Detection of Leptospira kirschneri in a short-beaked common dolphin (Delphinus delphis delphis) stranded off the coast of southern California, USA.

BACKGROUND: Pathogenic Leptospira species are globally important zoonotic pathogens capable of infecting a wide range of host species. In marine mammals, reports of Leptospira have predominantly been in pinnipeds, with isolated reports of infections in cetaceans. CASE PRESENTATION: On 28 June 2021, a 150.5 cm long female, short-beaked common dolphin (Delphinus delphis delphis) stranded alive on the coast of southern California and subsequently died. Gross necropsy revealed multifocal cortical pallor within the reniculi of the kidney, and lymphoplasmacytic tubulointerstitial nephritis was observed histologically. Immunohistochemistry confirmed Leptospira infection, and PCR followed by lfb1 gene amplicon sequencing suggested that the infecting organism was L.kirschneri. Leptospira DNA capture and enrichment allowed for whole-genome sequencing to be conducted. Phylogenetic analyses confirmed the causative agent was a previously undescribed, divergent lineage of L.kirschneri. CONCLUSIONS: We report the first detection of pathogenic Leptospira in a short-beaked common dolphin, and the first detection in any cetacean in the northeastern Pacific Ocean. Renal lesions were consistent with leptospirosis in other host species, including marine mammals, and were the most significant lesions detected overall, suggesting leptospirosis as the likely cause of death. We identified the cause of the infection as L.kirschneri, a species detected only once before in a marine mammal - a northern elephant seal (Mirounga angustirostris) of the northeastern Pacific. These findings raise questions about the mechanism of transmission, given the obligate marine lifestyle of cetaceans (in contrast to pinnipeds, which spend time on land) and the commonly accepted view that Leptospira are quickly killed by salt water. They also raise important questions regarding the source of infection, and whether it arose from transmission among marine mammals or from terrestrial-to-marine spillover. Moving forward, surveillance and sampling must be expanded to better understand the extent to which Leptospira infections occur in the marine ecosystem and possible epidemiological linkages between and among marine and terrestrial host species. Generating Leptospira genomes from different host species will yield crucial information about possible transmission links, and our study highlights the power of new techniques such as DNA enrichment to illuminate the complex ecology of this important zoonotic pathogen.

Characterising injuries and pathologies of common dolphin Delphinus delphis mortalities in the South Australian Sardine Fishery.

Mortality of dolphins in fishing operations is often under-estimated, as shown by studies of beach-washed carcasses. Linking evidence obtained during necropsies with fishing method is fundamental to understanding the extent of mortality and the manner in which animals die. The South Australian Sardine Fishery (SASF) has operated a purse-seine industry since 1991. This study characterised injuries, pathological changes and life history of 49 dead dolphins collected from SASF during 2006-2019. Histology examination was conducted on 25 animals. Neonates, calves and juveniles accounted for 63% of the sample. Of mature females (n = 14), 11 were pregnant or lactating, with cryptic mortality estimated to be 20% of dolphins studied. Body condition was robust in 48 dolphins. Net marks were seen on 82%, mostly on the head, trunk and peduncle. Broken/missing teeth were noted in 63%. All dolphins had subdermal haemorrhage (moderate to severe in 96%), particularly around the head. Deep haemorrhage was common, including around occipital and flipper condyles, and organs. Copious fluid was present in the thoracic (pleural) and abdominal (ascites) cavities of half of the dolphins. Within the lungs, watery fluid and froth were observed in 100 and 39%, respectively. Recent bone fractures were documented in 43% of dolphins, mostly associated with haemorrhage. Severe blunt trauma appeared to be the primary cause of death, and 10 dolphins also had other significant pathologies. Visceral organ congestion and mild cardiomyopathy were observed. Stomachs contained prey remains in 75% of cases. The results of this study may help identify unreported purse-seine mortalities washed up in South Australia and elsewhere.

Renal and vaginal calculi in a free-ranging long-beaked common dolphin Delphinus capensis.

