Uso de assobios na identificação de delfinídeos (Odontoceti: Delphinidae) para o oceano Atlântico Sul ocidental

O grupo dos Cetáceos, formado basicamente por baleias, botos e golfinhos evoluiu em um ambiente que propiciou o desenvolvimento de sistemas complexos de comunicação acústica. Devido às suas propriedades físicas, o som viaja cerca de cinco vezes mais rápido na água do que no ar, sendo uma das energias mais eficientes no meio aquático. Sendo assim, os cetáceos são animais vocalmente ativos. Golfinhos da família Delphinidae destacam-se por apresentarem um complexo comportamento vocal, formado por assobios, cliques de ecolocalização e pulsos explosivos. Esses sons são utilizados na realização de diversas tarefas, tais como socialização, caça, navegação e discriminação de objetos. Além de características morfológicas, como posição da nadadeira dorsal, presença de manchas ou padrões de coloração, os sinais acústicos produzidos por esses animais podem ser utilizados na identificação ao nível de espécie. Bioacústica é a ciência responsável por estudar os mecanismos e forças envolvidas na produção, recepção e propagação do som. Essa área do conhecimento tem crescido nos últimos anos para o estudo de cetáceos devido às dificuldades em estudar esses animais em seu habitat natural, que permanecem submersos por longos minutos e apresentam um comportamento que dificulta a aproximação de pesquisadores para identificação da espécie. Algoritmos de classificação acústica têm sido desenvolvidos e aprimorados por se mostrarem extremamente úteis em situações que impossibilitam ou dificultam a observação de delfinídeos. Condições meteorológicas adversas como ventos, chuvas, estado do mar alto, períodos noturnos e de baixa visibilidade podem comprometer a identificação visual e o estudo com esses mamíferos. Com base nisso, este trabalho buscou classificar espécies de delfinídeos com base apenas em seu repertório acústico para o oceano Atlântico Sul ocidental. Foi possível identificar acusticamente três espécies: Delphinus delphis, Stenella frontalis e Stenella longirostris. Essas espécies foram frequentemente avistadas durante o Projeto Talude, uma pesquisa realizada entre 2013 a 2015 nos taludes sul e sudeste do Brasil. Provavelmente essas espécies também estavam acusticamente disponíveis quando condições meteorológicas não propícias não permitiram a identificação visual pelos observadores de bordo. Trabalhos como esse podem contribuir com a conservação dos cetáceos, que sofrem constantemente com os impactos causados por humanos em seu ambiente.

Myoglobin Concentration and Oxygen Stores in Different Functional Muscle Groups from Three Small Cetacean Species

Compared with terrestrial mammals, marine mammals possess increased muscle myoglobin concentrations (Mb concentration, g Mb · 100g−1 muscle), enhancing their onboard oxygen (O2) stores and their aerobic dive limit. Although myoglobin is not homogeneously distributed, cetacean muscle O2 stores have been often determined by measuring Mb concentration from a single muscle sample (longissimus dorsi) and multiplying that value by the animal’s locomotor muscle or total muscle mass. This study serves to determine the accuracy of previous cetacean muscle O2 stores calculations. For that, body muscles from three delphinid species: Delphinus delphis, Stenella coeruleoalba, and Stenella frontalis, were dissected and weighed. Mb concentration was calculated from six muscles/muscle groups (epaxial, hypaxial and rectus abdominis; mastohumeralis; sternohyoideus; and dorsal scalenus), each representative of different functional groups (locomotion powering swimming, pectoral fin movement, feeding and respiration, respectively). Results demonstrated that the Mb concentration was heterogeneously distributed, being significantly higher in locomotor muscles. Locomotor muscles were the major contributors to total muscle O2 stores (mean 92.8%) due to their high Mb concentration and large muscle masses. Compared to this method, previous studies assuming homogenous Mb concentration distribution likely underestimated total muscle O2 stores by 10% when only considering locomotor muscles and overestimated them by 13% when total muscle mass was considered.

Aggressive Behaviors of Adult Male Atlantic Spotted Dolphins: Making Signals Count during Intraspecific and Interspecific Conflicts

