Alice Lima

The distribution of odontocetes is likely to be influenced by environmental and oceanographic factors, as well as prey availability, resulting in distinct habitat-use patterns among species. Cetaceans rely on acoustic communication for essential activities such as navigation, foraging, and social interactions. In southern Bahia, Brazil, the narrow continental shelf promotes the coexistence of coastal and offshore species within a restricted area, providing an opportunity to investigate spatial segregation and acoustic niche structure. We conducted simultaneous visual and acoustic monitoring along the coast of Ilhéus between January and December 2022 to assess species distribution, acoustic presence, and acoustic niche overlap. Six odontocete species were visually identified, with the prevalence of Sotalia guianensis in nearshore habitats, whereas the sperm whales (Physeter macrocephalus) was detected and identified exclusively by acoustic monitoring. A clear spatial segregation was observed between coastal and offshore species, indicating strong habitat partitioning at a fine spatial scale. Acoustic presence was significantly higher in coastal waters and during winter, suggesting seasonal and spatial variation in habitat use. Acoustic overlap analyses indicated spectral niche partitioning, with greater frequency overlap among species occupying adjacent zones and less overlap among species with greater spatial differentiation. This study provides the first integrated characterization of spatial distribution and acoustic patterns of odontocetes in southern Bahia, offering valuable baseline information to support the monitoring and conservation of these species, where an increase in anthropogenic activities is projected.

Production et perception des signaux acoustiques chez les grands dauphins (Tursiops truncatus) : utilisation contextuelle des signaux sociaux et reconnaissance de « labels » artificiels: Les études de bioacoustique animale, qui reposent traditionnellement sur des modèles primates non humains et oiseaux chanteurs, convergent vers l'idée que la vie sociale serait la principale force motrice de l'évolution de la complexité de la communication. La comparaison avec les cétacés est également particulièrement intéressante d'un point de vue évolutif. Ce sont des mammifères qui forment des liens sociaux complexes, ont des capacités de plasticité acoustique, mais qui ont dû s'adapter à la vie marine, faisant de l'habitat une autre force de sélection déterminante. Leur habitat naturel impose des contraintes sur la production sonore, l'utilisation et la perception des signaux acoustiques, mais, de la même manière, limite les observations éthologiques. Etudier les cétacés captifs devient alors une source importante de connaissances sur ces animaux. Au-delà de l'analyse des structures acoustiques, l'étude des contextes sociaux dans lesquels les différentes vocalisations sont utilisées est essentielle à la compréhension de la communication vocale. Par rapport aux primates et aux oiseaux, la fonction sociale des signaux acoustiques des dauphins reste largement méconnue. En outre, les adaptations morpho-anatomiques de l’appareil vocal et auditif des cétacés à une vie sous-marine sont uniques dans le règne animal. Leur capacité à percevoir les sons produits dans l'air reste controversée en raison du manque de démonstrations expérimentales. Les objectifs de cette thèse étaient, d'une part, d'explorer l'utilisation contextuelle spontanée des signaux acoustiques dans un groupe captif de dauphins et, d'autre part, de tester expérimentalement les capacités à percevoir les sons sous l’eau comme dans l’air. Notre première étude observationnelle décrit la vie quotidienne de dauphins en captivité et montre que les signaux vocaux reflètent, à grande échelle, la répartition temporelle des activités sociales et non sociales dans un établissement sous contrôle humain. Notre deuxième étude met l'accent sur le contexte d’émission des trois principales catégories acoustiques précédemment identifiées dans le répertoire vocal des dauphins, à savoir les sifflements, les sons pulsés et les séries de clics. Nous avons trouvé des associations préférentielles entre chaque catégorie vocale et certains types d'interactions sociales ainsi que des combinaisons sonores non aléatoires et également dépendantes du contexte. Notre troisième étude a testé expérimentalement, dans des conditions standardisées, la réponse des dauphins à des « labels » acoustiques individuels donnés par l’homme et diffusés dans l’eau et dans l’air. Nous avons constaté que les dauphins peuvent reconnaître et réagir uniquement à leur propre « label » sonore, même lorsqu'il est diffusé dans l’air. En plus de confirmer l'audition aérienne, ces résultats soutiennent l’idée que les dauphins possèdent une notion d'identité. Dans l'ensemble, les résultats obtenus au cours de cette thèse suggèrent que certains signaux sociaux dans le répertoire des dauphins peuvent être utilisés pour communiquer des informations spécifiques sur les contextes comportementaux des individus impliqués et que les individus sont capables de généraliser leur concept d'identité à des signaux générés par l'homme.

