Trawling and bottlenose dolphins' social structure

Human activities can affect the behaviour of mammals through the modification of habitats, changes in predation pressure or alterations in food distribution and availability. We analysed the association and ranging patterns of 242 individually identified bottlenose dolphins (Tursiops aduncus) in eastern Moreton Bay, Queensland, Australia, and distinguished two separate communities of dolphins. Unlike bottlenose dolphins elsewhere, the communities' core areas overlapped substantially. There was a correlation between the dolphins' responses to fishing activities and community membership-members of one community feed in association with trawlers and members of the other do not. Apart from feeding mode, the communities differed in habitat preference and group sizes. Inadvertent anthropogenic impacts on animals' societies are likely to be far more widespread than just this study and can increase conservation challenges. In this instance, managers need to consider the two communities' differing habitat requirements and their behavioural traditions in conservation planning.     

Orbital gland structure and secretions in the Atlantic bottlenose dolphin (Tursiops truncatus)

Orbital gland structure of the Atlantic bottlenose dolphin, Tursiops truncatus, was examined at the macroscopic, light microscopic, and electron microscopic levels. The gland completely encircles the ocular globe in a belt-like fashion near the conjunctival fornix but is considerably more developed medially. Duct openings are scattered throughout the fornix and over the surface of the palpebral conjunctiva. Microscopically, the gland has a tubuloalveolar arrangement; alveolar cells contain numerous secretory vesicles which can be interpreted as two structural types by light and electron microscopy. Histochemical staining demonstrates that both types contain glycosaminoglycans. Lipid analysis of the glandular secretion (dolphin tears) shows them to be non-oily and to contain only negligible amounts of cholesterol, triglycerides, phospholipids, and free fatty acids. The secretion is clear, slippery, and viscoelastic and well-adapted to protecting the eye and to reducing frictional forces between the eye surface and surrounding seawater.     

Passive hearing stability in the bottlenose dolphin Tursiops truncatus to low frequency noise spectrum deformation

In behavioral experiments on bottlenose dolphins there was evaluated efficiency of identification of the low frequency noises that represent a certain rhythmical sequence of impulses, at destabilization of their spectra by the method of frequency wobble. Results of the experiments have shown that disturbance of spectral structure at erosion of its discrete components does not lead to a decrease of efficiency of the noise identification, which indicates the greater significance of the time, rather than spectral mechanisms at processing of the complex acoustic signals by the dolphin auditory system.     

Congenital toxoplasmosis in a Indo-Pacific bottlenose dolphin (Tursiops aduncus)

Toxoplasma gondii was identified in tissues of a stillborn late-term fetus from an Indo-Pacific bottlenose dolphin (Tursiops aduncus). Myocardial necrosis and nonsuppurative inflammation in the heart and nonsuppurative necrotizing encephalitis were associated with tachyzoites and tissue cysts. The diagnosis was confirmed by immunohistochemical staining with anti-T. gondii-specific polyclonal rabbit serum.     

The structure of a bottlenose dolphin society is coupled to a unique foraging cooperation with artisanal fishermen

Diverse and localized foraging behaviours have been reported in isolated populations of many animal species around the world. In Laguna, southern Brazil, a subset of resident bottlenose dolphins (Tursiops truncatus) uses a foraging tactic involving cooperative interactions with local, beach-casting fishermen. We used individual photo-identification data to assess whether cooperative and non-cooperative dolphins were socially segregated. The social structure of the population was found to be a fission-fusion system with few non-random associations, typical for this species. However, association values were greater among cooperative dolphins than among non-cooperative dolphins or between dolphins from different foraging classes. Furthermore, the dolphin social network was divided into three modules, clustering individuals that shared or lacked the cooperative foraging tactic. Space-use patterns were not sufficient to explain this partitioning, indicating a behavioural factor. The segregation of dolphins using different foraging tactics could result from foraging behaviour driving social structure, while the closer association between dolphins engaged in the cooperation could facilitate the transmission and learning of this behavioural trait from conspecifics. This unique case of a dolphin-human interaction represents a valuable opportunity to explore hypotheses on the role of social learning in wild cetaceans.     

