Acoustic monitoring reveals diversity and surprising dynamics in tropical freshwater soundscapes

1. Freshwater systems are globally threatened and in need of enhanced monitoring and assessment. We applied soundscape recording and analysis—which presents an opportunity for long-term, high-resolution animal community monitoring and assessment—to a freshwater context to better understand the acoustic diversity and dynamics of these systems.
2. We recorded the aquatic soundscape of a Neotropical freshwater swamp in Costa Rica for 23 days in January and February 2015 during the dry season. We classified biological sound types in these recordings and developed measurements of richness and occupancy based on this classification. We also calculated six complementary acoustic indices to assess soundscape diversity and daily and longer-term soundscape dynamics, and we examined correlations between these acoustic indices and sound type metrics.
3. We found rich soundscapes in which biological sounds were almost always present, and we classified 18 sound types that we attribute to aquatic insects. These sound types showed distinct daily patterns and exhibited temporal and spectral acoustic niche partitioning. Sound type richness was most correlated with the number of peaks index (correlation = .36; p < .001), while sound type occupancy was most correlated with the Bioacoustic Index (correlation = .92; p < .001). In contrast to generally high levels of acoustic activity, there were brief (approximately 1 hr), unexpected quiet periods around dawn and dusk.
4. This study represents an early attempt to comprehensively describe tropical freshwater soundscapes in a systematic and quantitative manner. We demonstrate that sound type classification and the quantification of acoustic occupancy capture aspects of soundscape diversity and dynamics that are complementary to those assessed by acoustic indices. Our analyses reveal that the soundscapes of this tropical wetland were diverse and exhibited daily dynamics that differed from those found in other ecosystems.

     

Influence of acoustics on the collective behaviour of a shoaling freshwater fish

1. Understanding how collective behaviour of animals is influenced by anthropogenic activity is important for their conservation in an increasingly urbanised world. River infrastructure, e.g. for transport and electricity generation, and associated construction and operation, produces sound that can disrupt ecological processes.
2. Adopting a reductionist manipulative experimental approach using Eurasian minnow (Phoxinus phoxinus) as a model shoaling species, we compared the response of individuals and groups of five fish to a broadband acoustic stimulus in a tank containing still water.
3. Four metrics were calculated 10 min immediately before (control–sound stimulus absent) and during the acoustic treatment: (1) swimming speed, (2) persistence of swim paths, (3) cohesion of the group, and (4) orientation of group members.
4. On presentation of the stimulus, groups exhibited a consistent escape response compared to individuals for which behaviour was more variable. Thereafter, individuals swam faster and their swim paths were less persistent than during the control; no difference was observed for groups. Conversely, group integrity became more cohesive and members were more likely to orient in a common direction during the treatment compared to the control.
5. This study provides insight into the importance of collective behaviour of fish in relation to antipredator-like response to anthropogenic noise. Short-term shifts in behaviour are context specific and depend on whether fish are members of a shoal or solitary. The results indicate the potential for negative impacts of unnatural sound on the ecology of shoaling species that inhabit engineered freshwater environments.

     

Interspecific variation in the response of fish to anthropogenic noise

1. Elevated levels of anthropogenic noise, especially those observed through boating activity, can negatively impact fish species, but it remains unclear which species are most affected and which behavioural metrics are best used in assessing fish responses to underwater noise. The effects of boat sounds on freshwater species are of particular interest because freshwater environments are less studied than the marine realm despite comparably high levels of biodiversity.
2. In the current study, we examine the behavioural responses to boat noise in two freshwater species that differ in their hypothesised response to sound inputs: the spottail shiner (Notropis hudsonius), a species with known hearing specialisations, and the bluegill sunfish (Lepomis macrochirus), a species with more generalised hearing capabilities. Fish were presented with boat noise in a laboratory setting, and their swimming, escape and foraging behaviours were assessed to examine differential responses in relation to hypothesised hearing abilities.
3. Both species showed a decrease in general swimming behaviours but an increase in erratic movements in response to boat noise, indicative of stress responses for both species. Despite the similarities in response based on swimming behaviours however, only spottail shiners exhibited true escape responses to the onset of the noise stimulus, suggesting a more extreme reaction in the species with a more refined hearing ability.
4. Taken together, these results show that freshwater fish can respond to increased levels of anthropogenic noise, but that the severity of the response may differ based on auditory structures and therefore presumed hearing ability. The differences seen between behavioural metrics used (swimming vs. escape responses) also demonstrate how care must be taken in choosing a metric when developing exposure guidelines for underwater sound exposures, as different metrics could lead to differential impact assessments.

