Ecology of fish hearing

Yellowtail damselfish Chrysiptera parasema can associate predation risk with the acoustic call of a heterospecific damselfish following pairing with conspecific alarm cues

The ability to detect and respond to the presence of predation risk is under intense selection, especially for small-bodied fishes. Damselfishes (Pomacentridae) use auditory vocalizations during inter- and intrasexual interactions, but it is not known if they can use vocalizations in the context of predator-prey interactions. Here, we test if yellowtail damselfish, Chrysiptera parasema, can learn to associate the territorial vocalization of heterospecific humbug damselfish Dascyllus aruanus with predation risk. In conditioning trials yellowtail damselfish were presented with the territorial call of humbug damselfish while either blank water (control treatment) or chemical alarm cue derived from damaged skin of conspecific yellowtail damselfish was introduced. In conditioning trials, fish exposed to alarm cue exhibited increased activity and spent more time in the water column relative to fish that received the control treatment. After a single conditioning trial, conditioned fish were exposed again to the territorial call of humbug damselfish. Fish conditioned with the call + alarm cue showed increased activity and spent more time in the water column relative to fish that had been conditioned with the control treatment. These data indicate associative learning of an auditory stimulus with predation risk in a species that regularly uses auditory signalling in other contexts. Recordings of conditioning and test trials failed to detect any acoustic calls produced by test fish in response to the perception of predation risk. Thus, although yellowtail damselfish can associate risk with auditory stimuli, we found no evidence that they produce an alarm call.

Repeated boat noise exposure damages inner ear sensory hair cells and decreases hearing sensitivity in Atlantic croaker (Micropogonias undulatus)

Anthropogenic noise is becoming a major underwater pollutant because of rapidly increasing boat traffic worldwide. But its impact on aquatic organisms remains largely unknown. Previous studies have focused mainly on high-frequency and impulsive noises (i.e. sonar); however, boat noise is more pervasive, continuous, and its highest intensity and component frequencies overlap the auditory bandwidth of most fishes. We assessed the impacts of boat noise on saccular sensory hair cell density and hearing thresholds of a soniferous species, Atlantic croaker (Micropogonias undulatus). In two laboratory experiments, individuals were subjected to simulated boat noise: a single 15-min exposure and 3 days of intermittent noise (simulating passing vessels). Immediately after both experiments, fish were either (1) tested for hearing sensitivity with auditory evoked potential (AEP) tests or (2) euthanized for fluorescent phalloidin and TUNEL labeling for hair cell density counts. Relative to controls, no differences were observed in auditory thresholds nor hair cell density between individuals subjected to a single 15-min noise exposure. However, fish from the 3-day experiment showed decreased sensory hair cell density, increased apoptotic cells, and higher hearing thresholds than control fish at 300, 800 and 1000 Hz. Our results demonstrate that impacts from boat noise depend upon the duration and frequency of exposure. For a species reliant on vocalization for communication, these impacts may hinder spawning success, increase predation risks and significantly alter the ecosystem.

Finite element modelling of sound transmission in the Weberian apparatus of zebrafish (Danio rerio)

Zebrafish, an essential vertebrate model, has greatly expanded our understanding of hearing. However, one area that remains unexplored is the biomechanics of the Weberian apparatus, crucial for sound conduction and perception. Using micro-computed tomography (μCT) bioimaging, we created three-dimensional finite element models of the zebrafish Weberian ossicles. These models ranged from the exact size to scaled isometric versions with constrained geometry (1 to 10 mm in ossicular chain length). Harmonic finite element analysis of all 11 models revealed that the resonance frequency of the zebrafish's Weberian ossicular chain is approximately 900 Hz, matching their optimal hearing range. Interestingly, resonance frequency negatively correlated with size, while the ratio of peak displacement and difference of resonance frequency between tripus and scaphium remained constant. This suggests the transmission efficiency of the ossicular chain and the homogeneity of resonance frequency at both ends of the chain are not size-dependent. We conclude that the Weberian apparatus's resonance frequency can explain zebrafish's best hearing frequency, and their biomechanical characteristics are not influenced by isometric ontogeny. As the first biomechanical modelling of atympanic ear and among the few non-human ear modelling, this study provides a methodological framework for further investigations into hearing mechanisms and the hearing evolution of vertebrates.

