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Use of passive acoustic monitoring to fill knowledge gaps of fish global conservation status
Abstract
Knowledge of the ecology, spatial distribution and conservation status of fish populations is achieved by fishery‐dependent techniques, and by more recently developed non‐invasive fishery‐independent techniques. Passive acoustic monitoring (PAM) is a fishery‐independent method that provides remote sensing of soniferous species, populations, communities and ecosystems by recording soundscapes and their components.
A case study is presented to demonstrate how PAM can contribute to a dynamic understanding of fish distribution, ecological preferences and conservation status. This case study refers to the cusk‐eel Ophidion rochei (Ophidiiformes), a nocturnal, behaviourally cryptic, soniferous fish species, described as uncommon and rare in the scientific literature, and listed as Data Deficient in the IUCN Red List.
A systematized literature review was carried out using Ophidion+rochei as the search term, and by grouping records into two main categories: (i) traditional techniques (including all fishery‐dependent techniques and underwater visual census); and (ii) PAM.
This review highlights how PAM has provided new sightings of O. rochei at a rate three times higher than all other monitoring techniques combined. In contrast with the knowledge achieved to date by fishery‐dependent techniques, the reported acoustic mass phenomena indicate that this species can be very abundant. Ophidion rochei was found to inhabit a wide range of depths and ecosystems, at least throughout the Mediterranean basin.
This paper supports the urgency and the importance of relying on the integration of different fishery‐independent techniques for multidisciplinary monitoring, in line with the Goal 14 requirements of the UN Decade of Ocean Science for Sustainable Development.
Accurate species monitoring is foundational for understanding and assessing species extinction risk. Environmental DNA (eDNA) based species detection methods have been proposed as fast and powerful biodiversity monitoring tools. Yet, these methods are susceptible to errors that might hinder the assessment of species extinction risk. Samples may contain low DNA concentrations of the target taxa and/or exhibit high levels of PCR inhibitors, which can yield false negatives.
We investigated how adjusting the input sample volume in the eDNA‐based molecular assay improves detection of an endangered fish, Anaecypris hispanica , in highly eutrophic streams. Water samples were filtered and tested using a real‐time PCR (qPCR) assay varying the input volume of eDNA samples (i.e., 0.5X, 1X and 3.3X). From the positive detections obtained with different eDNA input volumes, we built species occurrence maps and estimated geographic range metrics used in species extinction risk assessment.
Although the number of sites with positive detections was similar among the input eDNA sample volumes tested, positive detections were not spatially redundant. When comparing the pooled results from all eDNA‐based trials to a fixed 1X eDNA volume, there was a nearly 75% increase in the number of sites with detections, consequently leading to increases in all geographic range metrics (i.e., extent of occurrence, area of occupancy number of locations).
Our results highlight that false negatives in eDNA‐based surveys are not to be overlooked. The success of species detection will likely vary on a case‐by‐case basis, depending on the DNA concentration of the target taxa and the concentration of potential inhibitors in bulk eDNA samples, both of which are generally unknown. Improved species detection may be achieved by running, in parallel, qPCR assays with different input volumes of bulk eDNA samples.
As interest grows in integrating eDNA‐based tools into species monitoring practices, it is essential to continuously refine protocols and carefully consider study design decisions to ensure robust results, advancing species management and conservation.
Invasive alien species have been rising exponentially in the last decades impacting biodiversity and ecosystem functioning. The soniferous weakfish, Cynoscion regalis, is a recent invasive sciaenid species in the Iberian Peninsula and was first reported in the Tagus estuary in 2015. There is concern about its possible impacts on native species, namely the confamiliar meagre, Argyrosomus regius, as there is overlap in their feeding regime, habitat use, and breeding behaviour. Here, we characterised the sciaenid-like sounds recently recorded in the Tagus estuary and showed that they are made by weakfish as they have similar numbers of pulses and pulse periods to the sounds made by captive breeding weakfish. We further demonstrate that breeding grunts from weakfish and the native sciaenid, recorded either in captivity or Tagus estuary, differ markedly in sound duration, number of pulses and pulse period in the two species, but overlap in their spectral features. Importantly, these differences are easily detected through visual and aural inspections of the recordings, making acoustic recognition easy even for the non-trained person. We propose that passive acoustic monitoring can be a cost-effective tool for in situ mapping of weakfish outside its natural distribution and an invaluable tool for early detection and to monitor its expansion.
Passive acoustic monitoring (PAM) has emerged as a transformative tool for applied ecology, conservation and biodiversity monitoring, but its potential contribution to fundamental ecology is less often discussed, and fundamental PAM studies tend to be descriptive, rather than mechanistic.
Here, we chart the most promising directions for ecologists wishing to use the suite of currently available acoustic methods to address long‐standing fundamental questions in ecology and explore new avenues of research. In both terrestrial and aquatic habitats, PAM provides an opportunity to ask questions across multiple spatial scales and at fine temporal resolution, and to capture phenomena or species that are difficult to observe. In combination with traditional approaches to data collection, PAM could release ecologists from myriad limitations that have, at times, precluded mechanistic understanding.
We discuss several case studies to demonstrate the potential contribution of PAM to biodiversity estimation, population trend analysis, assessing climate change impacts on phenology and distribution, and understanding disturbance and recovery dynamics. We also highlight what is on the horizon for PAM, in terms of near‐future technological and methodological developments that have the potential to provide advances in coming years.
Overall, we illustrate how ecologists can harness the power of PAM to address fundamental ecological questions in an era of ecology no longer characterised by data limitation.
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All anemonefish species can produce two types of sounds. The first class concerns agonistic sounds that are produced during territory defence and probably to establish social hierarchy between individuals. The second class relates to submissive sounds that are emitted in reaction to aggressive acts by dominant individuals. In both types of sounds, irrespective of the sexual status, frequency is highly related to fish size: smaller individuals produce pulses of higher frequency and shorter duration than larger individuals. Consequently, these sonic features within a group may convey information on the social rank of the emitter within the group. This relationship between fish size and both dominant frequency and pulse duration could concern all the Amphiprionini tribe. It highlights the use of a highly conservative vocalization mechanism. Aggressive sounds are initiated by buccal jaw teeth snapping caused by rapid mouth closure attributed to a sonic ligament. We hypothesize that the slam provokes bone vibrations. As the close association of the rib cage and the swimbladder wall would be analogous to a membrane loudspeaker, vibrations would cause shaking of this membrane and cause the second part of the sound. The sound-producing mechanism related to submissive sounds is still not known.