     

Acoustic detection and acoustic habitat characterisation of the critically endangered white-bellied heron (Ardea insignis) in Bhutan

1. Growing developmental activities, such as hydropower construction, farm roads, and other human activities, are affecting the critically endangered white-bellied heron (WBH). Out of a known global population of 60, 28 individuals inhabit the river basin area and freshwater lakes and ponds of Bhutan. Several constraints impede continuous monitoring of endangered species, such as the isolated and cryptic nature of the species and the remoteness of its habitat; to date, there are no long-term reference data or techniques implemented for continuous monitoring of this species.
2. In this study, we designed acoustic detection and habitat characterisation methods using long-duration recordings from three habitat areas in Bhutan. Acoustic indices were extracted and used to implement a species-specific call detector and to generate habitat soundscape representations. Using WBH calls annotated in month-long recordings from a known site, a novel indices-based detector was implemented and tested. A total of 960 hr of continuous audio recordings from three habitats in Bhutan were analysed.
3. We found that a species call detector implemented using a combination of acoustic indices (that includes measures of spectral and temporal entropy and different angles of spectral ridges) has a correct detection rate of 81%. Additionally, visual inspection of the species’ acoustic habitat using long-duration false-colour spectrograms enabled qualitative assessment of acoustic habitat structure and other dominant acoustic events.
4. This study proposes a combined approach of species acoustic detection and habitat soundscape analysis for holistic acoustic monitoring of endangered species. As a direct outcome of this work, we documented acoustic reference data on the critically endangered WBH from multiple habitat areas and have analysed its temporal vocalisation patterns across sites.

     

Effects of dams and their environmental impacts on the genetic diversity and connectivity of freshwater mussel populations in Poyang Lake Basin,China

1. Habitat fragmentation is one of the main threats to biodiversity. Barriers to dispersal caused by anthropogenic habitat alteration may affect phylogeographic patterns in freshwater mussels. Knowledge of the phylogenetic and phylogeographic patterns of unionoids is vital to inform protection of their biodiversity.
2. Here, we assessed influences of dams and their environmental effects on the genetic diversity and population connectivity of a broadly distributed freshwater mussel, Nodularia douglasiae, in Poyang Lake Basin.
3. The results showed high genetic diversity in areas without dams and low genetic diversity in areas with dams. High genetic differentiation and low gene flow were found among the 11 populations. Genetic variation was significantly correlated with dissolved oxygen levels.
4. The observation of low genetic diversity in populations separated by dams indicated that those populations were subjected to genetic erosion and demographic decline because they are disconnected from other populations with higher diversity. High genetic differentiation and low gene flow among the 11 populations could be correlated with anthropogenic habitat alteration.
5. These results indicated that anthropogenic habitat alterations have led to the decline in freshwater mussel diversity. Therefore, we recommend maintaining favourable habitat conditions and connectivity of rivers or lakes, and strengthening study of life histories with host-test experiments to identify potential host fish species to strengthen the knowledge base underpinning freshwater mussel conservation.

     

Automated acoustic monitoring of endangered common spadefoot toad populations reveals patterns of vocal activity

1. In the context of global amphibian decline, monitoring and restoration programmes are important. Acoustic monitoring is a possible approach for underwater vocalising species like the rapidly declining European common spadefoot toad (Pelobates fuscus). In this study, our aim was to design a dedicated software detector to be used in combination with programmable audio recorders to process the large amount of data generated by long-term acoustic monitoring and to use it for investigating the seasonal and circadian patterns of P. fuscus vocal activity.
2. The software detector targets advertisement calls of the species. Based on acoustic analysis of that call, we developed a detector that utilises both frequency and time features of the calls. Data collected during three breeding seasons in four known or potential P. fuscus breeding sites of north-eastern France were used to build a ground truth in order to test the performance of the detector. Then, we used the detector for analysing four acoustic monitoring campaigns conducted in two different sites over two breeding seasons to gain insight into the seasonal and circadian patterns of vocal activity of this species.
3. Evaluation of the P. fuscus call detector against a ground truth returned false-positive rates below 1.5% and true-positive rates ranging from 53% to 73%. These figures are compatible with long-term monitoring of the presence of the species. Running the software detector on standard hardware, the computation time for post-processing the 360 hr of a typical 3-month monitoring campaign was less than 1 day.
4. The seasonal pattern of P. fuscus underwater vocal activity is more complex than previously recognised. Over the whole ostensible 3-month breeding season, the actual time window for vocalising and breeding can last from a few days up to several weeks and may be split into clearly distinct episodes. When vocalisations occurred at both night- and daytime, the circadian vocal activity of P. fuscus occasionally proceeded uninterrupted for 24 hr but usually a several hour lull occurred immediately prior to sunset. When vocalisations occurred at both night- and daytime, the vocal activity pattern followed a bimodal distribution with a nocturnal highest peak of activity and a second peak occurring in the morning.
5. Our results demonstrate that it is feasible to monitor presence of P. fuscus in north-eastern France using a dedicated software detector combined with programmable audio recorders. Based on the outcomes of the detector applied to long-term audio data sets, we reveal temporal patterns of the vocal activity of the species and subsequently provide recommendations for attended and unattended acoustic monitoring.

