in the odds of pursuit by females and a 12.5% decrease in the odds of prey capture by both sexes. Moreover, all but one deep (≥75 m) foraging attempt with noise ≥110 dB re 1 μPa (15-45 kHz band; n = 6 dives by n = 4 whales) resulted in failed prey capture. These responses are consistent with an auditory masking mechanism. Our findings demonstrate the effects of vessel noise across multiple phases of odontocete foraging, underscoring the importance of managing anthropogenic inputs into soundscapes to achieve conservation objectives for acoustically sensitive species. While the timescales for recovering depleted prey species may span decades, these findings suggest that complementary actions to reduce ocean noise in the short term offer a critical pathway for recovering odontocete foraging opportunities.

Acoustic Monitoring of Professionally Managed Marine Mammals for Health and Welfare Insights

Research evaluating marine mammal welfare and opportunities for advancements in the care of species housed in a professional facility have rapidly increased in the past decade. While topics, such as comfortable housing, adequate social opportunities, stimulating enrichment, and a high standard of medical care, have continued to receive attention from managers and scientists, there is a lack of established acoustic consideration for monitoring the welfare of these animals. Marine mammals rely on sound production and reception for navigation and communication. Regulations governing anthropogenic sound production in our oceans have been put in place by many countries around the world, largely based on the results of research with managed and trained animals, due to the potential negative impacts that unrestricted noise can have on marine mammals. However, there has not been an established best practice for the acoustic welfare monitoring of marine mammals in professional care. By monitoring animal hearing and vocal behavior, a more holistic view of animal welfare can be achieved through the early detection of anthropogenic sound sources, the acoustic behavior of the animals, and even the features of the calls. In this review, the practice of monitoring cetacean acoustic welfare through behavioral hearing tests and auditory evoked potentials (AEPs), passive acoustic monitoring, such as the Welfare Acoustic Monitoring System (WAMS), as well as ideas for using advanced technologies for utilizing vocal biomarkers of health are introduced and reviewed as opportunities for integration into marine mammal welfare plans.

Acoustic characteristics from an in-water down-the-hole pile drilling activity

Sound generated by pile installation using a down-the-hole (DTH) hammer is not well documented and differs in character from sound generated by conventional impact and vibratory pile driving. This paper describes underwater acoustic characteristics from DTH pile drilling during the installation of 0.84-m shafts within 1.22-m steel piles in Ketchikan, Alaska. The median single-strike sound exposure levels were 138 and 142 dB re 1 μPa²s at 10 m for each of the two piles, with cumulative sound exposure levels of 185 and 193 dB re 1 μPa²s at 10 m, respectively. The sound levels measured at Ketchikan were significantly lower than previous studies, and the sound was determined to be non-impulsive in this study as compared to impulsive in previous studies. These differences likely result from the DTH hammer not making direct contact with the pile, as had been the case in previous studies. Therefore, we suggest using the term DTH pile drilling to distinguish from DTH pile driving when the hammer strikes the pile. Further research is needed to investigate DTH piling techniques and associated sound-generating mechanisms and to differentiate the various types of sound emitted, which has important implications for the underwater sound regulatory community.

Cetacean Acoustic Welfare in Wild and Managed-Care Settings: Gaps and Opportunities

Simple Summary

Whales and dolphins in managed-care and wild settings are exposed to human-made, anthropogenic sounds of varying degrees. These sounds can lead to potential negative welfare outcomes if not managed correctly in zoos or in the open ocean. Current wild regulations are based on generally broad taxa-based hearing thresholds, but there is movement to take other contextual factors into account, partially informed by researchers familiar with work in zoological settings. In this spirit, we present more nuanced future directions for the evaluation of acoustic welfare in both wild and managed-care settings, with suggestions for how research in both domains can inform each other as a means to address the paucity of research available on this topic, especially in managed-care environments.

Abstract

Cetaceans are potentially at risk of poor welfare due to the animals’ natural reliance on sound and the persistent nature of anthropogenic noise, especially in the wild. Industrial, commercial, and recreational human activity has expanded across the seas, resulting in a propagation of sound with varying frequency characteristics. In many countries, current regulations are based on the potential to induce hearing loss; however, a more nuanced approach is needed when shaping regulations, due to other non-hearing loss effects including activation of the stress response, acoustic masking, frequency shifts, alterations in behavior, and decreased foraging. Cetaceans in managed-care settings share the same acoustic characteristics as their wild counterparts, but face different environmental parameters. There have been steps to integrate work on welfare in the wild and in managed-care contexts, and the domain of acoustics offers the opportunity to inform and connect information from both managed-care settings and the wild. Studies of subjects in managed-care give controls not available to wild studies, yet because of the conservation implications, wild studies on welfare impacts of the acoustic environment on cetaceans have largely been the focus, rather than those in captive settings. A deep integration of wild and managed-care-based acoustic welfare research can complement discovery in both domains, as captive studies can provide greater experimental control, while the more comprehensive domain of wild noise studies can help determine the gaps in managed-care based acoustic welfare science. We advocate for a new paradigm in anthropogenic noise research, recognizing the value that both wild and managed-care research plays in illustrating how noise pollution affects welfare including physiology, behavior, and cognition.