Functional plasticity of the swim bladder as an acoustic organ for communication in a vocal fish

Teleost fishes have evolved a number of sound-producing mechanisms, including vibrations of the swim bladder. In addition to sound production, the swim bladder also aids in sound reception. While the production and reception of sound by the swim bladder has been described separately in fishes, the extent to which it operates for both in a single species is unknown. Here, using morphological, electrophysiological and modelling approaches, we show that the swim bladder of male plainfin midshipman fish (Porichthys notatus) exhibits reproductive state-dependent changes in morphology and function for sound production and reception. Non-reproductive males possess rostral 'horn-like' swim bladder extensions that enhance low-frequency (less than 800 Hz) sound pressure sensitivity by decreasing the distance between the swim bladder and inner ear, thus enabling pressure-induced swim bladder vibrations to be transduced to the inner ear. By contrast, reproductive males display enlarged swim bladder sonic muscles that enable the production of advertisement calls but also alter swim bladder morphology and increase the swim bladder to inner ear distance, effectively reducing sound pressure sensitivity. Taken together, we show that the swim bladder exhibits a seasonal functional plasticity that allows it to effectively mediate both the production and reception of sound in a vocal teleost fish.

Navigating noisy waters: A review of field studies examining anthropogenic noise effects on wild fisha)

Anthropogenic noise is globally increasing in aquatic ecosystems, and there is concern that it may have adverse consequences in many fish species, yet the effects of noise in field settings are not well understood. Concern over the applicability of laboratory-conducted bioacoustic experiments has led to a call for, and a recent increase in, field-based studies, but the results have been mixed, perhaps due to the wide variety of techniques used and species studied. Previous reviews have explored the behavioral, physiological, and/or anatomical costs of fish exposed to anthropogenic noise, but few, if any, have focused on the field techniques and sound sources themselves. This review, therefore, aims to summarize, quantify, and interpret field-based literature, highlight novel approaches, and provide recommendations for future research into the effects of noise on fish.

Biodiversity assessment using passive acoustic recordings from off-reef location-Unsupervised learning to classify fish vocalization

We present the quantitative characterization of Grande Island's off-reef acoustic environment within the Zuari estuary during the pre-monsoon period. Passive acoustic recordings reveal prominent fish choruses. Detailed characteristics of the call employing oscillograms and individual fish call parameters of the segmented data include vocal groups such as Sciaenidae, Terapon theraps, and planktivorous as well as invertebrate sounds, e.g., snapping shrimp. We calculated biodiversity parameters (i) Acoustic Evenness Index (AEI), (ii) Acoustic Complexity Index (ACI), and mean sound pressure level (SPLrms) for three frequency bands such as full band (50-22 050 Hz), the low-frequency fish band (100-2000 Hz), and the high-frequency shrimp band (2000-20 000 Hz). Here, ACI and AEI metrics characterize the location's soundscape data effectively indicating increased biodiversity of fish species for both the low-frequency and high-frequency bands. Whereas variations for SPLrms are prominent for three frequency bands. Moreover, we employ unsupervised classification through a hybrid technique comprising principal component analysis (PCA) and K-means clustering for data features of four fish sound types. Employed PCA for dimensionality reduction and related K-means clustering successfully provides 96.20%, 76.81%, 100.00%, and 86.36% classification during the dominant fish chorus. Overall, classification performance (89.84%) is helpful in the real-time monitoring of the fish stocks in the ecosystem.

Maritime traffic trends around the southern tip of Africa - Did marine noise pollution contribute to the local penguins' collapse?