Most grouper species worldwide are threatened by overfishing. Effective marine protected areas (MPAs) are known to enable population recovery, and consideration of vulnerable species’ reproductive behaviours is fundamental to monitoring and management plans. Many groupers produce sounds associated with reproductive behaviours. Recording these sounds helps to locate spawning sites and improve management efforts to ensure reproduction and viability. This study focuses on a poorly studied yet likely vulnerable grouper species, Mycteroperca rubra, providing novel insights into its reproductive biology by combining underwater visual census surveys, direct visual observations and passive acoustic monitoring within a Mediterranean MPA during two consecutive summers (2017 and 2018). Results indicate that M. rubra individuals were more abundant and larger at one of the protected study sites, where they also occasionally formed unusual aggregations (<30 individuals), likely for spawning. These aggregations and the observation of courtship behaviours suggest that M. rubra spawns in the surroundings of this study site. Moreover, grouper-like unknown sounds were recorded exclusively at this site, suggesting they are associated with M. rubra courtship behaviours. Therefore, this study provides a basis for validating M. rubra sound production and supports the monitoring of its spawning sites via passive acoustics to improve MPA conservation effectiveness.
Sound production in fishes is vital to an array of behaviors including territorial defense, reproduction, and competitive feeding. Unfortunately, recent passive acoustic monitoring efforts are revealing the extent to which anthropogenic forces are altering aquatic soundscapes. Despite the importance of fish sounds, extensive endeavors to document them, and the anthropogenic threats they face, the field of fish bioacoustics has been historically constrained by the lack of an easily accessible and comprehensive inventory of known soniferous fishes, as is available for other taxa. To create such an inventory while simultaneously assessing the geographic and taxonomic prevalence of soniferous fish diversity, we extracted information from 834 references from the years 1874–2020 to determine that 989 fish species from 133 families and 33 orders have been shown to produce active (i.e., intentional) sounds. Active fish sound production is geographically and taxonomically widespread—though not homogenous—among fishes, contributing a cacophony of biological sounds to the prevailing soundscape globally. Our inventory supports previous findings on the prevalence of actively soniferous fishes, while allowing novel species-level assessments of their distribution among regions and taxa. Furthermore, we evaluate commercial and management applications with passive acoustic monitoring, highlight the underrepresentation of research on passive (i.e., incidental) fish sounds in the literature, and quantify the limitations of current methodologies employed to examine fishes for sound production. Collectively, our review expands on previous studies while providing the foundation needed to examine the 96% of fish species that still lack published examinations of sound production.
Aquatic environments encompass the world’s most extensive habitats, rich with sounds produced by a diversity of animals. Passive acoustic monitoring (PAM) is an increasingly accessible remote sensing technology that uses hydrophones to listen to the underwater world and represents an unprecedented, non-invasive method to monitor underwater environments. This information can assist in the delineation of biologically important areas via detection of sound-producing species or characterization of ecosystem type and condition, inferred from the acoustic properties of the local soundscape. At a time when worldwide biodiversity is in significant decline and underwater soundscapes are being altered as a result of anthropogenic impacts, there is a need to document, quantify, and understand biotic sound sources–potentially before they disappear. A significant step toward these goals is the development of a web-based, open-access platform that provides: (1) a reference library of known and unknown biological sound sources (by integrating and expanding existing libraries around the world); (2) a data repository portal for annotated and unannotated audio recordings of single sources and of soundscapes; (3) a training platform for artificial intelligence algorithms for signal detection and classification; and (4) a citizen science-based application for public users. Although individually, these resources are often met on regional and taxa-specific scales, many are not sustained and, collectively, an enduring global database with an integrated platform has not been realized. We discuss the benefits such a program can provide, previous calls for global data-sharing and reference libraries, and the challenges that need to be overcome to bring together bio- and ecoacousticians, bioinformaticians, propagation experts, web engineers, and signal processing specialists (e.g., artificial intelligence) with the necessary support and funding to build a sustainable and scalable platform that could address the needs of all contributors and stakeholders into the future.
Biodiversity is a portmanteau word to indicate the variety of life at all levels from genes to ecosystems, but it is often simplistically equated to species richness; the word ecodiversity has thus been coined to address habitat variety. Biodiversity represents the core of the natural capital, and as such needs to be quantified and followed over time. Marine Protected Areas (MPAs) are a major tool for biodiversity conservation at sea. Monitoring of both species and habitat diversity in MPAs is therefore mandatory and must include both inventory and periodic surveillance activities. In the case of inventories, the ideal would be to census all species and all habitats, but while the latter goal can be within reach, the former seems unattainable. Species inventory should be commeasured to investigation effort, while habitat inventory should be based on mapping. Both inventories may profit from suitability spatial modelling. Periodic surveillance actions should privilege conspicuous species and priority habitats. Efficient descriptor taxa and ecological indices are recommended to evaluate environmental status. While it seems obvious that surveillance activities should be carried out with regular recurrence, diachronic inventories and mapping are rarely carried out. Time series are of prime importance to detect marine ecosystem change even in the absence of direct human impacts.
Background: Marine soundscape is the aggregation of sound sources known as geophony, biophony, and anthrophony. The soundscape analysis, in terms of collection and analysis of acoustic signals, has been proposed as a tool to evaluate the specific features of ecological assemblages and to estimate their acoustic variability over space and time. This study aimed to characterise the Capo Caccia-Isola Piana Marine Protected Area (Italy, Western Mediterranean Sea) soundscape over short temporal (few days) and spatial scales (few km) and to quantify the main anthropogenic and biological components, with a focus on fish biophonies.
Methods: Within the MPA, three sites were chosen each in a different protection zone (A for the integral protection, B as the partial protection, and C as the general protection). In each site, two underwater autonomous acoustic recorders were deployed in July 2020 at a depth of about 10 m on rocky bottoms. To characterise the contribution of both biophonies and anthrophonies, sea ambient noise (SAN) levels were measured as sound pressure level (SPL dB re: 1 m Pa-rms) at eight 1/3 octave bands, centred from 125 Hz to 16 kHz, and biological and anthropogenic sounds were noted. Fish sounds were classified and counted following a catalogue of known fish sounds from the Mediterranean Sea based on the acoustic characteristic of sound types. A contemporary fish visual census had been carried out at the test sites.
Results: SPL were different by site, time (day vs. night), and hour. SPLs bands centred at 125, 250, and 500 Hz were significantly higher in the daytime, due to the high number of boats per minute whose noise dominated the soundscapes. The loudest man-made noise was found in the A zone, followed by the B and the C zone, confirming that MPA current regulations do not provide protection from acoustic pollution. The dominant biological components of the MPA soundscape were the impulsive sounds generated by some invertebrates, snapping shrimps and fish. The vast majority of fish sounds were recorded at the MPA site characterized by the highest sound richness, abundance, and Shannon-Wiener index, coherently with the results of a fish visual census. Moreover, the acoustic monitoring detected a sound associated with a cryptic species (Ophidion spp.) never reported in the study area before, further demonstrating the usefulness of passive acoustic monitoring as a complementary technique to species census. This study provides baseline data to to detect future changes of the marine soundscapes and some suggestions to reduce the impact of noise on marine biodiversity.