     

Six steps towards operationalising freshwater ecoacoustic monitoring

1. Applications in bioacoustics and its sister discipline ecoacoustics have increased exponentially over the last decade. However, despite knowledge about aquatic bioacoustics dating back to the times of Aristotle and a vast amount of background literature to draw upon, freshwater applications of ecoacoustics have been lagging to date.
2. In this special issue, we present nine studies that deal with underwater acoustics, plus three acoustic studies on water-dependent birds and frogs. Topics include automatic detection of freshwater organisms by their calls, quantifying habitat change by analysing entire soundscapes, and detecting change in behaviour when organisms are exposed to noise.
3. We identify six major challenges and review progress through this special issue. Challenges include characterisation of sounds, accessibility of archived sounds as well as improving automated analysis methods. Study design considerations include characterisation analysis challenges of spatial and temporal variation. The final key challenge is the so far largely understudied link between ecological condition and underwater sound.
4. We hope that this special issue will raise awareness about underwater soundscapes as a survey tool. With a diverse array of field and analysis tools, this issue can act as a manual for future monitoring applications that will hopefully foster further advances in the field.

     

Spatio-temporal heterogeneity in river sounds: Disentangling micro- and macro-variation in a chain of waterholes

1. Passive acoustic monitoring is gaining momentum as a viable alternative method to surveying freshwater ecosystems. As part of an emerging field, the spatio-temporal replication levels of these sampling methods need to be standardised. However, in shallow waters, acoustic spatio-temporal patchiness remains virtually unexplored.
2. In this paper, we specifically investigate the spatial heterogeneity in underwater sounds observed within and between waterholes of an ephemeral river at different times of the day and how it could affect sampling in passive acoustic monitoring.
3. We recorded in the Einasleigh River, Queensland in August 2016, using a linear transect of hydrophones mounted on frames. We recorded four times a day: at dawn, midday, dusk, and midnight. To measure different temporal and spectral attributes of the recorded sound, we investigated the mean frequency spectrum and computed acoustic indices.
4. Both mean frequency spectrum and index analyses revealed that the site and diel activity patterns significantly influenced the sounds recorded, even for adjacent sites with similar characteristics along a single river. We found that most of the variation was due to temporal patterns, followed by between-site differences, while within-site differences had limited influence.
5. This study demonstrates high spatio-temporal acoustic variability in freshwater environments, linked to different species or species groups. Decisions about sampling design are vital to obtain adequate representation. This study thus emphasises the need to tailor spatio-temporal settings of a sampling design to the aim of the study, the species and the habitat.

     

Post-stocking movement and survival of hatchery-reared bloater (Coregonus hoyi) reintroduced to Lake Ontario