The rapid increase in seaborn trade since the 1990s has resulted in an increase in vessel-derived noise pollution, yet there is little evidence linking these activities to a decline in many marine taxa, such as seabirds. Algoa Bay, South Africa, is a marine biodiversity hotspot, providing habitats for the largest populations of endangered African Penguins (Spheniscus demersus), as well as other endangered seabirds, cetaceans and seals. The bay is situated on a major shipping route and since 2016 has hosted the first offshore ship-to-ship (STS) bunkering operations in the country, i.e. the supplying of fuel from one ship to another outside of harbours. Using Automatic Identification System (AIS) data, we estimated noise emissions from vessels as a proxy for underwater ambient noise levels within the core penguin utilisation area. Frequency of vessels using the bay doubled during our study, with numbers of bulk carriers increasing ten-fold. Ambient underwater noise levels were generally high in the bay (ca 140 dB re 1 μPa since 2015) but significantly increased by 2 dB SPL after the initiation of STS bunkering in 2016, corresponding to double the underwater noise intensity. This increase coincided with a significant and dramatic decline by 85% in penguin numbers from St Croix Island since 2016. Algoa Bay is now one of the noisiest bays in the world. This is the first study to assess the potential impact of vessel-derived underwater noise levels on a seabird population. Penguins, like marine mammal species, are known to be sensitive to marine noise pollution and urgent management interventions are required to mitigate this recent disturbance, to preserve the remaining stronghold of the African penguin and the marine mammals' populations sharing the penguins' habitat.

Soundscapes as heard by invertebrates and fishes: Particle motion measurements on coral reefs

Coral reef soundscapes are increasingly studied for their ecological uses by invertebrates and fishes, for monitoring habitat quality, and to investigate effects of anthropogenic noise pollution. Few examinations of aquatic soundscapes have reported particle motion levels and variability, despite their relevance to invertebrates and fishes. In this study, ambient particle acceleration was quantified from orthogonal hydrophone arrays over several months at four coral reef sites, which varied in benthic habitat and fish communities. Time-averaged particle acceleration magnitudes were similar across axes, within 3 dB. Temporal trends of particle acceleration corresponded with those of sound pressure, and the strength of diel trends in both metrics significantly correlated with percent coral cover. Higher magnitude particle accelerations diverged further from pressure values, potentially representing sounds recorded in the near field. Particle acceleration levels were also reported for boat and example fish sounds. Comparisons with particle acceleration derived audiograms suggest the greatest capacity of invertebrates and fishes to detect soundscape components below 100 Hz, and poorer detectability of soundscapes by invertebrates compared to fishes. Based on these results, research foci are discussed for which reporting of particle motion is essential, versus those for which sound pressure may suffice.

Underwater Chatter for the Win: A First Assessment of Underwater Soundscapes in Two Bays along the Eastern Cape Coast of South Africa

In 2014, the South African government launched ‘Operation Phakisa’ under which port developments play a significant role in supporting ocean economic growth. These developments will likely increase vessel traffic to and from South African ports, making it imperative to monitor for changes in underwater sound budgets with potential negative effects on marine life. However, no soundscape studies have been conducted around South Africa, resulting in an absence of baseline measurements. This study provides a first description of the underwater soundscape in St. Francis Bay and Algoa Bay, Eastern Cape. Soundscape measurements identified major soundscape contributors, temporal patterns in broadband sound levels, and underlying environmental drivers. Applicability of modelled vessel noise and wind noise maps to predict large-scale spatial variation in sound budgets was assessed. Our study shows that sounds from biological sources and wind dominated at all recording sites, with fish choruses driving temporal patterns as a function of time of year and position of the sun. Sound from vessels was present at all sites but most notable in long-term spectral levels measured in Algoa Bay. Sound propagation models predicted a further increase in the contribution of vessel noise towards shipping lanes and east Algoa Bay. Our study provides a building block to monitor for shifts in sound budgets and temporal patterns in these two bays under a developing ocean economy. Furthermore, our study raises concerns that vessel noise is likely a significant contributor in shallow waters elsewhere along the South African coast where vessel density is known to be higher (i.e., Durban and Cape Town).

