Sound pressure and particle acceleration audiograms in three marine fish species from the Adriatic Sea

Electric boat underwater radiated noise and its potential impact on species of conservation interest

Electric boats are thought to be noiseless, but in-situ measurements are generally rare. The Underwater Radiated Noise (URN) of 8-m Trimaran Pontoon Boat with two outboard electric engines was measured in the Miramare Marine Protected Area (Trieste, Italy), together with the URN of a fibreglass 5-m boat, with a outboard gasoline engine, for comparisons. International standards and guidelines for shallow waters were considered. URN were provided in one-third octave band and in narrow band spectra. The electric boat produced a low input of underwater noise at low frequencies. Given a low-frequency hearing sensitivity, the listening space reduction (LSR) was lower when generated by the electric than by combustion engine boat for the brown meagre, a local Teleost fish. No difference was found for the bottlenose dolphin LSR although continuous, tonal, high frequency components generated by the electric boat are expected to be highly detrimental for the bottlenose dolphin.

Sound frequencies detectable by grass (Ctenopharyngodon idella) and black (Mylopharyngodon pisceus) carp determined with auditory evoked potentialsa)

Grass (Ctenopharyngodon idella) and black (Mylopharyngodon piceus) carp were imported to the United States as biocontrol agents in aquaculture facilities; however, due to intentional stocking or accidental release, invasive populations have become established. Invasive bigheaded carps display negative phonotaxis to sound, suggesting acoustic deterrents as a potential management tool. Grass and black carp frequency detection in response to 0.2-6 kHz sound was evaluated using auditory evoked potentials (AEPs) and determined for sound pressure level (SPL) and particle acceleration level (PAL). AEPs were detectable in response to pure tone stimuli from 0.2 to 4 kHz. The lowest SPL thresholds for grass carp were at 0.3 kHz (87.0 ± 3.6 dB re 1 μPa SPLrms; mean ± standard deviation), and the lowest PAL thresholds were at 0.4 kHz (-65.8 ± 3.2 dB re 1 ms-2 PALrms). For black carp, the lowest SPL and PAL thresholds were at 0.3 kHz (93.4 ± 3.0 dB re 1 μPa SPLrms, -60.8 ± 1.5 dB re 1 ms-2 PALrms). These results indicate that the ranges of detectable frequencies for grass and black carp overlap with those reported for bigheaded carps. However, behavioral studies are needed to determine potential efficacy of acoustic deterrents for these fish.

Comparison of auditory evoked potential thresholds in three shark species

Auditory sensitivity measurements have been published for only 12 of the more than 1150 extant species of elasmobranchs (sharks, skates and rays). Thus, there is a need to further understand sound perception in more species from different ecological niches. In this study, the auditory evoked potential (AEP) technique was used to compare hearing abilities of the bottom-dwelling New Zealand carpet shark (Cephaloscyllium isabellum) and two benthopelagic houndsharks (Triakidae), the rig (Mustelus lenticulatus) and the school shark (Galeorhinus galeus). AEPs were measured in response to tone bursts (frequencies: 80, 100, 150, 200, 300, 450, 600, 800 and 1200 Hz) from an underwater speaker positioned 55 cm in front of the shark in an experimental tank. AEP detection thresholds were derived visually and statistically, with statistical measures slightly more sensitive (∼4 dB) than visual methodology. Hearing abilities differed between species, mainly with respect to bandwidth rather than sensitivity. Hearing was least developed in the benthic C. isabellum [upper limit: 300 Hz, highest sensitivity: 100 Hz (82.3±1.5 dB re. 1 µm s-2)] and had a wider range in the benthopelagic rig and school sharks [upper limit: 800 Hz; highest sensitivity: 100 Hz (79.2±1.6 dB re. 1 µm s-2) for G. galeus and 150 Hz (74.8±1.8 dB re. 1 µm s-2) for M. lenticulatus]. The data are consistent with those known for 'hearing non-specialist' teleost fishes that detect only particle motion, not pressure. Furthermore, our results provide evidence that benthopelagic sharks exploit higher frequencies (max. 800 Hz) than some of the bottom-dwelling sharks (max. 300 Hz). Further behavioural and morphological studies are needed to identify what ecological factors drive differences in upper frequency limits of hearing in elasmobranchs.

Effects of amplitude and duration of noise exposure on the hearing and anti-predator behaviour of common roach (Rutilus rutilus) and sand goby (Pomatoschistus minutus)

This study investigates whether an exposure to two different received sound pressure levels at equal cumulative energy affects anti-predator behaviour and auditory detection thresholds of common roach (Rutilus rutilus) and sand goby (Pomatoschistus minutus) differently. This was examined in regard to a vessel slowdown as a management strategy to decrease vessel noise impact on fishes. Using continuous broadband noise, we found significant temporary threshold shifts (TTS) in roach, with 11.9 and 13.4 dB at 250 and 1000 Hz respectively, for the louder exposure. In contrast, gobies exhibited a non-significant shift of 6.6 dB at 125 Hz. Group cohesion increased in roach exposed to an artificial predator in the control group, but not during noise exposures. Gobies showed an initial freezing reaction towards the predator stimulus remaining motionless regardless of treatment. Our results show that a reduction in vessel speed with a corresponding reduction in source level could mitigate the effects on the auditory senses of sensitive fish, but does not appear to have any mitigating effect on their noise-induced behavioural changes. Further studies should investigate the effects of multiple vessel passages, but also the ecological consequences of the described effects on hearing and behaviour at individual and population level.