1. Determining the movement and fate of fishes post-stocking is challenging due to the difficulty in monitoring them, particularly immediately after release. Bloater (Coregonus hoyi; Salmonidae) is a deepwater cisco that has been extirpated from Lake Ontario for several decades and is presently the focus of binational restoration stocking efforts; however, there is limited information to evaluate the efficacy of these efforts. The aim of this study was to examine the initial post-release survival, 3D movement, and behaviour of hatchery-reared bloater stocked in Lake Ontario to expand knowledge of post-stocking ecology of fish and inform stocking practices for deepwater ciscoes.
2. In total, 74 hatchery-reared bloater were tagged with acoustic transmitters with depth and temperature sensors in 2016, 2017, and 2018 and passively monitored on an array of 105 69-kHz acoustic receivers deployed in north-eastern Lake Ontario. Several spatial metrics analysed movements after release to investigate immediate post-stocking survival and behaviour for the first time in a pelagic freshwater forage fish.
3. Estimated survival for tagged bloater was low (≤42%) and detection periods of live bloater ranged from 0.2 to 12.1 days (mean ± SD: 2.9 ± 2.9 days). Following release, tagged bloater dispersed quickly and exhibited an association with deeper water (>40 m). Despite overlap in space use for some bloater, there was no evidence of schooling behaviour. Bloater underwent extensive diel vertical migration from near bottom to within metres of the surface. These results demonstrated that, despite high initial mortality, some hatchery-reared bloater survived the initial stress of release and displayed characteristic behaviour of the species.
4. This study demonstrated the value of acoustic telemetry in restoration efforts and revealed survival and behaviour of bloater that has never been observed at this resolution, providing novel information for the management of reintroduced species. Establishment of a self-sustaining population of bloater will help restore fish native to Lake Ontario thus increasing prey fish diversity, improving ecological integrity and resilience, and serving as a model for the reintroduction and management of other native species throughout the Great Lakes.

     

Linking flow and upper thermal limits of freshwater mussels to inform environmental flow benchmarks

1. Freshwater ecosystems are experiencing shifts in the natural range and variation of water temperatures due to anthropogenic activity, and these shifts can negatively affect survival, growth, and reproduction of aquatic species. Among the groups most affected are freshwater mussels of the family Unionidae. Knowledge of sublethal and lethal effects on mussels from changes in water temperature are largely unknown, especially for species from arid and semi-arid regions such as the south-western U.S.A. This limits the ability to assess, forecast, and adaptively manage this threat for those species and to understand how temperature influences population performance and community structure.
2. To determine the effects of elevated water temperature on mussels from the south-western U.S.A., we evaluated the upper thermal tolerances of adults of three species (Amblema plicata, Cyclonaias necki, and Fusconaia mitchelli) from the Guadalupe River. Mussels were acclimated to 27°C and then tested across a range of experimental temperatures (30–39°C) in standard acute (96-hr) and chronic (10-day) laboratory tests. The acute and chronic thresholds identified in thermal tolerance testing were then related to in situ water temperature and flows using a uniform continuous above-threshold analysis, which evaluates the duration and frequency of continuous events above a specified temperature threshold.
3. Median lethal temperature in 96-hr tests averaged 36.4°C and ranged from 33.7 to 37.5°C, while the chronic 10-day tests averaged 35.9°C and ranged from 32.4 to 37.5°C. Thermal tolerances of F. mitchelli were significantly lower than both A. plicata and C. necki, and the uniform continuous above-threshold analysis showed that temperature affecting 5% of the population thresholds were exceeded for F. mitchelli in the Guadalupe River at both acute (96-hr) and chronic (10-day) values (30.5 and 28.4°C, respectively).
4. Findings from this study indicate that freshwater mussels from the arid and semi-arid regions of the south-west U.S.A. are already at risk from rising environmental temperatures and altered hydrology. However, by incorporating laboratory thermal tolerance estimates with in situ temperature and discharge data, we provide a range of hydrologic thresholds to inform environmental flow recommendations and potentially mitigate thermal stress occurring during periods of low flow. In addition, this method can be readily adapted to other arid regions to guide flow recommendations or assess whether flow standards are sufficient to protect freshwater mussel populations during severe droughts and low flow periods.

     

Singing streams: Describing freshwater soundscapes with the help of acoustic indices

1. Understanding soundscapes, that is, the totality of sounds within a location, helps to assess nature in a more holistic way, providing a novel approach to investigating ecosystems. To date, very few studies have investigated freshwater soundscapes in their entirety and none across a broad spatial scale.
2. In this study, we recorded 12 freshwater streams in South East Queensland continuously for three days and calculated three acoustic indices for each minute in each stream. We then used principal component analysis of summary statistics for all three acoustic indices to investigate acoustic properties of each stream and spatial variation in their soundscapes.
3. All streams had a unique soundscape with most exhibiting diurnal variation in acoustic patterns. Across these sites, we identified five distinct groups with similar acoustic characteristics. We found that we could use summary statistics of AIs to describe daytimes across streams as well. Most difference in stream soundscapes was observed during the daytime with significant variation in soundscapes both between hours and among sites.
4. Synthesis and Application. We demonstrate how to characterize stream soundscapes by using simple summary statistics of complex acoustic indices. This technique allows simple and rapid investigation of streams with similar acoustic properties and the capacity to characterize them in a holistic and universal way. While we developed this technique for freshwater streams, it is also applicable to terrestrial and marine soundscapes.