Monitoring the biodiversity of key habitats and understanding the drivers across spatial scales is essential for preserving ecosystem functions and associated services. Coralligenous reefs are threatened marine biodiversity hotspots that are challenging to monitor. As fish sounds reflect biodiversity in other habitats, we unveiled the biogeography of coralligenous reef sounds across the north-western Mediterranean using data from 27 sites covering 2000 km and 3 regions over a 3-year period. We assessed how acoustic biodiversity is related to habitat parameters and environmental status. We identified 28 putative fish sound types, which is up to four times as many as recorded in other Mediterranean habitats. 40% of these sounds are not found in other coastal habitats, thus strongly related to coralligenous reefs. Acoustic diversity differed between geographical regions. Ubiquitous sound types were identified, including sounds from top-predator species and others that were more specifically related to the presence of ecosystem engineers (red coral, gorgonians), which are key players in maintaining habitat function. The main determinants of acoustic community composition were depth and percentage coverage of coralligenous outcrops, suggesting that fish-related acoustic communities exhibit bathymetric stratification and are related to benthic reef assemblages. Multivariate analysis also revealed that acoustic communities can reflect different environmental states. This study presents the first large-scale map of acoustic fish biodiversity providing insights into the ichthyofauna that is otherwise difficult to assess because of reduced diving times. It also highlights the potential of passive acoustics in providing new aspects of the correlates of biogeographical patterns of this emblematic habitat relevant for monitoring and conservation.
Although we are currently experiencing worldwide biodiversity loss, local species richness does not always decline under anthropogenic pressure. This conservation paradox may also apply in protected areas but has not yet received conclusive evidence in marine ecosystems. Here, we survey fish assemblages in six Mediterranean no-take reserves and their adjacent fishing grounds using environmental DNA (eDNA) while controlling for environmental conditions. We detect less fish species in marine reserves than in nearby fished areas. The paradoxical gradient in species richness is accompanied by a marked change in fish species composition under different managements. This dissimilarity is mainly driven by species that are often overlooked by classical visual surveys but detected with eDNA: crypto-benthic, pelagic, and rare fishes. These results do not negate the importance of reserves in protecting biodiversity but shed new light on how under-represented species groups can positively react to fishing pressure and how conservation efforts can shape regional biodiversity patterns.
A recurrent question arising in fish bioacoustics research concerns the number of vocal fish species that may exist. Although it is not possible to provide a precise globally valid number, an estimation based on recordings already collected at coral reefs (Moorea) and on morphological approaches indicates that approximately half of the fish families of this particular environment has at least one known sound-producing species. In light of this, acoustic behaviour should be fully considered in biology, ecology and management plans as it may provide information on a consistent portion of fish biodiversity. Fish bioacoustics has switched from anecdotal reports to long-term, large-scale monitoring studies, capable of providing high resolution information on fish populations' composition and dynamics. This information is vital for successful management plans in our quickly changing seas.
The genus Pygocentrus contains three valid piranha species (P. cariba, P. nattereri and P. piraya) that are allopatric in tropical and subtropical freshwater environments of South America. This study uses acoustic features to differentiate the three species. Sounds were recorded in P. cariba, two populations of P. nattereri (red- and yellow-bellied) and P. piraya; providing sound description for the first time in P. cariba and P. piraya. Calls of P. cariba were distinct from all the other studied populations. Red- and yellow-bellied P. nattereri calls were different from each other but yellow-bellied P. nattereri calls were similar to those of P. piraya. These observations can be explained by considering that the studied specimens of yellow-bellied P. nattereri have been wrongly identified and are actually a sub-population of P. piraya. Morphological examinations and recent fish field recordings in the Araguari River strongly support our hypothesis. This study shows for the first time that sounds can be used to discover identification errors in the teleost taxa.
Ecosystems and the communities they support are changing at alarmingly rapid rates. Tracking species diversity is vital to managing these stressed habitats. Yet, quantifying and monitoring biodiversity is often challenging, especially in ocean habitats. Given that many animals make sounds, these cues travel efficiently under water, and emerging technologies are increasingly cost-effective, passive acoustics (a long-standing ocean observation method) is now a potential means of quantifying and monitoring marine biodiversity. Properly applying acoustics for biodiversity assessments is vital. Our goal here is to provide a timely consideration of emerging methods using passive acoustics to measure marine biodiversity. We provide a summary of the brief history of using passive acoustics to assess marine biodiversity and community structure, a critical assessment of the challenges faced, and outline recommended practices and considerations for acoustic biodiversity measurements. We focused on temperate and tropical seas, where much of the acoustic biodiversity work has been conducted. Overall, we suggest a cautious approach to applying current acoustic indices to assess marine biodiversity. Key needs are preliminary data and sampling sufficiently to capture the patterns and variability of a habitat. Yet with new analytical tools including source separation and supervised machine learning, there is substantial promise in marine acoustic diversity assessment methods.
Atlantic cod Gadus morhua populations in the northeast USA have failed to recover since major declines in the 1970s and 1990s. To rebuild these stocks, managers need reliable information on spawning dynamics in order to design and implement control measures; discovering cost-effective and non-invasive monitoring techniques is also favorable. Atlantic cod form dense, site-fidelic spawning aggregations during which they vocalize, permitting acoustic detection of their presence at such times. The objective of this study was to detect spawning activity of Atlantic cod using multiple fixed-station passive acoustic recorders to sample across Massachusetts Bay during the winter spawning period. A generalized linear modeling approach was used to investigate spatio-temporal trends of cod vocalizing over 10 consecutive winter spawning seasons (2007-2016), the longest such timeline of any passive acoustic monitoring of a fish species. The vocal activity of Atlantic cod was associated with diel, lunar, and seasonal cycles, with a higher probability of occurrence at night, during the full moon, and near the end of November. Following 2009 and 2010, there was a general decline in acoustic activity. Furthermore, the northwest corner of Stellwagen Bank was identified as an important spawning location. This project demonstrated the utility of passive acoustic monitoring in determining the presence of an acoustically active fish species, and provides valuable data for informing the management of this commercially, culturally, and ecologically important species.
The health of the ocean, central to human well-being, has now reached a critical point. Most fish stocks are overexploited, climate change and increased dissolved carbon dioxide are changing ocean chemistry and disrupting species throughout food webs, and the fundamental capacity of the ocean to regulate the climate has been altered. However, key technical, organizational, and conceptual scientific barriers have prevented the identification of policy levers for sustainability and transformative action. Here, we recommend key strategies to address these challenges, including (1) stronger integration of sciences and (2) ocean-observing systems, (3) improved science-policy interfaces, (4) new partnerships supported by (5) a new ocean-climate finance system, and (6) improved ocean literacy and education to modify social norms and behaviors. Adopting these strategies could help establish ocean science as a key foundation of broader sustainability transformations.