Reproductive state modulates utricular auditory sensitivity in a vocal fish

The plainfin midshipman, Porichthys notatus, is a seasonally breeding vocal fish that relies on acoustic communication to mediate nocturnal reproductive behaviors. Reproductive females use their auditory senses to detect and localize "singing" males that produce multiharmonic advertisement (mate) calls during the breeding season. Previous work showed that the midshipman saccule, which is considered the primary end organ used for hearing in midshipman and most other fishes, exhibits reproductive state and hormone-dependent changes that enhance saccular auditory sensitivity. In contrast, the utricle was previously posited to serve primarily a vestibular function, but recent evidence in midshipman and related toadfish suggests that it may also serve an auditory function and aid in the detection of behaviorally relevant acoustic stimuli. Here, we characterized the auditory-evoked potentials recorded from utricular hair cells in reproductive and nonreproductive female midshipman in response to underwater sound to test the hypothesis that variation in reproductive state affects utricular auditory sensitivity. We show that utricular hair cells in reproductive females exhibit up to a sixfold increase in the utricular potential magnitude and have thresholds based on measures of particle acceleration (re: 1 ms-2) that are 7-10 dB lower than nonreproductive females across a broad range of frequencies, which include the dominant harmonics of male advertisement calls. This enhanced auditory sensitivity of the utricle likely plays an essential role in facilitating midshipman social and reproductive acoustic communication.NEW & NOTEWORTHY In many animals, vocal-acoustic communication is fundamental for facilitating social behaviors. For the vocal plainfin midshipman fish, the detection and localization of social acoustic signals are critical to the species' reproductive success. Here, we show that the utricle, an inner ear end organ often thought to primarily serve a vestibular function, serves an auditory function that is seasonally plastic and modulated by the animal's reproductive state effectively enhancing auditory sensitivity to courting male advertisement calls.

Response of toadfish (Opsanus tau) utricular afferents to multimodal inputs

The inner ear of teleost fishes is composed of three paired multimodal otolithic end organs (saccule, utricle, and lagena), which encode auditory and vestibular inputs via the deflection of hair cells contained within the sensory epithelia of each organ. However, it remains unclear how the multimodal otolithic end organs of the teleost inner ear simultaneously integrate vestibular and auditory inputs. Therefore, microwire electrodes were chronically implanted using a 3D printed micromanipulator into the utricular nerve of oyster toadfish (Opsanus tau) to determine how utricular afferents respond to conspecific mate vocalizations termed boatwhistles (180 Hz fundamental frequency) during movement. Utricular afferents were recorded while fish were passively moved using a sled system along an underwater track at variable speeds (velocity: 4.0 - 12.5 cm/s; acceleration: 0.2 - 2.6 cm/s²) and while fish freely swam (velocity: 3.5 - 18.6 cm/s; acceleration: 0.8 - 29.8 cm/s²). Afferent fiber activities (spikes/s) increased in response to the onset of passive and active movements; however, afferent fibers differentially adapted to sustained movements. Additionally, utricular afferent fibers remained sensitive to playbacks of conspecific male boatwhistle vocalizations during both passive and active movements. Here, we demonstrate in alert toadfish that utricular afferents exhibit enhanced activity levels (spikes/s) in response to behaviorally-relevant acoustic stimuli during swimming.

Numerical investigation of vibration and noise radiation of a water supply pipeline

The vibration and noise radiation from underwater structures can be harmful for aquatic ecosystems, especially for endangered species which are sensitive to particle motion and sound pressure. In this study, a water supply pipeline was chosen to investigate the flow-induced vibration and underwater noise radiation. A finite element model was developed to predict the vibration of the pipeline-tunnel-soil coupling system using fluid-structure interaction analysis. Next, a three-demission boundary element acoustic model was developed to simulate underwater noise radiation and propagation. Parametric analysis was conducted to investigate the influence of scouring depth on vibration and acoustic radiation. The results showed the flowing fluid-induced vibration produced broad band noise radiation, with dominant frequency range from 3 to 25 Hz. The sound pressure radiated from the model with once-in-a-century scouring depth was about 3 dB larger than the model with normal depth due to thinner sediment. The sourcing depth has significant influence on the noise distribution and radiation directivity. The simulated sound pressure level and water particle motion can exceed the threshold of some underwater species in certain frequency range, especially for the once-in-a-century scouring depth. The proposed methodology can be used for acoustic radiation prediction in further study to reduce the influence on aquatic environment.

Boat-induced pressure does not influence breeding site selection of a vulnerable fish species in a highly anthropized coastal area

The brown meagre (Sciaena umbra) is a vulnerable vocal fish species that may be affected by boat noise. The breeding site distribution along the anthropized Venice sea inlets was investigated, by using the species' chorusing activity as a proxy of spawning. Passive acoustic campaigns were repeated at 40 listening points distributed within the three inlets during three-time windows in both summer 2019 and 2020. The role of temporal, morphological, and hydrodynamic variables explaining the observed distribution patterns was evaluated using a GLM approach, considering also human-induced pressures among the candidate predictors. The GLM analysis indicates a higher probability of recording S. umbra chorus after sunset in deeper areas of the inlets, characterized by low water current, while the underwater noise overlapping the species' hearing range and boat abundance did not play any role. This suggests that the species' breeding site choice in the inlets was not influences by boat-induced pressure.

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.

Environmental and human health impacts of cruise tourism: A review

The intensive growth of cruise tourism worldwide during recent decades is leading to growing concerns over the sector's global environmental and health impacts. This review combines for the first time various sources of information to estimate the magnitude of the cruise industry's environmental and public health footprints. This research shows that cruising, despite technical advances and some surveillance programmes, remains a major source of air, water (fresh and marine) and land pollution affecting fragile habitats, areas and species, and a potential source of physical and mental human health risks. Health risks impact both the people on board (crew and passengers) and on land (workers of shipyards where cruise ships are dismantled and citizens inhabiting cities with cruise ports and shipyards). In this context, we argue that the cruise industry should be held accountable with more monitoring and regulation to prevent or minimize the growing negative environmental and human health impacts.

