Classificação dos assobios do Boto-de-Lahille, tursiops truncatus gephyreus (Lahille, 1908), através do monitoramento acústico

Abstract

The Lahille's dolphin (Tursiops truncatus gephyreus) is a coastal subspecies recently classified as Endangered (EN) by the IUCN (2025) due to its continuous decline trend, with distribution in the Western South Atlantic, along the Brazilian ( PR, SC and RS), Uruguayan and Argentin-ian coast. Because this subspecies prefers coastal environments, it constantly experiences the impacts caused by human activities, some examples being: incidental catches in fishing nets, environmental degradation (chemical, residual and noise pollution), depletion of its prey, intru-sions and human disturbances caused by activities such as uncontrolled urban growth and acci-dental collisions with vessels, leading these animals to exhibit stress. Given the importance of acoustic communication for the ecology and survival of these animals, this study aimed to eval-uate, classify, and describe the vocalizations of the species, as well as identify underwater noises in the Barra da Laguna de Tramandaí (RS). Acoustic monitoring took place over three days in January 2023, using a C57 hydrophone and a Tascam DR-100 MKIII recorder. The recordings were analyzed using Raven Pro software version 1.6.5 (Cornell Lab of Ornithology, 2019). The results obtained were from 191 whistles, which were analyzed, obtaining an average duration of 0.30 ± 0.13 s, with whistle frequencies ranging between 2.7 kHz and 21.4 kHz; these values are compatible with records of Tursiops spp. The qualitative analysis identified six modulation patterns, the most frequent being: ascending (A): 44.5%, parabola (C): 20.9%, de-scending (B): 15.2%. The ecological importance of the research is reinforced by the identifica-tion of "anthropophony," which consists of noise of human origin, evidenced in the soundscape at the study site. The noise caused by boat engines, for example, occurs in frequency ranges below and beyond the frequency range of the acoustic repertoire of the species in question, which ultimately reduces the communication, navigation, and foraging capabilities of dolphins, representing a critical risk for a population that is already endangered, indicating a high risk of extinction in the wild. This work demonstrates that acoustic monitoring is an essential tool, mainly because it is non-invasive, serving to evaluate, classify, and describe vocalizations in the underwater environment. Acoustic monitoring allows us to observe whether the species may exhibit behaviors such as increasing the maximum frequency of its whistles to compensate for excessive noise, which can be an indicator of ecological stress.