Our civilization needs a clean, resilient, productive, safe, well-observed, documented and predicted ocean. “The ocean we need for the future we want” was the motto of the Intergovernmental Oceanographic Commission proposal to the United Nations to consider the merit of an Ocean Science Decade. By proclaiming the Decade, the UN General Assembly offered the oceanographic community a unique, once in a life-time, opportunity to change the way we do things, make oceanography fit for purpose of effectively supporting sustainable development, and energize the ocean sciences for future generations. The Decade is the chance to put in place a more complete and sustainable observing system and feed the resulting data into a science-based informed decision-making system allowing increased reliance of our civilization on the ocean, its ecosystem services and, at the same time, preserving ocean health. Strong and proactive engagement of the oceanographic community in the design of the Decade and its observing component and subsequent energetic implementation of the ideas are sought. Participants in OceanObs’19 are invited to consider the additional possibilities and requirements associated with the Decade in their contributions to and brainstorming at the Conference. It is essential to use collective wisdom of OceanObs’19 to help developing an ambitious and also realistic implementation plan for the Decade, with a strong observational component.
The /Kwa/ vocalization dominates the soundscape of Posidonia
oceanica meadows but the identity of the species emitting this
peculiar fish sound remains a mystery. Information from sounds
recorded in the wild indicates that the emitting candidates should be
abundant, nocturnal and benthic. Scorpaena spp. combine all these
characteristics. This study used an interdisciplinary approach to
investigate the vocal abilities of Scorpaena spp.; morphological,
histological and electrophysiological examinations were interpreted
together with visual and acoustic recordings conducted in seminatural conditions. All observed Scorpaena spp. (S. porcus, S. scrofa
and S. notata) share the same sonic apparatus at the level of
the abdominal region. This apparatus, present in both males and
females, consists of 3 bilaterally symmetrical muscular bundles,
having 3–5 long tendons, which insert on ventral bony apophyses of
the vertebral bodies. In all chordophones (stringed instruments), the
frequency of the vibration is dependent on the string properties and
not on the rate at which the strings are plucked. Similarly, we suggest
that each of the 3–5 tendons found in the sonic mechanism of
Scorpaena spp. acts as a frequency multiplier of the muscular bundle
contractions, where the resonant properties of the tendons determine the peak frequency of the /Kwa/, its frequency spectra and pseudoharmonic profile. The variability in the length and number of tendons found between and within species could explain the high variability of /Kwa/ acoustic features recorded in the wild. Finally, acoustic and behavioural experiments confirmed that Scorpaena spp. can emit the /Kwa/ sound.
Biodiversity loss is a major challenge. Over the past century, the average rate of vertebrate extinction has been about 100-fold higher than the estimated background rate and population declines continue to increase globally. Birth and death rates determine the pace of population increase or decline, thus driving the expansion or extinction of a species. Design of species conservation policies hence depends on demographic data (e.g., for extinction risk assessments or estimation of harvesting quotas). However, an overview of the accessible data, even for better known taxa, is lacking. Here, we present the Demographic Species Knowledge Index, which classifies the available information for 32,144 (97%) of extant described mammals, birds, reptiles, and amphibians. We show that only 1.3% of the tetrapod species have comprehensive information on birth and death rates. We found no demographic measures, not even crude ones such as maximum life span or typical litter/clutch size, for 65% of threatened tetrapods. More field studies are needed; however, some progress can be made by digitalizing existing knowledge, by imputing data from related species with similar life histories, and by using information from captive populations. We show that data from zoos and aquariums in the Species360 network can significantly improve knowledge for an almost eightfold gain. Assessing the landscape of limited demographic knowledge is essential to prioritize ways to fill data gaps. Such information is urgently needed to implement management strategies to conserve at-risk taxa and to discover new unifying concepts and evolutionary relationships across thousands of tetrapod species.
In the Southeast USA, major contributors to estuarine soundscapes are the courtship calls produced by fish species belonging to the family Sciaenidae. Long-term monitoring of sciaenid courtship sounds may be valuable in understanding reproductive phenology, but this approach produces massive acoustic datasets. With this in mind, we designed a feature-based, signal detector for sciaenid fish calls and tested the efficacy of this detector against manually reviewed data. Acoustic recorders were deployed to collect sound samples for 2 min every 20 min at four stations in the May River estuary, South Carolina, USA from February to November, 2014. Manual analysis of acoustic files revealed that four fish species, belonging to the family Sciaenidae, were the major sound producers in this estuarine soundscape, and included black drum (Pogonias cromis), silver perch (Bairdiella chrysoura), spotted seatrout (Cynoscion nebulosus), and red drum (Sciaenops ocellatus). Recorded calls served as an acoustic library of signature features that were used to create a signal detector to automatically detect, classify, and quantify the number of calls in each acoustic file. Correlation between manual and automatic detection was significant and precision varied from 61% to 100%. Automatic detection provided quantitative data on calling rates for this long-term data set. Positive temperature anomalies increased calling rates of black drum, silver perch, and spotted seatrout, while negative anomalies increased calling rates of red drum. Acoustic monitoring combined with automatic detection could be an additional or alternative method for monitoring sciaenid spawning and changes in phenology associated with climate change.
Depuis quelques années, un petit groupe de plongeurs passionnés de poissons marins réalisent le long de la côte méditerranéenne française une quarantaine de plongées par an. L'objectif est d’inventorier la diversité spécifique et de dresser les listes les plus
complètes possibles des poissons qu’ils détectent par observation directe, de jour ou de nuit, et ce dans le maximum d’habitats différents.
Ce compte-rendu présente les données les plus intéressantes recueillies en 2016.
Assessing fish biodiversity patterns is a major concern in aquatic science and conservation. To be effectively used, fish diversity assessments benefit from the use of integrated complementary approaches. Passive acoustics has received increasing attention as a non-invasive, long-term monitoring tool, as it uses biological sounds produced incidentally or intentionally as natural tags to identify and estimate animal diversity. In the marine environment, there is little evidence about the link between taxonomic diversity (different species) and acoustic diversity (different sound types). Here we used underwater visual census fish data collected over multiple years from 3 sites within a Mediterranean Marine Protected Area as comprehensive information on local fish assemblages to be compared with acoustic recordings obtained in September 2015. Richness, diversity and community similarity indices as well as abundance analyses revealed a strong relationship between taxonomic diversity and acoustic diversity. Overall, acoustic communities showed pronounced differences between the study sites that were not observed in the respective taxonomic assemblages. Despite the lower number of sound type categories (12) compared to taxa (53) and the short recording period, passive acoustics showed a high discriminating potential and asserts its suitability as a complementary approach to visual-based surveys. Finally, the here established fish sound repertoire was organized in a dichotomic tree based on acoustic characteristics that contributes to the development of automatic acoustic biodiversity appraisal tools for resource monitoring and management.
• Rare and cryptic fish species such as the cusk‐eel Ophidion rochei (Műller, 1845) (Ophidiiformes), an endemic sand‐dwelling Mediterranean fish, are likely to go undetected by traditional non‐invasive monitoring techniques commonly used to survey biodiversity.