Fish hearing "specialization" - A re-valuation

Investigators working with fish bioacoustics used to refer to fishes that have a narrow hearing bandwidth and poor sensitivity as "hearing generalists" (or "non-specialists"), while fishes that could detect a wider hearing bandwidth and had greater sensitivity were referred to as specialists. However, as more was learned about fish hearing mechanism and capacities, these terms became hard to apply since it was clear there were gradations in hearing capabilities. Popper and Fay, in a paper in Hearing Research in 2011, proposed that these terms be dropped because of the gradation. While this was widely accepted by investigators, it is now apparent that the lack of relatively concise terminology for fish hearing capabilities makes it hard to discuss fish hearing. Thus, in this paper we resurrect the terms specialist and non-specialist but use them with modifiers to express the specific structure of function that is considered a specialization. Moreover, this resurrection recognizes that hearing specializations in fishes may not only be related to increased bandwidth and/or sensitivity, but to other, perhaps more important, aspects of hearing such as sound source localization, discrimination between sounds, and detection of sounds in the presence of masking signals.

Sex Associated Effects of Noise Pollution in Stone Sculpin (Paracottus knerii) as a Model Object in the Context of Human-Induced Rapid Environmental Change

Simple Summary

In this comprehensive multidisciplinary study, we applied a novel multilevel approach to stone sculpins Paracottus knerii Dybowski, 1874, as model organisms and test for the first time the hypothesis of sex-dependent differences in response to long-term noise exposure in fish. The results testify that the stone sculpin females appeared to experience excessive stress, while the males showed adaptive recalibrations. These effects may be explained by a unique adaptive strategy of offspring care in the stone sculpin males and their biological role in reproductive behavior within the species. The findings obtained may help to elucidate the links between noise exposure in the context of human-induced rapid environmental change (HIREC), long-term sex-related changes in fishes, and the possible further evolutionary success of a species. Such HIREC modeling not only provides information about the potential consequences under anthropogenic pressure but also can help identify the natural mechanisms of stress resistance in different species, including those related to sex, and also contribute to the development of effective environmental management practices.

Abstract

This work simulates the consequences of HIREC using stone sculpins as model organisms. Sex-dependent effects of long-term noise exposure at mean sound pressure levels of 160–179 dB re 1 μPa (SPL_pk–pk) were measured. We applied a multilevel approach to testing the stress response: a comparative analysis of the macula sacculi and an assessment of hematological and molecular stress responses. Noise exposure resulted in hair cell loss, changes in some cytometric parameters in blood, and an increase in the number of functionally active mitochondria in the red blood cells of males and its decrease in females, demonstrating a mitochondrial allostatic load and depletion of functional reserve. Finally, a statistically significant decrease in the telomerase activity of the auditory epithelium and a shortening of telomere length in the brain as molecular markers of stress were observed after noise exposure only in females. No significant decrease in telomerase activity and shortening of telomere length in nerve target tissues were observed in stressed males. However, we recorded an increase in the telomerase activity in male gonads. This sex-dependent difference in load may be associated with accelerated cellular aging in females and lower stress-related long-term risk in males. In this article, we discuss possible reasons for these noise-induced stress effects.

Noise pollution on coral reefs? - A yet underestimated threat to coral reef communities

Noise pollution is an anthropogenic stressor that is increasingly recognized for its negative impact on the physiology, behavior and fitness of marine organisms. Driven by the recent expansion of maritime shipping, artisanal fishing and tourism (e.g., motorboats used for recreational purpose), underwater noise increased greatly on coral reefs. In this review, we first provide an overview on how reef organisms sense and use sound. Thereafter we review the current knowledge on how underwater noise affects different reef organisms. Although the majority of available examples are limited to few fish species, we emphasize how the impact of noise differs based on an organisms' acoustic sensitivity, mobility and developmental stage, as well as between noise type, source and duration. Finally, we highlight measures available to governments, the shipping industry and individual users and provide directions for polices and research aimed to manage this global issue of noise emission on coral reefs.

