Threshold for onset of injury in Chinook salmon from exposure to impulsive pile driving sounds

The risk of effects to fishes and other aquatic life from impulsive sound produced by activities such as pile driving and seismic exploration is increasing throughout the world, particularly with the increased exploitation of oceans for energy production. At the same time, there are few data that provide insight into the effects of these sounds on fishes. The goal of this study was to provide quantitative data to define the levels of impulsive sound that could result in the onset of barotrauma to fish. A High Intensity Controlled Impedance Fluid filled wave Tube was developed that enabled laboratory simulation of high-energy impulsive sound that were characteristic of aquatic far-field, plane-wave acoustic conditions. The sounds used were based upon the impulsive sounds generated by an impact hammer striking a steel shell pile. Neutrally buoyant juvenile Chinook salmon (Oncorhynchus tshawytscha) were exposed to impulsive sounds and subsequently evaluated for barotrauma injuries. Observed injuries ranged from mild hematomas at the lowest sound exposure levels to organ hemorrhage at the highest sound exposure levels. Frequency of observed injuries were used to compute a biological response weighted index (RWI) to evaluate the physiological impact of injuries at the different exposure levels. As single strike and cumulative sound exposure levels (SEL(ss), SEL(cum) respectively) increased, RWI values increased. Based on the results, tissue damage associated with adverse physiological costs occurred when the RWI was greater than 2. In terms of sound exposure levels a RWI of 2 was achieved for 1920 strikes by 177 dB re 1 μPa(2)?s SEL(ss) yielding a SEL(cum) of 210 dB re 1 μPa(2)?s, and for 960 strikes by 180 dB re 1 μPa(2)?s SEL(ss) yielding a SEL(cum) of 210 dB re 1 μPa(2)?s. These metrics define thresholds for onset of injury in juvenile Chinook salmon.     

Common sole larvae survive high levels of pile-driving sound in controlled exposure experiments

In view of the rapid extension of offshore wind farms, there is an urgent need to improve our knowledge on possible adverse effects of underwater sound generated by pile-driving. Mortality and injuries have been observed in fish exposed to loud impulse sounds, but knowledge on the sound levels at which (sub-)lethal effects occur is limited for juvenile and adult fish, and virtually non-existent for fish eggs and larvae. A device was developed in which fish larvae can be exposed to underwater sound. It consists of a rigid-walled cylindrical chamber driven by an electro-dynamical sound projector. Samples of up to 100 larvae can be exposed simultaneously to a homogeneously distributed sound pressure and particle velocity field. Recorded pile-driving sounds could be reproduced accurately in the frequency range between 50 and 1000 Hz, at zero to peak pressure levels up to 210 dB re 1μPa(2) (zero to peak pressures up to 32 kPa) and single pulse sound exposure levels up to 186 dB re 1μPa(2)s. The device was used to examine lethal effects of sound exposure in common sole (Solea solea) larvae. Different developmental stages were exposed to various levels and durations of pile-driving sound. The highest cumulative sound exposure level applied was 206 dB re 1μPa(2)s, which corresponds to 100 strikes at a distance of 100 m from a typical North Sea pile-driving site. The results showed no statistically significant differences in mortality between exposure and control groups at sound exposure levels which were well above the US interim criteria for non-auditory tissue damage in fish. Although our findings cannot be extrapolated to fish larvae in general, as interspecific differences in vulnerability to sound exposure may occur, they do indicate that previous assumptions and criteria may need to be revised.     

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.     

Exposure of fish to high‐intensity sonar does not induce acute pathology

This study investigated immediate effects of intense sound exposure associated with low‐frequency (170–320 Hz) or with mid‐frequency (2·8–3·8 kHz) sonars on caged rainbow trout Oncorhynchus mykiss, channel catfish Ictalurus punctatus and hybrid sunfish Lepomis sp. in Seneca Lake, New York, U.S.A. This study focused on potential effects on inner ear tissues using scanning electron microscopy and on non‐auditory tissues using gross and histopathology. Fishes were exposed to low‐frequency sounds for 324 or 628 s with a received peak signal level of 193 dB re 1 µPa (root mean square, rms) or to mid‐frequency sounds for 15 s with a received peak signal level of 210 dB re 1 µPa (rms). Although a variety of clinical observations from various tissues and organ systems were described, no exposure‐related pathologies were observed. This study represents the first investigation of the effects of high‐intensity sonar on fish tissues in vivo. Data from this study indicate that exposure to low and midfrequency sonars, as described in this report, might not have acute effects on fish tissues.     

