Adult Bottlenose Dolphins Research Articles

Dolphin continuous auditory vigilance for five days

The present report describes the first study of continuous vigilance in dolphins. Two adult bottlenose dolphins (Tursiops truncatus), WEN (male) and SAY (female), maintained a very high detection rate of randomly presented, infrequent, 1.5-s target tones in a background of frequent 0.5-s equal-amplitude tones over five continuous 120-h sessions. The animals were able to maintain high levels (WEN 97, 87, 99%; SAY 93, 96%) of target detection without signs of sleep deprivation as indicated by behavior, blood indices or marked sleep rebound during 24 h of continuous post-experiment observation. Target response time overall (F = 0.384; P = 0.816) did not change between day 1 and day 5. However, response time was significantly slower (F = 21.566, P = 0.019) during the night (21.00-04.00 h) when the dolphins would have ordinarily been resting or asleep.

Oral administration of sucrose solutions and measurement of serum sucrose concentrations to evaluate gastric permeability in adult bottlenose dolphins (Tursiops truncatus)

To measure concentrations of sucrose in the serum of captive dolphins after oral administration of a sucrose solution and determine the suitability of this method for use as a test to detect gastric ulcers. 8 adult captive bottlenose dolphins (Tursiops truncatus). Blood samples were collected from the ventral fluke vein of dolphins before and 45 minutes after oral administration of 500 mL of solution containing 25 or 50 g of sucrose; oral administration was achieved by use of gastric intubation. Serum was separated, diluted in a solution of 90% acetonitrile-to 10% water that contained 10 ng of an internal standard (trichlormethiazide)/microL, mixed, and centrifuged. Supernatant was analyzed by use of liquid chromatography-mass spectrometry-mass spectrometry (LC-MS-MS). Serum sucrose concentrations of dolphins were at or less than the limits of detection before oral administration. Values after administration of sucrose solution varied among dolphins and were higher and more variable after administration of 50 g, compared with concentrations after administration of 25 g. Serum sucrose concentrations in samples collected during routine health evaluations of captive dolphins can be reliably measured by use of LC-MS-MS. Correlating serum sucrose concentrations with endoscopic observations of the gastric mucosa of dolphins will validate this approach for use in screening for the prevalence and severity of gastric ulcers and determining the efficacy of treatment regimens.

Signature whistle use by temporarily restrained and free-swimming bottlenose dolphins, Tursiops truncatus

Prior work on the signature whistles of bottlenose dolphins has focused on captive or temporarily restrained wild dolphins. Here we examine whistle production by free-ranging adult bottlenose dolphins. Whistles were recorded from each of 13 dolphins while they were restrained and free-swimming. Eleven of the 13 animals produced whistles while free-swimming that matched whistles produced while restrained. On average, 51% of the whistles an animal produced while free-swimming matched whistles recorded while that animal was gently restrained. Of those free-swimming whistles that matched restrained whistles, 76% matched signature whistles. A further analysis was conducted to determine the social contexts in which free-swimming dolphins produced signature whistles. An adult, allied male was most likely to produce signature whistles when voluntarily separated from his partner, and least likely to when together with his partner. These results suggest that wild bottlenose dolphins use signature whistles as contact calls, similar to captive dolphins. The majority of whistles produced by a pair of allied males in a consortship with a female were variant whistles. A final analysis showed that signature whistles appear individually distinctive, consistent with their use as contact calls, while variant whistles do not.

Male-male aggression renders bottlenose dolphin (<I>Tursiops truncatus</I>) unconscious

Intraspecie c aggression constitutes a signie cant proportion of conspecie c behaviours among many mammal species. Agonistic interactions among male bottlenose dolphins ( Tursiops truncatus ) have been documented in several di Verent regions, including escalated aggression involving coalitions comprised of several males. However, despite many hours of direct observation most of these encounters are evidenced by minor injuries and often, physical wounds are not visible. Herein, we describe a unique encounter involving a long-term male alliance competing with a ‘ solo’ male that resulted in the temporary loss of consciousness of the lone male following repeated physical blows to his head region. This observation supports the increased e tness experienced by males in alliances and illustrates the potential severity of aggressive interactions among adult bottlenose dolphins.

SKULL MORPHOMETRY OF BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) FROM THE GULF OF MEXICO

Skull morphometry of 206 stranded juvenile and adult bottlenose dolphins (Tursiops truncatus) from Texas and Florida were examined. Juveniles differed significantly from adults in both Texas and Florida populations. Sexual dimorphism was present in skulls from Texas but not from Florida. Regional differences in females from Texas and Florida were apparent, especially in braincase height, whereas male bottlenose dolphins did not differ between regions. Females could be distinguished accurately to region (90% classification success) using skull morphometry. Cranial morphometrics of T. truncatus are concrete values that may aid in identification of a type specimen for each population. Furthermore, these results can be used as a standard for Tursiops in the Gulf of Mexico.