     

Ecoacoustics can detect ecosystem responses to environmental water allocations

1. Globally, water abstraction for human consumption and irrigated agriculture leads to significant changes in aquatic ecosystems. To counter these detrimental effects, water releases—often termed environmental water allocations—restore overbank flow or are delivered to artificially disconnected wetlands. While a suite of monitoring methods is available, few programmes track continuous change in biota, mainly because repeated remote site visits can be prohibitively expensive.
2. In this paper, we propose a new approach to environmental flow monitoring, using ecoacoustic methods. We test acoustic monitoring of frog and waterbird responses to environmental water deliveries in the Goulburn Broken, a valley in the southern Murray–Darling river system. Response to three major environmental water deliveries within 2 years was monitored at four sites along Reedy swamp. Every 2 weeks, 30 s were recorded every 30 min, for a total of 24 hr.
3. We used two analysis strategies—manual counts of bird calls, as well as ecoacoustic indices, which describe the sonic properties of the acoustic spectrum at a site. Manual counts demonstrated that water-dependent birds were clearly responding to environmental water deliveries, whereas non-water-dependent species did not show any increases in activity. After restricting the analysis to the dawn chorus of birds and frogs, two acoustic indices (the median amplitude and the acoustic complexity index) showed responses to watering events.
4. Ecoacoustic methods show promise for continuous response monitoring to environmental water allocations. However, the first strategy—manual annotation of calls—might be too labour intensive for standard monitoring programmes. The second strategy—index-based approaches—can also detect ecological responses, although further investigation using control sites is needed. Automated call classifiers are an alternative that is currently being developed for endangered species. We also encourage simultaneous monitoring of the soundscape above and under water.

     

Looking for love under the ice: Using passive acoustics to detect burbot (Lota lota: Gadidae) spawning activity

1. Burbot (Lota lota: Gadidae) is a difficult species to manage effectively due to its preference for deep-water habitats and under-ice spawning behaviour, resulting in a poor understanding of its reproductive activity. However, the use of acoustic signalling by burbot as part of their mating system has recently been described and this behaviour may provide a means of investigating questions regarding the spatial and temporal distribution of spawning aggregations using passive acoustic monitoring.
2. We used audio and video recording to confirm that burbot vocalise and that these vocalisations can be detected under field conditions as well as to characterise the relationship between burbot acoustic signalling and spawning behaviour. We also evaluated the feasibility of locating and monitoring burbot spawning aggregations in real time using passive acoustics.
3. Burbot vocalisations were difficult to identify with only about 6% of the recordings containing calls being successfully identified as such in the field. Burbot vocalised more often between sundown and sunrise than during daylight hours. Calls recorded at night tended to be lower frequency, longer duration, and have lower bandwidth than those made during the day.
4. Burbot vocalisations could not be recorded in conjunction with video recordings of spawning activity, indicating that burbot may not call during active spawning, but may use acoustic communication to signal the onset of reproductive readiness and to form pre-spawning aggregations.
5. While burbot calls were readily identifiable, observers had a difficult time identifying burbot calls in real time under field conditions. Passive acoustic monitoring demonstrates considerable potential as a management tool to locate burbot spawning grounds and identify periods of activity, but may not be an appropriate technique for monitoring spawning activity in real time.

     

Response of maize stemborers and associated parasitoids to the spread of grasses in the rainforest zone of Kisangani,DR Congo: effect on stemborers biological control

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Combined effects of salinity and infectious disease on Daphnia dentifera at multiple scales

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Habitat loss and degradation due to farming intensification modify the floral visitor assemblages of a semiarid keystone shrub

1. The expansion of intensive agriculture has severely altered landscapes, a process that has been aggravated by the increase of greenhouse agriculture. However, few studies have considered the combined effects of habitat loss/degradation and greenhouse farming on insect visitors to native plants.
2. We analysed how habitat loss/degradation and greenhouse farming are related to the composition, abundance, and richness of the insect assemblages visiting flowers in a semiarid keystone shrub (Ziziphus lotus) in southeast Spain, home to Europe's largest area of greenhouses. We studied 21 populations distributed across a gradient of greenhouse intensification and habitat loss.
3. The composition, abundance, and richness of the Ziziphus insect assemblage substantially varied between populations and were differently affected by natural habitat-remnant and landscape degradation and population isolation.
4. Insect abundance was negatively affected by habitat loss at population level but positively affected at individual Ziziphus scale. Honey-bee relative abundance increased in highly degraded landscapes and isolated populations, being positively associated with hoverflies and negatively with ants and bee-flies. Wild bees, carrion flies, and wasps remain neutral along the degradation axes. Insect visitor abundance per plant affected positively the flower visitation rate, which was also favoured by the relative abundance of honey bees, wild bees, and hoverflies. Species richness was not influenced by anthropogenic degradation, and did not affect flower visitation rate.
5. Our results highlight the fragility of wild pollinator communities to landscape and habitat degradation, and the need to regulate intensive farming practices to preserve wild insect pollinator assemblages in semiarid habitats.

