Carmen Andrés-Hervías

Understanding reproductive performance is essential for assessing the viability of small, threatened marine mammal populations in degraded coastal ecosystems. The bottlenose dolphin Tursiops...

Mediterranean monk seals (Monachus monachus) are the world's rarest seal species, with fewer than 1000 individuals remaining across fragmented subpopulations. Monitoring this species is challenging due to their low densities and difficult-to-access habitats. Passive acoustic monitoring (PAM) data can be used to detect small numbers of animals over large areas, but for effective long-term PAM, it is essential to characterize the species' vocalizations throughout its range. This study provides a comprehensive description of the monk seal vocal repertoire in the Inner Ionian Sea Archipelago, Greece, and the first published documentation of the species vocalizing underwater. Acoustic recorders collected continuous data over 16 days during the breeding season in 2021. We identified 3442 calls, 1855 of which were determined to be high-quality and classified into ten call types within three broader categories. Video footage collected in 2019 and 2021 documented the seals producing five common call types, which comprised ∼87% of the recorded calls. Our findings offer insights into the structure of the monk seal vocal repertoire and lay the groundwork for long-term monitoring for this rare species using PAM, which could be an important tool for monitoring monk seals going forwards.

Assessing trends in population abundance and demographics is crucial for managing long‐lived and slow‐reproducing species. Obtaining demographic data, and age‐structure information, is challenging, notably for cetaceans. To address this, we combined Unoccupied Aerial System (UAS; drone) photogrammetry data with long‐term (>20 years) photo identification data to assess the age‐structure of the critically endangered sub‐population of common bottlenose dolphins (Tursiops truncatus) of the Gulf of Ambracia, Greece. We compared our findings with two extensively studied non‐endangered bottlenose dolphin populations (T. aduncus in Shark Bay, Australia, and T. truncatus in Sarasota Bay, USA). Using a log‐linear model, we estimated the total body lengths (TL) of 160 known‐aged dolphins between 2021 and 2023 from blowhole‐to‐dorsal‐fin distance (BHDF) measurements collected during surfacing. Subsequently, we tested four growth models to establish an age‐length growth curve. We assessed the sub‐population's age‐structure using three methods: (1) UAS‐derived TL estimates, (2) age‐length growth curve and (3) long‐term monitoring data (i.e. actual age‐structure). UAS‐measured TL (247.6 ± 32.2 cm) and UAS‐estimated TL (246.0 ± 34.7 cm) of the Greek sub‐population showed no differences. The Richards Growth model suggested an asymptotic length of 258.5 cm. In Greece, resulting age‐structure estimates across the three methods revealed no significant differences (P > 0.1). The Gulf of Ambracia and Shark Bay populations shared similar age‐structures, while Sarasota had higher proportions of 2–10 year‐olds and lower proportions of 10+ year‐olds. All populations had a comparable proportion of 0–2 year‐olds (~14%), indicating a similar reproductive rate. Our findings suggest stability in the Greek sub‐population; however, additional monitoring of reproductive parameters is essential before concluding its status. We demonstrated the effectiveness of UAS‐photogrammetry in rapidly quantifying population age‐structure, including scenarios with limited or no demographic data. This technique shows promise for enhancing precision, timeliness, cost‐effectiveness and efficiency in population monitoring and informing timely conservation management decisions.

Marine aquaculture, and its fast‐growing development, has the potential for wider environmental, ecosystem, and biodiversity impacts. This study assesses the impact of fish farming on a bottlenose dolphin (Tursiops truncatus) population within the Gulf of Ambracia (western Greece) between 2007 and 2018. Two different study areas were defined in order to investigate differences on occurrence, abundance, behaviour, and seasonal fluctuations between them: a ‘control area’, in the north‐western side of the Gulf; and a ‘fish farm area’, in the south west, where the highest density of fish farm cages is found. A total of 169 daily surveys were dedicated to the control area and 74 days were dedicated to the fish farm area, yielding 104 and 37 sightings, respectively. Both the probability of detecting dolphins (U = 6,763.000, P = 0.002) and the group sizes (U = 578.000, P < 0.001) were smaller around fish farms. Seasonality analyses were restricted to 2007–2008, as this was the period with year‐round effort. Results revealed that dolphins were more frequently seen around fish farms in the winter (Kruskal–Wallis test, P = 0.036). From the 40 identified individuals that were re‐sighted at least 10 times during the study period, 21 used the fish farm area less than expected according to sampling effort, and 10 of them were never observed in that area (binomial test, P < 0.05). The results revealed an impact of fish farms on the distribution of bottlenose dolphins in the Gulf of Ambracia. This information should be taken into consideration when defining ecosystem‐based management measures within the management plan, which is currently in preparation for this Natura 2000 site.