• Although the cusk‐eel is distributed along the eastern coast of the Adriatic Sea, no study to date has reported its presence along the north‐western coastline.
• Despite this, passive acoustic monitoring carried out during summer 2009 at the WWF‐Miramare Marine Protected Area, located on the northernmost shore of the Adriatic Sea (Trieste Gulf, Italy), revealed loud sounds with characteristics similar to those of O. rochei.
• The sounds were long trains of low‐frequency pulses, showing the typical and unique pulse period alternation pattern of O. rochei adult male reproductive calls. The consistency of these peculiar call features indicates that O. rochei is present in the marine protected area, where it is likely to reproduce. The results are further discussed in light of the occasional presence of the congeneric snake blenny Ophidion barbatum (Linnaeus, 1975).
• This is the first reported case in which passive acoustic monitoring enabled the identification of a cryptic fish species in a marine protected area where visual census surveys of the fish fauna, carried out for decades on a monthly basis, failed to detect the presence of this species.
• Passive acoustic monitoring is a powerful tool for both conservation and fishery science that should be coupled with visual surveys in order to improve the resolution of fish biodiversity assessments.
Soundscape ecology is a rapidly growing field with approximately 93% of all scientific articles on this topic having been published since 2010 (total about 610 publications since 1985). Current acoustic technology is also advancing rapidly, enabling new devices with voluminous data storage and automatic signal detection to define sounds. Future uses of passive acoustic monitoring (PAM) include biodiversity assessments, monitoring habitat health, and locating spawning fishes. This paper provides a review of ambient sound and soundscape ecology, fish acoustic monitoring, current recording and sampling methods used in long-term PAM, and parameters/metrics used in acoustic data analysis.
Although many fish are soniferous, few of their sounds have been identified, making passive acoustic monitoring (PAM) ineffective. To start addressing this issue, a portable 6-hydrophone array combined with a video camera was assembled to catalog fish sounds in the wild. Sounds are detected automatically in the acoustic recordings and localized in three dimensions using time-difference of arrivals and linearized inversion. Localizations are then combined with the video to identify the species producing the sounds. Uncertainty analyses show that fish are localized near the array with uncertainties < 50 cm. The proposed system was deployed off Cape Cod, MA and used to identify sounds produced by tautog (Tautoga onitis), demonstrating that the methodology can be used to build up a catalog of fish sounds that could be used for PAM and fisheries management.
In the Mediterranean Sea, the seagrass Posidonia oceanica plays a key ecological role, and is protected by a range of legislation. Standard Posidonia monitoring programmes generally focus on the plant at different spatial and short temporal scales, without considering the organisms dependent on the ecosystem. Passive acoustic monitoring (PAM) has a high potential to non-intrusively monitor biological activities and biodiversity at high temporal resolution, and to assess ecosystem health. This is particularly relevant considering that Posidonia meadows host numerous sound-producing fish species. In this study, bottom-moored hydrophones were deployed in nine Western Mediterranean meadows covering a distance of more than 200 km to identify acoustic features potentially relevant to monitor this critical habitat. Among eight identified fish sound categories, we found a single type of sound (that we will refer to as /kwa/) dominating the soundscape of Posidonia meadows over a time span of 7 months. Compared to other low-frequency sounds, the /kwa/ presented unique characteristics that suggest it is produced by a fish via fast contracting muscles. The /kwa/ was the only sound detectable under anthropogenic noise conditions, and little affected by it. Cluster analyses performed on 13 acoustic features revealed a high degree of call diversity. /Kwa/ diversity, combined with its large-scale (all meadows), long-term (7 months) occurrence and low noise interference, make the /kwa/ a promising candidate for PAM of Posidonia meadows. Furthermore, variability in acoustic features suggests a central role of the /kwa/ in communication. Overall, this work sets the basis for establishing the relevance of the /kwa/ in monitoring P. oceanica meadows and developing PAM techniques for this critical habitat.
In this study, our goal was to perform acoustic monitoring of the May River, South Carolina (USA), for a 9 mo period and estimate reproductive timelines for a community of soniferous fishes. Acoustic recorders were deployed to collect sound samples for 2 min, every 20 min at 4 stations from the source to the mouth from February to November 2013. We detected the acoustic presence of 6 fish species: Atlantic croaker Micropogonias undulatus, black drum Pogonias cromis, silver perch Bairdiella chrysoura, oyster toadfish Opsanus tau, spotted seatrout Cynoscion nebulosus, and red drum Sciaenops ocellatus. Acoustic detection rates and diversity of soniferous fish were higher near the mouth and decreased towards the source, suggesting a selection of deeper water and/or more stable water quality conditions for spawning. We estimated the start and end dates of the spawning season and calculated the total hours of chorusing for silver perch, oyster toadfish, spotted seatrout, and red drum. Each species followed a specific seasonal and daily pattern of calling, and we observed synchrony of these calling patterns among stations. For silver perch, oyster toadfish, black drum, and spotted seatrout, a negative temperature anomaly correlated with decreased calling intensity, while a positive anomaly increased sound production. For oyster toadfish and spotted seatrout, the lunar phase significantly influenced calling. These data serve as a foundation for future studies that are investigating how climate variability may affect seasonal spawning timelines and year class strength of fish populations using passive acoustic monitoring.
Many studies stress the usefulness of fish calls as effective indicators of distinct species occurrence. However, most of these studies have been undertaken in a given area and during restricted periods of time. There is a need to show passive acoustic monitoring is a reliable method to study vocal species over space and time. This study aims to use passive acoustic methods to follow the brown meagre Sciaena umbra at relevant temporal and spatial scales. Specimens of S. umbra were recorded in both aquarium and in the field. In situ recordings were made at two regions (Corsica and Sardinia) during four summers (2008–2012–2013–2015). Temporal and frequency parameters of the fish calls were collected by different teams and compared to test the ability to unequivocally identify the fish sound. The comparison between our data and the bibliography highlights the capability to identify S. umbra during a period of 17 years in different Mediterranean regions, clearly supporting the usefulness of acoustic monitoring to discover and protect aggregation sites of this endangered species. The sound producing mechanism in S. umbra consists of high-speed sonic muscles surrounding dorsally the posterior end of the swim bladder, which can explain the low acoustic variability that helps in the species identification. Similar mechanisms are found in other Sciaenidae, suggesting that a similar conclusion can be drawn for many other adult sciaenids that could be used as sentinel species. This study should be of high interest to policymakers and scientists because it shows passive acoustic can be confidently used in resource management.
The Mediterranean cusk eels Ophidion barbatum and O.rochei have often been mistaken for each other. Reviews of past work have not completely clarified the differentiation. Apart from the differences between this two species, the morphometric characters and the relative growth indices analysed have shown highly significant differences between males and females of both species.
