Tursiops Research Articles

Supplemental Material for Hearing “Number”?: Relative Quantity Judgments Through the Echolocation by Bottlenose Dolphins (Tursiops truncatus)

Supplemental Material for Hearing “Number”?: Relative Quantity Judgments Through the Echolocation by Bottlenose Dolphins (Tursiops truncatus)

Stable isotope ratios indicate trophic niche overlap in three sympatric delphinid species in the Eastern Ionian Sea

AbstractStudying the sympatric ecology of closely related marine top predator species is of interest both from an ecological and conservation standpoint, because it provides insights into ecosystem functioning, how such species avoid competitive exclusion, and how human stressors may impact these patterns. In this study, we examine the isotopic niche of three sympatric dolphin species that inhabit the eastern Ionian Sea: the common dolphin (Delphinus delphis), the striped dolphin (Stenella coeruleoalba), and the common bottlenose dolphin (Tursiops truncatus). We used carbon, nitrogen, and sulfur isotope ratios to construct three‐dimensional isotope niches and calculate niche sizes and their overlaps among the three species to study interspecific competition for resources. Common dolphin niche overlapped with that of the striped dolphin by 77%, suggesting potential resource competition between these two species. The niche overlap between striped/common dolphins and bottlenose dolphins was much lower (47%). Large differences in isotopic ratios were found between the bottlenose dolphins of the Ionian Sea and those of a largely isolated population in the adjacent semienclosed Gulf of Ambracia, further corroborating the previously documented isolation between the two populations.

Herpesvirus surveillance in stranded striped dolphins (Stenella coeruleoalba) and bottlenose dolphins (Tursiops truncatus) from Italy with emphasis on neuropathological characterization.

Herpesvirus (HV) is widely distributed among cetacean populations, with the highest prevalence reported in the Mediterranean Sea. In this study, a comprehensive analysis was conducted, including epidemiological, phylogenetic, and pathological aspects, with particular emphasis on neuropathology, to better understand the impact of HV in these animals. Our results show a higher presence of HV in males compared to females, with males exhibiting a greater number of positive tissues. Additionally, adults were more frequently affected by HV infection than juveniles, with no infections detected in calves or neonates. The affected species were striped (Stenella coeruleoalba) and bottlenose dolphins (Tursiops truncatus). The highest positivity rates were observed in the genital system, cerebrum, and skin tissues. Phylogenetic analysis indicated a higher occurrence of Gammaherpesvirus (GHV) sequences but increased genetic diversity within Alphaherpesvirus (AHV). Key neuropathological features included astro-microgliosis (n = 4) and meningitis with minimal to mild perivascular cuffing (n = 2). The presence of concurrent infections with other pathogens, particularly cetacean morbillivirus (CeMV), underscores the complex nature of infectious diseases in cetaceans. However, the presence of lesions at the Central Nervous System (CNS) with molecular positivity for GHV, excluding the involvement of other potential neurotropic agents, would confirm the potential of this HV subfamily to induce neurological damage. Pathological examination identified lesions in other organs that could potentially be associated with HV, characterized by lymphoid depletion and tissue inflammation. These findings enhance our understanding of HV in odontocetes and highlight the need for ongoing research into the factors driving these infections and their broader implications.

Demographic History and Adaptive Evolution of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in Western Australia.

