Male Dolphins Research Articles

Anatomic site and interanimal variability in morphologic characteristics of bottlenose dolphin (Tursiops truncatus) skin likely to affect dermal absorption studies

Abstract Objective To investigate anatomic site and interanimal variability in dolphin skin for use in development of models for cutaneous absorption studies. Sample Population Skin from 30 healthy free-ranging bottlenose dolphins (17 males and 13 females grouped by age) and 10 captive males between 13 and 19 years old. Procedure Biopsy specimens were collected from the 10 male dolphins at 3 anatomic sites and from the 30 dolphins at 1 site; specimens were evaluated by light microscopy. Stratum externum thickness, minimal depth to the vasculature, and maximal epidermal depth were measured at 4 locations on 4 sequential sections. Comparisons of replicate measurements for 3 skin characteristics were made within and among anatomic sites, between dolphins of the same sex and approximate age, and across males and females of various ages. Results The stratum externum in male dolphins was thicker. Differences attributable to age and anatomic site were not significant. Variation attributable to differences in stratum externum thickness between dolphins was significant. Differences among body sites within the same dolphin were significant but were not consistent from dolphin to dolphin. Mean stratum externum thickness was not different between males of the 2 cohorts, but mean maximal epidermal depth and mean minimal depth to the vasculature were different. Variances within the 2 male cohorts were not significantly different. Conclusions Studies affected by stratum externum thickness should eliminate the effect attributable to sex difference by using dolphins of the same sex or grouping analytical data by sex. Precision could be improved without increasing the total number of dolphins by collecting more than 1 sample/dolphin. (Am J Vet Res 1998;59:1398–1403)

A First Eastern Canadian Stranding Record for Risso's Dolphin, Grampus griseus

We discovered a dead male Risso's dolphin, Grampus griseus, on Sable Island, Nova Scotia, Canada on January 7 1994. The 277 cm long corpse was unmarked by net entanglement or propeller scarring. Transverse sections of fusiform teeth exhibited 13 incremental growth layers in the dentine, in addition to a neonatal line. No other specimens of this species have been reported on the island. Risso's dolphins are not sighted commonly in Canadian waters and we are aware of no other published sightings or stranding records for this species within 100 km of the island. The pristine condition of this corpse, and the fact that it was not seen during regular beach surveys prior to discovery, indicates that it was a recent stranding. If this dolphin had died at sea, it did so close enough to Sable Island as to preclude scavenging by aerial or marine organisms before washing ashore.

The slippery slope of a Johnsonian ear: Natural variability versus natural loss

The normal audiogram of the bottlenosed dolphin, first established by Johnson [C. S. Johnson, in Marine Bio-Acoustics, edited by W. N. Tavolga (1967), pp. 247–260], has been pivotal to nearly three decades of underwater echolocation research, most of which focused on the mechanisms and analytical limits of dolphin sonar. One important aspect of dolphin hearing that has escaped investigation is what are normal audiometric ranges, or, more important, how to determine whether differences seen in audiometric responses of a new animal represent normal variants or a pathologically impaired ear. In this study, radiologic data and audiograms from animals tested by Brill et al. (this session) were compared with results from postmortem histologic analyses of ears from dolphins with known hearing losses. Structural alterations in the ear x rays of the older, male dolphins were consistent with obstructive disease processes and demineralization of temporal bones from dolphins with conductive and progressive sensorineural loss. These findings imply that specific features of the older male’s audiogram, such as the relatively flat, elevated, midfrequency thresholds and the rapid decrement of high-frequency responses, are diagnostic correlates for chronic infection and age-related retrograde neural loss. [Work supported by ONR N000149310940.]