Bilateral nephrolithiasis with a concurrent vaginal calculus was identified in a stranded free-ranging long-beaked common dolphin Delphinus capensis. Necropsy and radiologic examinations of the sexually mature D. capensis revealed multiple small irregularly round nephroliths and a 6.4 × 4.1 × 9.2 cm vaginal calculus weighing 182 g. Nephroliths numbered 68 and 71 in the left and right kidneys, respectively, and ranged from 1.7 to 6.9 mm in diameter. Nephroliths were composed of 100% ammonium urate, which has been found in captive dolphin populations. However, the vaginolith consisted of struvite and calcium carbonate suggesting an alternate etiology. The composition of the vaginolith suggests that bacterial vaginitis could have served as the predisposing condition. Renal lesions included chronic tubulointerstitial nephritis with tubular degeneration and loss, likely secondary to the nephroliths. The pathogenesis of ammonium urate nephrolithiasis in managed care is suspected to be linked to diet and age but in this case may be due to metabolic disruption. However, if environmental changes cause a shift in prey species, the risk of nephrolithiasis in free-ranging cetaceans could increase. Careful surveillance for nephroliths in free-ranging populations should be considered by researchers.

Qualitative and Quantitative Analysis of Primary Neocortical Areas in Selected Mammals.

The present study focuses on the relationship between neocortical structures and functional aspects in three selected mammalian species. Our aim was to compare cortical layering and neuron density in the projection areas (somatomotor, M1; somatosensory, S1; auditory, A1; and visual, V1; each in a wider sense). Morphological and design-based stereological analysis was performed in the wild boar (Sus scrofa scrofa) as a representative terrestrial hoofed animal (artiodactyl) and the common dolphin (Delphinus delphis) as a highly derived related aquatic mammal (cetartiodactyl). For comparison, we included the human (Homo sapiens) as a well-documented anthropoid primate. In the cortex of many mammals, layer IV (inner granular layer) is the main target of specific thalamocortical inputs while layers III and V are the main origins of neocortical projections. Because the fourth layer is indistinct or mostly lacking in the primary neocortex of the wild boar and dolphins, respectively, we analyzed the adjacent layers III and V in these animals. In the human, all the three layers were investigated separately. The stereological data show comparatively low neuron densities in all areas of the wild boar and high cell counts in the human (as expected), particularly in the primary visual cortex. The common dolphin, in general, holds an intermediate position in terms of neuron density but exhibits higher values than the human in a few layers. With respect to the situation in the wild boar, stereological neuron counts in the dolphin are consistently higher, with a maximum in layer III of the visual cortex. The extended auditory neocortical field in dolphins and the hypertrophic auditory pathway indicate secondary neurobiological adaptations to their aquatic habitat during evolution. The wild boar, however, an omnivorous quadruped terrestrial mammal, shows striking specializations as to the sensorimotor neurobiology of the snout region.

Directional Hearing and Head-Related Transfer Function in Odontocete Cetaceans.

The head-related transfer function (HRTF) is an important descriptor of spatial sound field reception by the listener. In this study, we computed the HRTF of the common dolphin Delphinus delphis. The received sound pressure level at various locations within the acoustic fats of the internal pinna near the surface of the tympanoperiotic complex (TPC) was calculated for planar incident waves directed toward the animal. The relative amplitude of the received pressure versus the incident pressure was the representation of the HRTF from the point of view of the animal. It is of interest that (1) different locations on the surface of the TPC resulted in different HRTFs, (2) the HRTFs for the left and right ears were slightly asymmetric, and (3) the locations of the peaks of the HRTF depended on the frequency of the incident wave.

Natural and anthropogenic organic brominated compounds in the southwestern Atlantic ocean: Bioaccumulation in coastal and oceanic dolphin species.