Demographic processes can substantially affect a species' response to changing ecological conditions, necessitating the combined consideration of genetic responses to environmental variables and neutral genetic variation. Using a seascape genomics approach combined with population demographic modelling, we explored the interplay of demographic and environmental factors that shaped the current population structure in Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the Western Australian coastline. We combined large-scale environmental data gathered via remote sensing with RADseq genomic data from 133 individuals at 19 sampling sites. Using population genetic and outlier detection analyses, we identified three distinct genetic clusters, coinciding with tropical, subtropical and temperate provincial bioregions. In contrast to previous studies, our demographic models indicated that populations occupying the paleo-shoreline split into two demographically independent lineages before the last glacial maximum (LGM). A subsequent split after the LGM 12-15 kya gave rise to the Shark Bay population, thereby creating the three currently observed clusters. Although multi-locus heterozygosity declined from north to south, dolphins from the southernmost cluster inhabiting temperate waters had higher heterozygosity in potentially adaptive loci compared to dolphins from subtropical and tropical waters. These findings suggest ongoing adaptation to cold-temperate waters in the southernmost cluster, possibly linked to distinct selective pressures between the different bioregions. Our study demonstrated that in the marine realm, without apparent physical boundaries, only a combined approach can fully elucidate the intricate environmental and genetic interactions shaping the evolutionary trajectory of marine mammals.

Polyomavirus surveillance in cetaceans of Brazil: first detection of polyomavirus in Guiana dolphins (Sotalia guianensis)

Polyomaviruses (PyVs) are small double-stranded DNA viruses able to infect species across all vertebrate taxa. In cetaceans, PyVs have been reported only in short-beaked common dolphin (Delphinus delphis), common bottlenose dolphin (Tursiops truncatus) and killer whale (Orcinus orca). Herein, we surveyed PyV in 119 cetaceans (29 mysticetes and 90 odontocetes) stranded along the Brazilian coast, from 2002 to 2022, comprising 18 species. DNA extracted from the lungs was tested using a nested PCR targeting the major capsid protein gene of PyV. Polyomavirus was detected in lung samples of 1.7% (2/119) cetaceans: two juvenile female Guiana dolphins (Sotalia guianensis) stranded in Rio de Janeiro (Rio de Janeiro state) and Guriri (Espírito Santo state), in 2018. Both retrieved sequences were identical and presented 93.3% amino acid identity with Zetapolyomavirus delphini, suggesting a novel species. On histopathology, one of the PyV-positive individuals presented basophilic intranuclear inclusion bodies morphologically consistent with polyomavirus in the lungs. Other available tissues from both cases were PyV-PCR-negative; however, both individuals tested positive for Guiana dolphin morbillivirus. To our knowledge, this is the first report of PyV infection in cetaceans of the Southern Hemisphere and the first description of a co-infection with morbillivirus.

Influence of Dolphin-Watching Tourism Vessels on the Whistle Emission Pattern of Common Dolphins and Bottlenose Dolphins

Recent years have seen a notable rise in dolphin-watching boat activities along the Algarve coast in Portugal, potentially affecting the common dolphin (Delphinus delphis) and bottlenose dolphin (Tursiops truncatus) local populations. This study examines the impact of increasing underwater noise levels from these boats on dolphin vocalizations. Field recordings were conducted from June to September 2022, analyzing dolphin whistles in various boat presence scenarios. The results indicate significant changes in whistle-frequency characteristics with boat presence, including increased start, low, and high frequencies, alongside a decrease in the number of inflection points in modulated whistles. The changes might negatively impact dolphin populations viability, underscoring the need for further research. Additionally, improved mitigation strategies may be necessary to reduce the potential negative effects of dolphin watching on cetacean communication and behavior in the Algarve region.

Environmental DNA as a complementary tool for biodiversity monitoring: A multi-technique and multi-trophic approach to investigate cetacean distribution and feeding ecology.

The use of environmental DNA (eDNA) to assess the presence of biological communities has emerged as a promising monitoring tool in the marine conservation landscape. Moreover, advances in Next-Generation Sequencing techniques, such as DNA metabarcoding, enable multi-species detection in mixed samples, allowing the study of complex ecosystems such as oceanic ones. We aimed at using these molecular-based techniques to characterize cetacean communities, as well as potential prey on the northern coast of Mainland Portugal. During four seasonal campaigns (summer 2021 to winter 2022/2023), seawater samples were collected along with visual records of cetacean occurrence. The eDNA isolated from 64 environmental samples was sequenced in an Illumina platform, with universal primers targeting marine vertebrates. Five cetacean species were identified by molecular detection: common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus), Risso's dolphin (Grampus griseus), harbor porpoise (Phocoena phocoena) and fin whale (Balaenoptera physalus). Overall, except for the latter (not sighted during the campaigns), this cetacean community composition was similar to that obtained through visual monitoring, and the complementary results suggest their presence in the region all year round. In addition, the positive molecular detections of Balaenoptera physalus are of special relevance since there are no records of this species reported on scientific bibliography in the area. The detection of multiple known prey of the identified dolphins indicates an overlap between predator and prey in the study area, which suggests that these animals may use this coastal area for feeding purposes. While this methodological approach remains in a development stage, the present work highlights the benefits of using eDNA to study marine communities, with specific applications for research on cetacean distribution and feeding ecology.

