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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.

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Introduction: False killer whale (Pseudorca crassidens) is a tropical and subtropical social species that live in groups with individuals of mixed ages and sex classes. False killer whales have been documented since the late 1990s in Southwestern Costa Rica. Objective: To estimate the abundance of false killer whales in Osa Peninsula waters. Methods: Cetacean surveys off the Osa Peninsula Waters (OPW), Costa Rica, yielded opportunistic encounters with false killer whales in Drake Bay and Caño Island (2001-2019) and observations during formal surveys in Golfo Dulce (2005-2015). Photo-identification data was analyzed using capture-mark-recapture models in the study area, through an open population (POPAN) framework, considering the effect of time on the parameters apparent survival and capture probability, producing an abundance estimate for a superpopulation in the entire study area. Results: False killer whale abundance in OPW is characterized by a small population size of no more than 100 individuals, complemented by a very low probability of encounter and a contrasting high apparent survival. Conclusions: This population estimate should be taken as conservative, however, the small population size of less than 100 individuals should be considered vulnerable, in contrast to the increasing anthropogenic impacts in the coastal seascape. We argue the potential occurrence of population units along the coastal seascape of the Pacific littoral and oceanic island-associated units at Isla del Coco.

Introducción: La falsa orca es una especie gregaria tropical y subtropical, que vive en grupos con individuos de diferentes clases de edad y sexo. La falsa orca ha sido documentada en el sur-oeste de Costa Rica desde finales de los 90s. Objetivo: Evaluar el uso de hábitat de la especie en términos de abundancia. Métodos: Observaciones en campo para cetáceos en aguas de la Península de Osa (APO), incluyen encuentros oportunísimos en Bahía de Drake y la Isla del Caño (2001-2019), así como observaciones directas de Pseudorca crassidens, durante muestreos formales en Golfo Dulce (2005-2015). Se analizaron datos sobre foto-identificación utilizando modelos de marcaje captura y recaptura, considerando un enfoque para población abierta (POPAN), el cual considera el efecto del tiempo en los parámetros demográficos: supervivencia aparente (ф) y probabilidad de captura (P), produciendo un estimado de abundancia que comprende toda la superpoblación en el área de estudio. Resultados: La abundancia de la falsa orca en APO se caracteriza por un tamaño poblacional pequeño, de menos de 100 individuos, que se complementa por una muy baja probabilidad de captura, en contraste con una supervivencia aparente alta. Conclusión: Este estimado debe tratarse como conservativo, no obstante, el pequeño número poblacional, de menos de 100 individuos debe considerarse como vulnerable, en contraste con el incremento del impacto antropogénico del paisaje marino costero. Se discute la posible presencia de unidades poblacionales en el paisaje costero del litoral Pacífico y de unidades oceánicas asociadas a la Isla del Coco.

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Coastal and freshwater cetaceans are particularly vulnerable due to their proximity to human activity, localized distributions, and small home ranges. These species include Sotalia guianensis, found in the Atlantic and Caribbean coastal areas of central and South America, and Sotalia fluviatilis, distributed in the Amazon River and tributaries. We investigated the population structure and genetic diversity of these 2 species by analyses of mtDNA control region and 8-10 microsatellite loci. MtDNA analyses revealed strong regional structuring for S. guianensis (i.e., Colombian Caribbean vs. Brazilian Coast, FST = 0.807, ΦST = 0.878, P < 0.001) especially north and south of the Amazon River mouth. For S. fluviatilis, population structuring was detected between the western and eastern Amazon (i.e., Colombian Amazon vs. Brazilian Amazon, FST = 0.085, ΦST = 0.277, P < 0.001). Haplotype and nucleotide diversity were higher for S. fluviatilis. Population differentiation was supported by analysis of the microsatellite loci (S. guianensis, northern South America vs. southern South America FST = 0.275, Jost's D = 0.476, P < 0.001; S. fluviatilis, western and eastern Amazon FST = 0.197, Jost's D = 0.364, P < 0.001). Most estimated migration rates in both species overlapped with zero, suggesting no measurable migration between most of the sampling locations. However, for S. guianensis, there was measurable migration in neighboring sampling locations. These results indicate that the small home ranges of these species may act to restrict gene flow between populations separated by relatively short distances, increasing the risk of extirpation of some localized populations in the future if existing threats are not minimized.

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A new small probable Oligocene dolphin from Ecuador represents a new genus and species, Urkudelphis chawpipacha. The new taxon is known from a single juvenile skull and earbones; it differs from other archaic dolphins in features including widely exposed frontals at the vertex, a dorsally wide open vomer at the mesorostral groove, and a strongly projected and pointed lateral tuberosity of the periotic. Phylogenetic analysis places it toward the base of the largely-extinct clade Platanistoidea. The fossil is one of a few records of tropical fossil dolphins.