Auditory masking in killer whales (Orcinus orca): Critical ratios for tonal signals in Gaussian noise

Masked detection thresholds were measured for two killer whales (Orcinus orca) using a psychoacoustic, adaptive-staircase procedure. Noise bands were 1-octave wide continuous Gaussian noise. Tonal signals extended between 500 Hz and 80 kHz. Resulting critical ratios increased with the signal frequency from 15 dB at 500 Hz up to 32 dB at 80 kHz. Critical ratios for killer whales were similar to those of other odontocetes despite considerable differences in size, hearing morphology, and hearing sensitivity between species.

Underwater noise characterization of down-the-hole pile driving activities off Biorka Island, Alaska

Although down-the-hole (DTH) pile driving is increasingly used for in-water pile installation, the characteristics of underwater noise from DTH pile driving is largely undocumented and unstudied. This study presents a comprehensive analysis of the noise characteristics during DTH pile driving of two steel pipe piles in shallow waters off southeast Alaska. The results showed that single-strike sound exposure levels measured at 10 m were 147 and 145 dB re 1 μPa²s with a total of 21,742 and 38,631 hammer strikes, with cumulative sound exposure levels to install each pile at 192 and 191 dB re 1 μPa²s, respectively. Though noise levels from a single strike was lower than impact pile driving of a similar pile, the cumulative sound exposure levels are likely comparable due to the much higher striking rate.

Influence of acoustic habitat variation on Indo-Pacific humpback dolphin (Sousa chinensis) in shallow waters of Hainan Island, China

The Indo-Pacific humpback dolphin (IPHD, Sousa chinensis) is a coastal species inhabiting tropical and warm-temperate waters. The presence of this vulnerable dolphin was recently discovered in shallow waters southwest of Hainan Island, China. The influence of the acoustic habitat on the distribution and behavior of IPHD was investigated using an array of passive acoustic platforms (n = 6) that spanned more than 100 km of coastline during a 75-day monitoring period. Its presence was assessed within 19 215 five-min recordings by classifying echolocation clicks using machine learning techniques. Spectrogram analysis was applied to further investigate the acoustic behavior of IPHD and to identify other prominent sound sources. The variation in the ambient noise levels was also measured to describe the spatiotemporal patterns of the acoustic habitat among the different sampling sites. Social and feeding sounds of IPHD (whistles and click-series of pulsed sounds) were identified together with other biological sources (finless porpoise, soniferous fishes, and snapping shrimps) and anthropogenic activities (ship noise, explosions, and sonars). Distribution, acoustic behavior, and habitat use of this nearshore dolphin species were strongly influenced by the abundance of soniferous fishes, and under similar conditions, the species was more acoustically active in locations with lower noise levels.

Inter- and intraspecific vigilance patterns of two sympatric Tibetan ungulates

Vigilance is an important antipredation technique that can be affected by many factors, such as body size and group size. Small animals are more vulnerable than large ones, so the former are expected to behave more vigilantly than the latter. This effect of body size on vigilance may occur inter- or intraspecifically. We studied the vigilance behavior of two sympatric wild ungulates, Tibetan antelopes (Pantholops hodgsonii) and Tibetan gazelles (Procapra picticaudata). Tibetan antelopes, with a body size of 33 kg are much larger than Tibetan gazelles, with a body size of approximately 14 kg. Tibetan antelopes are sexually and body-size dimorphic; that is, males are much heavier than females. Alternately, Tibetan gazelles are sexually dimorphic but the sexes do not differ in weight. Tibetan gazelles scanned their environment more frequently than Tibetan antelopes did. Small female Tibetan antelopes scanned their environment more frequently than males did, whereas male Tibetan gazelles scanned their environment more frequently than females did. Group size did not affect the vigilance of Tibetan gazelle, but its negative effect on the vigilance of male Tibetan antelopes was marginally significant. In female Tibetan antelopes, vigilance in large groups was high probably because of scramble competition and social monitoring. Our results suggested that body mass and group size play an important role in shaping the vigilance of these two rare Tibetan ungulates.