First evidence of microplastic inhalation among free-ranging small cetaceans.

Plastic is a ubiquitous environmental contaminant, resulting in widespread exposure across terrestrial and marine spaces. In the environment, plastics can degrade into microparticles where exposure has been documented in a variety of fauna at all trophic levels. Human epidemiological studies have found relationships between inhaled microplastics and oxidative stress and inflammation. Previous studies of bottlenose dolphins (Tursiops truncatus) have reported prevalent exposure to plasticizing chemicals (e.g., phthalates) as well as particle loads in gastrointestinal tracts, but exposure from inhalation has not yet been studied. The objective of this study was to determine if inhalation is a viable route of microplastic exposure for free-ranging dolphins. Exhalation samples were opportunistically collected from dolphins residing in Sarasota Bay, Florida (n = 5) and Barataria Bay, Louisiana (n = 6) during catch-and-release health assessments to screen for microplastic particles. All dolphin samples contained at least one suspected microplastic particle, and polymer composition was determined for 100% of a subset (n = 17) of samples. Additional studies are warranted to better understand the extent of inhaled microplastics, as well as to explore impacts, given potential risks to lung function and health.

Establishment of the first dermal fibroblast cell line derived from the Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) and its response to pollutant exposure

The Indo-Pacific bottlenose dolphin (Tursiops aduncus), classified as a new species since 1998, is underexplored in ecotoxicology owing to ethical constraints and the lack of specific in vitro models. Herein, we established the first skin fibroblast cell line (TaSF) from an Indo-Pacific bottlenose dolphin stranded along the Pearl River Estuary, China. TaSF cells exhibited strong proliferation in early passages but ceased mitosis at passage 19, likely owing to reaching the Hayflick limit. Morphology and immunofluorescence tests confirmed the fibroblastic nature of these cells. Karyotyping revealed 21 pairs of autosomes and 1 pair of sex chromosomes (XY), consistent with many cetaceans. To facilitate long-term future studies, TaSF cells were immortalized with exogenous simian virus 40 T antigen, creating the TaSFT cell line. The cytotoxic effects of 27 contaminants, including 6 organotins (OTs), 10 per- and polyfluoroalkyl substances (PFASs), and 11 phthalates (PAEs), on TaSFT cells were evaluated after 24-h exposure. Among these chemicals, OTs exhibited the strongest cytotoxicity, and both OTs and PFASs showed structure-related toxicity. These findings confirm the feasibility of TaSFT cells as a novel tool for ecotoxicity research on the Indo-Pacific bottlenose dolphin and highlight the need for further investigation into the environmental contaminant pressures on this species.

Determination of PCB and PAH tissue levels in bottlenose dolphins that stranded in the Mississippi sound before and after the unusual mortality event in 2019