Some species exhibit behavioral plasticity by altering their aggressive behavior based on their opponent. Atlantic spotted dolphins (Stenella frontalis) and bottlenose dolphins (Tursiops truncatus) are two sympatric species resident to the northern Bahamas. We examined whether groups of adult male spotted dolphins demonstrated behavioral plasticity during two different types of aggressive interactions. We described and compared the types of aggressive behaviors used during intraspecific aggression and interspecific aggression with bottlenose dolphins. Between the years 1991-2004, twenty-two aggressive encounters (11 intraspecific (spotted only), 11 interspecific (spotted vs. bottlenose)) were behaviorally analyzed. Twenty-three specific aggressive Behavioral Events, further grouped into three Behavioral Types, were examined throughout these encounters. Similarities and differences in the use of the Behavioral Types occurred during intra- and interspecific aggression. Groups of male Atlantic spotted dolphins altered their behavior during aggressive encounters with male bottlenose dolphins. Spotted dolphins increased their use of the Pursuit Behavioral Type and did not use the Display Behavioral Type significantly more than the Contact Behavioral Type during interspecific aggression. The increased use of a more overt and energy intensive Behavioral Type, Pursuit, suggests that Atlantic spotted dolphins altered their behavior during aggressive encounters with bottlenose dolphins to compensate during fights with a larger species and/or to effectively communicate with a different species.

Individual home ranges of Tursiops truncatus and their overlap with ranges of Stenella frontalis and fishermen in Aragua, Venezuela, South Caribbean

The coast of Aragua is a home of bottlenose dolphins (BND), Atlantic spotted dolphins (ASD) and fishermen (FIS) from four towns. A photo-identification study was carried out on BND to estimate their home ranges. From 2004 to 2008, 100 field surveys were carried out along 30 km of coastline (92.12 km2). In each sighting of BND, information regarding date, time, latitude/longitude and photographs were registered (ASD and FIS were registered without photography). The data were analysed using a Geographic Information System to estimate Minimum Convex Polygon (MCP) and Fixed Kernel (FK) at 95%. The home ranges of BND were estimated for seven individuals. This included three females (29–31 sightings) with estimated areas ranging from 33.90–39.90 km2 with MCP (36.79–43.31% of the study area) and from 80.47–101.31 km2 with FK (109.97–104.26%). For the remaining four dolphins (14–20 sightings) the estimated areas ranged from 9.67–22.34 km2 (MCP), the predominant depth of these home ranges varied from 51–100 m (χ2 = 24.5, df = 2, P = 4.785 × 10−6). For the pods of ASD the estimated area ranged 75.23 km2 with MCP (81.66%) and 119.86 km2 with FK (130.11%) with predominant depths of 101–200 m (χ2 = 24.5, df = 2, P = 4.785 × 10−6). The area used by FIS ranged 93.27 km2 by MCP and 228.49 km2 by FK. Finally, the overlap area of BND, ASD and FIS ranged 24.75 km2 (26.86%). We point out this locality presents important oceanographic and ecological aspects which deserve to be the subject of application of management plans for the conservation of its habitat and species.

Methodological Considerations for Comparison of Cross-species Use of Tactile Contact

Cross-species comparisons are benefited by compatible datasets; conclusions related to phylogenetic comparisons, questions on convergent and divergent evolution, or homologs versus analogs can only be made when the behaviors being measured are comparable. A direct comparison of the social function of physical contact across two disparate taxa is possible only if data collection and analyses methodologies are analogous. We identify and discuss the parameters, assumptions and measurement schemes applicable to multiple taxa and species that facilitate cross-species comparisons. To illustrate our proposed guidelines for evaluating the role played by tactile contact in social behavior across disparate taxa, this paper presents data on mother-offspring relationships in the two species studied by the authors: chimpanzees (Pan troglodytes schweinfurthii) and dolphins (bottlenose and spotted, Tursiops truncatus and Stenella frontalis, respectively). Cross-species comparative studies allow for a more comprehensive assessment of the similarities and differences with respect to how animals traverse the relationships that form their social groups and societies.

Interactions between cetaceans and artisanal fishermen from Ilhéus, Bahia - Brazil

Ethnobiological studies are necessary to understand the relationships between fishers and cetaceans. The aim of this study was to describe the interactions between cetaceans and artisanal fishers and the possible conflicts that can arise as a result. Semi-structured interviews were conducted from February to September 2017 with 35 fishermen from the municipality of Ilhéus, Brazil. All fishermen reported both positive and negative interactions with Megaptera novaeangliae, Tursiops truncatus and Sotalia guianensis and only negative interactions with Balaenoptera acutorostrata (n=14) and Stenella frontalis (n=4). The positive interactions consisted of playful relationships and collaborative fishing. Negative interactions (bycatch, entanglement, collisions) affect both the fishermen and cetaceans. S. guianensis is the species most affected by bycatch in fishing nets and M. novaeangliae by entanglement and collision with vessels. The results of this study highlight the value of bringing together scientific and fishing communities to understand conflicts by monitoring interactions in order to assess the impact of fishing activity on cetacean populations. Fishers have a positive perception of cetaceans, know the areas where accidents occur and would like to avoid them. They can contribute to research on these animals and to the development of management plans appropriate to the local reality. This points out the need to integrate scientific and local knowledge for the conservation of cetaceans and for the sustainability of fishing practices.