Herpes simplex-like infection in a bottlenose dolphin stranded in the Canary Islands

A bottlenose dolphin, stranded in the Canary Islands in 2001 exhibited non-suppurative encephalitis. No molecular detection of cetacean morbillivirus (CeMV) was found, but a herpesviral-specific band of 250 bp was detected in the lung and brain. The sequenced herpesviral PCR product was compared with GenBank sequences, obtaining 98% homology (p-distance of 0.02) with Human herpesvirus 1 (herpes simplex virus 1 or HSV-1). This is the first report of a herpes simplex-like infection in a stranded dolphin.     

Evidence for social role in a dolphin social network

Social animals have to take into consideration the behaviour of conspecifics when making decisions to go by their daily lives. These decisions affect their fitness and there is therefore an evolutionary pressure to try making the right choices. In many instances individuals will make their own choices and the behaviour of the group will be a democratic integration of everyone’s decision. However, in some instances it can be advantageous to follow the choice of a few individuals in the group if they have more information regarding the situation that has arisen. Here I provide early evidence that decisions about shifts in activity states in a population of bottlenose dolphin follow such a decision-making process. This unshared consensus is mediated by a non-vocal signal, which can be communicated globally within the dolphin school. These signals are emitted by individuals that tend to have more information about the behaviour of potential competitors because of their position in the social network. I hypothesise that this decision-making process emerged from the social structure of the population and the need to maintain mixed-sex schools.     

Population genetic structure and social kin associations of franciscana dolphin, Pontoporia blainvillei

We investigated population and social structure of the franciscana dolphin, Pontoporia blainvillei, an endemic and the most endangered cetacean of the southwestern Atlantic Ocean. We analyzed samples from the Rio de la Plata estuary obtained in Uruguayan waters and from the Atlantic Ocean obtained in both Uruguayan and Brazilian waters. Mitochondrial and microsatellite DNA markers were used to study differentiation between the estuary and the ocean and the association between kinship and social group structure. Although multilocus analyses suggested that franciscanas are structured into 2 subpopulations (K = 2, divergence among clusters: F(ST) = 0.06, P = 0.002; R(ST) = 0.3, P = 0.001), mitochondrial markers did not support such divergence (F(ST) = 0.02, P = 0.12; Ф(ST) = 0.06, P =0.06). However, these units are not entirely segregated geographically. Regarding social structure, some groups are composed by first-order related individuals (R ≥ 0.5, P < 0.5). Overall, the data suggest that matrilines could be the social unit in this species. We argue that the divergence found could be associated to local adaptation and social structure, resulting from either feature leading to a recent divergence or reflecting equilibrium between local differentiation and gene flow. This evidence supports considering franciscanas from the Rio de la Plata estuary a discrete management unit.     

Thirty year retrospective evaluation of pneumonia in a bottlenose dolphin Tursiops truncatus population

Pneumonia is one of the most common causes of morbidity in bottlenose dolphins Tursiops truncatus. To better understand associations of pneumonia with demographics, microbiology, pathology, and histopathology, a retrospective study on 42 dolphins from the US Navy Marine Mammal Program dolphin population was conducted (1980 to 2010). A total of 21 (50%) of the dolphins evaluated had pneumonia confirmed by histopathology. Bacterial and fungal pneumonia was present in 42.9 and 28.6% of cases (9 and 6 cases), respectively, with Staphylococcus aureus as the most common confirmed pathogen (4 cases, 19%). Other pathogens identified as the cause of pneumonia were Cryptococcus neoformans, Erysipelothrix rhusiopathiae, Histoplasma capsulatum, parainfluenza virus, Proteus species, Pseudomonas aeruginosa, and Streptococcus zooepidemicus. Neither sex nor age was a predictor of pneumonia. While many of the infections involved disseminated disease, lungs were consistently the most severely affected organs. The present study demonstrates the high susceptibility of dolphins to respiratory infections. Areas that warrant further investigation include eosinophilic pneumonia, chronic infections, co-infections, and metabolic or iron-storage diseases. There is a continuing need to improve the early diagnosis and effective treatment of pneumonia in dolphins.     