Cetaceans are regarded as a sentinel species because their health and population changes can serve as indicators of effects on marine ecosystems. We characterized levels of 24 polycyclic aromatic hydrocarbons (PAHs) and 7 polychlorinated biphenyls (PCBs) in blubber, kidney, liver, and muscle of 138 bottlenose dolphins (Tursiops truncatus) that stranded in the Mississippi Sound (MSS) between 2010 and 2021. The samples were divided into four time periods: 2010–2018, 2019, 2020, and 2021, to assess whether there was a significant association between chemical levels in dolphin tissues and the 2019 unusual mortality event (UME) in the MSS resulting from the unprecedented freshwater incursion from 2 openings of the Bonnet Carré Spillway (BCS). We found 7 PCBs were readily detected in all tissues across time, and the major PAH was naphthalene, with detection of biphenyl and acenaphthene at lower levels and frequency. There was little change in tissue PCB levels over time; only naphthalene in the blubber was higher in tissues from dolphins that stranded before 2019. However, there were not significant changes in chemical levels in tissues from stranded bottlenose dolphins in the MSS before or after the UME in 2019.

Seasonal and diel patterns in Black Sea harbour porpoise acoustic activity in 2020-2022.

The Black Sea is a semi-enclosed inland sea with an unevenly distributed extensive coastal shelf area and anoxic deep waters. It is inhabited by common and bottlenose dolphins, as well as harbour porpoises, all represented by local subspecies. Between September 2020 and October 2022, 19 F-PODs deployed by research teams from Bulgaria, Georgia, Romania, Türkiye and Ukraine collected data on acoustic activity of Black Sea harbour porpoises. Strong seasonal and diel patterns were found, which varied in three regions. In the south-eastern part of the Black Sea, harbour porpoise acoustic activity was higher from January to May, with a peak in April. This pattern agrees with the seasonal anchovy migration from the winter spawning grounds in warmer waters in the south-eastern region to feeding grounds on the productive shallow north-west shelf. The diel pattern showed strong nocturnal acoustic activity, which is consistent with anchovy vertical migration. Porpoises on the western side of the Black Sea exhibited a bimodal seasonal pattern in acoustic activity, with a larger peak in April and a smaller one in October. Diel activity was primarily nocturnal. On the north-west shelf, harbour porpoise acoustic activity was mostly recorded during the warm period from April to October. The diel pattern showed activity mainly during daylight with two peaks: a smaller one approximately at dawn and a larger one at dusk. This pattern is similar to the vertical migrations of sprat. Overall, the results of the study were consistent with the prey being an important driver of seasonal and diel dynamics of harbour porpoise acoustic activity.

Smiling underwater: Exploring playful signals and rapid mimicry in bottlenose dolphins

Smiling underwater: Exploring playful signals and rapid mimicry in bottlenose dolphins

Ecological interactions and unique resource partitioning between dolphins in the ultraoligotrophic eastern Mediterranean Sea

This study delves into the eco-dynamics of three dolphin species in the ultra-oligotrophic waters off the southern Israeli Mediterranean coast - two neritic: the common bottlenose dolphin (Tursiops truncatus) and the common dolphin (Delphinus delphis) and one pelagic: the striped dolphin (Stenella coeruleoalba). It utilizes compound-specific stable isotope analysis of individual amino acids to investigate carbon and nitrogen source variability and trophic positioning among the three species. Muscle samples from stranded individuals were analyzed for carbon (δ13C) and nitrogen (δ15N) isotopic ratios of amino acids, with Δδ15N (Glutamate-Phenylalanine) acting as an indicator of relative trophic position. The findings reveal minor differences in carbon source signatures and trophic position among species, but distinct nitrogen source signatures. The latter indicate discrete foraging habitats for bottlenose and striped dolphins and suggest that common dolphins transition between shallow benthic and deep pelagic feeding areas during the day and night, respectively, as part of their survival strategy.

