This study focuses on the acoustic classification of delphinid species at the southern continental slope of Brazil. Recordings were collected between 2013 and 2015 using towed arrays and were processed using a classifier to identify the species in the recordings. Using Raven Pro 1.6 software (Cornell Laboratory of Ornithology, Ithaca, NY), we analyzed whistles for species identification. The random forest algorithm in R facilitates classification analysis based on acoustic parameters, including low, high, delta, center, beginning, and ending frequencies, and duration. Evaluation metrics, such as correct and incorrect classification percentages, global accuracy, balanced accuracy, and p-values, were employed. Receiver operating characteristic curves and area-under-the-curve (AUC) values demonstrated well-fitting models (AUC ≥ 0.7) for species definition. Duration and delta frequency emerged as crucial parameters for classification, as indicated by the decrease in mean accuracy. Multivariate dispersion plots visualized the proximity between acoustic and visual match data and exclusively acoustic encounter (EAE) data. The EAE results classified as Delphinus delphis (n = 6), Stenella frontalis (n = 3), and Stenella longirostris (n = 2) provide valuable insights into the presence of these species between approximately 23° and 34° S in Brazil. This study demonstrates the effectiveness of acousting classification in discriminating delphinids through whistle parameters.

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.

River dolphins (Sotalia fluviatilis and Inia spp.) rely on sound for navigation, foraging, and communication, making passive acoustic monitoring a promising research tool. We present a preliminary assessment of the PODs detections across five South American countries. A total of 486 816 minutes of recordings were collected, with 18% showing positive detections. Detection rates varied among sites and were generally higher in confluences, lakes, and in a dam reservoir than in other habitats. Although PODs cannot reliably distinguish among sympatric species and may miss weak signals, our results show that they can provide useful information on dolphin occurrence in remote freshwater systems, supporting their use as a complementary tool for broad-scale monitoring.

The pygmy ( Kogia breviceps ) and dwarf ( Kogia sima ) sperm whales are cryptic cetaceans characterized by inconspicuous surfacing behavior, small group sizes, and deep‐diving habits, making visual detection particularly challenging. Here, we present the first broad‐scale passive acoustic monitoring (PAM) assessment of Kogia spp. occurrence along the Brazilian coast, spanning both the Equatorial Atlantic Ocean (EAO) and Southwestern Atlantic Ocean (SWAO). Across 25 survey campaigns, 504 survey days, and more than 6441 h of acoustic recordings, 94 acoustic detections were identified, predominantly within the Brazilian Equatorial Margin (BEM), resulting in substantially higher detection‐per‐unit‐effort values in the EAO than in the SWAO. Two rare visual‐acoustic encounters of Kogia sima were also documented, including one detection incorporated into the dataset. A total of 2796 echolocation clicks were analyzed, exhibiting the characteristic narrow‐band high‐frequency acoustic profile of Kogia spp. (mean peak frequency = 126.2 ± 3.8 kHz; mean −3 dB bandwidth = 4.7 ± 2.56 kHz; mean inter‐click interval = 141 ± 97 ms). Detections occurred across a broad bathymetric range (9–4411 m), and kernel density analyses revealed spatial heterogeneity in occurrence patterns, with recurrent detection areas concentrated within the BEM. Collectively, these findings demonstrate the effectiveness of PAM for studying elusive deep‐diving cetaceans and provide an important baseline for future ecological monitoring, impact assessment, and conservation efforts targeting Kogia spp. in the western Atlantic.