Behavioural and temporal partitioning of dolphin social groups in the northern Adriatic Sea

Complex social structure is a prominent feature in several mammal species. Such structure may lead to behavioural diversity not only among populations, but also within a single population, where different subsets of a population may exhibit different types of behaviour. As a consequence, understanding social structure is not only interesting biologically, but may also help conservation and management efforts, because not all segments of a population necessarily respond to or interact with human activities in the same way, or at the same time. In this study, we examined the social structure of common bottlenose dolphins (Tursiops truncatus) in the Gulf of Trieste and adjacent waters (northern Adriatic Sea), based on a 9-year dataset, using social network metrics and association indices. We assessed whether different segments of the population show differences in behaviour and interactions with fisheries. Dolphin social network was structured into distinct social clusters of mixed sexes. We found no evidence of male alliances. The two largest social clusters overlapped spatially, but not temporally, as they used the same area at different times of day. Such diel temporal partitioning does not appear to have been documented in cetaceans previously. The two clusters also differed in ways they interact with fisheries, as one regularly interacted with trawlers, while the other did not. This study demonstrates how different segments of animal populations can interact differently with human activities and in turn respond differently to anthropogenic impacts.Publisher PDFPeer reviewe

A deep learning approach to photo–identification demonstrates high performance on two dozen cetacean species

We thank the countless individuals who collected and/or processed the nearly 85,000 images used in this study and those who assisted, particularly those who sorted these images from the millions that did not end up in the catalogues. Additionally, we thank the other Kaggle competitors who helped develop the ideas, models and data used here, particularly those who released their datasets to the public. The graduate assistantship for Philip T. Patton was funded by the NOAA Fisheries QUEST Fellowship. This paper represents HIMB and SOEST contribution numbers 1932 and 11679, respectively. The technical support and advanced computing resources from University of Hawaii Information Technology Services—Cyberinfrastructure, funded in part by the National Science Foundation CC* awards # 2201428 and # 2232862 are gratefully acknowledged. Every photo–identification image was collected under permits according to relevant national guidelines, regulation and legislation.Peer reviewedPublisher PD

Drivers of population structure of the bottlenose dolphin (Tursiops truncatus) in the Eastern Mediterranean Sea

The drivers of population differentiation in oceanic high dispersal organisms, have been crucial for research in evolutionary biology. Adaptation to different environments is commonly invoked as a driver of differentiation in the oceans, in alternative to geographic isolation. In this study, we investigate the population structure and phylogeography of the bottlenose dolphin (Tursiops truncatus) in the Mediterranean Sea, using microsatellite loci and the entire mtDNA control region. By further comparing the Mediterranean populations with the well described Atlantic populations, we addressed the following hypotheses: (1) bottlenose dolphins show population structure within the environmentally complex Eastern Mediterranean Sea; (2) population structure was gained locally or otherwise results from chance distribution of preexisting genetic structure; (3) strong demographic variations within the Mediterranean basin have affected genetic variation sufficiently to bias detected patterns of population structure. Our results suggest that bottlenose dolphin exhibits population structures that correspond well to the main Mediterranean oceanographic basins. Furthermore, we found evidence for fine scale population division within the Adriatic and the Levantine seas. We further describe for the first time, a distinction between populations inhabiting pelagic and coastal regions within the Mediterranean. Phylogeographic analysis suggests that current genetic structure, results mostly from stochastic distribution of Atlantic genetic variation, during a recent postglacial expansion. Comparison with Atlantic mtDNA haplotypes, further suggest the existence of a metapopulation across North Atlantic/Mediterranean, with pelagic regions acting as source for coastal environments

Population ecology, behaviour and conservation status of common bottlenose dolphins (Tursiops truncatus) in the Gulf of Trieste and adjacent waters of the northern Adriatic Sea

This thesis aims to explore a combination of distinct but interconnected aspects of dolphin population ecology, behaviour and interactions with human activities in the Gulf of Trieste and adjacent waters of the northern Adriatic Sea. Boat surveys, photo-identification techniques and biopsy sampling between 2003 and 2018 were used to investigate social structure, interactions with local fisheries, isotopic niche variation and levels of organochlorine contaminants, and estimate dolphin abundance. The population was found to be structured into distinct social clusters, two of which displayed marked differences in fisheries-related behaviour and temporal partitioning previously unknown for this species or marine mammals generally. Stable isotope analysis showed isotopic niche differences among social groups. Levels of polychlorinated biphenyls (PCBs) were high, with evidence of maternal offloading of these pollutants to offspring, but no differences among social groups. Abundance estimates suggest that the total abundance of bottlenose dolphins in the study area during 2013–2018 ranged between 161 (95% CI = 153–170) and 245 (95% CI = 219–273). Finally, a novel method for individually identifying dolphins by facial features is described, which can complement existing photo-identification techniques. Together, these results provide a reasonably holistic picture of the dolphin population inhabiting the Gulf of Trieste and provide insights into social, ecological and anthropogenic drivers of its population dynamics. This study extends the available knowledge on Adriatic dolphins and provides a baseline for further studies