Marine pollution is considered a current driver of change in the oceans and despite the urgency to develop more studies, there is limited information in the southern hemisphere. This study aimed to analyze the levels and profiles of natural (MeO-PBDEs) and anthropogenic (BFRs: PBDEs, HBB, PBEB) organic brominated compounds in adipose tissue of two species of dolphins with different distribution and trophic requirements from the Southwestern Atlantic Ocean; the short-beaked common dolphin (Delphinus delphis) and the Fraser's dolphin (Lagenodelphis hosei). In addition, we aim to investigate maternal transfer and biological pattern relationship (sex, age, sexual maturity) in short-beaked common dolphin bioaccumulation. The levels of both groups of contaminants were in the same order of magnitude as those reported for other marine mammals on both a regional and global scale. BFRs profiles were dominated by BDE 28 and BDE 47 in short-beaked common dolphin and Fraser's dolphin, respectively, whereas 2-MeO-BDE 68 was the most abundant natural compound in both species. Evidence of maternal transfer, temporary increase in BDE 154 levels and no influence of sex, age, or sexual maturity on brominated compound concentration was observed in short-beaked common dolphin. This study fills a gap in the knowledge of the Southwestern Atlantic Ocean providing new information on emerging organic pollutants bioavailability for dolphins and, therefore, for the different trophic webs. In addition, it serves as a baseline for further contamination assessments.

Emaciated enigma: Decline in body conditions of common dolphins in the Celtic Seas ecoregion.

Monitoring the nutritional health of cetaceans has become increasingly important in a changing environment, where multiple stressors impact animals. Particularly for those species that require consumption of energy-dense prey, such as the common dolphin. Thus far, no uniform measure for monitoring body condition has been recommended across cetaceans, and species-specific measures may need to be developed if employed as a population condition indicator under Descriptor 1 of the Marine Strategy Framework Directive. Here, nine morphometric body condition indices were applied to long-term common dolphin stranding data sets originating from Ireland and the UK. We report a recent decline in the nutritional health of common dolphins in the Celtic Seas ecoregion comparing animals from 2017 to 2019 to animals from 1990 to 2006, with an increase in cases of animals dying due to starvation. Using ordinal regression trees, ventral blubber thickness (VBT) was identified as the most important index to predict nutritional status, defined at necropsy, followed by the scaled mass index (SMI). Using generalised linear models, both the VBT and SMI indices differentiated individuals that died from chronic and acute causes of death (i.e., bycatch), where animals in chronic conditions had significantly thinner VBT and lower SMI. Both significant temporal and seasonal patterns in VBT were identified, with poorer body conditions observed during the autumn and better body conditions observed during the spring, as well as an overall decline detected in VBT during the study period. While VBT was positively correlated with total body length, SMI showed the opposite trend. The VBT index is recommended for monitoring nutritional health within the species when total body length and season are considered. Further research is needed to understand the underlying causes for the observed decline, including shifts in prey availability and/or quality, to inform targeted conservation management strategies.

Sounds in common: Time-frequency as the classification parameters for pulsed sounds produced by Delphinus delphis.

Sounds produced by dolphins can be grouped into tonal (whistles) and pulsed sounds (e.g., echolocation clicks and burst sounds). Clicks are broadband pulses temporarily spaced to allow echo processing between the sound source and the object. Echolocation is related mainly to prey detection and environmental recognition. Echolocation click trains tend to present a decreasing inter-click interval due to a continuous changing of the target's location when the animal approaches to capture the prey. In addition to foraging and feeding contexts, burst pulsed sounds have been associated with short social communication. Although echolocation clicks are relatively well documented, there is no consensus regarding the broad variety of the burst pulsed signals. The present study analyzed time-frequency characteristics by conducting a clustering and discrimination analysis to classify pulsed sounds. A total of 64 click trains were analyzed from short-beaked common dolphins recorded in the slope region of the western South Atlantic Ocean. Three analyses (time; frequency; and combined time-frequency parameters) were compared through k-means clustering and posterior cluster validation using Random forest analysis. The k-means clustering resulted in four clusters for all groups of analysis. The time parameters were the most accurate among the comparisons, with the first two-dimensional axis corresponding to 87 % (Dim1 = 70.2 % and Dim2 = 17.2 %). The random forest analysis showed that the time-frequency dataset was the best classification of pulsed sounds in D. delphis (Accuracy = 84.6 %; confidence interval CI = 65.1 %-95.6 %; p < 0.01). This result considers the animal an acoustical identity, emphasizing the importance of certain parameters that influence this identity and thus reflecting the energy-cost optimization for sound production.

