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.

ABSTRACT Cetaceans depend highly on acoustic signals, such as whistles, for social communication. Mixed-species associations (MSAs), temporary or long-term encounters between different species, may play an important role on the acoustic dynamics of the species involved. Because of whistles’ communication function, we used these sounds to investigate the acoustic relationships of Tursiops truncatus when involved in different group contexts: in MSAs with two other delphinid species and in single species group. Acoustic recordings of T. truncatus single species groups and in associations with Globicephala melas and Grampus griseus were collected in the Western South Atlantic Ocean through a towed array of hydrophones. A total of 1267 whistles were analysed and acoustical parameters were extracted. To verify the differences among whistles produced in such contexts a support vector machine and random forest analysis were implemented. Both analyses revealed a clear separation of whistles from the single species versus the MSA as well as between both MSAs. The results indicate that interspecific associations may influence the whistle structure and suggests that T. truncatus whistles can be modified during interspecific interactions. These findings are useful to elucidate the possible factors underlying behavioural plasticity and interspecific associations and to understand dolphins’ acoustic communication.

Sperm whales live in culture-based multilevel societies in which the fundamental social level is the nearly permanent social unit of females and immature individuals, and the largest level is the clan constituted by social units that share a common coda repertoire. This study describes the coda repertoire and vocal clans of sperm whales in Brazilian waters recorded between 2011 and 2016. Inter-click intervals of codas were used to quantify similarity between repertoires. The analysis showed two evident clans, in the north and the south, distinct in their repertoires. The clan of the north, termed the "5R" clan, presented a predominant production of codas containing five regularly spaced clicks, not found in the clan of the south, termed "D" clan, which repertoire was dominated by long codas with 10-13 clicks with descending inter-click intervals. Codas with five regularly spaced clicks with the same rhythm and tempo as those found in the "5R" clan of Brazil are also predominant in sperm whales recorded in the Island of Dominica, at a distance of approximately 2700 km from the north of Brazil, which corresponds to the extension of the areas of sympatric clans. The sharing of 5R type by the both distinct clans is likely the result of cultural transmission in which conformism through social learning homogenizes coda repertoire. The results of this study corroborated the hypothesis that social boundaries, here the clan level, are maintained by cultural identities.

This study presents an integrative bioacoustics approach to discriminate eight species of odontocetes found on the outer continental shelf and slope of the western South Atlantic Ocean. Spinner, Atlantic spotted, rough-toothed, Risso's, bottlenose, short-beaked common dolphins, killer and long-finned pilot whales were visually confirmed during recordings with a 3-element omnidirectional hydrophone array. Spectral and time parameters of whistles and echolocation clicks were used in a discriminant function analysis and a classification tree model. As a first step, whistles and clicks were analysed separately; a further analysis consisted of both vocalisations jointly classified. All species showed species-specific properties in their vocalisations. Whistles had greater misclassification rates when compared to clicks. The correct classification was enhanced by the joint step, given the 5.8% error in the discriminant function analysis and a misclassification rate of 18.8% in the tree model. In addition, Receiver Operating Characteristic curves resulting from the tree algorithm analysis exhibited better model efficiency for all species in the joint classification. These findings on acoustical discrimination of such abundant and cosmopolitan species contribute to delphinid classification systems.

The vocal repertoire of the Amazon river dolphin and its geographic variations are still poorly known, especially in relation to ecological variables. Here the acoustic characteristics of low frequency pulsed vocalizations, with single or multiple pulses, recorded in two protected areas of the Amazon were described and differences in acoustic emissions related to water properties were analyzed. Both frequency and time parameters differ relative to abiotic condition of water turbidity. Changes in the animals' acoustic behavior might be due to differences in sound propagation between rich-sediment water and clear water. Geographic variation was found in frequency and time parameters, requiring further investigation.

Acoustic parameters for the spinner dolphins' bioacoustic sounds have previously been described. However, the dolphins in the Southwest Atlantic Ocean were only recently studied near the Fernando de Noronha Archipelago. Therefore, to contribute to additional knowledge of this cosmopolitan species, this study compares previous results with a Brazilian recording. Despite statistically significant differences, the mean value comparison indicated that Hawaiian and Southwest Atlantic Ocean spinners emit similar whistles. The fact that geographical isolation does not lead the dissemblance nor the similarity of the acoustic variations in this species raises the possibility of other factors influencing those emissions. Here those differences and similarities are discussed, thereby contributing to an understanding of how distinct populations and/or species communicate through different ocean basins. (C) 2015 Acoustical Society of America.

Acoustic parameters for the spinner dolphins' bioacoustic sounds have previously been described. However, the dolphins in the Southwest Atlantic Ocean were only recently studied near the Fernando de Noronha Archipelago. Therefore, to contribute to additional knowledge of this cosmopolitan species, this study compares previous results with a Brazilian recording. Despite statistically significant differences, the mean value comparison indicated that Hawaiian and Southwest Atlantic Ocean spinners emit similar whistles. The fact that geographical isolation does not lead the dissemblance nor the similarity of the acoustic variations in this species raises the possibility of other factors influencing those emissions. Here those differences and similarities are discussed, thereby contributing to an understanding of how distinct populations and/or species communicate through different ocean basins.