Boat noise affects meagre (Argyrosomus regius) hearing and vocal behaviour

Aquatic noise has increased in last decades imposing new constraints on aquatic animals' acoustic communication. Meagre (Argyrosomus regius) produce loud choruses during the breeding season, likely facilitating aggregations and mating, and are thus amenable to being impacted by anthropogenic noise. We assessed the impact of boat noise on this species acoustic communication by: evaluating possible masking effects of boat noise on hearing using Auditory Evoked Potentials (AEP) and inspecting changes in chorus sound levels from free ranging fish upon boat passages. Our results point to a significant masking effect of anthropogenic noise since we observed a reduction of ca. 20 dB on the ability to discriminate conspecific calls when exposed to boat noise. Furthermore, we verified a reduction in chorus energy during ferryboat passages, a behavioural effect that might ultimately impact spawning. This study is one of few addressing the effects of boat noise by combining different methodologies both in the lab and with free ranging animals.

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.

From the Reef to the Ocean: Revealing the Acoustic Range of the Biophony of a Coral Reef (Moorea Island, French Polynesia)

The ability of different marine species to use acoustic cues to locate reefs is known, but the maximal propagation distance of coral reef sounds is still unknown. Using drifting antennas (made of a floater and an autonomous recorder connected to a hydrophone), six transects were realized from the reef crest up to 10 km in the open ocean on Moorea island (French Polynesia). Benthic invertebrates were the major contributors to the ambient noise, producing acoustic mass phenomena (3.5–5.5 kHz) that could propagate at more than 90 km under flat/calm sea conditions and more than 50 km with an average wind regime of 6 knots. However, fish choruses, with frequencies mainly between 200 and 500 Hz would not propagate at distances greater than 2 km. These distances decreased with increasing wind or ship traffic. Using audiograms of different taxa, we estimated that fish post-larvae and invertebrates likely hear the reef at distances up to 0.5 km and some cetaceans would be able to detect reefs up to more than 17 km. These results are an empirically based validation from an example reef and are essential to understanding the effect of soundscape degradation on different zoological groups.

It Is Not Just a Matter of Noise: Sciaena umbra Vocalizes More in the Busiest Areas of the Venice Tidal Inlets

Boat noise is known to have a detrimental effect on a vulnerable Mediterranean sciaenid, the brown meagre Sciaena umbra. During summer 2019, two acoustic surveys were conducted at 40 listening points distributed within the inlet areas of Venice (northern Adriatic Sea). Two five-minute recordings were collected per each point during both the boat traffic hours and the peak of the species’ vocal activity with the aims of (1) characterizing the local noise levels and (2) evaluating the fish spatial distribution by means of its sounds. High underwater broadband noise levels were found (sound pressure levels (SPLs)50–20kHz 107–137 dB re 1 μPa). Interestingly, a significantly higher background noise within the species’ hearing sensibility (100–3150 Hz) was highlighted in the afternoon (113 ± 5 dB re 1 μPa) compared to the night (103 ± 7 dB re 1 μPa) recordings due to a high vessel traffic. A cluster analysis based on Sciaena umbra vocalizations separated the listening points in three groups: highly vocal groups experienced higher vessel presence and higher afternoon noise levels compared to the lower ones. Since the species’ sounds are a proxy of spawning events, this suggests that the reproductive activity was placed in the noisier part of the inlets.

Age-related loss of auditory sensitivity in the zebrafish (Danio rerio)

Age-related hearing loss (ARHL), also known as presbycusis, is a widespread and debilitating condition impacting many older adults. Conventionally, researchers utilize mammalian model systems or human cadaveric tissue to study ARHL pathology. Recently, the zebrafish has become an effective and tractable model system for a wide variety of genetic and environmental auditory insults, but little is known about the incidence or extent of ARHL in zebrafish and other non-mammalian models. Here, we evaluated whether zebrafish exhibit age-related loss in auditory sensitivity. The auditory sensitivity of adult wild-type zebrafish (AB/WIK strain) from three adult age subgroups (13-month, 20-month, and 37-month) was characterized using the auditory evoked potential (AEP) recording technique. AEPs were elicited using pure tone stimuli (115-4500 Hz) presented via an underwater loudspeaker and recorded using shielded subdermal metal electrodes. Based on measures of sound pressure and particle acceleration, the mean AEP thresholds of 37-month-old fish [mean sound pressure level (SPL) = 122.2 dB ± 2.2 dB SE re: 1 μPa; mean particle acceleration level (PAL) = -27.5 ± 2.3 dB SE re: 1 ms^-2] were approximately 9 dB higher than that of 20-month-old fish [(mean SPL = 113.1 ± 2.7 dB SE re: 1 μPa; mean PAL = -37.2 ± 2.8 dB re: 1 ms^-2; p = 0.007)] and 6 dB higher than that of 13-month-old fish [(mean SPL = 116.3 ± 2.5 dB SE re: 1 μPa; mean PAL = -34.1 ± 2.6 dB SE re: 1 ms^-2; p = 0.052)]. Lowest AEP thresholds for all three age groups were generally between 800 Hz and 1850 Hz, with no evidence for frequency-specific age-related loss. Our results suggest that zebrafish undergo age-related loss in auditory sensitivity, but the form and magnitude of loss is markedly different than in mammals, including humans. Future work is needed to further describe the incidence and extent of ARHL across vertebrate groups and to determine which, if any, ARHL mechanisms may be conserved across vertebrates to support meaningful comparative/translational studies.