Similarity learning networks uniquely identify individuals of four marine and terrestrial species

AbstractEstimating the size of animal populations plays an important role in evidence‐based conservation and management. Some methods for estimating population size rely on animals being individually identifiable. Traditionally, this has been done by marking physically captured animals, but increasingly, animals with distinctive natural markings are surveyed noninvasively using cameras. Animal reidentification from photographs is usually done manually, which is expensive, laborious, and requires considerable skill. An alternative is to develop computer vision methods that can support or replace the manual identification task. We developed an automated approach using deep learning to identify whether a pair of photographs is of the same individual or not. The core of the approach is a similarity learning network that uses paired convolutional neural networks with a triplet loss function to summarize image pairs and decide whether they are from the same individual. Prior to the main matching step, two additional convolutional neural networks perform image segmentation, cropping the animal object within the image, and orientation prediction, deciding which side of the animal was photographed. We applied the approach to four species, with images of the same individual often spanning several years: systematic surveys of bottlenose dolphins (Tursiops truncatus, 2008–2019) and harbor seals (Phoca vitulina, 2015–2019), a citizen science dataset of western leopard toads (Sclerophrys pantherina, unknown dates), and a publicly available repository of humpback whale images (Megaptera novaeangliae, unknown dates). For these species, our best‐performing models were able to identify whether a pair of images were from the same individual or different individuals in 95.8%, 94.6%, 88.2%, and 83.8% of the cases, respectively. We found that triplet loss functions outperformed binary cross‐entropy loss functions and that data augmentation and additional manual curation of training data provided small but consistent improvements in performance. These results demonstrate the potential of deep learning to replace or, more likely, support and facilitate manual individual identification efforts.

Communication range predicts dolphin alliance size in a cooperative mating system

It is well known that communication range, often termed active space,1 varies with habitat structure, and this variation can influence individual vocal behavior across taxa.2,3 While theoretical predictions imply that communication distances can drive the evolution of mammalian alliance sizes,4 empirical tests of this hypothesis are currently lacking. In Shark Bay, Western Australia, unrelated male bottlenose dolphins form multilevel alliances, where males work together in pairs or trios to herd single estrus females.5,6,7,8 Here, we use empirical measures of male dolphin vocalizations, ambient noise levels, and high-resolution bathymetry data to estimate variation in active space across the study site. We combine this with long-term data on male alliance behavior to determine how active space influences alliance group size and mating success. We show that the active space of vocalizations used by allied males in a reproductive context predicts the number of preferred alliance partners with whom individuals cooperate over the longer term, ultimately contributing significantly to male access to mating opportunities. These results reveal that variation in sensory ecology driven by heterogeneous habitat influences optimal cooperative group size and mating success within a single population of wild animals.

Trophic guilds and niche segregation among marine megafauna in the Bay of Biscay

The structure and functioning of ecosystems are largely determined by the interactions between species within a biological community. Among these interactions, species exhibiting similar vertical and spatial prey preferences can be identified, thereby belonging to the same trophic guild. Our study explored some trophic characteristics of a diverse megafaunal community (cetaceans, tunas, seabirds) in the Bay of Biscay (BoB). Using stable isotope analysis (SIA), we explored the dietary habits and niche overlap among predators. The degree of isotopic niche overlap was generally low, but with certain species exhibiting large and narrow isotopic niche areas (long-finned pilot whales and Balearic shearwaters, respectively). Our results revealed a diversity of dietary preferences leading to the identification of three distinct trophic guilds based on prey functional groups and spatial preferences: cephalopod feeders (e.g. long-finned pilot whales, Cuvier's beaked whales, striped dolphins), crustacean feeders (e.g. fin whales, albacores), and piscivores (e.g. common dolphins, harbour porpoises, bottlenose dolphins, Atlantic bluefin tunas, Balearic shearwaters). Our findings showed resource partitioning and niche differentiation among the megafaunal community, highlighting the complexity of BoB's marine ecosystem. The insights derived from this study hold important implications for ecosystem management and the implementation of conservation initiatives.