Hypertrophic osteopathy in a common dolphin (Delphinus delphis) with concurrent pulmonary Halocercus delphini infestation.

Dolphins are marine mammals that often live in coastal habitats. Common causes of severe skeletal disorders among wild dolphins are congenital vertebral anomalities, collisions with sea vessels, trauma, hunting-related injury, infectious diseases, environmental pollution, and tumors. A free-ranging male, 3-year-old common dolphin (Delphinus delphis) was found dead in the coast of Asturias in northern Spain. Postmortem examination revealed lordosis in the caudal vertebral column, while X-ray imaging and computer tomography showed well-organized palisade-like periosteal proliferation, appearing as florid-like accretions, along the spinous apophysis of 26 lumbar-caudal vertebrae. The transverse apophysis was affected on only a few caudal vertebrae. The cortical layer remained intact. Histology of vertebra tissue showed periosteal proliferation of cancellous bone. The animal was diagnosed with hypertrophic osteopathy. The lungs showed diffuse parasitic granulomatous bronchointerstitial pneumonia caused by Halocercus delphini, consolidation of the pulmonary tissue, congestion, and alveolar edema. The animal was also afflicted by parasitic granulomatous gastritis caused by Anisakis simplex sensu lato and tattoo skin disease. The dolphin suffered from hypertrophic osteopathy associated with pulmonary Halocercus delphini infestation. This syndrome, known as hypertrophic pulmonary osteopathy, has been described in diverse terrestrial mammals, including domestic animals, wildlife and humans, but not in dolphins. This case reports the first description of hypertrophic osteopathy associated to a pulmonary disorder in dolphin, and it provides insights into factors that can induce column malformation in dolphins, suggesting the importance of taking thoracic lesions into account during differential diagnosis.

Integrating remote sensing methods during controlled exposure experiments to quantify group responses of dolphins to navy sonar.

Human noise can be harmful to sound-centric marine mammals. Significant research has focused on characterizing behavioral responses of protected cetacean species to navy mid-frequency active sonar (MFAS). Controlled exposure experiments (CEE) using animal-borne tags have proved valuable, but smaller dolphins are not amenable to tagging and groups of interacting individuals are more relevant behavioral units for these social species. To fill key data gaps on group responses of social delphinids that are exposed to navy MFAS in large numbers, we describe novel approaches for the coordinated collection and integrated analysis of multiple remotely-sensed datasets during CEEs. This involves real-time coordination of a sonar source, shore-based group tracking, aerial photogrammetry to measure fine-scale movements and passive acoustics to quantify vocal activity. Using an example CEE involving long-beaked common dolphins (Delphinus delphis bairdii), we demonstrate how resultant quantitative metrics can be used to estimate behavioral changes and noise exposure-response relationships.

Two cetacean species reveal different long-term trends for toxic trace elements in European Atlantic French waters.

Cetaceans have been naturally exposed to toxic trace elements (TEs) on an evolutionary time scale. Hence, they have developed mechanisms to control and/or mitigate their toxic effects. These long-lived species located at high trophic positions and bioaccumulating toxic elements are assumed to be good biomonitoring organisms. However, anthropogenic emissions have strongly increased environmental levels of toxic TEs in the last decades, questioning the efficiency of the detoxication mechanisms in cetaceans. In this context, temporal trends of mercury (Hg), cadmium (Cd) and lead (Pb) concentrations were studied through the analysis of 264 individuals from two cetacean species the common dolphin (Delphinus delphis) and the harbour porpoise (Phocoena phocoena) and belonging to two different Management Units (MUs) for the latter. These individuals stranded along the French Atlantic coasts from 2000s to 2017. All the trends presented were age- and sex-corrected and stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were measured as proxies of their feeding ecology. Results showed that Pb concentrations clearly decreased over time in both species and MUs. This decrease agrees with the lead petrol regulation after 2000s, supporting the use of these species as valuable bioindicators of changes for TE levels in the marine environment. A significant long-term increase of total Hg concentrations was only observed in common dolphins. Cadmium concentrations also revealed different trends over the period in both species. The different Hg and Cd trends observed in the two species, probably reflected a contrasted contamination of habitat and prey species than a global increase of the contamination in the environment. These results highlight the necessity and gain of using different species to monitor changes in marine environments, each of them informing on the contamination of its own ecological niche. Lastly, the Se:Hg molar ratios of species suggested a low risk for Hg toxicity over time.