Auditory evoked potentials of utricular hair cells in the plainfin midshipman, Porichthys notatus

The plainfin midshipman, Porichthys notatus, is a soniferous marine teleost fish that generates acoustic signals for intraspecific social communication. Nocturnally active males and females rely on their auditory sense to detect and locate vocally active conspecifics during social behaviors. Previous work showed that the midshipman inner ear saccule and lagena are highly adapted to detect and encode socially relevant acoustic stimuli, but the auditory sensitivity and function of the midshipman utricle remain largely unknown. Here, we characterized the auditory evoked potentials from hair cells in the utricle of non-reproductive type I males and tested the hypothesis that the midshipman utricle is sensitive to behaviorally relevant acoustic stimuli. Hair cell potentials were recorded from the rostral, medial and caudal regions of the utricle in response to pure tone stimuli presented by an underwater speaker. We show that the utricle is highly sensitive to particle motion stimuli produced by an underwater speaker positioned in the horizontal plane. Utricular potentials were recorded across a broad range of frequencies with lowest particle acceleration (dB re. 1 m s-2) thresholds occurring at 105 Hz (lowest frequency tested; mean threshold -32 dB re. 1 m s-2) and highest thresholds at 605-1005 Hz (mean threshold range -5 to -4 dB re. 1 m s-2). The high gain and broadband frequency sensitivity of the utricle suggest that it likely serves a primary auditory function and is well suited to detect conspecific vocalizations including broadband agonistic signals and the multiharmonic advertisement calls produced by reproductive type I males.

Swim bladder enhances lagenar sensitivity to sound pressure and higher frequencies in female plainfin midshipman (Porichthys notatus)

The plainfin midshipman fish (Porichthys notatus) is an established model for investigating acoustic communication because the reproductive success of this species is dependent on the production and reception of social acoustic signals. Previous work showed that female midshipman have swim bladders with rostral horn-like extensions that project close to the saccule and lagena, while nesting (type I) males lack such rostral swim bladder extensions. The relative close proximity of the swim bladder to the lagena should increase auditory sensitivity to sound pressure and higher frequencies. Here, we test the hypothesis that the swim bladder of female midshipman enhances lagenar sensitivity to sound pressure and higher frequencies. Evoked potentials were recorded from auditory hair cell receptors in the lagena in reproductive females with intact (control condition) and removed (treated condition) swim bladders while pure tone stimuli (85-1005 Hz) were presented by an underwater speaker. Females with intact swim bladders had auditory thresholds 3-6 dB lower than females without swim bladders over a range of frequencies from 85 to 405 Hz. At frequencies from 545 to 1005 Hz, only females with intact swim bladders had measurable auditory thresholds (150-153 dB re. 1 µPa). The higher percentage of evoked lagenar potentials recorded in control females at frequencies >505 Hz indicates that the swim bladder extends the bandwidth of detectable frequencies. These findings reveal that the swim bladders in female midshipman can enhance lagenar sensitivity to sound pressure and higher frequencies, which may be important for the detection of behaviorally relevant social signals.

Particle motion measurements near a rocky shore off Cabo Frio Island

This paper describes the lessons learned from the experiment BIOCOM'19 carried out in January 2019, in a shallow water bay off the island of Cabo Frio (RJ, Brazil). A dual accelerometer vector sensor hydrophone was deployed for two days, near a rocky shore covered with a significant benthic fauna. The results show that the frequency band above approximately 1.5 kHz is mostly associated with invertebrate biological noise and that the acoustic and the particle motion fields have a similar behavior, following the usual dawn-dusk activity pattern, and a coherent directivity content. At low frequencies, below ∼300 Hz, the acoustic pressure and the particle acceleration fields have significantly different spectral content along time. Many of these differences are due to anthropogenic noise sources related with nearby boating activity, while during quiet periods, they may be attributed to the biological activity from the rocky shore.

Impacts of broadband sound on silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp hearing thresholds determined using auditory evoked potential audiometry

Invasive silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp, collectively referred to as bigheaded carps, threaten aquatic ecosystems of the Upper Midwestern USA. Due to the extensive ecological impacts associated with these species, prevention of their further range expansion is the aim for fisheries management. Recent behavioral studies indicate bigheaded carps are deterred by acoustic barriers and exhibit negative phonotaxis in response to anthropogenic sound sources (≥ 150 dB re 1 μPa). However, the impact of long-term exposure to these sounds on the hearing capabilities of bigheaded carps has not been well documented. In this study, the auditory evoked potential (AEP) technique was used to determine auditory thresholds among bigheaded carps before and after exposure to high intensity (155.7 ± 4.7 dB re 1 μPa SPL_rms; - 8.0 ± 4.7 dB re 1 ms^-2 PAL_rms; mean ± SD) broadband sound. Fish were exposed to sound for 30 min or 24 h and AEP measurements were taken at three time points: immediately after exposure, 48 h, or 96 h later. Results indicate that silver and bighead carp experience temporary threshold shifts (TTSs) in frequency detection following sound exposure with the magnitude and length of TTS correlated with exposure duration. The findings from this study will be used to increase the long-term efficacy of acoustical deterrent measures aimed at preventing further range expansion of bigheaded carps.

Underwater hearing in sea snakes (Hydrophiinae): first evidence of auditory evoked potential thresholds

The viviparous sea snakes (Hydrophiinae) are a secondarily aquatic radiation of more than 60 species that possess many phenotypic adaptations to marine life. However, virtually nothing is known of the role and sensitivity of hearing in sea snakes. This study investigated the hearing sensitivity of the fully marine sea snake Hydrophis stokesii by measuring auditory evoked potential (AEP) audiograms for two individuals. AEPs were recorded from 40 Hz (the lowest frequency tested) up to 600 Hz, with a peak in sensitivity identified at 60 Hz (163.5 dB re. 1 µPa or 123 dB re. 1 µm s^-2). Our data suggest that sea snakes are sensitive to low-frequency sounds but have relatively low sensitivity compared with bony fishes and marine turtles. Additional studies are required to understand the role of sound in sea snake life history and further assess these species' vulnerability to anthropogenic noise.