Behavioral responses of satellite tracked Blainville's beaked whales (Mesoplodon densirostris) to mid-frequency active sonar

The vulnerability of beaked whales (Family: Ziphiidae) to intense sound exposure has led to interest in their behavioral responses to mid-frequency active sonar (MFAS, 3–8 kHz). Here we present satellite-transmitting tag movement and dive behavior records from Blainville's beaked whales (Mesoplodon densirostris) tagged in advance of naval sonar exercises at the Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. This represents one of the largest samples of beaked whales individually tracked during sonar operations (n = 7). The majority of individuals (five of seven) were displaced 28–68 km after the onset of sonar exposure and returned to the AUTEC range 2–4 days after exercises ended. Modeled sound pressure received levels were available during the tracking of four individuals and three of those individuals showed declines from initial maxima of 145–172 dB re 1 μPa to maxima of 70–150 dB re 1 μPa following displacements. Dive behavior data from tags showed a continuation of deep diving activity consistent with foraging during MFAS exposure periods, but also suggested reductions in time spent on deep dives during initial exposure periods. These data provide new insights into behavioral responses to MFAS and have important implications for modeling the population consequences of disturbance.     

REACTION OF FIN WHALES BALAENOPTERA PHYSALUS TO AN EARTHQUAKE

ABSTRACT

Whales living within seismically active regions are subject to intense disturbances from strong sounds produced by earthquakes that can kill or injure individuals. Nishimura & Clark (1993) relate the possible effects of underwater earthquake noise levels in marine mammals, adducing that T-phase source signal level (10- to 30- Hz range) can exceed 200 dB re: 1 μPa at 1 m, for a magnitude 4–5 earthquake, sounds audible to fin whales which produce low frequency sounds of 16–20/25–44 Hz over 0.5–1s, typically of 183 dB re: 1 μPa at 1 m. Here we present the response of a fin whale to a 5.5 Richter scale earthquake that took place on 22 February 2005, in the Gulf of California. The whale covered 13 km in 26 min (mean speed = 30.2 km/h). We deduce that the sound heard by this whale might have triggered the costly energy expenditure of high speed swimming as a seismic-escape response. These observations support the hypothesis of Richardson et al. (1995) that cetaceans may flee from loud sounds before they are injured, when exposed to noise in excess of 140 dB re: 1 μPa 1 m.     

Quantitative and temporal relationships of egg production and sound production by black drum Pogonias cromis

The timing and levels of black drum Pogonias cromis sound production and egg production were compared in an estuarine canal basin of Cape Coral in south-west Florida. Surface plankton samples were collected hourly from 1800 to 0400 on two consecutive nights while continuous acoustic recordings were made simultaneously at five locations in the canal basin. Five pairs of nights were sampled during a part of the spawning season from late January to early April 2006. Pogonias cromis sound production and egg production occurred on all evenings that samples were collected; however, both the timing and levels of sound production were negatively associated with those of egg production. Egg production estimates ranged from a low of 4·8 eggs m(-3) in February to a high of 2889·2 eggs m(-3) in April. Conversely, maximum nightly sound pressure levels (SPL) ranged from a low of 89·5 dB in April to a high of 131·9 dB (re: 1 μPa) in February. The temporal centre of sound production was relatively stable among all nights sampled but spawning occurred earlier in the day as the season progressed and exhibited a strong, positive association with increased water temperature. The negative relationship between the levels of sound production and egg production was unexpected given the usefulness of sound production as a proxy for reproduction on a seasonal basis and may possibly be explained by differences in the spawning potential of the female population in the study area on nights sampled. Egg mortality rates increased throughout the season and were positively associated with densities of hydrozoans and ctenophores.     