An evening chorus centered at near 2.2 kHz was detected across the years 2000 to 2014 from seabed receivers in 430–490 m depth overlooking the Perth Canyon, Western Australia. The chorus reached a maximum level typically 2.1 h post-sunset and normally ran for 2.1 h (between 3 dB down points). It was present at lower levels across most of the hours of darkness. Maximum chorus spectrum levels were 74–76 dB re 1 μPa²/Hz in the 2 kHz 1/3 octave band, averaging 6–12 dB and up to 30 dB greater than pre-sunset levels. The chorus displayed highest levels over April to August each year with up to 10 dB differences between seasons. The spatial extent of the chorus was not determined but exceeded the sampling range of 13–15 km offshore from the 300 m depth contour and 33 km along the 300 m depth contour. The chorus comprised short damped pulses. The most likely chorus source is considered to be fishes of the family Myctophidae foraging in the water column. The large chorus spatial extent and its apparent correlation with regions of high productivity suggest it may act as an acoustic beacon to marine fauna indicating regions of high biomass.
It is my proposal that the “data deficient” category be renamed a more precautionary “assume threatened” status, with the description of the category emphasizing that the burden of proof to say that the species is not, in fact threatened, is on those wishing to conduct activities that could impact one of these species, relieving the current burden which is largely that of the conservation science community. The IUCN's description of the “data deficient” category states that there is: “the possibility that future research will show that threatened classification is appropriate. It is important to make positive use of whatever data are available…If the range of a taxon is suspected to be relatively circumscribed, and a considerable period of time has elapsed since the last record of the taxon, threatened status may well be justified” (IUCN, 2001). While this wording suggests that the precautionary approach could be taken with this category, it does so weakly, and this suggestion for precaution is somewhat overwhelmed by the empathic statement in the same description that “data deficient is therefore not a category of threat” (IUCN, 2001). There is, thus, little formal incentive for policy makers or managers to commit resources to data deficient species. However, if species were classified as “assumed threatened” there would likely be considerably less risk that rare, or hard to study species, may go extinct before scientists have a chance to document their status. Moreover, there would be a major incentive for developers and policy makers to commit resources to evaluate these data deficient species.
Passive acoustic recording (PAR) systems are non-invasive and allow researchers to collect data on large spatial and temporal scales. Since fish sounds are species-specific and repetitive, PAR can provide a large amount of data about spatio-temporal variation in fish distribution and behaviors. Ophidion rochei is a sand-dwelling species from Mediterranean and Black Sea meaning the behavior of this discreet nocturnal fish cannot be observed in the field. Fortunately, male O. rochei produce long multiple-pulsed calls that are easy to identify. The aim of this study was to determine that male calls are linked to reproduction behaviors. If so, PAR would allow a fine description of the seasonal and daily cycles in O. rochei reproduction. A hydrophone was deployed from 18 July 2011 to 21 June 2012 and from 7 June 2013 to 2 July 2013 on a sandy area (42.5801° N, 8.7285° E) in front of the STARESO research station (NW Corsica). Male sounds were obtained only at night from late spring to early fall. The annual sound production period corresponds to the reproductive season of O. rochei. Sound production followed diel cycles: it was sustained for the entire night at the beginning of the sound production season but limited to shorter periods in the evening during the second half of the season. These differences in daily and seasonal sound production tempo can be used in future recordings to make inter-annual comparisons and estimate the physiological state of the fish.
An acoustic community is defined as an aggregation of species that produces sound by using internal or extra-body sound-producing tools. Such communities occur in aquatic (freshwater and marine) and terrestrial environments. An acoustic community is the biophonic component of a soundtope and is characterized by its acoustic signature, which results from the distribution of sonic information associated with signal amplitude and frequency. Distinct acoustic communities can be described according to habitat, the frequency range of the acoustic signals, and the time of day or the season. Near and far fields can be identified empirically, thus the acoustic community can be used as a proxy for biodiversity richness.
Although the sound production mechanisms of male and female Ophidion rochei (Ophidiidae) differ
significantly, temperature affects them in the same manner. In both sexes, temperature correlated negatively
with pulse period and positively with sound frequencies but had no, or weak effects on other
sound characteristics.
1. Sound production represents an integral part of social communication in many teleost fish; however, few studies have investigated the structure, organization and variability of fish sounds at the community level.
2. Fish acoustic community structure was recorded simultaneously in three sites located along the Mediterranean basin within the endemic habitat of Posidonia oceanica seagrass beds. Acoustic diversity and species-specific sound features were expected to differ between locations. We predicted that, in communities characterized by higher acoustic richness, fish species would specialize in their use of acoustic resources (i.e. realized acoustic niche compression), while the overall allocation of resources within the community signal space would expand.
3. The fish acoustic communities inhabiting Posidonia beds were characterized by the same main contributors (the /Kwa/, Ophidion rochei and Sciaena umbra sound types). However, their relative occurrence, abundances and use of acoustic resources were site-specific. Acoustic diversity differed between geographic locations. The range of spectral and temporal resources exploited by the fish acoustic community was wider in sites where acoustic richness was at its highest score. Ophidion rochei was highly specialized in its use of temporal resources where acoustic richness was higher, whilst S. umbra appeared less efficient in specializing the use of spectral and temporal resources.
4. By showing that the same species can exploit different acoustic resources between locations, this study supports the concept of Acoustic Niche plasticity (i.e. plasticity of acoustic resources allocation within a species). The results suggest that the degree of acoustic niche plasticity might be determined by the species-specific degree of sound-producing system plasticity. In turn, different degrees of acoustic niche plasticity might determine different species-specific levels of acoustic adaptability to changing biotic or environmental conditions.
Biodiversity is a portmanteau word to indicate the variety of life at all levels from genes to ecosystems, but it is often simplistically equated to species richness; the word ecodiversity has thus been coined to address habitat variety. Biodiversity represents the core of the natural capital, and as such needs to be quantified and followed over time. Marine Protected Areas (MPAs) are a major tool for biodiversity conservation at sea. Monitoring of both species and habitat diversity in MPAs is therefore mandatory and must include both inventory and periodic surveillance activities. In the case of inventories, the ideal would be to census all species and all habitats, but while the latter goal can be within reach, the former seems unattainable. Species inventory should be com-measured to investigation effort, while habitat inventory should be based on mapping. Both inventories may profit from suitability spatial modelling. Periodic surveillance actions should privilege conspicuous species and priority habitats. Efficient descriptor taxa and ecological indices are recommended to evaluate environmental status. While it seems obvious that surveillance activities should be carried out with regular recurrence, diachronic inventories and mapping are rarely carried out. Time series are of prime importance to detect marine ecosystem change even in the absence of direct human impacts.