Sexually dimorphic swim bladder extensions enhance the auditory sensitivity of female plainfin midshipman fish, Porichthys notatus

The plainfin midshipman fish, Porichthys notatus, is a seasonally breeding, nocturnal marine teleost fish that produces acoustic signals for intraspecific social communication. Females rely on audition to detect and locate 'singing' males that produce multiharmonic advertisement calls in the shallow-water, intertidal breeding environments. Previous work showed that females possess sexually dimorphic, horn-like rostral swim bladder extensions that extend toward the primary auditory end organs, the saccule and lagena. Here, we tested the hypothesis that the rostral swim bladder extensions in females increase auditory sensitivity to sound pressure and higher frequencies, which potentially could enhance mate detection and localization in shallow-water habitats. We recorded the auditory evoked potentials that originated from hair cell receptors in the saccule of control females with intact swim bladders and compared them with those from treated females (swim bladders removed) and type I males (intact swim bladders lacking rostral extensions). Saccular potentials were recorded from hair cell populations in vivo while behaviorally relevant pure-tone stimuli (75-1005 Hz) were presented by an underwater speaker. The results indicate that control females were approximately 5-11 dB re. 1 µPa more sensitive to sound pressure than treated females and type I males at the frequencies tested. A higher percentage of the evoked saccular potentials were recorded from control females at frequencies >305 Hz than from treated females and type I males. This enhanced sensitivity in females to sound pressure and higher frequencies may facilitate the acquisition of auditory information needed for conspecific localization and mate choice decisions during the breeding season.

Lagenar potentials of the vocal plainfin midshipman fish, Porichthys notatus

The plainfin midshipman fish (Porichthys notatus) is a species of marine teleost that produces acoustic signals that are important for mediating social behavior. The auditory sensitivity of the saccule is well established in this species, but the sensitivity and function of the midshipman's putative auditory lagena are unknown. Here, we characterize the auditory-evoked potentials from hair cells in the lagena of reproductive type I males to determine the frequency response and auditory sensitivity of the lagena to behaviorally relevant acoustic stimuli. Lagenar potentials were recorded from the caudal and medial region of the lagena, while acoustic stimuli were presented by an underwater speaker. Our results indicate that the midshipman lagena has a similar low-frequency sensitivity to that of the midshipman saccule based on sound pressure and acceleration (re: 1 µPa and 1 ms^-2, respectively), but the thresholds of the lagena were higher across all frequencies tested. The relatively high auditory thresholds of the lagena may be important for encoding high levels of behaviorally relevant acoustic stimuli when close to  a sound source.

Larval Zebrafish Lateral Line as a Model for Acoustic Trauma

Excessive noise exposure damages sensory hair cells, leading to permanent hearing loss. Zebrafish are a highly tractable model that have advanced our understanding of drug-induced hair cell death, yet no comparable model exists for noise exposure research. We demonstrate the utility of zebrafish as model to increase understanding of hair cell damage from acoustic trauma and develop protective therapies. We created an acoustic trauma system using underwater cavitation to stimulate lateral line hair cells. We found that acoustic stimulation resulted in exposure time- and intensity-dependent lateral line and saccular hair cell damage that is maximal at 48–72 h post-trauma. The number of TUNEL+ lateral line hair cells increased 72 h post-exposure, whereas no increase was observed in TUNEL+ supporting cells, demonstrating that acoustic stimulation causes hair cell-specific damage. Lateral line hair cells damaged by acoustic stimulation regenerate within 3 d, consistent with prior regeneration studies utilizing ototoxic drugs. Acoustic stimulation-induced hair cell damage is attenuated by pharmacological inhibition of protein synthesis or caspase activation, suggesting a requirement for translation and activation of apoptotic signaling cascades. Surviving hair cells exposed to acoustic stimulation showed signs of synaptopathy, consistent with mammalian studies. Finally, we demonstrate the feasibility of this platform to identify compounds that prevent acoustic trauma by screening a small redox library for protective compounds. Our data suggest that acoustic stimulation results in lateral line hair cell damage consistent with acoustic trauma research in mammals, providing a highly tractable model for high-throughput genetic and drug discovery studies.

Impact of motorboats on fish embryos depends on engine type

Human generated noise is changing the natural underwater soundscapes worldwide. The most pervasive sources of underwater anthropogenic noise are motorboats, which have been found to negatively affect several aspects of fish biology. However, few studies have examined the effects of noise on early life stages, especially the embryonic stage, despite embryo health being critical to larval survival and recruitment. Here, we used a novel setup to monitor heart rates of embryos from the staghorn damselfish (Amblyglyphidodon curacao) in shallow reef conditions, allowing us to examine the effects of in situ boat noise in context with real-world exposure. We found that the heart rate of embryos increased in the presence of boat noise, which can be associated with the stress response. Additionally, we found 2-stroke outboard-powered boats had more than twice the effect on embryo heart rates than did 4-stroke powered boats, showing an increase in mean individual heart rate of 1.9% and 4.6%, respectively. To our knowledge this is the first evidence suggesting boat noise elicits a stress response in fish embryo and highlights the need to explore the ecological ramifications of boat noise stress during the embryo stage. Also, knowing the response of marine organisms caused by the sound emissions of particular engine types provides an important tool for reef managers to mitigate noise pollution.