Behavioural response thresholds in New Zealand crab megalopae to ambient underwater sound

A small number of studies have demonstrated that settlement stage decapod crustaceans are able to detect and exhibit swimming, settlement and metamorphosis responses to ambient underwater sound emanating from coastal reefs. However, the intensity of the acoustic cue required to initiate the settlement and metamorphosis response, and therefore the potential range over which this acoustic cue may operate, is not known. The current study determined the behavioural response thresholds of four species of New Zealand brachyuran crab megalopae by exposing them to different intensity levels of broadcast reef sound recorded from their preferred settlement habitat and from an unfavourable settlement habitat. Megalopae of the rocky-reef crab, Leptograpsus variegatus, exhibited the lowest behavioural response threshold (highest sensitivity), with a significant reduction in time to metamorphosis (TTM) when exposed to underwater reef sound with an intensity of 90 dB re 1 μPa and greater (100, 126 and 135 dB re 1 μPa). Megalopae of the mud crab, Austrohelice crassa, which settle in soft sediment habitats, exhibited no response to any of the underwater reef sound levels. All reef associated species exposed to sound levels from an unfavourable settlement habitat showed no significant change in TTM, even at intensities that were similar to their preferred reef sound for which reductions in TTM were observed. These results indicated that megalopae were able to discern and respond selectively to habitat-specific acoustic cues. The settlement and metamorphosis behavioural response thresholds to levels of underwater reef sound determined in the current study of four species of crabs, enables preliminary estimation of the spatial range at which an acoustic settlement cue may be operating, from 5 m to 40 km depending on the species. Overall, these results indicate that underwater sound is likely to play a major role in influencing the spatial patterns of settlement of coastal crab species.     

Discrimination between high and low repetition rates of ultrasonic pulses by the cod

Cod were trained to detect a shift in the repetition rate of intense ultrasonic pulses (approximately 210 dB re 1 μPa). For cod exposed to predation by toothed whales, this ability may provide information to guide evasive manoeuvres.     

REACTIONS OF CAPTIVE HARBOR PORPOISES (PHOCOENA PHOCOENA) TO PINGER-LIKE SOUNDS

Pingers on gill nets can reduce bycatch of harbor porpoises. If harbor porpoises habituate to pingers, the effect may be reduced or lost. Two captive harbor porpoises were exposed to three sound types. All sounds were in the frequency band from 100 kHz to 140 kHz, 200 ms long, and presented once per 4 s. The source level was 153 dB re 1 μPa RMS at 1 m. Each session consisted of a 10‐min presound, a 5‐min sound, and a 10‐min postsound period. Behavior was recorded on video and on dataloggers placed on the dorsal fin of one animal. The loggers recorded heart rate, swimming speed, dive duration, and depth. The animals responded most strongly to the initial presentations of a sound. Surface time decreased, the heart rate dropped below the normal bradycardia, and echolocation activity decreased. The reactions of both animals diminished rapidly in the following sessions. Should the waning of responsiveness apply to wild animals, porpoises may adapt to the sounds but still avoid nets, or the bycatch may increase after some time. The success of long‐term use of pingers may then depend on the variety of sounds and rates of exposure.     

A simulation approach to assessing environmental risk of sound exposure to marine mammals

Intense underwater sounds caused by military sonar, seismic surveys, and pile driving can harm acoustically sensitive marine mammals. Many jurisdictions require such activities to undergo marine mammal impact assessments to guide mitigation. However, the ability to assess impacts in a rigorous, quantitative way is hindered by large knowledge gaps concerning hearing ability, sensitivity, and behavioral responses to noise exposure. We describe a simulation‐based framework, called SAFESIMM (Statistical Algorithms For Estimating the Sonar Influence on Marine Megafauna), that can be used to calculate the numbers of agents (animals) likely to be affected by intense underwater sounds. We illustrate the simulation framework using two species that are likely to be affected by marine renewable energy developments in UK waters: gray seal (Halichoerus grypus) and harbor porpoise (Phocoena phocoena). We investigate three sources of uncertainty: How sound energy is perceived by agents with differing hearing abilities; how agents move in response to noise (i.e., the strength and directionality of their evasive movements); and the way in which these responses may interact with longer term constraints on agent movement. The estimate of received sound exposure level (SEL) is influenced most strongly by the weighting function used to account for the specie's presumed hearing ability. Strongly directional movement away from the sound source can cause modest reductions (~5 dB) in SEL over the short term (periods of less than 10 days). Beyond 10 days, the way in which agents respond to noise exposure has little or no effect on SEL, unless their movements are constrained by natural boundaries. Most experimental studies of noise impacts have been short‐term. However, data are needed on long‐term effects because uncertainty about predicted SELs accumulates over time. Synthesis and applications. Simulation frameworks offer a powerful way to explore, understand, and estimate effects of cumulative sound exposure on marine mammals and to quantify associated levels of uncertainty. However, they can often require subjective decisions that have important consequences for management recommendations, and the basis for these decisions must be clearly described.     