Abundance, Distribution, and Habitat Suitability Prediction of the Guiana Dolphin and Common Bottlenose Dolphin in the Gulf of Urabá, Colombian Caribbean

Abundance, Distribution, and Habitat Suitability Prediction of the Guiana Dolphin and Common Bottlenose Dolphin in the Gulf of Urabá, Colombian Caribbean

Fishers' perception and activity shifts in a dolphin bycatch mitigation context

Fishing exclusion zones aim to reduce cetacean bycatch, but often neglect social and ecological side effects, exacerbating social injustices and reshaping fishing practices. We present a case study of an endangered population of Lahille's bottlenose dolphins (Tursiops truncatus gephyreus) in a Brazilian coastal lagoon, known for its unique cooperation with net-casting fishers. However, the local small-scale fisheries (SSF) also employ other fishing gears that contribute to dolphin bycatch, prompting the enforcement of a fishing ban in the area. We investigated fishers' socioeconomic conditions, evidence of social disparities, perceptions on dolphin bycatch, and projected changes on fisheries activities to understand the repercussions of the ban. We categorized 128 surveyed fishers into five groups based on socioeconomic factors and their reliance on dolphin-cooperative and gillnet fisheries. Our findings revealed significant disparities in social capital among fishers and their different attitudes towards dolphin bycatch, highlighting unforeseen consequences. To investigate how fishers would likely shift fishing practices, we considered two management scenarios: 1) should dolphin-fishing cease due to unsuccessful bycatch mitigation, fishing efforts would shift towards shrimp trawling, seine nets, and gillnet effort; 2) if gillnet-fishing is successfully banned as a bycatch mitigation measure, a shift to shrimp trawling and cast net effort. Both scenarios would intensify pressure on shrimp stocks, which are already heavily exploited in this socioecological system. Our research underscores the importance of contemplating alternatives to achieve sustainable outcomes when designing bycatch mitigation measure. Furthermore, our results point to the importance of a participatory governance approach, grounded in the socioeconomic context, to safeguard the livelihoods of small-scale fishers and foster broader conservation efforts beyond species-specific concerns.

Molecular investigation of endoparasites of marine mammals (Cetacea: Mysticeti, Odontoceti) in the Western Mediterranean.

Whales, dolphins, and porpoises are susceptible to infections by protozoan and metazoan parasites. In this study, tissue samples, as well as flatworms and roundworms, were collected from a common bottlenose dolphin (Tursiops truncatus), three short-beaked common dolphins (Delphinus delphis), two striped dolphins (Stenella coeruleoalba), a harbor porpoise (Phocoena phocoena), a long-finned pilot whale (Globicephala melas), and a fin whale (Balaenoptera physalus). These samples were molecularly analyzed. In one D. delphis, Toxoplasma gondii was detected in multiple organs, including the cerebellum. The cysts of the tapeworms Clistobothrium delphini and Clistobothrium grimaldii were identified in G. melas. Flukes collected from D. delphis belong to Brachycladium atlanticum, while those removed from S. coeruleoalba probably represent a new species. Four species of lungworms were also identified: Halocercus delphini in S. coeruleoalba, Halocercus sp. in T. truncatus, Stenurus globicephalae in G. melas, and a potentially new Pharurus sp. in P. phocoena. These findings show, to the best of our knowledge, for the first time, the presence of T. gondii DNA in D. delphis. The cerebellum of the animal was Toxoplasma-infected, which might be relevant to inadvertent stranding. In this study, new genetic markers were sequenced for several helminth parasites of marine mammals, possibly including undescribed species.

Cardiopulmonary adaptations of a diving marine mammal, the bottlenose dolphin: Physiology during anesthesia.

Diving marine mammals are a diverse group of semi- to completely aquatic species. Some species are targets of conservation and rehabilitation efforts; other populations are permanently housed under human care and may contribute to clinical and biomedical investigations. Veterinary medical care for species under human care, at times, may necessitate the use of general anesthesia for diagnostic and surgical indications. However, the unique physiologic and anatomic adaptations of one representative diving marine mammal, the bottlenose dolphin, present several challenges in providing ventilatory and cardiovascular support to maintain adequate organ perfusion under general anesthesia. The goal of this review is to highlight the unique cardiopulmonary adaptations of the completely aquatic bottlenose dolphin (Tursiops truncatus), and to identify knowledge gaps in our understanding of how those adaptations influence their physiology and pose potential challenges for sedation and anesthesia of these mammals.