Fatal Streptococcus iniae Infection in a Juvenile Free-Ranging Short-Beaked Common Dolphin (Delphinus delphis).

Streptococcus iniae (S. iniae) is a significant aquatic pathogen of farmed fish species, important zoonotic pathogen, and reported cause of disease in captive Amazon River dolphins (Inia geoffrensis) and a bottlenose dolphin (Tursiops truncatus). Here we report S. iniae as the cause of subcutaneous abscesses, sepsis and mortality in a juvenile free-ranging short-beaked common dolphin (Delphinus delphis) found deceased on a metropolitan Australian beach. Body surfaces were covered by multifocal, depressed, deep, irregular cutaneous ulcerations, which microscopically were characterised by ruptured subcutaneous abscesses with intralesional cocci. Routine microbiological investigations revealed a heavy growth of beta-haemolytic Streptococcus sp. identified as Streptococcus iniae in skin lesions as well as from heart blood, the latter supportive of sepsis. Tissues were negative for cetacean morbillivirus and no other disease processes were identified. S. iniae has not been reported in free-ranging marine mammals, nor in Australian delphinids, previously. More notably a pathogen of captive animals, this case report identifies S. iniae as a pathogen of wild dolphins also. In addition to expanding the host reservoir of a significant zoonotic pathogen, determining the source of infection as well as possible consequences for other marine mammals and wild and intensive fish stocks warrants further investigations.

Species information in whistle frequency modulation patterns of common dolphins.

The most flexible communication systems are those of open-ended vocal learners that can acquire new signals throughout their lifetimes. While acoustic signals carry information in general voice features that affect all of an individual's vocalizations, vocal learners can also introduce novel call types to their repertoires. Delphinids are known for using such learned call types in individual recognition, but their role in other contexts is less clear. We investigated the whistles of two closely related, sympatric common dolphin species, Delphinus delphis and Delphinus bairdii, to evaluate species differences in whistle contours. Acoustic recordings of single-species groups were obtained from the Southern California Bight. We used an unsupervised neural network to categorize whistles and compared the resulting whistle types between species. Of the whistle types recorded in more than one encounter, 169 were shared between species and 60 were species-specific (32 D. delphis types, 28 D. bairdii types). Delphinus delphis used 15 whistle types with an oscillatory frequency contour while only one such type was found in D. bairdii. Given the role of vocal learning in delphinid vocalizations, we argue that these differences in whistle production are probably culturally driven and could help facilitate species recognition between Delphinus species. This article is part of the theme issue 'Vocal learning in animals and humans'.

Endoscopic Study of the Oral and Pharyngeal Cavities in the Common Dolphin, Striped Dolphin, Risso's Dolphin, Harbour Porpoise and Pilot Whale: Reinforced with Other Diagnostic and Anatomic Techniques.

In this work, the fetal and newborn anatomical structures of the dolphin oropharyngeal cavities were studied. The main technique used was endoscopy, as these cavities are narrow tubular spaces and the oral cavity is difficult to photograph without moving the specimen. The endoscope was used to study the mucosal features of the oral and pharyngeal cavities. Two pharyngeal diverticula of the auditory tubes were discovered on either side of the choanae and larynx. These spaces begin close to the musculotubaric channel of the middle ear, are linked to the pterygopalatine recesses (pterygoid sinus) and they extend to the maxillopalatine fossa. Magnetic Resonance Imaging (MRI), osteological analysis, sectional anatomy, dissections, and histology were also used to better understand the function of the pharyngeal diverticula of the auditory tubes. These data were then compared with the horse's pharyngeal diverticula of the auditory tubes. The histology revealed that a vascular plexus inside these diverticula could help to expel the air from this space to the nasopharynx. In the oral cavity, teeth remain inside the alveolus and covered by gums. The marginal papillae of the tongue differ in extension depending on the fetal specimen studied. The histology reveals that the incisive papilla is vestigial and contain abundant innervation. No ducts were observed inside lateral sublingual folds in the oral cavity proper and caruncles were not seen in the prefrenular space.