Stress and Auditory Responses of the Otophysan Fish,Cyprinella venusta,to Road Traffic Noise

Noise pollution from anthropogenic sources is an increasingly problematic challenge faced by many taxa, including fishes. Recent studies demonstrate that road traffic noise propagates effectively from bridge crossings into surrounding freshwater ecosystems; yet, its effect on the stress response and auditory function of freshwater stream fishes is unexamined. The blacktail shiner (Cyprinella venusta) was used as a model to investigate the degree to which traffic noise impacts stress and hearing in exposed fishes. Fish were exposed to an underwater recording of traffic noise played at approximately 140 dB re 1 μPa. Waterborne cortisol samples were collected and quantified using enzyme immunoassay (EIA). Auditory thresholds were assessed in control and traffic exposed groups by measuring auditory evoked potentials (AEPs). After acute exposure to traffic noise, fish exhibited a significant elevation in cortisol levels. Individuals exposed to 2 hours of traffic noise playback had elevated hearing thresholds at 300 and 400 Hz, corresponding to the most sensitive bandwidth for this species.     

Repeated exposure reduces the response to impulsive noise in European seabass

Human activities have changed the acoustic environment of many terrestrial and aquatic ecosystems around the globe. Mounting evidence indicates that the resulting anthropogenic noise can impact the behaviour and physiology of at least some species in a range of taxa. However, the majority of experimental studies have considered only immediate responses to single, relatively short‐term noise events. Repeated exposure to noise could lead to a heightened or lessened response. Here, we conduct two long‐term (12 week), laboratory‐based exposure experiments with European seabass (Dicentrarchus labrax) to examine how an initial impact of different sound types potentially changes over time. Naïve fish showed elevated ventilation rates, indicating heightened stress, in response to impulsive additional noise (playbacks of recordings of pile‐driving and seismic surveys), but not to a more continuous additional noise source (playbacks of recordings of ship passes). However, fish exposed to playbacks of pile‐driving or seismic noise for 12 weeks no longer responded with an elevated ventilation rate to the same noise type. Fish exposed long‐term to playback of pile‐driving noise also no longer responded to short‐term playback of seismic noise. The lessened response after repeated exposure, likely driven by increased tolerance or a change in hearing threshold, helps explain why fish that experienced 12 weeks of impulsive noise showed no differences in stress, growth or mortality compared to those reared with exposure to ambient‐noise playback. Considering how responses to anthropogenic noise change with repeated exposure is important both when assessing likely fitness consequences and the need for mitigation measures.     

Early postnatal sound exposure induces lasting neuronal changes in the inferior colliculus of senescence accelerated mice (SAMP8): a morphometric study on GABAergic neurons and NMDA expression

Senescence-acceleration-prone mice (SAMP8) provide a model to study the influence of early postnatal sound exposure upon the aging auditory midbrain. SAMP8 were exposed to a 9-kHz monotone of either 53- or 65-dB sound pressure level during the first 30 postnatal days, the neurons in the auditory midbrain responding selectively to 9 kHz were localized by c-fos immunohistochemistry and the following parameters were compared to control SAMP8 not exposed to sound: mortality after sound exposure, dendritic spine density, and quantitative neurochemical alterations in this 9-kHz isofrequency lamina. For morphometric analysis, animals were examined at 1, 4, and 8 months of age. Serial sections of the inferior colliculus were Golgi impregnated or stained immunohistochemically for the expression of 1 subunit of NMDA receptor or GABA. Mortality after exposure to 53 dB was the same as in controls, but was markedly increased from 7 months of age onward after postnatal exposure to 65 dB. No gross morphological alterations were observed in the auditory midbrain after sound exposure. However, sound exposure to 53 or 65 dB significantly reduced dendritic spine density by 11% at 4 months or by 11–17% both at 1 and 4 months of age, respectively. The effect of sound exposure upon neurons expressing the NMDA1 subunit was dose-dependent. Increasing with age until 4 months in control mice and remaining essentially stable thereafter, the percentage of NMDA1-immunoreactive neurons was significantly elevated by 40–66% in 1- and 8-month-old SAMP8 exposed to 53 dB, whereas no significant effect of 65 dB was apparent. The proportion of GABAergic cells declined with age in controls. It was significantly decreased at 1 month after 53 and 65 dB sound exposure. In contrast, it was elevated at later stages, being significantly increased at 4 months after exposure to 53 dB and at 8 months after exposure to 65 dB. The total cell number in the 9-kHz isofrequency lamina of SAMP8 decreased with age, but was not affected by exposure to either 53 or 65 dB. The present results indicate that early postnatal exposure to a monotone of mild intensity has long-term effects upon the aging auditory brain stem. Some of the changes induced by sound exposure, e.g., decline in spine density, are interpreted as accelerations of the normal aging process, whereas other effects, e.g., increased NMDA1 expression after 53 dB and elevated GABA expression after both 53 and 65 dB, are not merely explicable by accelerated aging.     