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Acoustic studies of Guiana dolphin have been focused on whistles, with little known about pulse signals in this species. This study characterized the temporal and spectral properties of Guiana dolphin burst pulses. Groups of 2 to 23 Guiana dolphins were recorded while feeding and socializing in shallow waters in Guanabara Bay, southeastern Brazil, in 2013 and 2014. Burst pulse analysis involved two steps: signal detection and acoustic parameter analysis. Eight variables were analyzed for 197 total burst pulses: number of clicks, burst pulse duration, interclick interval, click duration, peak frequency, center frequency, -3 dB bandwidth, and -10 dB bandwidth. Mean burst pulse duration was 108.6 ms [standard deviation (SD) = 91.3] with a mean of 168 clicks (SD = 137.3). Burst pulses had short interclick interval (0.7 ms, SD = 0.3) and mean click duration of 300 µs (SD = 100). Mean peak frequency and center frequency were 28 kHz (SD = 11.6) and 29 kHz (SD = 11.0), respectively. Mean -3 dB bandwidth was 15 kHz (SD = 7.5) and mean -10 dB bandwidth was 40.5 kHz (SD = 14.3). The quantitative characterization of Guiana dolphin burst pulses is an important step in describing the full acoustic repertoire of this species.

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Franciscana dolphin (Pontoporia blainvillei) whistles were documented for the first time during 2003-2013 in Babitonga Bay estuary, South Brazil, together with burst pulses. Recordings were made from small boats under good sea conditions, and recording equipment that allowed analysis of sounds up to 96 kHz. The recordings were made in the presence of 2-31 franciscana dolphins. During 23 h and 53 min, 90 whistles and 51 burst pulse series were recorded. Although Guiana dolphins (Sotalia guianensis) inhabit nearby waters, none were observed in the area during the recordings. The authors recorded ten types of whistles. The initial frequency varied between 1.6 and 94.6 kHz, and the final frequency varied between 0.7 and 94.5 kHz; the authors were not able to determine if dolphin whistles exceeded the 96 kHz recording limit of the authors' equipment, although that is likely, especially because some whistles showed harmonics. Whistle duration varied between 0.008 and 0.361 s. Burst pulses had initial frequencies between 69 and 82.1 kHz (77 ± 3.81). These results showed that P. blainvillei produces whistles and burst pulses, although they seem to be produced infrequently.

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Temporal and spatial patterns of cetacean diversity and distribution were investigated through eight ship-based surveys carried out during spring and autumn between 2009 and 2014 on the outer continental shelf (~150m) and slope (1500m) off southeastern and southern Brazil (~23°S to ~34°S). The survey area was divided into southeast and south areas according to their oceanographic characteristics. Twenty-one species were observed in 503 sightings. The overall number of species was similar between the two areas, though it was higher in the spring in the south area. Five species were dominant and diversity varied more seasonally than spatially. ANOVA and kernel analyses showed that overall cetacean densities were higher in spring compared to autumn. Physeter macrocephalus, the most frequent species, concentrated throughout the south area at depths over 1000m in both seasons. Despite the overlapped occurrence at a broader scale, small delphinids presented latitudinal and in-offshore gradients as well as seasonal variation in distribution patterns, which could indicate habitat partitioning between some species. Delphinus delphis was only recorded in the south and its density decreased in areas where the presence of Stenella frontalis increased, mainly beyond the 250m isobath. Densities of S. longirostris and S. attenuata increased in lower latitudes and beyond the shelf break. The large delphinids Tursiops truncatus and Globicephala melas formed mixed groups in many occasions and were observed along the study area around depths of 500m. Grampus griseus was twice as frequent in the south area and densities increased in waters deeper than 600m. As expected, densities of both small and large migratory whales were higher during spring, over the continental slope, in the southeast area. The results presented here provided strong evidence on the importance of the outer continental shelf and slope to a diverse community of cetaceans occurring in the subtropical Southwestern Atlantic.

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The present study evaluates variations in frequency and duration parameters of whistles of four dolphin species (Sotalia guianensis, Steno bredanensis, Stenella frontalis, and Tursiops truncatus), recorded in the Rio de Janeiro State Coast, Southeastern Brazil. A total of 487 whistles were analyzed. Acoustic parameters of the whistles were classified to species by discriminant function analysis. Overall classification score was 72.5%, with the highest classification score obtained for whistles of S. bredanensis and the lowest obtained for S. frontalis. Most differences were among S. bredanensis and S. guianensis, species that did not have their repertoires compared in other studies.

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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.

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The reproductive morphology of cetaceans is poorly studied and, despite the large number of strandings, reports on this subject are scarce due to access to carcasses mostly in an advanced state of decomposition. The present study aimed to describe histological characteristics of the female genital tract of Sotalia guianensis, in order to assist in future studies on the reproductive biology of these animals. Females of different ages, from stranding events on beaches in northeastern Brazil, were used. Fragments of all organs were collected and processed for light and scanning electron microscopy. Histological analyses showed that these structures were similar to those found in terrestrial mammals, with some peculiarities, such as the presence of differentiated cells in the vulvar subepidermal layer, not described in the literature on cetaceans. Reproductive studies with a morphological description of the female genital organs are extremely important, since they would enable a better understanding of the species reproductive physiology and assist in the development of new strategies for the species conservation.

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