A QUANTITATIVE ASSESSMENT OF DOMINANCE RELATIONS AMONG BOTTLENOSE DOLPHINS

AbstractAgonistic behavior of bottlenose dolphins was studied at Brookfield Zoo for nearly 4.5 yr, and dominance relationships were determined using a quantitative technique adapted from primate behavioral research. Dominance relations among dolphins were influenced by the gender of participants. Male dolphins were clearly and consistently dominant to females, and intersexual agonism occurred at moderate rates with seasonal peaks in spring and fall. Dominance relationships among female dolphins were age‐ordered and stable, even though agonism among females did occur at uniformly low rates. In contrast, the two males had a changeable dominance relationship in which periods of stability and low‐level agonism were interspersed with episodes of intense competition. Zoo‐based research revealed patterns of behavior that conformed to current knowledge about bottlenose dolphin social structure. Moreover, research in a zoo setting facilitated development of a quantitative technique that can be used to assess cetacean dominance relationships in field research.

Hearing deficits measured in some Tursiops truncatus, and discovery of a deaf/mute dolphin

Eight bottlenose dolphins Tursiops truncatus (four male, four female) were trained to respond to 100-ms tones. Three male dolphins (ages 23, 26, and 34) exhibited hearing disability at four higher frequencies-70, 80, 100, and 120 kHz even at 111-135 dB re: 1 microPa. Two females (ages 32 and 35) responded to all frequencies as did a male (age 7) and a female (age 11). One female (age 33) responded to all tones at 80 kHz and below; however, she failed to respond at 100 or 120 kHz. One young female dolphin (age 9) exhibited no perception of sound to behavioral or electrophysiological tests. This young female was not only deaf, but mute. The dolphin was monitored periodically by hydrophone and daily by trainers (by ear in air) for 7 years until she was age 16. The animal never whistled or made echolocation pulses or made burst pulse sounds as other dolphins do.

DEVELOPMENT AND SOCIAL FUNCTIONS OF SIGNATURE WHISTLES IN BOTTLENOSE DOLPHINS TURSIOPS TRUNCATUS

ABSTRACT Bottlenose dolphins Tursiops truncatus produce individually distinctive signature whistles. Dolphins recognize the signature whistles of animals with which they share a social bond. Signature whistles develop within the first few months of life and are stable for a lifetime. Vocal learning appears to play a role in the development of signature whistles in bottlenose dolphins. The signature whistles of most female dolphins and about half of male dolphins differ from those of their mothers. Some dolphin calves born in captivity develop a signature whistle that matches either man-made whistles or those of an unrelated dolphin. Dolphins retain the ability as adults to imitate the whistles of animals with which they share strong individual-specific social relationships, bonds which may change throughout their lifetime. The exceptional imitative abilities of dolphin infants and the retention of this ability in adults may be related to the maintenance of changing individual specific social relationships. Individual recognition by the voice may differ in marine vs terrestrial mammals. Diving marine mammals may not be able to rely upon involuntary voice cues for individual recognition, but rather may require vocal learning to maintain a stable signature as their vocal tract changes shape with increasing pressure during a dive.

Elevated Accumulation of Tributyltin and Its Breakdown Products in Bottlenose Dolphins (Tursiops truncatus) Found Stranded along the U.S. Atlantic and Gulf Coasts

Butyltin compounds, including mono- (MBT), di- (DBT), and tributyltin (TBT), were determined in the liver, kidney, and muscle of bottlenose dolphins (Tursiops truncatus) found stranded along the southeast U.S. Atlantic and Gulf coasts during 1989−1994. Total butyltin (BTs: MBT + DBT + TBT) concentrations in dolphin liver ranged between 110 and 11 340 ng/g (wet wt) with a mean value of 1400 ng/g. Butyltin concentrations in bottlenose dolphins were higher than those reported from other locations. The liver of a adult male dolphin collected in 1989 had the highest BT concentration (11 340 ng/g wet wt) reported. The concentrations of butyltins increased during the early life stages until maturity, for both sexes, and then tended to remain constant. Analysis of fish muscle collected from the Gulf of Mexico indicated the existence of recent inputs of TBT. The biomagnification factor of BTs in dolphins, on average, was 1.0 with the highest value of 6.8. In addition to polychlorinated biphenyls (PCBs), the presence of noticeable concentrations of TBT and DBT, which are potential immunosuppressing agents, might have also contributed to bottlenose dolphin mortality events in the U.S. Atlantic and Gulf coasts.