The effect of stimulus type and background noise on hearing abilities of the round goby Neogobius melanostomus

The auditory abilities of the round goby Neogobius melanostomus were quantified using auditory evoked potential recordings, using tone bursts and conspecific call stimuli. Fish were tested over a range of sizes to assess effects of growth on hearing ability. Tests were also run with and without background noise to assess the potential effects of masking in a natural setting. Neogobius melanostomus detected tone bursts from 100 to 600 Hz with no clear best frequency in the pressure domain but were most sensitive to 100 Hz tone stimuli when examined in terms of particle acceleration. Responses to a portion of the N. melanostomus call occurred at a significantly lower threshold than responses to pure tone stimulation. There was no effect of size on N. melanostomus hearing ability, perhaps due to growth of the otolith keeping pace with growth of the auditory epithelium. Neogobius melanostomus were masked by both ambient noise and white noise, but not until sound pressure levels were relatively high, having a 5-10 dB threshold shift at noise levels of 150 dB re 1 μPa and higher but not at lower noise levels.     

UNDERWATER NOISE OF WHALE-WATCHING BOATS AND POTENTIAL EFFECTS ON KILLER WHALES (ORCINUS ORCA), BASED ON AN ACOUSTIC IMPACT MODEL

Underwater noise of whale-watching boats was recorded in the popular killer whale-watching region of southern British Columbia and northwestern Washington State. A software sound propagation and impact assessment model was applied to estimate zones around whale-watching boats where boat noise was audible to killer whales, where it interfered with their communication, where it caused behavioral avoidance, and where it possibly caused hearing loss. Boat source levels ranged from 145 to 169 dB re 1 μPa @ 1 m, increasing with speed. The noise of fast boats was modeled to be audible to killer whales over 16 km, to mask killer whale calls over 14 km, to elicit a behavioral response over 200 m, and to cause a temporary threshold shift (TTS) in hearing of 5 dB after 30–50 min within 450 m. For boats cruising at slow speeds, the predicted ranges were 1 km for audibility and masking, 50 m for behavioral responses, and 20 m for TTS. Superposed noise levels of a number of boats circulating around or following the whales were close to the critical level assumed to cause a permanent hearing loss over prolonged exposure. These data should be useful in developing whale-watching regulations. This study also gave lower estimates of killer whale call source levels of 105–124 dB re 1 μPa.     

Acoustic overstimulation activates 5'-AMP-activated protein kinase through a temporary decrease in ATP level in the cochlear spiral ligament prior to permanent hearing loss in mice