Linking the sounds of dolphins to their locations and behavior using video and multichannel acoustic recordings.

It is difficult to attribute underwater animal sounds to the individuals producing them. This paper presents a system developed to solve this problem for dolphins by linking acoustic locations of the sounds of captive bottlenose dolphins with an overhead video image. A time-delay beamforming algorithm localized dolphin sounds obtained from an array of hydrophones dispersed around a lagoon. The localized positions of vocalizing dolphins were projected onto video images. The performance of the system was measured for artificial calibration signals as well as for dolphin sounds. The performance of the system for calibration signals was analyzed in terms of acoustic localization error, video projection error, and combined acoustic localization and video error. The 95% confidence bounds for these were 1.5, 2.1, and 2.1 m, respectively. Performance of the system was analyzed for three types of dolphin sounds: echolocation clicks, whistles, and burst-pulsed sounds. The mean errors for these were 0.8, 1.3, and 1.3 m, respectively. The 95% confidence bound for all vocalizations was 2.8 m, roughly the length of an adult bottlenose dolphin. This system represents a significant advance for studying the function of vocalizations of marine animals in relation to their context, as the sounds can be identified to the vocalizing dolphin and linked to its concurrent behavior.

Evidence for infanticide in bottlenose dolphins of the western North Atlantic.

Nine bottlenose dolphin (Tursiops truncatus) calves that stranded in Virginia in 1996 and 1997 died of severe blunt-force trauma. Injuries were concentrated on the head and chest and multiple rib fractures, lung lacerations, and soft tissue contusions were prominent. Skeletal and/or soft tissue trauma occurred bilaterally in all of the calves. One had a bite wound across the left mandible that exhibited deep punctures consistent with the tooth placement in an adult bottlenose dolphin. The lesions were not compatible with predation, boat strike, fisheries interactions, rough-surf injury, or blast injury. However, they were similar to traumatic injuries described in stranded bottlenose dolphin calves and harbor porpoises (Phocoena phocoena) in Great Britain attributed to violent dolphin interactions. The evidence suggests that violent dolphin behavior was the cause of the trauma in the nine calves reported here and that infanticide occurs in bottlenose dolphins of the western North Atlantic.

Anatomy and three-dimensional reconstructions of the brain of a bottlenose dolphin (Tursiops truncatus) from magnetic resonance images.

Cetacean (dolphin, whale, and porpoise) brains are among the least studied mammalian brains because of the formidable challenge of collecting and histologically preparing such relatively rare and large specimens. Magnetic resonance imaging offers a means of observing the internal structure of the brain when traditional histological procedures are not practical. Furthermore, internal structures can be analyzed in their precise anatomic positions, which is difficult to accomplish after the spatial distortions often accompanying histological processing. In this study, images of the brain of an adult bottlenose dolphin, Tursiops truncatus, were scanned in the coronal plane at 148 antero-posterior levels. From these scans a computer-generated three-dimensional model was constructed using the programs VoxelView and VoxelMath (Vital Images, Inc.). This model, wherein details of internal and external morphology are represented in three-dimensional space, was then resectioned in orthogonal planes to produce corresponding series of virtual sections in the horizontal and sagittal planes. Sections in all three planes display the sizes and positions of major neuroanatomical features such as the arrangement of cortical lobes and subcortical structures such as the inferior and superior colliculi, and demonstrate the utility of MRI for neuroanatomical investigations of dolphin brains.

Concentrations of Progesterone in Milk from Bottlenose Dolphins during Different Reproductive States

There are few published reports of an alternative, less invasive method than blood sampling to obtain reproductive hormone concentrations from captive dolphins. The aims of this study were to: (1) validate milk as an effective alternative to blood plasma for determining progesterone concentrations; and (2) utilize milk samples collected frequently to obtain progesterone concentration profiles and determine reproductive status. During the course of this study 16 plasma/milk sample pairs were collected from four adult bottlenose dolphins to correlate plasma and milk concentrations of progesterone. Milk samples were also collected approximately weekly for 4–5 months during three independent lactational periods. Additionally, milk samples were collected daily for approximately 1 year during three other independent lactational periods. A highly significant correlation was found between progesterone concentrations in plasma and milk (r2=0.91, P<0.01). Progesterone contained in milk whey, fat, and solids were 3.95 ± 1.3, 8.5 ± 1.1, and 52.0 ± 0.6%, respectively. Progesterone profiles from milk samples collected from two dolphins during 1995 indicated pregnancies (with progesterone concentrations between 8 and 46.5 ng/ml) which resulted in parturition. High progesterone concentrations in a third dolphin that did not give birth indicated a possible pseudopregnancy or fetal resorption. A possible ovulation not resulting in pregnancy was evident in one female in 1998, follicular activity in another female in 1998, and a year-long anestrous period in the third animal studied in 1998. It is confirmed that dolphins can become pregnant while lactating and that the approximate time of conception is identifiable in milk profiles, illustrating the potential application of this method in pregnancy detection and reproductive monitoring.