Adrenocortical color darkness and correlates as indicators of continuous acute premortem stress in chased and purse-seine captured male dolphins

A 2- to 3-h purse-seine set on dolphins to catch yellowfin tuna, including chase, net deployment, and closed net confinement, generates stressful stimuli. In most mammals, lipid depletion and hyperemia in adrenal cortices indicate a continuous acute stress (CAS) response, causing cortices to darken from beige to reddish-brown within a few hours in lab animals. To investigate suspected dolphin CAS, we examined cortices of 262 male spinner and spotted dolphins that died after varying periods of chase, net deployment, and confinement. About 95% were dark, and a subsample showed sparse or absent lipids and no vascular hemorrhage. This shows that most specimens were affected by CAS long enough to cause lipid depletion and hyperemia. Dolphins asphyxiate underwater in < 15 min, insufficient time for CAS signs to occur from entanglement alone. Spotted dolphins showed a significant trend of cortical darkening with lengthening chase and net-deployment periods (P < 0.01), but not confinement periods (P = 0.82). Thus, they were under CAS as early as chase stage; confinement did not augment the response. Possible roles of CAS in mortality are considered.

Dance of the dolphin: transformation and disenchantment in the Amazonian imagination

In folktales told throughout much of the Brazilian Amazon, dolphins take human form, attend raucous dances and festivals, seduce men and women, and carry them away to a city beneath the river. They are encantados, or Enchanted Beings, capable of provoking death or madness, but also called upon to help shamanic healers. Male dolphins - accomplished dancers who appear dressed in dapper straw hats, white suits and with shiny black shoes - reportedly father numerous children. The females are said to lure away solitary fishermen. Both sinister and charming, these characters resist definition and thus domination; greedy and lascivious outsiders, they are increasingly symbolic of a distinctly Amazonian culture politically, socially, economically and environmentally under seige. Candace Slater examines these stories in this book, both as folk narratives and as representations of culture and conflict in Amazonia. Her study discusses the tales from the viewpoints of genre, performance and gender, but centres on them as responses to the great changes sweeping the Amazon today. According to Slater, these surprisingly widespread tales reflect Amazonians' own mixed reactions to the ongoing destruction of the rainforest and the resulting transformations in the social as well as physical landscape. Offering an informed view of Brazilian culture, this book crosses the boundaries of folklore, literature, anthropology and Latin American studies.

Associations among photographically identified Hector's dolphins

Associations among Hector's dolphins photographically identified in the waters off Banks Peninsula, New Zealand, were studied using cluster analyses of simple and half-weight association indices. In addition, we carried out a temporal analysis of association patterns, plotting changes in the standardized reassociation rate over time. Some individually identified Hector's dolphins were photographed in the study area in successive seasons and years, and appeared to be resident in the area. Social organization was characterized by relatively fluid association patterns, with little stability over periods longer than a few days. Both male and female Hector's dolphins interacted with a large number of other individuals, males more so than females. Association patterns and other evidence support the hypothesis that Hector's dolphins have a promiscuous mating system.