Reexamining the frequency range of hearing in silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp

Silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) carp (collectively bigheaded carp) are invasive fish that threaten aquatic ecosystems in the upper Midwest United States and the Laurentian Great Lakes. Controlling bigheaded carp is a priority of fisheries managers and one area of focus involves developing acoustic deterrents to prevent upstream migration. For an acoustic deterrent to be effective however, the hearing ability of bigheaded carp must be characterized. A previous study showed that bigheaded carp detected sound up to 3 kHz but this range is narrower than what has been reported for other ostariophysans. Therefore, silver and bighead carp frequency detection was evaluated in response to 100 Hz to 9 kHz using auditory evoked potentials (AEPs). AEPs were recorded from 100 Hz to 5 kHz. The lowest thresholds were at 500 Hz for both species (silver carp threshold: 80.6 ± 3.29 dB re 1 μPa SPL_rms, bighead carp threshold: 90.5 ± 5.75 dB re 1 μPa SPL_rms; mean ± SD). These results provide fisheries managers with better insight on effective acoustic stimuli for deterrent systems, however, to fully determine bigheaded carp hearing abilities, these results need to be compared with behavioral assessments.

In-situ visualization of sound-induced otolith motion using hard X-ray phase contrast imaging

Regarding the basics of ear structure-function relationships in fish, the actual motion of the solid otolith relative to the underlying sensory epithelium has rarely been investigated. Otolith motion has been characterized based on a few experimental studies and on approaches using mathematical modeling, which have yielded partially conflicting results. Those studies either predicted a simple back-and-forth motion of the otolith or a shape-dependent, more complex motion. Our study was designed to develop and test a new set-up to generate experimental data on fish otolith motion in-situ. Investigating the basic parameters of otolith motion requires an approach with high spatial and temporal resolution. We therefore used hard X-ray phase contrast imaging (XPCI). We compared two anatomically well-studied cichlid species, Steatocranus tinanti and Etroplus maculatus, which, among other features, differ in the 3D shape of their otoliths. In a water-filled tank, we presented a pure tone of 200 Hz to 1) isolated otoliths embedded in agarose serving as a simple model or 2) to a fish (otoliths in-situ). Our new set-up successfully visualized the motion of otoliths in-situ and therefore paves the way for future studies evaluating the principles of otolith motion.

Anthropogenic noise compromises the anti-predator behaviour of the European seabass, Dicentrarchus labrax (L.)

Anthropogenic noise is a significant pollutant of the world's oceans, affecting behavioural and physiological traits in a range of species, including anti-predator behaviours. Using the open field test, we investigated the effects of recordings of piling and drilling noise on the anti-predator behaviour of captive juvenile European seabass in response to a visual stimulus (a predatory mimic). The impulsive nature of piling noise triggered a reflexive startle response, which contrasted the behaviour elicited by the continuous drilling noise. When presented with the predatory mimic, fish exposed to both piling and drilling noise explored the experimental arena more extensively than control fish exposed to ambient noise. Fish under drilling and piling conditions also exhibited reduced predator inspection behaviour. Piling and drilling noise induced stress as measured by ventilation rate. This study provides further evidence that the behaviour and physiology of European seabass is significantly affected by exposure to elevated noise levels.

Noise elicits hematological stress parameters in Mediterranean damselfish (Chromis chromis, perciformes): A mesocosm study

In the last few decades, technological developments and the widespread rise of anthropic activities have increased the exposure of organisms to noise pollution, thus evoking great interest in its biological effects, particularly on the immune system. The aim of the present work was to investigate some of the biochemical parameters in the blood of Chromis chromis (Linnaeus, 1758) following in vivo exposure to noise levels of 200 and 300 Hz. Our results revealed that, compared to the control specimens, the fish exposed to noise had significantly increased levels of stress biomarkers such as glucose, lactate and total proteins in plasma, as well as a rise in the expression of heat shock protein 70 (HSP70).

Behavioral response of brown meagre (Sciaena umbra) to boat noise

Underwater man-made noise is recognized as a major global pollutant in the 21st Century, and its reduction has been included in national and international regulations. Despite the fact that many studies have pointed out the ecological impact of noise on marine organisms, few studies have investigated - in a field context - the behavioral response to boat noise in fish. In the present study we measure how Sciaena umbra reacts to boat noise. We found that boat noise: i) increased duration of flight reactions and number of individuals performing them, ii) increased the frequency of hiding behaviors, and iii) did not elicit a change in fish activity level and sound emission. Flights and hiding behavior, usually related to predation risk, were not uniform between individuals and showed a quick recovery after noise exposure. On the basis of these results, potential metabolic, physiological and behavioral consequences are discussed and management recommendations are proposed.

Communicating the Issue of Underwater Noise Pollution: The Deaf as a Fish Project

Aquatic noise pollution is largely ignored by the lay public. How experts communicate this issue is critical to move public opinion. In 2010, the Cassa di Risparmio di Gorizia (CaRiGO) bank sponsored the Deaf as a Fish project that included local underwater noise monitoring, a boat census, a pamphlet for nonexperts, and some seminars and public meetings. This project allowed us to raise interest in this issue. Using accurate and understandable language in a light-humored setting goes far toward cultivating trust from a public audience that can be intimidated or suspicious of complicated scientific messaging.

Acoustic Communication in Butterflyfishes: Anatomical Novelties, Physiology, Evolution, and Behavioral Ecology

Coral reef fishes live in noisy environments that may challenge their capacity for acoustic communication. Butterflyfishes (Family Chaetodontidae) are prominent and ecologically diverse members of coral reef communities worldwide. The discovery of a novel association of anterior swim bladder horns with the lateral line canal system in the genus Chaetodon (the laterophysic connection) revealed a putative adaptation for enhancement of sound reception by the lateral line system and/or the ear. Behavioral studies show that acoustic communication is an important component of butterflyfish social behavior. All bannerfish (Forcipiger, Heniochus, and Hemitaurichthys) and Chaetodon species studied thus far produce several sound types at frequencies of <1 to >1000 Hz. Ancestral character state analyses predict the existence of both shared (head bob) and divergent (tail slap) acoustic behaviors in these two clades. Experimental auditory physiology shows that butterflyfishes are primarily sensitive to stimuli associated with hydrodynamic particle accelerations of ≤500 Hz. In addition, the gas-filled swim bladder horns in Chaetodon are stimulated by sound pressure, which enhances and extends their auditory sensitivity to 1700-2000 Hz. The broadband spectrum of ambient noise present on coral reefs overlaps with the frequency characteristics of their sounds, thus both the close social affiliations common among butterflyfishes and the evolution of the swim bladder horns in Chaetodon facilitate their short-range acoustic communication. Butterflyfishes provide a unique and unexpected opportunity to carry out studies of fish bioacoustics in the lab and the field that integrate the study of sensory anatomy, physiology, evolution, and behavioral ecology.

