Anthropogenic underwater noise has become a major environmental and ocean-governance concern affecting marine mammals worldwide, motivating increasing attention within international conservation bodies such as the International Whaling Commission (IWC). Here, we reconstruct how acoustics and anthropogenic underwater noise emerged, expanded, and diversified within the IWC Scientific Committee through a PRISMA-guided document screening combined with scientometric and qualitative classification analyzes. A total of 7,830 Scientific Committee documents produced between 1951 and 2024 were compiled and screened using an automated keyword strategy, yielding 2,949 records for eligibility assessment. Following screening, 644 documents were retained for analysis, encompassing both acoustic-related studies and documents addressing anthropogenic underwater noise as an environmental or management issue. Among these, 594 documents (7.4%) addressed acoustics, spanning 50 years (1962–2024) with a marked increase from the late 1990s onwards. Explicit underwater-noise content was identified in 180 documents (2.16%), first appearing in 1979 and recurring across 38 years, with contributions concentrated in the Environmental Concerns, Small Cetaceans, and Whale Watching subcommittees. Ten standardized sound-source categories were identified, dominated by shipping, seismic surveys, and sonar, while additional sources emerged progressively over time. Reported impacts were primarily behavioral and spatial, whereas auditory damage and mortality were associated with high-intensity sources. Institutional participation was extensive, involving 559 institutions across 75 countries, but remained highly concentrated among a limited number of recurrent contributors. Together, these findings provide the first long-term synthesis of how underwater noise evolved within the Scientific Committee from a specialized acoustic topic into a policy-relevant environmental issue, revealing how scientific knowledge, institutional priorities, and governance discussions co-evolved within the IWC framework.

IntroductionHuman activities are significantly altering the marine soundscape. Seismic exploration generates high-intensity sounds that propagate over large spatial and temporal scales and can adversely affect cetaceans, which rely on sound for communication, foraging, navigation, and survival.MethodsThis study investigates the acoustic responses of pantropical spotted dolphins (Stenella attenuata) and spinner dolphins (Stenella longirostris) to seismic airgun noise in the Southwestern Atlantic Ocean between 2017 and 2026. The effects of seismic prospection activity noise on the acoustic parameters of both species were assessed using permutation tests, Principal Coordinates Analysis (PCoA), and a Random Forest Algorithm (RFA).ResultsClassification accuracy within the RFA increased during active seismic conditions due to a reduction in acoustic parameter variance, a trend mirrored by clearer PCoA cluster segregation for echolocation clicks. Whistles and click trains analysed under active and inactive airgun conditions revealed species-specific response patterns. S. attenuata reduced whistle frequency parameters and duration, narrowing its overall bandwidth, whereas S. longirostris increased whistle duration. Conversely, for click trains, both species exhibited a significant reduction in inter-click intervals alongside a narrower distributional range of click peak frequency values.DiscussionThese findings indicate that exposure to seismic noise elicits complex, multi-parametric adjustments that alter signal features. Beyond documenting these patterns, this study demonstrates that machine learning frameworks are effective tools for diagnosing shifts in cetacean acoustic profiles under anthropogenic disturbance. Recognising that distinct parameters within whistles and clicks respond differently under acoustic pressure is necessary for ensuring the accuracy of acoustic monitoring used during mitigation frameworks. Incorporating these variations into regulatory guidelines prevents automated detection errors, improving the management and protection of marine species within industrialised soundscapes.

Conventional visual surveys of the cryptic franciscana dolphin Pontoporia blainvillei are constrained by turbid near-shore waters and the species’ tendency to cluster in small groups. We combined passive acoustic monitoring (PAM) with drone counts to calibrate an acoustic footprint detection model and infer group size from acoustic data. Click trains were detected in PAMGuard, localized, and clustered with HDBSCAN into click-train clusters (CTCs). Drones provided visual group sizes during synchronized sections. A 2-step spatiotemporal matching paired CTCs to visual groups. An independent manual audit estimated a 6.4% false-positive rate, used to correct automated counts. For paired clusters, we fit GLMs with an offset for animal-seconds and alternative distance terms; AIC selected a linear negative binomial model. The calibrated baseline acoustic footprint at the trackline was r0 = 0.028 click trains animal-1 s-1 (95% CI: 0.014-0.056; CV = 0.34; R2 = 0.54), equivalent to 1.68 (CI: 0.84-3.36) min-1. We obtained 28 paired CTCs from 8 visual groups and applied the calibration to 267 unpaired CTCs. Predicted group sizes had a median of 1.34 individuals (95% CI: 0.79-2.57; CV = 0.15), consistent with predominantly small units. This framework provides a pathway from clicks to counts and delivers an important step required for passive acoustic density estimation of this species.