High-frequency hearing loss in old (25+ years old) male dolphins

Eight bottlenose dolphins (four male, four female) were studied in an acoustic response time task [Ridgway et al., J. Acoust. Soc. Am. 89, 1967–1968 (A) (1991)]. The animals were trained to station 1 m below the water surface and respond to a stimulus tone (St) delivered through a hydrophone located 1 m in front of the blowhole. St duration varied from 60 to 450 ms and frequencies were 20, 40, 50, 60, 70, 80, 100, and 120 kHz. St were 120 dB (re: 1 μPa peak to peak at 1 m) ±24 dB in 6-dB steps. With the dolphin at 1-m depth and 1 m from the St hydrophone, the trainer started a randomly variable 3- to 20-St block. The computer selected St from a file in random sequence and interval (1.1 to 2.1 s in 0.1-s steps) and offered St via a St generator. Animal responses (ARs are the whistle or pulse train) were received by another hydrophone, digitized, and stored. Each AR file with 20 to 200 St was edited on a CRT display of a 700 ms St window. No-AR trials, noisy trials, and wrong ARs were identified. Three males (ages 25, 29, and 35) exhibited hearing disability at the four higher frequencies. One female (age 33) showed some loss above 80 kHz, but two females (age 32 and 36) responded to all frequencies as did a male (age 9) and a female (age 13).

Patterns of growth in wild bottlenose dolphins, Tursiops truncatus

The growth of bottlenose dolphins is described from observations made during a capture release programme that has operated in coastal waters of the eastern Gulf of Mexico from 1970 to the present. Measurements of standard length, girth and body mass were recorded from 47 female and 49 male dolphins, some captured as many as nine times. Ages were known from approximate birth dates or estimated from counts of dentinal growth layers. In all three measurements. females grew at a faster initial rate than males, but reached asymptotic size at an earlier age. This extended period of growth in males resulted in significant sexual dimorphism in length, girth and mass at physical maturity. The growth of both sexes was well described by three‐parameter Gompertz models using either cross‐sectional data or a mixture of longitudinal and cross‐sectional data. There was considerable variation in size‐at‐age for both sexes in all year classes. Residuals of size measurements were used to derive measures of relative size for individual dolphins; most dolphins demonstrated little ontogenetic change in relative size. Body mass was adequately predicted by multiple regression equations that incorporated both length and girth as independent variables.

Matching-to-sample by an echolocating dolphin (Tursiops truncatus).

An adult male dolphin was trained to perform a three-alternative delayed matching-to-sample task while wearing eyecups to occlude its vision. Sample and comparison stimuli consisted of a small and a large PVC plastic tube, a water-filled stainless steel sphere, and a solid aluminum cone. Stimuli were presented under water and the dolphin was allowed to identify the stimuli through echolocation. The echolocation clicks emitted by the dolphin to each sample and each comparison stimulus were recorded and analyzed. Over 48 sessions of testing, choice accuracy averaged 94.5% correct. This high level of accuracy was apparently achieved by varying the number of echolocation clicks emitted to various stimuli. Performance appeared to reflect a preexperimental stereotyped search pattern that dictated the order in which comparison items were examined and a complex sequential-sampling decision process. A model for the dolphin's decision-making processes is described.

Organochlorine chemical and heavy metal contaminants in white-beaked dolphins (Lagenorhynchus albirostris) and pilot whales (Globicephala melaena) from the coast of Newfoundland, Canada.

Polychlorinated biphenyls (∑PCB), DDT isomers (∑DDT), chlordanes (∑CHLOR), toxaphene, chlorobenzenes and hexachlorocyclohexane isomers and seven elements (As, Cd, Cu, Hg, Pb, Se, Zn) were determined in tissues of 41 stranded pilot whales (Globicephala melaena) and 27 ice-entrapped white-beaked dolphins (Lagenorhynchus albirostris) from Newfoundland, Canada. Cadmium, Hg, As and Se were significantly higher in pilot whale kidney and liver than in dolphin tissues. Mercury in liver and blubber, and Cd in kidney, of pilot whales were positively correlated with age. Cadmium levels in both species were much higher than reported for other cetaceans from Canadian east coast waters. Lead concentrations in dolphin kidney and mucles were 5 times higher than in pilot whales. Levels of ∑PCB (sum of 49 congeners) in blubber samples ranged from 31 to 61 mg/kg (lipid wt) in female and male dolphins, respectively, and from 5.6 to 12 mg/kg in female and male pilot whales. ∑DDT and toxaphene were present at similar levels to ∑PCB while mean ∑CHLOR (sum of seven components) ranged from 1.6 to 17 mg/kg in blubber of pilot whales and dolphins, respectively. The presence of high levels of toxaphene in the blubber of both species was unexpected and may be due to increased use of this pesticide during the 1970's. Higher levels of all organochlorine chemicals in blubber, as well as Pb in kidney and muscle, of dolphins than in pilot whales may reflect greater exposure to contaminants because of overwintering and feeding in Gulf of St. Lawrence waters.