This study compared the size and composition of humpback whale groups estimated from boat-based observations and drone video analysis during the 2022 and 2023 breeding seasons in Ilhéus, Brazil. Data from 43 groups showed that drone consistently recorded larger group sizes than boat-based observations, with a strong positive correlation between the two methods (r=0.94, p<0.001). Drone also enabled more accurate identification of group composition, detecting additional individuals and more complex group types - such as large competitive groups - than the boat-based method. A significant association between method and group composition was found (p<0.001), with drones identifying more groups composed of four or more adults or a mother-calf pair with several escorts. These findings underscore the advantages of drone-based surveys for improving assessments of group structure, contributing to more accurate data to monitor and conserve cetacean populations.

This study aimed to investigate whether the use of space and movements of Guiana dolphins were altered during the construction of a cable-stayed bridge at the mouth of the Cachoeira River estuary in Ilhéus, Brazil. We described and compared the visitation rate, use of space, and movements of the Guiana dolphins across two periods: before the construction began (2015–2016) and during the construction of the bridge (2017–2020). A theodolite and a total station were used to observe and record the trajectories of the dolphins. From these trajectories, we estimated the Utilization Distribution (UD) using the biased random bridge kernel (BRBK) method, the area of use, and the core area, based on the 95% and 50% BRBK density, respectively. The dolphins did not change their visitation frequency to the estuary. No significant change in area fidelity was identified by comparing the overlap of areas used during two-month periods. No change occurred in the velocity and linearity of the trajectories of the dolphins swimming close to the bridge. However, contrary to expectations, the results indicated an increase in the use of areas close to the bridge during its construction. This may have been caused by the change in the distribution of their prey in the estuary due to the emergence of a sandbank near the bridge. Bridge construction work seems not to have directly affected the Guiana dolphins’ use of the area, but the impact of the construction on the local topography has changed their areas of use and core areas of activity.

This note reports an unusual observation of a mother and calf pair of southern right whales on 27 July 2021 off the coast of Ilhéus, Bahia state, northeastern Brazil. The sighting was made from a 29ft cruiser boat (brand Cabrasmar), with a 225HP inboard engine, during a whale watching tour in a humpback whale (Megaptera novaeangliae) breeding area.

Under natural conditions bottlenose dolphins (Tursiops truncatus) spend their time mostly feeding and then travelling, socializing, or resting. These activities are not randomly distributed, with feeding being higher in early morning and late afternoon. Social activities and vocal behavior seem to be very important in dolphin daily activity. This study aimed to describe the activity time‐budget and its relation to vocal behavior for dolphins in a zoological park. We recorded behaviors and vocalizations of six dolphins over 2 months. All subjects performed more non‐agonistic social interactions and play in the morning than in the afternoon. The different categories of vocalizations were distributed non‐randomly throughout the day, with more chirps in the afternoon, when the animals were “less social.” The most striking result was the strong correlation between activities and the categories of vocalizations produced. The results confirm the association between burst pulses and whistles with social activities, but also reveal that both are also associated with solitary play. More chirps were produced when dolphins were engaged in socio‐sexual behaviors, emphasizing the need for further questioning about the function of this vocal category. This study reveals that: (i) in a group kept in zoological management, social activities are mostly present in the morning; and (ii) the acoustic signals produced by dolphins may give a reliable representation of their current activities. While more studies on the context of signal production are needed, our findings provide a useful tool for understanding free ranging dolphin behavior when they are not visible.