In situ mortality experiments with juvenile sea bass (Dicentrarchus labrax) in relation to impulsive sound levels caused by pile driving of windmill foundations

Impact assessments of offshore wind farm installations and operations on the marine fauna are performed in many countries. Yet, only limited quantitative data on the physiological impact of impulsive sounds on (juvenile) fishes during pile driving of offshore wind farm foundations are available. Our current knowledge on fish injury and mortality due to pile driving is mainly based on laboratory experiments, in which high-intensity pile driving sounds are generated inside acoustic chambers. To validate these lab results, an in situ field experiment was carried out on board of a pile driving vessel. Juvenile European sea bass (Dicentrarchus labrax) of 68 and 115 days post hatching were exposed to pile-driving sounds as close as 45 m from the actual pile driving activity. Fish were exposed to strikes with a sound exposure level between 181 and 188 dB re 1 µPa².s. The number of strikes ranged from 1739 to 3067, resulting in a cumulative sound exposure level between 215 and 222 dB re 1 µPa².s. Control treatments consisted of fish not exposed to pile driving sounds. No differences in immediate mortality were found between exposed and control fish groups. Also no differences were noted in the delayed mortality up to 14 days after exposure between both groups. Our in situ experiments largely confirm the mortality results of the lab experiments found in other studies.

Ontogenetic investigation of underwater hearing capabilities in loggerhead sea turtles (Caretta caretta) using a dual testing approach

Sea turtles reside in different acoustic environments with each life history stage and may have different hearing capacity throughout ontogeny. For this study, two independent yet complementary techniques for hearing assessment, i.e. behavioral and electrophysiological audiometry, were employed to (1) measure hearing in post-hatchling and juvenile loggerhead sea turtles Caretta caretta (19-62 cm straight carapace length) to determine whether these migratory turtles exhibit an ontogenetic shift in underwater auditory detection and (2) evaluate whether hearing frequency range and threshold sensitivity are consistent in behavioral and electrophysiological tests. Behavioral trials first required training turtles to respond to known frequencies, a multi-stage, time-intensive process, and then recording their behavior when they were presented with sound stimuli from an underwater speaker using a two-response forced-choice paradigm. Electrophysiological experiments involved submerging restrained, fully conscious turtles just below the air-water interface and recording auditory evoked potentials (AEPs) when sound stimuli were presented using an underwater speaker. No significant differences in behavior-derived auditory thresholds or AEP-derived auditory thresholds were detected between post-hatchling and juvenile sea turtles. While hearing frequency range (50-1000/1100 Hz) and highest sensitivity (100-400 Hz) were consistent in audiograms pooled by size class for both behavior and AEP experiments, both post-hatchlings and juveniles had significantly higher AEP-derived than behavior-derived auditory thresholds, indicating that behavioral assessment is a more sensitive testing approach. The results from this study suggest that post-hatchling and juvenile loggerhead sea turtles are low-frequency specialists, exhibiting little differences in threshold sensitivity and frequency bandwidth despite residence in acoustically distinct environments throughout ontogeny.

Hearing capacities and otolith size in two ophidiiform species (Ophidion rochei and Carapus acus)

Numerous studies have highlighted the diversity of fish inner ear morphology. However, the function of shape, size, and orientation of the different structures remains poorly understood. The saccule (otolithic endorgan) is considered as the principal hearing organ in fishes and it has been hypothesized that sagitta (saccular otolith) shape and size affect hearing capacities: large sagittae are thought to increase sensitivity. The sagittae of many ophidiids and carapids occupy a large volume inside the neurocranium. Hence they are of great interest to test the size hypothesis. The main aim of this study was to investigate hearing capacities and inner ear morphology in two ophidiiform species: Ophidion rochei and Carapus acus. We used a multidisciplinary approach that combines dissections, μCT-scan examinations, and auditory evoked potential technique. Carapus acus and O. rochei sagittae have similar maximal diameter, both species have larger otoliths than many non-ophidiiform species especially compared to the intra-neurocranium (INC) volume. Both species are sensitive to sounds up to 2100 Hz. Relative to the skull, O. rochei had smaller sagittae than the carapid but better hearing capacities from 300 to 900 Hz and similar sensitivities at 150 Hz and from 1200 to 2100 Hz. Results show that hearing capacities of a fish species cannot be predicted only based on sagitta size. Larger otoliths (in size relative to the skull) may have evolved mainly for performing vestibular functions in fishes, especially those ones that need to execute precise and complex movements.

Contribution to the study of acoustic communication in two Belgian river bullheads (Cottus rhenanus and C. perifretum) with further insight into the sound-producing mechanism

BACKGROUND

The freshwater sculpins (genus Cottus) are small, bottom-living fishes widely distributed in North America and Europe. The taxonomy of European species has remained unresolved for a long time due to the overlap of morphological characters. Sound production has already been documented in some cottid representatives, with sounds being involved in courtship and agonistic interactions. Although the movements associated with sound production have been observed, the underlying mechanism remains incomplete. Here, we focus on two closely related species from Belgium: C. rhenanus and C. perifretum. This study aims 1) to record and to compare acoustic communication in both species, 2) to give further insight into the sound-producing mechanism and 3) to look for new morphological traits allowing species differentiation.