Inner ear disorders are known to be elicited by mitochondrial dysfunction, which decreases the ATP level in the inner ear. 5′-AMP-activated protein kinase (AMPK) is a serine/threonine kinase activated by metabolic stress and by an increase in the AMP/ATP ratio. To elucidate the involvement of AMPK-derived signals in noise-induced hearing loss, we investigated whether in vivo acoustic overstimulation would activate AMPK in the cochlea of mice. Std-ddY mice were exposed to 8 kHz octave band noise at a 90-, 110- or 120-dB sound pressure level (SPL) for 2 h. Exposure to the noise at 110 or 120 dB SPL produced outer hair cell death in the organ of Corti and permanent hearing loss. Exposure to the noise at 120-dB SPL elevated the level of the phospho-AMPK α-subunit (p-AMPKα), without affecting the protein level of this subunit, immediately and at 12-h post-exposure in the lateral wall structures including the spiral ligament and stria vascularis. In the hair cells and spiral ganglion cells, no marked change in the level of p-AMPKα was observed at any time post-exposure. The level of phospho-c-Jun N-terminal kinase (p-JNK) was increased in the lateral wall structures at 2- to 4-h post-exposure at 120 dB SPL. Noise exposure significantly, but temporarily, decreased the ATP level in the spiral ligament, in an SPL-dependent manner at 110 dB and above. Likewise, elevation of p-AMPKα and p-JNK levels was also observed in the lateral wall structures post-exposure to noise at an SPL of 110 dB and above. Taken together, our data suggest that AMPK and JNK were activated by ATP depletion in the cochlear spiral ligament prior to permanent hearing loss induced by in vivo acoustic overstimulation.     

褐菖鲉的听觉阈值研究

利用听觉诱发电位记录技术研究了褐菖鲉(Sebasticus marmoratus)的听觉阈值。通过采用听觉生理系统记录和分析了8尾褐菖鲉对频率范围在100—1000 Hz的7种不同频率的声音刺激的诱发电位反应。结果表明, 褐菖鲉的听觉阈值在整体上随着频率增加而增加, 对100—300 Hz的低频声音信号敏感, 最敏感频率为150 Hz, 对应的听觉阈值为70 dB re 1 μPa。褐菖鲉的听觉敏感区间与其发声频率具有较高的匹配性, 表明其声讯交流的重要性。同时, 人为低频噪声可能对其声讯交流造成影响。     

Temporal and Spatial Comparisons of Underwater Sound Signatures of Different Reef Habitats in Moorea Island,French Polynesia

As environmental sounds are used by larval fish and crustaceans to locate and orientate towards habitat during settlement, variations in the acoustic signature produced by habitats could provide valuable information about habitat quality, helping larvae to differentiate between potential settlement sites. However, very little is known about how acoustic signatures differ between proximate habitats. This study described within- and between-site differences in the sound spectra of five contiguous habitats at Moorea Island, French Polynesia: the inner reef crest, the barrier reef, the fringing reef, a pass and a coastal mangrove forest. Habitats with coral (inner, barrier and fringing reefs) were characterized by a similar sound spectrum with average intensities ranging from 70 to 78 dB re 1μPa.Hz^-1. The mangrove forest had a lower sound intensity of 70 dB re 1μPa.Hz^-1 while the pass was characterized by a higher sound level with an average intensity of 91 dB re 1μPa.Hz^-1. Habitats showed significantly different intensities for most frequencies, and a decreasing intensity gradient was observed from the reef to the shore. While habitats close to the shore showed no significant diel variation in sound intensities, sound levels increased at the pass during the night and barrier reef during the day. These two habitats also appeared to be louder in the North than in the West. These findings suggest that daily variations in sound intensity and across-reef sound gradients could be a valuable source of information for settling larvae. They also provide further evidence that closely related habitats, separated by less than 1 km, can differ significantly in their spectral composition and that these signatures might be typical and conserved along the coast of Moorea.     

Dietary vitamin E protects the fathead minnow, Pimephales promelas, against noise exposure

The fathead minnow (Pimephales promelas) was employed to examine if dietary vitamin E supplementation could protect the inner ear from the deleterious effects of noise. Fish were fed one of the three experimental diets containing either: (1) low vitamin E content (14.5 mg/kg diet as alpha-tocopheryl acetate), (2) an adequate amount of vitamin E (50 mg/kg), or (3) high vitamin E content (450 mg/kg). After 4 weeks on the diet, fish were exposed to either 2 or 24 h of intense white noise (142 dB re: 1 microPa, bandwidth 0.3-4.0 kHz). Auditory thresholds were measured, using the auditory brainstem response (ABR) technique, within 0.5 days following noise exposure or within a recovery period of 1.5 days. Additionally, liver samples were analyzed for vitamin E content. Increased vitamin E supplementation was dose-dependently associated with a reduction in statistically significant threshold shifts after noise exposure and an enhancement of recovery (i.e., more complete recovery over a shorter period) for fish exposed to either 2 or 24 h of noise. The results obtained suggest that dietary vitamin E affords protection against noise exposure in a cyprinid fish.