Interacting effects of vessel noise and shallow river depth elevate metabolic stress in Ganges river dolphins

In riverine ‘soundscapes’, complex interactions between sound, substrate type, and depth create difficulties in assessing impacts of anthropogenic noise pollution on freshwater fauna. Underwater noise from vessels can negatively affect endangered Ganges river dolphins (Platanista gangetica), which are ‘almost blind’ and rely entirely on high-frequency echolocation clicks to sense their environment. We conducted field-based acoustic recordings and modelling to assess acoustic responses of Platanista to underwater noise exposure from vessels in the Ganga River (India), which is now being transformed into a major waterway. Dolphins showed enhanced activity during acute noise exposure and suppressed activity during chronic exposure. Increase in ambient noise levels altered dolphin acoustic responses, strongly masked echolocation clicks, and more than doubled metabolic stress. Noise impacts were further aggravated during dry-season river depth reduction. Maintaining ecological flows, downscaling of vessel traffic, and propeller modifications to reduce cavitation noise, could help mitigate noise impacts on Ganges river dolphins.

Effects of pollution on marine organisms

This review covers selected 2018 articles on the biological effects of pollutants, including human physical disturbances, on marine and estuarine plants, animals, ecosystems, and habitats. The review, based largely on journal articles, covers field and laboratory measurement activities (bioaccumulation of contaminants, field assessment surveys, toxicity testing, and biomarkers) as well as pollution issues of current interest including endocrine disrupters, emerging contaminants, wastewater discharges, marine debris, dredging, and disposal. Special emphasis is placed on effects of oil spills and marine debris due largely to the 2010 Deepwater Horizon oil blowout in the Gulf of Mexico and proliferation of data on the assimilation and effects of marine debris. Several topical areas reviewed in the past (e.g., mass mortalities ocean acidification) were dropped this year. The focus of this review is on effects, not on pollutant sources, chemistry, fate, or transport. There is considerable overlap across subject areas (e.g., some bioaccumulation data may be appear in other topical categories such as effects of wastewater discharges, or biomarker studies appearing in oil toxicity literature). Therefore, we strongly urge readers to use keyword searching of the text and references to locate related but distributed information. Although nearly 400 papers are cited, these now represent a fraction of the literature on these subjects. Use this review mainly as a starting point. And please consult the original papers before citing them.

The effect of jamming stimuli on the echolocation behavior of the bottlenose dolphin, Tursiops truncatus

Echolocating bats and odontocetes face the potential challenge of acoustic interference from neighbors, or sonar jamming. To counter this, many bat species have adapted jamming avoidance strategies to improve signal detection, but any such avoidance strategies in dolphins is unknown. This study provides an investigation into whether dolphins modify echolocation behavior during jamming scenarios. Recorded echolocation clicks were projected at different click repetition rates and at different aspect angles relative to two dolphins' heads while each dolphin was performing a target detection task. Changes in the timing, amplitude, and frequency of structure of the dolphin's emitted signals were compared to determine if and how dolphins modify echolocation when faced with potentially interfering conspecific echolocation signals. The results indicate that both dolphins demonstrated different responses when faced with jamming scenarios, which may reflect optimal strategies according to individual auditory perception abilities.

Dolphins maintain high echolocation vigilance for eight hours without primary (food) reinforcement

Studies have demonstrated that dolphins can maintain continuous auditory or echolocation vigilance for up to 5 to 15 days when provided with continuous primary reinforcement (i.e., food reward after each correct detection). The goals of this study were to examine whether dolphins could perform an 8-h echolocation vigilance task featuring variable reinforcement schedules, where correct responses were intermittently rewarded, and variable acoustic secondary reinforcement (feedback) patterns. Three dolphins were trained to echolocate simulated targets and press a response paddle upon detecting echoes. Three conditioned reinforcement conditions were utilized: no (acoustic) feedback, acoustic feedback, and structured acoustic feedback. The probability of primary reinforcement following a correct response began at 50% for all dolphins but was sequentially reduced to 25%, 12%, 6%, and 0% each time performance criteria were met. Conditions including acoustic feedback resulted in two dolphins successfully performing the echolocation vigilance task under the 0% primary reinforcement schedule (8 h before receiving primary reinforcement). None of the animals reached 0% reinforcement probability in the no feedback condition. The results demonstrate that dolphins can perform experimental echolocation tasks for extended time periods without primary reinforcement and suggest that secondary reinforcement may be important to maintain this behavior.