RESULTS

Both Cottus species produce multiple-pulsed agonistic sounds using a similar acoustic pattern: the first interpulse duration is always longer, making the first pulse unit distinct from the others. Recording sound production and hearing abilities showed a clear relationship between the sound spectra and auditory thresholds in both species: the peak frequencies of calls are around 150 Hz, which corresponds to their best hearing sensitivity. However, it appears that these fishes could not hear acoustic signals produced by conspecifics in their noisy habitat considering their hearing threshold expressed as sound pressure (~ 125 dB re 1 μPa). High-speed video recordings highlighted that each sound is produced during a complete back and forth movement of the pectoral girdle.

CONCLUSIONS

Both Cottus species use an acoustic pattern that remained conserved during species diversification. Surprisingly, calls do not seem to have a communicative function. On the other hand, fish could detect substrate vibrations resulting from movements carried out during sound production. Similarities in temporal and spectral characteristics also suggest that both species share a common sound-producing mechanism, likely based on pectoral girdle vibrations. From a morphological point of view, only the shape of the spinelike scales covering the body allows species differentiation.

Hearing in cichlid fishes under noise conditions

Background

Hearing thresholds of fishes are typically acquired under laboratory conditions. This does not reflect the situation in natural habitats, where ambient noise may mask their hearing sensitivities. In the current study we investigate hearing in terms of sound pressure (SPL) and particle acceleration levels (PAL) of two cichlid species within the naturally occurring range of noise levels. This enabled us to determine whether species with and without hearing specializations are differently affected by noise.

Methodology/Principal Findings

We investigated auditory sensitivities in the orange chromide Etroplus maculatus, which possesses anterior swim bladder extensions, and the slender lionhead cichlid Steatocranus tinanti, in which the swim bladder is much smaller and lacks extensions. E. maculatus was tested between 0.2 and 3kHz and S. tinanti between 0.1 and 0.5 kHz using the auditory evoked potential (AEP) recording technique. In both species, SPL and PAL audiograms were determined in the presence of quiet laboratory conditions (baseline) and continuous white noise of 110 and 130 dB RMS. Baseline thresholds showed greatest hearing sensitivity around 0.5 kHz (SPL) and 0.2 kHz (PAL) in E. maculatus and 0.2 kHz in S. tinanti. White noise of 110 dB elevated the thresholds by 0–11 dB (SPL) and 7–11 dB (PAL) in E. maculatus and by 1–2 dB (SPL) and by 1–4 dB (PAL) in S. tinanti. White noise of 130 dB elevated hearing thresholds by 13–29 dB (SPL) and 26–32 dB (PAL) in E. maculatus and 6–16 dB (SPL) and 6–19 dB (PAL) in S. tinanti.

Conclusions

Our data showed for the first time for SPL and PAL thresholds that the specialized species was masked by different noise regimes at almost all frequencies, whereas the non-specialized species was much less affected. This indicates that noise can limit sound detection and acoustic orientation differently within a single fish family.

Auditory evoked potential audiometry in fish

A recent survey lists more than 100 papers utilizing the auditory evoked potential (AEP) recording technique for studying hearing in fishes. More than 95 % of these AEP-studies were published after Kenyon et al. introduced a non-invasive electrophysiological approach in 1998 allowing rapid evaluation of hearing and repeated testing of animals. First, our review compares AEP hearing thresholds to behaviorally gained thresholds. Second, baseline hearing abilities are described and compared in 111 fish species out of 51 families. Following this, studies investigating the functional significance of various accessory hearing structures (Weberian ossicles, swim bladder, otic bladders) by eliminating these morphological structures in various ways are dealt with. Furthermore, studies on the ontogenetic development of hearing are summarized. The AEP-technique was frequently used to study the effects of high sound/noise levels on hearing in particular by measuring the temporary threshold shifts after exposure to various noise types (white noise, pure tones and anthropogenic noises). In addition, the hearing thresholds were determined in the presence of noise (white, ambient, ship noise) in several studies, a phenomenon termed masking. Various ecological (e.g., temperature, cave dwelling), genetic (e.g., albinism), methodical (e.g., ototoxic drugs, threshold criteria, speaker choice) and behavioral (e.g., dominance, reproductive status) factors potentially influencing hearing were investigated. Finally, the technique was successfully utilized to study acoustic communication by comparing hearing curves with sound spectra either under quiet conditions or in the presence of noise, by analyzing the temporal resolution ability of the auditory system and the detection of temporal, spectral and amplitude characteristics of conspecific vocalizations.

The contribution of the lateral line to 'hearing' in fish

In the underwater environment, sound propagates both as a pressure wave and as particle displacement, with particle displacement dominating close to the source (the nearfield). At the receptor level, both the fish ear and the neuromast hair cells act as displacement detectors and both are potentially stimulated by the particle motion component of sound sources, especially in the nearfield. A now common way to test 'hearing' in fish involves auditory evoked potentials (AEPs), with recordings made from electrodes implanted near the auditory brainstem. These AEP recordings are typically conducted in enclosed acoustic environments with the fish well within the nearfield, especially for lower frequencies. We tested the contribution of neuromast hair cells to AEP by first testing intact goldfish (Carassius auratus), then ablating their neuromasts with streptomycin sulphate--disabling superficial and canal neuromasts--and retesting the same goldfish. We performed a similar experiment where only the superficial neuromasts were physically ablated. At 100 and 200 Hz, there was a 10-15 dB increase in threshold after streptomycin treatment but no significant difference at higher frequencies. There was no difference in threshold in control fish or in fish that only had superficial neuromasts removed, indicating that the differential responses were driven by canal neuromasts. Taken together, these results indicate that AEP results at lower frequencies should be interpreted as multimodal responses, rather than as 'hearing'. The results also suggest that in natural situations both the ear and lateral line likely play an integrative role in detecting and localising many types of 'acoustic' stimuli.