Human impacts on marine ecosystems are increasing and the number of fish species listed in the Red List is constantly growing. In the Mediterranean Sea, seven of the 10 bony fishes defined as Threatened by the IUCN are known to be vocal, including the target species of this study: the shi drum (Umbrina cirrosa Linnaeus, 1758) and the brown meagre (Sciaena umbra Linnaeus, 1758). As a result, non‐invasive passive acoustic monitoring (PAM) can be used to pinpoint their distribution at sea. However, for PAM to be effective, reliable acoustic discrimination is required because the sounds they emit during reproduction are remarkably similar (i.e. short broadband pulsed sounds).
The shi drum and the brown meagre are closely related, elusive, vocal sciaenids, partially overlapping in their ecological niche. During summer 2019, three PAM surveys were conducted along the tidal inlets of the Venice lagoon (Italy). Here, the calls of both species have been recognized according to their temporal features: shi drum sounds were made up of a lower number of longer pulses with a different envelope, repeated at a lower rate than those of the brown meagre. Further, shi drum and brown meagre sounds of different origins (aquaculture and semi‐natural conditions) were analysed and compared with those collected during the survey of the study area in order to validate the field collected data.
Call discrimination allowed for a fine‐scale species mapping, showing a partially overlapping distribution of the two species along the inlets. This is the first case in which two sciaenids have been documented to share their reproductive habitat in the Mediterranean Sea.
This study demonstrates that it is feasible to acoustically monitor the target species even in those parts of the Mediterranean Sea where they co‐exist. This, in its turn, could provide managers with the required data for effective conservation measures to be implemented.
Environmental DNA (eDNA) is increasingly being used to document species distributions and habitat use in marine systems, with much of the recent effort focused on leveraging advances in next-generation DNA sequencing to assess and track biodiversity across taxonomic groups. Environmental DNA offers a number of important advantages over traditional survey techniques, including non-invasive sampling, sampling where traditional approaches are impractical or inefficient (e.g. deep oceans), reduced cost, and increased detection sensitivity. However, eDNA applications are currently limited because of an insufficient understanding of the influence of sample source, analytical approach, and marker type on eDNA detections. Because approaches vary considerably among eDNA studies, we present a summary of the current state of the field and emerging best practices. The impact of observed variation in rates of eDNA production, persistence, and transport are also discussed and future research needs are highlighted with the goal of expanding eDNA applications, including the development of statistical models to improve the predictability of eDNA detection and quantification.
Although several bioacoustics investigations have shed light on the acoustic communication of Mediterranean fish
species, the occurrence of fish sounds has never been reported below 40 m depth. This study assessed the
occurrence of fish sounds at greater depths by monitoring the soundscape of a Mediterranean submarine canyon
(Calvi, France) thanks to a combination of Static Acoustic Monitoring (three stations, from 125 to 150 m depth,
3 km from coastline) and of hydrophone-integrated gliders (Mobile Acoustic Monitoring; from 60 to 900 m
depth, 3–6 km from coastline). Biological sounds were detected in 38% of the audio files; ten sound types (for a total
of more than 9.000 sounds) with characteristics corresponding to those emitted by vocal species, or known as produced by fish activities, were found. For one of these sound types, emitter identity was inferred at the genus level
(Ophidion sp.). An increase of from 10 to 15 dB re 1 lPa in sea ambient noise was observed during daytime hours
due to boat traffic, potentially implying an important daytime masking effect. This study shows that monitoring the
underwater soundscape of Mediterranean submarine canyons can provide holistic information needed to better
understand the state and the dynamics of these heterogeneous, highly diverse environments.
VC 2020 Acoustical Society of America. https://doi.org/10.1121/10.0001101
In the current extinction crisis, emerging technologies can support the urgent need to document biodiversity worldwide. Automated acoustic recorders are increasingly being used to remotely monitor species and soundscapes across the planet, generating a growing and valuable sound collection from present ecosystems. Such a collection can become a benchmark for future ecological research and shed light on our understanding of global change. Here we discuss the challenges and potential of acoustic monitoring to compose bioacoustic time capsules, environmental recordings capable to document, for future generations, how the planet’s acoustic communities were in the past. For the present, acoustic monitoring can assist in ecological research and increase the chances of a species being detected, described, and hence protected. For the future, the collected time-series of audio recordings will compose bioacoustic time capsules, providing singular historical information on the structure and dynamics of past ecosystems and the activity of extinct fauna (acoustic fossils). Thus, we claim that acoustic monitoring should be included in biologist’s toolbox to optimize the diligent task of documenting and protecting biodiversity.
Passive acoustics is well suited to assess the diversity and/or activity of marine animals, particularly if cryptic or difficult to observe as in seagrass Posidonia oceanica meadows. The ability to locate the
emitters allows not only to detect the presence of a specific sound or specie but also to estimate source levels, the communicative space with respect to ambient noise and anthropogenic impact, the density of vocalizing animals, their movements and potentially home ranges, etc. Here, we located fishes in seagrass meadows (Calvi, France). Two particular sounds dominated the acoustic scene of seagrass meadows: the: 300Hz drums of Ophidion rochei and the ubiquitous 800Hz /kwa/ sound of unknown origin. The wavelengths of these fish sounds range from 5 meters to 2 meters. During six 48-hours periods, we deployed a squared array of 4 hydrophones (20x50x50 meters). Here we describe the algorithm for automated fish sound detection and 3D localization of the sources and assess their performances on our real data. Over 1000 fish sounds were detected per night. These detections were used to create localization maps and study the spatial distribution of fish sound production, estimate source levels and the density of the vocalizing fishes within the meadow and their limits.
Soundscapes are strongly linked with the physical structure and biological features of the habitats and their study can reveal ecological processes of the underwater environment. Objective of this study is to characterize two Mediterranean habitats, the Posidonia oceanica meadow and the sandy bottom, and demonstrate their acoustic diversification basing on their soundscapes. Firstly, the habitats have been compared using two different acoustic metrics, the Power Spectral Density (PSD) and the Acoustic Complexity Index (ACI), measured in different frequency band. Then, the acoustic biological component of the habitats has been identified and characterized: five biological signals were described and their acoustic properties and temporal patterns were defined. Finally, the geophonical and anthropogenic components of the two habitats have been compared. In the low frequency (<0.5 kHz) the sandy habitat showed higher values of PSD and lower valuesof ACI. From 0.5–24 kHz the greatest values ofboth parameters were recorded in the Posidonia habitat due to the acoustic activity of snapping shrimps and fishes. The wind speed resulted significantly correlated with PSD from 0.1 to 2 kHz for both habitats, but the correlation is less intense in Posidonia habitat suggesting a noise attenuation phenomenon. The two habitats present biophonical component belonged to different fish species and invertebrates; they showed alternated temporal pattern and different frequency allocation. The Posidonia habitat resulted acoustically richer than sandy habitat, confirming the importance of ecoacoustic method to study ecological processes. Finally, a strong acoustic impact from the anthropogenic component was revealed: it achieves 60% of daytime during the summer, especially in sandy habitat. Results demonstrated not only the possibility to discriminate habitats through the sound information but also the need to protect marine ecosystems from the human noise.