Spermatozoa of the Atlantic bottlenosed dolphin, Tursiops truncatus.

Semen from a male dolphin in captivity was collected by electro-ejaculation and frozen to -176 degrees C. Sperm motility was excellent after thawing 10 days later. Electron microscopy showed 14-16 parallel ridges in the post-acrosomal region and two types of mitochondria in the mid-piece. The spermatozoa were capable of fusing with zona-free hamster eggs only after preincubation for 2 h, suggesting the need for sperm capacitation and acrosome reaction before fertilization in this species.

Food Habits and Sex Ratios of Dolphin Coryphaena hippurus Captured in the Western Atlantic Ocean off Hatteras, North Carolina

Abstract Dolphin caught by charter boats fishing over the Continental Shelf in 1961–63 were examined to determine food habits and sex ratios. Most important prey (listed according to percent of total prey weight) were: Exocoetidae (26%), Scombridae (22%), Carangidae(12%), Balistidae (9%), and Coryphaenidae (5%). Males constituted a significant majority (61%) of large dophin (801–1,275 mm fork length). Most (71%) small dolphin (450–600 mm) were females. Large dolphin of both sexes were generally captured in open water, while small female dolphin were usually associated with tide-lines (areas where current patterns cause accumulations of floating Sargassum and other flotsam). In 1963, tide-lines were infrequently encountered by charter boats. Decreased charter boat catches, increased abundance of young males in the fishery, and impaired foraging by small female dolphin resulted. We hypothesize that male dolphin (which are heavier than females of similar length) leave the sanctuary of the tide-line at an ear...

Age and Growth of the Dolphin, Coryphaena hippurus (Linnaeus), in North Carolina Waters

Abstract The validity of age determinations from scales of dolphin (Coryphaena hippurus) captured off the North Carolina coast is established. Specimens were obtained from the local charter boat fishery. The greatest age of dolphin examined was 3 years. None of the 3-year-old fish and few of the 2-year-old fish were females. Predominance of males in age-groups II and III is believed to be caused by differential feeding habits of the sexes. Analysis of stomach contents indicates that older males may be more voracious feeders than older females; and, therefore, are more susceptible to capture by the hook-and-line fishery. Males are heavier than females throughout their complete length range. The body-scale relation is efficiently described by linear regression. Theoretical fish length at the time of scale formation was 93.75 mm. Growth in length of male and female dolphin was not significantly different. Rate of growth was independent of year of collection. Length at time of first annular formation was 653 ...

Age, Growth, and Reproduction of the Dolphin, Coryphaena hippurus, in the Straits of Florida

The dolphin grows rapidly throughout its life. Check marks believed to be annuli were formed from November through February. Average growth was 725 mm fork length the first year and 450 mm the second year. One older fish belonged to age-group III (1425 mm long), and another to age-group IV (1525 mm). A male dolphin in the reef tank of the Miami Seaquarium, Miami, Florida, grew from about 0.5 kg (one lb.) to 16.3 kg (36 lb.) in about eight months. Maximum life span is probably about four years. Male dolphin longer than about 450 mm were heavier than females of the same length. Reproduction was studied by gross observation of the gonads, measurements of egg diameters, and counts of maturing eggs. Changes in the gonads through the year indicated that the spawning season in the Florida Current extends from November through July and is at its peak in March. Female dolphin begin to mature at 350 mm fork length, and all are mature by 550 mm. Males begin to mature at a slightly larger size. Female dolphin produce 80,000-1,000,000 eggs at each spawning and spawn twice (perhaps as many as three times) per year.