The diving physiology of bottlenose dolphins (Tursiops truncatus). II. Biomechanics and changes in buoyancy at depth.

During diving, marine mammals must balance the conservation of limited oxygen reserves with the metabolic costs of swimming exercise. As a result, energetically efficient modes of locomotion provide an advantage during periods of submergence and will presumably increase in importance as the animals perform progressively longer dives. To determine the effect of a limited oxygen supply on locomotor performance, we compared the kinematics and behavior of swimming and diving bottlenose dolphins. Adult bottlenose dolphins (Tursiops truncatus) were trained to swim horizontally near the water surface or submerged at 5 m and to dive to depths ranging from 12 to 112 m. Swimming kinematics (preferred swimming mode, stroke frequency and duration of glides) were monitored using submersible video cameras (Sony Hi-8) held by SCUBA divers or attached to a pack on the dorsal fin of the animal. Drag and buoyant forces were calculated from patterns of deceleration for horizontally swimming and vertically diving animals. The results showed that dolphins used a variety of swimming gaits that correlated with acceleration. The percentage of time spent gliding during the descent phase of dives increased with depth. Glide distances ranged from 7.1+/-1.9 m for 16 m dives to 43.6+/-7.0 m (means +/- s.e.m.) for 100 m dives. These gliding patterns were attributed to changes in buoyancy associated with lung compression at depth. By incorporating prolonged glide periods, the bottlenose dolphin realized a theoretical 10-21 % energetic savings in the cost of a 100 m dive in comparison with dives based on neutral buoyancy models. Thus, modifying locomotor patterns to account for physical changes with depth appears to be one mechanism that enables diving mammals with limited oxygen stores to extend the duration of a dive.

The diving physiology of bottlenose dolphins (Tursiops truncatus). I. Balancing the demands of exercise for energy conservation at depth.

During diving, marine mammals must rely on the efficient utilization of a limited oxygen reserve sequestered in the lungs, blood and muscles. To determine the effects of exercise and apnea on the use of these reserves, we examined the physiological responses of adult bottlenose dolphins (Tursiops truncatus) trained to breath-hold on the water surface or to dive to submerged targets at depths between 60 and 210 m. Changes in blood lactate levels, in partial pressures of oxygen and carbon dioxide and in heart rate were assessed while the dolphins performed sedentary breath-holds. The effects of exercise on breath-hold capacity were examined by measuring heart rate and post-dive respiration rate and blood lactate concentration for dolphins diving in Kaneohe Bay, Oahu, Hawaii. Ascent and descent rates, stroke frequency and swimming patterns were monitored during the dives. The results showed that lactate concentration was 1.1+/-0.1 mmol l(-1) at rest and increased non-linearly with the duration of the sedentary breath-hold or dive. Lactate concentration was consistently higher for the diving animals at all comparable periods of apnea. Breakpoints in plots of lactate concentration and blood gas levels against breath-hold duration (P(O2), P(CO2)) for sedentary breath-holding dolphins occurred between 200 and 240 s. In comparison, the calculated aerobic dive limit for adult dolphins was 268 s. Descent and ascent rates ranged from 1.5 to 2.5 m s(-1) during 210 m dives and were often outside the predicted range for swimming at low energetic cost. Rather than constant propulsion, diving dolphins used interrupted modes of swimming, with more than 75 % of the final ascent spent gliding. Physiological and behavioral measurements from this study indicate that superimposing swimming exercise on apnea was energetically costly for the diving dolphin but was circumvented in part by modifying the mode of swimming.

Enrofloxacin serum bioactivity in bottlenose dolphins, Tursiops truncatus, following oral administration of 5 mg/kg in whole fish.

Eight adult bottlenose dolphins Tursiops truncatus (six male, two female) were employed in a single-dose study of orally administered enrofloxacin dosed at 5 mg/kg body weight. Blood samples were obtained from all animals at 0, 2, 4, 8, 12 and 24 h following administration of the dose in the animals morning ration of fish. Serum antimicrobial activity concentrations (SAAC) were determined using bioassay. The mean elimination half-life (t1/2) of enrofloxacin and its major metabolites was 6.4+/-2.0 h with a range of 3-9.4 h. The time of maximal serum concentration (tmax) occurred at approximately 4 h with a range of 2-8 h following a single oral dose of 5 mg/kg. This variation in tmax most likely resulted from individual differences in absorption because of variations in the storage and digestion of the fish ration containing the drug dose within the compartmentalized cetacean stomach.