Beaked whales, deep-diving cetaceans from the family Ziphiidae, exhibit cryptic behaviors, and data on these species in Brazilian waters are limited to strandings and isolated sightings. This study characterizes the occurrence and acoustic behavior of beaked whales in the Foz do Amazonas Basin using combined visual and passive acoustic monitoring along the Brazilian Equatorial Margin. Audio files were analyzed to identify clicks with frequency-modulated pulses, a diagnostic characteristic of beaked whales. The PAMpal package in R was used to calculate acoustic parameters, including peak frequency, 3- and 10-dB bandwidths, and inter-pulse intervals. Three sightings, eight acoustic detections, and one combined visual-acoustic detection were recorded. Based on diagnostic features, sighting D01 likely corresponds to Mesoplodon europaeus, D05 may represent Mesoplodon, and D06 could belong to either Ziphius or Mesoplodon. Unsupervised clustering based on peak frequency and inter-pulse intervals revealed three distinct acoustic clusters, suggesting that at least three different beaked whale species were detected. Further acoustic classification studies are needed to determine the specific species associated with each cluster. These findings contribute to a broader understanding of the distribution and acoustic ecology of deep-diving beaked whales in the Foz do Amazonas Basin, a region where information on marine megafauna remains scarce.

We applied passive acoustic monitoring and Hierarchical Density-Based Spatial Clustering of Applications with Noise clustering to define spatiotemporally cohesive groupings of franciscana dolphin (Pontoporia blainvillei) echolocation click trains. This unsupervised, objective method identified biologically relevant click train clusters, offering rare insights into the species' social organization. The observed structure revealed consistent intra-cluster cohesion and inter-cluster separation, supporting the effectiveness of the approach. Our findings demonstrate that clustering acoustic detections can serve as a robust framework for delineating social groups and can be integrated into future density estimation protocols, enhancing the ecological understanding and conservation potential for this cryptic and vulnerable species.

Muriquis (Brachyteles sp.) are endemic to the Brazilian Atlantic Forest; its genus is divided into two species, the northern muriqui (Brachyteles hypoxanthus), and the southern muriqui (Brachyteles arachnoides), both assessed as Critically Endangered by the IUCN Red List. The endangered status of muriquis is associated with habitat loss, fragmentation, hunting, and other anthropogenic actions, confining the species to fragments, mostly, in protected areas. One of these important protected areas is in the Serra da Mantiqueira, the Environmental Protection Area Serra da Mantiqueira, that has a sizable continuous remnant of the Atlantic Forest with a high degree of biological diversification, where both species of muriquis occur. This designation highlights the region as one of the most critical regions for the genus Brachyteles. Nonetheless, new records may fill gaps in the distribution limit between the two muriquis species, identifying whether there is a possible barrier or possible overlapping area. However, recording and estimating primate populations over large areas through standard field techniques, such as linear transects, can be costly in terms of time and financial resources. In addition, given its altitude gradient, the Serra da Mantiqueira region is remote and difficult to access for systematic biodiversity surveys. Thus, aerial surveys were carried out using thermal sensors attached to drones, which made it possible to record two new groups of southern muriquis in Serra da Mantiqueira. Thus, we confirm that this new method represents an effective way to survey highly threatened primates.

The limited temporal completeness and taxonomic accuracy of species lists, made available in a traditional manner in scientific publications, has always represented a problem. These lists are invariably limited to a few taxonomic groups and do not represent up-to-date knowledge of all species and classifications. In this context, the Brazilian megadiverse fauna is no exception, and the Catalogo Taxonomico da Fauna do Brasil (CTFB) (http://fauna.jbrj.gov.br/), made public in 2015, represents a database on biodiversity anchored on a list of valid and expertly recognized scientific names of animals in Brazil. The CTFB is updated in near real time by a team of more than 800 specialists. By January 1, 2024, the CTFB compiled 133,691 nominal species, with 125,138 that were considered valid. Most of the valid species were arthropods (82.3%, with more than 102,000 species) and chordates (7.69%, with over 11,000 species). These taxa were followed by a cluster composed of Mollusca (3,567 species), Platyhelminthes (2,292 species), Annelida (1,833 species), and Nematoda (1,447 species). All remaining groups had less than 1,000 species reported in Brazil, with Cnidaria (831 species), Porifera (628 species), Rotifera (606 species), and Bryozoa (520 species) representing those with more than 500 species. Analysis of the CTFB database can facilitate and direct efforts towards the discovery of new species in Brazil, but it is also fundamental in providing the best available list of valid nominal species to users, including those in science, health, conservation efforts, and any initiative involving animals. The importance of the CTFB is evidenced by the elevated number of citations in the scientific literature in diverse areas of biology, law, anthropology, education, forensic science, and veterinary science, among others.