Exploiting common senses: sensory ecology meets wildlife conservation and management

Multidisciplinary approaches to conservation and wildlife management are often effective in addressing complex, multi-factor problems. Emerging fields such as conservation physiology and conservation behaviour can provide innovative solutions and management strategies for target species and systems. Sensory ecology combines the study of 'how animals acquire' and process sensory stimuli from their environments, and the ecological and evolutionary significance of 'how animals respond' to this information. We review the benefits that sensory ecology can bring to wildlife conservation and management by discussing case studies across major taxa and sensory modalities. Conservation practices informed by a sensory ecology approach include the amelioration of sensory traps, control of invasive species, reduction of human-wildlife conflicts and relocation and establishment of new populations of endangered species. We illustrate that sensory ecology can facilitate the understanding of mechanistic ecological and physiological explanations underlying particular conservation issues and also can help develop innovative solutions to ameliorate conservation problems.

Changes in feeding behavior of longfin squid (Doryteuthis pealeii) during laboratory exposure to pile driving noise

Anthropogenic noise can cause diverse changes in animals' behaviors, but effects on feeding behaviors are understudied, especially for key invertebrate taxa. With the offshore wind industry expanding, concern exists regarding potential impacts of pile driving noise on squid and other commercially and ecologically vital taxa. We investigated changes in feeding and alarm (defense) behaviors of squid, Doryteuthis pealeii, predating on killifish, Fundulus heteroclitus, during playbacks of pile driving noise recorded from wind farm construction within squids' habitat. Fewer squid captured killifish during noise exposure compared to controls. Squid had more failed predation attempts when noise was started during predation sequences. Alarm responses to noise were similar whether or not squid were hunting killifish, indicating similar vigilance to threat stimuli in these contexts. Additionally, novel hearing measurements on F. heteroclitus confirmed they could detect the noise. These results indicate noise can disrupt feeding behaviors of a key invertebrate species, and will leverage future studies on how noise may disrupt squids' vital ecological interactions.

Physical effects of sound exposure from underwater explosions on Pacific sardines (Sardinops sagax)

Explosions from activities such as construction, demolition, and military activities are increasingly encountered in the underwater soundscape. However, there are few scientifically rigorous data on the effects of underwater explosions on aquatic animals, including fishes. Thus, there is a need for data on potential effects on fishes collected simultaneously with data on the received signal characteristics that result in those effects. To better understand potential physical effects on fishes, Pacific sardines (Sardinops sagax) were placed in cages at mid-depth at distances of 18 to 246 m from a single mid-depth detonation of C4 explosive (4.66 kg net explosive weight). The experimental site was located in the coastal ocean with a consistent depth of approximately 19.5 m. Following exposure, potential correlations between blast acoustics and observed physical effects were examined. Acoustic metrics were calculated as a function of range, including peak pressure, sound exposure level, and integrated pressure over time. Primary effects related to exposure were damage to the swim bladder and kidney. Interestingly, the relative frequency of these two injuries displayed a non-monotonic dependence with range from the explosion in relatively shallow water. A plausible explanation connecting swim bladder expansion with negative pressure as influenced by bottom reflection is proposed.

The effect of biological and anthropogenic sound on the auditory sensitivity of oyster toadfish, Opsanus tau

Many aquatic organisms use vocalizations for reproductive behavior; therefore, disruption of their soundscape could adversely affect their life history. Male oyster toadfish (Opsanus tau) establish nests in shallow waters during spring and attract female fish with boatwhistle vocalizations. Males exhibit high nest fidelity, making them susceptible to anthropogenic sound in coastal waters, which could mask their vocalizations and/or reduce auditory sensitivity levels. Additionally, the effect of self-generated boatwhistles on toadfish auditory sensitivity has yet to be addressed. To investigate the effect of sound exposure on toadfish auditory sensitivity, sound pressure and particle acceleration sensitivity curves were determined using auditory evoked potentials before and after (0-, 1-, 3-, 6- and 9-day) exposure to 1- or 12-h of continuous playbacks to ship engine sound or conspecific vocalization. Exposure to boatwhistles had no effect on auditory sensitivity. However, exposure to anthropogenic sound caused significant decreases in auditory sensitivity for at least 3 days, with shifts up to 8 dB SPL and 20 dB SPL immediately following 1- and 12-h anthropogenic exposure, respectively. Understanding the effect of self-generated and anthropogenic sound exposure on auditory sensitivity provides an insight into how soundscapes affect acoustic communication.