The composition and structure of discard, as well as the damage caused to target and non-target species, was analyzed in 95 commercial fishing hauls carried out between March 2013 and March 2014 by the mechanized dredging fleet targeting wedge clam (Donax trunculus) in the northern Alboran Sea (southern Spain). A large proportion of the catch (ca. 42% weight) is discarded, mainly wedge clam undersized individuals and non-commercial molluscs, decapods and echinoderms. Total discards within the study period showed a high species richness, with a total of 84 taxa discarded, and biomasses ranging from 337.1 to 8532.5 g haul⁻¹ (1579.9 ± 157.9 g haul⁻¹, mean ± SE), with maxima in spring. The composition, structure and biomass of discards displayed significant differences among study sites due to differences in the benthic communities of the fishing grounds. Individuals displaying intermediate (intermediate survival chance) and severe (low survival chance) damage in the discard displayed higher values when gravel and bioclastic material was more abundant in the catch. Overall, 15% of the discarded individuals displayed any type of damage, from which 12% were severely damaged, and with Echinoderms displaying the highest mean proportion of damaged individuals (79.5 ± 2.9% of individuals). The target species displayed a high proportion of undamaged individuals to fishing impacts, which may represent an important factor for the maintenance of populations of this commercial species on the fishing grounds.
The timing of migration is one of the key life-history parameters of migratory birds. It is expected to be under strong selection, to be sensitive to changing environmental conditions and to have implications for population dynamics. However, most phenological studies do not describe arrival and departure phenologies for a species in a way that is robust to potential biases, or that can be clearly related to breeding populations. This hampers our ability to understand more fully how climate change may affect species’ migratory strategies, their life histories and ultimately their population dynamics. Using Generalized Additive Models (GAMs) and extensive large-scale data collected in the UK over a forty-year period, we present standardised measures of migration phenology for common migratory birds, and examine how the phenology of bird migration has changed in the UK since the 1960s. Arrival dates for 11 of 14 common migrants became significantly earlier, with six species advancing their arrival by more than ten days. These comprised two species, Blackcap Sylvia atricapilla and Chiffchaff Phylloscopus collybita, which winter closest to Britain in southern Europe and the arid northern zone of Africa, Common Redstart Phoenicurus phoenicurus, which winters in the arid zone, and three hirundines (Sand Martin Riparia riparia, House Martin Delichon urbicum and Barn Swallow Hirundo rustica) which winter in different parts of Africa. Concurrently, departure dates became significantly later for four of the 14 species and included species that winter in southern Europe (Blackcap and Chiffchaff) and in humid zones of Africa (Garden Warbler Sylvia borin and Whinchat Saxicola rubetra). Common Swift Apus apus was the exception in departing significantly earlier. The net result of earlier arrival and later departure for most species was that length of stay has become significantly longer for nine of the 14 species. Species that have advanced their timing of arrival showed the most positive trends in abundance, in accordance with previous studies. Related in part to earlier arrival and the relationship above, we also show that species extending their stay in Great Britain have shown the most positive trends. Further applications of our modelling approach will provide opportunities for more robust tests of relationships between phenological change and population dynamics than have been possible previously. This article is protected by copyright. All rights reserved.
Assessment and monitoring of exploited fish populations are challenged by costs, logistics and negative impacts on target populations. These factors therefore limit large‐scale effective management strategies.
Evidence is growing that the quantity of eDNA may be related not only to species presence/absence, but also to species abundance. In this study, the concentrations of environmental DNA ( eDNA ) from a highly prized sport fish species, Lake Trout Salvelinus namaycush (Walbaum 1792) , were estimated in water samples from 12 natural lakes and compared to abundance and biomass data obtained from standardized gillnet catches as performed routinely for fisheries management purposes. To reduce environmental variability among lakes, all lakes were sampled in spring, between ice melt and water stratification.
The eDNA concentration did not vary significantly with water temperature, dissolved oxygen, pH and turbidity, but was significantly positively correlated with relative fish abundance estimated as catch per unit effort ( CPUE ), whereas the relationship with biomass per unit effort ( BPUE ) was less pronounced.
The value of eDNA to inform about local aquatic species distribution was further supported by the similarity between the spatial heterogeneity of eDNA distribution and spatial variation in CPUE measured by the gillnet method.
Synthesis and applications . Large‐scale empirical evidence of the relationship between the eDNA concentration and species abundance allows for the assessment of the potential to integrate eDNA within fisheries management plans. As such, the eDNA quantitative method represents a promising population abundance assessment tool that could significantly reduce the costs associated with sampling and increase the power of detection, the spatial coverage and the frequency of sampling, without any negative impacts on fish populations.
Using data collected simultaneously from a trawl and a hydrophone, we found that temporal and spatial trends in densities of juvenile Atlantic croaker (Micropogonias undulatus) in the Neuse River estuary in North Carolina can be identified by monitoring their sound production. Multivariate analysis of covariance (MANCOVA) revealed that catch per unit of effort (CPUE) of Atlantic croaker had a significant relationship with the dependent variables of sound level and peak frequency of Atlantic croaker calls. Tests of between-subject correspondence failed to detect relationships between CPUE and either of the call parameters, but statistical power was low. Williamson's index of spatial overlap indicated that call detection rate (expressed by a 0-3 calling index) was correlated in time and space with Atlantic croaker CPUE. The correspondence between acoustic parameters and trawl catch rates varied by month and by habitat. In general, the calling index had a higher degree of overlap with this species' density than did the received sound level of their calls. Classification and regression tree analysis identified calling index as the strongest correlate of CPUE. Passive acoustics has the potential to be an inexpensive means of identifying spatial and temporal trends in abundance for soniferous fish species.
Sound production by the dusky grouper Epinephelus marginatus was monitored both in captivity and at two Mediterranean spawning sites during the summers of 2012 and 2013. The results of long-term passive acoustic recordings provide for the first time a description of the sounds produced by E. marginatus. Two types of sounds were mainly recorded and consisted of low-frequency booms that can be produced singly or in series with dominant frequencies below 100 Hz. Recordings in captivity validated these sounds as belonging to E. marginatus and suggested that they may be associated with reproductive displays usually performed during early stages of courtship behaviour. This study also allowed the identification of a third, low-frequency growl-like type of sound typically found in other grouper species. These growls were, however, not recorded in tanks and it is cautiously proposed that they are produced by E. marginatus. Acoustic signals attributed to E. marginatus were produced throughout the spawning season, with a diel pattern showing an increase before dusk, i.e. from 1900 to 2200 hours, before decreasing until the morning. The occurrence of sounds during the spawning season of this species suggests that they are probably involved in social activity occurring close to aggregation sites. Passive acoustics offer a helpful tool to monitor aggregation sites of this emblematic species in order to improve conservation efforts.
© 2015 The Fisheries Society of the British Isles.