     

Intrapopulation variability in a functional trait: Susceptibility of Daphnia to limitation by dietary fatty acids

1. Functional traits are measurable characteristics of an organism that have an impact on its fitness. Variation in functional traits between and among species has been suggested to represent the basis for competition and selection, thus allowing for evolution in natural populations.
2. In freshwater ecosystems, the availability of essential polyunsaturated fatty acids (PUFAs), in particular ω3‐ and ω6‐PUFAs, determines the food quality of phytoplankton for the herbivorous zooplankton Daphnia, an unselective filter feeder. The content of such essential PUFAs in the phytoplankton is thus a functional phytoplankton trait affecting the trophic transfer efficiency and dynamics at the pelagic plant–herbivore interface.
3. In turn, the susceptibility of consumers to become limited by the availability of essential PUFAs is a fitness‐determining trait of Daphnia genotypes, and variability of this herbivore trait may thus affect the daphnids’ intrapopulation competition. To estimate the intrapopulation variation in susceptibility, we isolated clonal lines of Daphnia longispina from a natural population and compared the strength of their limitation by dietary PUFA availability via standardised laboratory growth assays. We used a liposome supplementation technique to enrich a PUFA‐poor green alga with essential ω3‐ and ω6‐PUFAs and determined juvenile somatic growth rate of different D. longispina genotypes as a fitness proxy.
4. As expected, D. longispina genotypes that coexisted in a natural population differed markedly in their specific patterns of susceptibility to dietary PUFA availability. On average, the D. longispina population was more strongly susceptible to limitations in the availability of the ω6‐PUFA arachidonic acid (20:4ω6) than to limitations in the availability of ω3‐PUFAs α‐linolenic acid (18:3ω3) and eicosapentaenoic acid (20:5ω3).
5. The ability to cope with PUFA limitation is thus a crucial trait that can probably affect intraspecific competition and Daphnia population structure. Therefore, we suggest that such intrapopulation variation in susceptibility to absence of dietary PUFAs might be one of the driving forces of natural selection and local adaptation among freshwater zooplankton.

     

Passive acoustic monitoring as a potential tool to survey animal and ecosystem processes in freshwater environments

1. Biodiversity in freshwater habitats is decreasing faster than in any other type of environment, mostly as a result of human activities. Monitoring these losses can help guide mitigation efforts. In most studies, sampling strategies predominantly rely on collecting animal and vegetal specimens. Although these techniques produce valuable data, they are invasive, time-consuming and typically permit only limited spatial and temporal replication. There is need for the development of complementary methods.
2. As observed in other ecosystems, freshwater environments host animals that emit sounds, either to communicate or as a by-product of their activity. The main freshwater soniferous groups are amphibians, fish, and macroinvertebrates (mainly Coleoptera and Hemiptera, but also some Decapoda, Odonata, and Trichoptera). Biophysical processes such as flow or sediment transport also produce sounds, as well as human activities within aquatic ecosystems.
3. Such animals and processes can be recorded, remotely and autonomously, and provide information on local diversity and ecosystem health. Passive acoustic monitoring (PAM) is an emerging method already deployed in terrestrial environments that uses sounds to survey environments. Key advantages of PAM are its non-invasive nature, as well as its ability to record autonomously and over long timescales. All these research topics are the main aims of ecoacoustics, a new scientific discipline investigating the ecological role of sounds.
4. In this paper, we review the sources of sounds present in freshwater environments. We then underline areas of research in which PAM may be helpful emphasising the role of PAM for the development of ecoacoustics. Finally, we present methods used to record and analyse sounds in those environments.
5. Passive acoustics represents a potentially revolutionary development in freshwater ecology, enabling continuous monitoring of dynamic bio-physical processes to inform conservation practitioners and managers.