Evidence for infanticide in bottlenose dolphins: an explanation for violent interactions with harbour porpoises?

Most harbour porpoises found dead on the north-east coast of Scotland show signs of attack by sympatric bottlenose dolphins, but the reason(s) for these violent interactions remain(s) unclear. Post-mortem examinations of stranded bottlenose dolphins indicate that five out of eight young calves from this same area were also killed by bottlenose dolphins. These data, together with direct observations of an aggressive interaction between an adult bottlenose dolphin and a dead bottlenose dolphin calf, provide strong evidence for infanticide in this population. The similarity in the size range of harbour porpoises and dolphin calves that showed signs of attack by bottlenose dolphins suggests that previously reported interspecific interactions could be related to this infanticidal behaviour. These findings appear to provide the first evidence of infanticide in cetaceans (whales, dolphins and porpoises). We suggest that infanticide must be considered as a factor shaping sociality in this and other species of cetaceans, and may have serious consequences for the viability of small populations.

A New Quantitative Technique for Categorizing Whistles Using Simulated Signals and Whistles from Captive Bottlenose Dolphins (Delphinidae,Tursiops truncatus)

AbstractA widespread problem in the study of animal vocalizations is evaluating the acoustic similarity of signals both between individuals of a social group and between social groups. This problem becomes especially salient when classifying the narrow‐band frequency‐modulated signals, such as whistles, found in many avian and mammalian species. Whistles are usually characterized by their relative change in frequency over time, known as whistle ‘contour’. Measuring such a characteristic is difficult as it is not a single measurement, such as the mean frequency or duration of a signal, but several associated measurements of frequency across time. This paper reports on a new quantitative technique for determining whistle types based on whistle contour similarity and an application of this technique to the whistles of bottlenose dolphins to demonstrate its utility. This ‘contour similarity’ technique (CS technique) uses cluster analysis to group the correlation coefficients of frequency measurements from a data set of signals. To demonstrate the efficacy of this CS technique, three data sets were analysed, two using computer‐generated signals and a third using adult bottlenose dolphin whistles, to (1) examine the efficacy of correlation coefficients for grouping signals by their similarity in whistle contour and (2) determine the viability of this technique for categorizing bottlenose dolphin whistles. Measured actual frequencies and correlation matrices from the four simulated signal types and a correlation matrix from the whistles of five captive adult bottlenose dolphins were each subjected to K‐means cluster analysis and the resulting signal types were evaluated. Results indicated that the technique grouped actual frequencies according to the amount of shared actual frequencies and grouped correlation coefficients successfully according to signal contour. This result endured even if contours differed in overall duration or actual frequency or were expanded or compressed with respect to frequency or time. The results suggest that this approach is a viable method for assigning whistle contours to categories in bottlenose dolphins or any other species with narrow‐band, frequency‐modulated signals.

Quantitative Comparison of Whistle Repertoires from Captive Adult Bottlenose Dolphins (Delphinidae, Tursiops truncatus): a Re‐evaluation of the Signature Whistle Hypothesis

AbstractThe prevailing view among researchers of dolphin communication is that bottlenose dolphins possess an individualized whistle contour; known as the ‘signature whistle’, it accounts for 74–95 % of a dolphin's whistle repertoire and functions to signal the individual identity of the whistler. This study used a new quantitative technique, termed the contour similarity technique (CS technique), and reports on the quantitative comparison of whistles from the individuals of three different social groups of bottlenose dolphins in socially interactive contexts. Results suggest that captive adult dolphins share several different whistle types including one predominant whistle type shared by all individuals across three different social groups. These analyses suggest a different interpretation of the dolphin whistle repertoire than has previously been proposed by proponents of the signature whistle hypothesis. In addition, results from our study support the results of early studies, published before the advent of the signature whistle hypothesis, in which investigators reported a large whistle repertoire within socially interactive captive and free‐ranging groups and a predominant whistle type similar to that found in our study. Our results, combined with the results from earlier studies of dolphin vocal behaviour, suggest that the signature whistle hypothesis is incomplete and that dolphin whistle repertoires need to be analysed with respect to behavioural context and social relationships. In addition, these results suggest that contour discrimination and other acoustic features of whistles need to be tested in perception and categorization experiments.

BLOOD CHEMISTRY OF THE BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS).

The blood chemistry of six adult bottlenose dolphins ( Tursiops truncatus) kept in an artificial environment (simulated sea water) has been studied. Whole blood, plasma, and serum constituents are compared to those of the dog and horse. The plasma sodium, plasma chloride, and serum albumin levels appear to be higher while the α1, α2, and ß-globulin levels appear to be lower than those found in dogs and horses. The blood urea nitrogen values (mercury-combining capacity) are considerably higher than those found in dogs and horses.