An overview of fish bioacoustics and the impacts of anthropogenic sounds on fishes

Fishes use a variety of sensory systems to learn about their environments and to communicate. Of the various senses, hearing plays a particularly important role for fishes in providing information, often from great distances, from all around these animals. This information is in all three spatial dimensions, often overcoming the limitations of other senses such as vision, touch, taste and smell. Sound is used for communication between fishes, mating behaviour, the detection of prey and predators, orientation and migration and habitat selection. Thus, anything that interferes with the ability of a fish to detect and respond to biologically relevant sounds can decrease survival and fitness of individuals and populations. Since the onset of the Industrial Revolution, there has been a growing increase in the noise that humans put into the water. These anthropogenic sounds are from a wide range of sources that include shipping, sonars, construction activities (e.g., wind farms, harbours), trawling, dredging and exploration for oil and gas. Anthropogenic sounds may be sufficiently intense to result in death or mortal injury. However, anthropogenic sounds at lower levels may result in temporary hearing impairment, physiological changes including stress effects, changes in behaviour or the masking of biologically important sounds. The intent of this paper is to review the potential effects of anthropogenic sounds upon fishes, the potential consequences for populations and ecosystems and the need to develop sound exposure criteria and relevant regulations. However, assuming that many readers may not have a background in fish bioacoustics, the paper first provides information on underwater acoustics, with a focus on introducing the very important concept of particle motion, the primary acoustic stimulus for all fishes, including elasmobranchs. The paper then provides background material on fish hearing, sound production and acoustic behaviour. This is followed by an overview of what is known about effects of anthropogenic sounds on fishes and considers the current guidelines and criteria being used world-wide to assess potential effects on fishes. Most importantly, the paper provides the most complete summary of the effects of anthropogenic noise on fishes to date. It is also made clear that there are currently so many information gaps that it is almost impossible to reach clear conclusions on the nature and levels of anthropogenic sounds that have potential to cause changes in animal behaviour, or even result in physical harm. Further research is required on the responses of a range of fish species to different sound sources, under different conditions. There is a need both to examine the immediate effects of sound exposure and the longer-term effects, in terms of fitness and likely impacts upon populations.

Ecology of sound communication in fishes

Fishes communicate acoustically under ecological constraints which may modify or hinder signal transmission and detection and may also be risky. This makes it important to know if and to what degree fishes can modify acoustic signalling when key ecological factors-predation pressure, noise and ambient temperature-vary. This paper reviews short-time effects of the first two factors; the third has been reviewed recently (Ladich, 2018). Numerous studies have investigated the effects of predators on fish behaviour, but only a few report changes in calling activity when hearing predator calls as demonstrated when fish responded to played-back dolphin sounds. Furthermore, swimming sounds of schooling fish may affect predators. Our knowledge on adaptations to natural changes in ambient noise, for example caused by wind or migration between quiet and noisier habitats, is limited. Hearing abilities decrease when ambient noise levels increase (termed masking), in particular in taxa possessing enhanced hearing abilities. High natural and anthropogenic noise regimes, for example vessel noise, alter calling activity in the field and laboratory. Increases in sound pressure levels (Lombard effect) and altered temporal call patterns were also observed, but no switches to higher sound frequencies. In summary, effects of predator calls and noise on sound communication are described in fishes, yet sparsely in contrast to songbirds or whales. Major gaps in our knowledge on potential negative effects of noise on acoustic communication call for more detailed investigation because fishes are keystone species in many aquatic habitats and constitute a major source of protein for humans.