Comparative Anatomy of the Nasal Cavity in the Common Dolphin Delphinus delphis L., Striped Dolphin Stenella coeruleoalba M. and Pilot Whale Globicephala melas T.: A Developmental Study.

Our goal was to analyze the main anatomical structures of the dolphin external nose and nasal cavity from fetal developmental stages to adult. Endoscopy was used to study the common development of the external nose and the melon, and nasal mucosa. Magnetic resonance imaging (MRI) and anatomical sections were correlated with anatomical sections. Computed tomography (CT) was used to generate 3D reconstructions of the nasal bones and nasal cavities to study its development. Dissections, histological and pathological studies were carried out on the nasal mucosa to understand its function. These results were compared with the horse. Endoscopy showed an external nose with two lips and the upper lip is divided by a groove due to the nasal septum and an obstruction of right nasal cavity was diagnosed in a newborn. Two diverticula (air sacs) were found in the nasal vestibule and an incisive recess (premaxillary sac) in the nasal cavity. These findings were corroborated by 3D reconstructions of the nasal cavities, MRI, anatomical sections and dissections. The presphenoid and ethmoid bones were fused at early stages of fetal development. The ethmoid is the last bone to ossify in the nasal cavity.

Citizen science in the marine environment: estimating common dolphin densities in the north-east Atlantic.

BACKGROUND: Citizen science is increasingly popular and has the potential to collect extensive datasets at lower costs than traditional surveys conducted by professional scientists. Ferries have been used to collect data on cetacean populations for decades, providing long-term time series for monitoring of cetacean populations. One cetacean species of concern is the common dolphin, which has been found stranded around the north-east Atlantic in recent years, with high numbers on French coasts being attributed to fisheries bycatch. We estimate common dolphin densities in the north-east Atlantic and investigate the ability of citizen science data to identify changes in marine mammal densities and areas of importance. MATERIALS AND METHODS: Data were collected by citizen scientists on ferries between April and October in 2006-2017. Common dolphin sightings data from two ferry routes across three regions, Bay of Biscay (n = 569); south-west United Kingdom to the Isles of Scilly in the Celtic Sea (n = 260); and English Channel (n = 75), were used to estimate density across ferry routes. Two-stage Density Surface Models accounted for imperfect detection, and tested the influence of environmental (chlorophyll a, sea surface temperature, depth, and slope), spatial (latitude and longitude) and temporal terms (year and Julian day) on occurrence. RESULTS: Overall detection probability was highest in the areas sampled within the English Channel (0.384) and Bay of Biscay (0.348), and lowest on the Scilly's route (0.158). Common dolphins were estimated to occur in higher densities on the Scilly's route (0.400 per km2) and the Bay of Biscay (0.319 per km2), with low densities in the English Channel (0.025 per km2). Densities on the Scilly's route appear to have been relatively stable since 2006 with a slight decrease in 2017. Densities peaked in the Bay of Biscay in 2013 with lower numbers since. Densities in the English Channel appear to have increased over time since 2009. DISCUSSION: This study highlights the effectiveness of citizen science data to investigate the distribution and density of cetaceans. The densities and temporal changes shown by this study are representative of those from wider-ranging robust estimates. We highlight the ability of citizen science to collect data over extensive periods of time which complements dedicated, designed surveys. Such long-term data are important to identify changes within a population; however, citizen science data may, in some situations, present challenges. We provide recommendations to ensure high-quality data which can be used to inform management and conservation of cetacean populations.

Empirical evidence that large marine predator foraging behavior is consistent with area-restricted search theory.