Quantification of ECoG stages of sleep in the bottlenose dolphin

Single-hemisphere low-wave sleep was shown to be the dominant form of natural sleep according to quantitative analysis of duration of ECoG sleep phases. Combined variants of bilateral and unilateral ECoG synchronization total 33.4% of the 24-h cycle, of which unilateral slow-wave sleep accounts for 28.8%. Each of the bottlenose dolphin's two hemispheres remains in a state of slow-wave ECoG for an average of 19% of the cycle. The highest percentage duration of sleep occurred during the afternoon and nighttime. Overall duration of ECoG synchronization may differ in the two hemispheres but evens out in the dolphin over a number of 24-h cycles. Spells of single-hemisphere sleep tend to alternate between the two different hemispheres.A. N. Severtsov Institute of Evolutionary Morphology and Animal Ecology. Translated from Neirofiziologiya, Vol. 20, No. 4, pp. 532–538, July–August, 1988.     

Left hemispheric advantage for numerical abilities in the bottlenose dolphin

In a two-choice discrimination paradigm, a bottlenose dolphin discriminated relational dimensions between visual numerosity stimuli under monocular viewing conditions. After prior binocular acquisition of the task, two monocular test series with different number stimuli were conducted. In accordance with recent studies on visual lateralization in the bottlenose dolphin, our results revealed an overall advantage of the right visual field. Due to the complete decussation of the optic nerve fibers, this suggests a specialization of the left hemisphere for analysing relational features between stimuli as required in tests for numerical abilities. These processes are typically right hemisphere-based in other mammals (including humans) and birds. The present data provide further evidence for a general right visual field advantage in bottlenose dolphins for visual information processing. It is thus assumed that dolphins possess a unique functional architecture of their cerebral asymmetries.     

Struvite calculus in the vagina of a bottlenose dolphin (Tursiops truncatus)

On 27 January 2000, a struvite calculus was observed in the vagina during necropsy of a 138-cm-long female bottlenose dolphin (Tursiops truncatus) collected from the Stono River, South Carolina (USA). Vaginal calculi have been reported in other species of cetaceans but not in bottlenose dolphins. Urinary tract infection might have been an underlying cause of the calculus. While urinary tract inflammation was not detected by light microscopic evaluation of sections of the urinary tract, it is conceivable that sufficient time had lapsed following voiding of the calculus through the urethra for urinary tract infection to have resolved. To further define the prevalence and significance of urolithiasis, prosectors of dead stranded marine mammals are encouraged to closely observe their urinary and genital tracts for calculi and to submit them for quantitative analysis.     

Uterine adenocarcinoma with generalised metastasis in a bottlenose dolphin Tursiops truncatus from northern Patagonia,Argentina

An endometrial adenocarcinoma with areas of squamous differentiation and generalised metastasis was observed in a bottlenose dolphin Tursiops truncatus stranded in northern Patagonia in July 1997. This is the second report of a uterine adenocarcinoma in a free-living cetacean and the first in a Delphinidae. This neoplasm likely compromised reproduction for several years. In addition, the dolphin presented tattoo-like skin lesions and its digestive tract was infested by Anisakis simplex, Pseudoterranova sp., Braunina cordiformis and Corynosoma australe.     

Characterization of beam patterns of bottlenose dolphin in the transverse plane

The characteristics of absolute auditory sensitivity of the bottlenose dolphin (Tursiops truncatus) in the transverse plane have been measured using short broadband stimuli simulating dolphin clicks (with energy maximum at frequencies 8, 16, 30, 50 and 100 kHz). Experiments were performed using the method of conditioned reflexes with food reinforcement. It is shown that, in the frequency range of 8–30 kHz, the absolute sensitivity of dolphin hearing in any ventral and lateral directions of the transverse plane is only 2–8 dB worse than in the rostral direction. Moreover, it is 25–30 dB better than at 50–100 kHz. At 8–30 kHz, pronounced dorsoventral asymmetry has been observed. In this frequency range, it reaches 15–18 dB whereas at 50–100 kHz this asymmetry decreases to 2–3 dB. In the dorsal direction, the auditory sensitivity is 18 dB worse than in the rostral one at ∼8 kHz, and the difference rises smoothly to 33 dB at ∼100 kHz. At 50–100 kHz, the acoustical thresholds in the transverse plane relative to those for the with rostral direction get worse almost uniformly in all directions by 25–33 dB. As a result, in the transverse plane the beam patterns are nearly circular, unlike those at 8–30 kHz. The results are discussed in terms of the model of sound perception through the left and right mental foramens. The biological relevance of such asymmetry is emphasized.