When prey is patchily distributed, predators are expected to spend more time searching for food in proximity of recent prey captures before searching in other areas. This behavior, known as area-restricted search, results in predators remaining localized in areas where prey had been detected previously because of the higher probability of encountering additional prey. However, few studies have tested these predictions on marine species because of the difficulties of observing feeding behavior. In this study, we utilized passive acoustic detections of echolocating dolphins to identify foraging behavior. C-PODs (click train detectors) were deployed for two years with an acoustic recorder attached to the same mooring during the second year. The time series of feeding buzzes, indicative of foraging behavior, revealed that both bottlenose (Tursiops truncatus) and common dolphins (Delphinus delphis) were more likely to stay in the area longer when foraging activity was high at the beginning of the encounter. The probability of foraging was also higher following previous foraging activity. This suggests that dolphins were feeding on spatially patchy prey and previous foraging experience influenced their movement behavior. This is consistent with the predictions of area-restricted search behavior, a nonrandom foraging strategy.

Microplastics in the stomach contents of common dolphin (Delphinus delphis) stranded on the Galician coasts (NW Spain, 2005-2010).

Plastic debris is currently recognised as one of the major global threats to marine life. However, few data exist on the presence and abundance of microplastics (plastics < 5 mm in size) in marine mammals. This is the first record of the presence of microplastics in the digestive tracts of marine mammals from the Iberian Peninsula. This study made use of 35 samples of common dolphin stomach contents. Microplastics were identified in all the samples analysed, an average of 12 items per stomach although abundance varied widely from one stomach to another. Most plastic items were small fibres although some fragments and a bead were also found. Excluding the smallest fibres as possible airborne contamination, the estimated occurrence of microplastics could drop to as low as 94%. Although factors affecting accumulation of microplastics and their effect on common dolphins are unknown, the fact that all stomachs analysed contained microplastics is a cause for concern.

Temporal and geographic patterns of kinship structure in common dolphins (Delphinus delphis) suggest site fidelity and female-biased long-distance dispersal.

ABSTRACT: Social structure plays a crucial role in determining a species' dispersal patterns and genetic structure. Cetaceans show a diversity of social and mating systems, but their effects on dispersal and genetic structure are not well known, in part because of technical difficulties in obtaining robust observational data. Here, we combine genetic profiling and GIS analysis to identify patterns of kin distribution over time and space, to infer mating structure and dispersal patterns in short-beaked common dolphins (Delphinus delphis). This species is highly social, and exhibits weak spatial genetic structure in the Northeast Atlantic and Mediterranean Sea, thought to result from fluid social structure and low levels of site fidelity. We found that although sampled groups were not composed of closely related individuals, close kin were frequently found in the same geographic location over several years. Our results suggest that common dolphin exhibits some level of site fidelity, which could be explained by foraging for temporally varying prey resource in areas familiar to individuals. Dispersal from natal area likely involves long-distance movements of females, as males are found more frequently than females in the same locations as their close kin. Long-distance dispersal may explain the near panmixia observed in this species. By analysing individuals sampled in the same geographic location over multiple years, we avoid caveats associated with divergence-based methods of inferring sex-biased dispersal. We thus provide a unique perspective on this species' social structure and dispersal behaviour, and how it relates to the observed low levels of population genetic structure in European waters. SIGNIFICANCE STATEMENT: Movement patterns and social interactions are aspects of wild animal's behaviour important for understanding their ecology. However, tracking these behaviours directly can be very challenging in wide-ranging species such as whales and dolphins. In this study, we used genetic information to detect how patterns of kin associations change in space and time, to infer aspects of movement and social structure. We identified previously unknown site fidelity, and suggested that dispersal usually involves females, travelling long distances from the natal area. Our data analysis strategy overcomes known limitations of previously used genetic inference methods, and provides a new approach to identify differences in dispersal between the sexes, which contribute to better understanding of the species' behaviour and ecology. In this case, we suggest that females are more likely to disperse than males, a pattern unusual amongst mammals.

Primary central nervous system T-cell lymphoma in a common dolphin (Delphinus delphis).

This report describes the pathological findings in an adult female short-beaked common dolphin (Delphinus delphis) stranded alive in the Canary Islands. Necropsy examination revealed the presence of a nodular neoplastic growth in the central nervous system (CNS) at the level of the thalamus. Microscopical examination revealed the mass to be a lymphoma and immunohistochemical labelling demonstrated a T-cell origin. No significant lesions were observed in other organs, including lymphoid organs. This is the first report of a primary T-cell lymphoma in the CNS in cetaceans.