Free-ranging Dolphins Research Articles

Estimated transmission beam pattern of clicks recorded from free-ranging white-beaked dolphins (Lagenorhynchus albirostris).

Recordings were made from white-beaked dolphins in Icelandic waters using a four-hydrophone array in a star configuration. The acoustic signals were amplified and sampled to a hard disk at a rate of 800 kHz per channel. The 3 and 10 dB beamwidths were calculated to be 8 degrees and 10 degrees, respectively, indicating a narrower transmission beam for white-beaked dolphins than that reported for bottlenose dolphins (Tursiops truncatus). The beamwidth was more similar to that found for belugas (Delphinapterus lucas). The measured beam pattern included large side lobes, perhaps due to the inclusion of off-axis clicks, even after applying several criteria to select only on-axis clicks. The directivity index was calculated to be 18 dB when using all data for angles from 0 degrees-50 degrees. The calculated sound radiation from a circular piston with a radius of 6 cm driven by a white-beaked dolphin click had a beam pattern very similar to the measured beam pattern for the main transmission lobe of the white-beaked dolphin. The directivity index was 29 dB. This is the first attempt to estimate the directionality index of dolphins in the field.

Automatic gain control in the echolocation system of dolphins.

In bats and technological sonars, the gain of the receiver is progressively increased with time after the transmission of a signal to compensate for acoustic propagation loss. The current understanding of dolphin echolocation indicates that automatic gain control is not a part of their sonar system. In order to test this understanding, we have performed field measurements of free-ranging echolocating dolphins. Here we show that dolphins do possess an automatic gain control mechanism, but that it is implemented in the transmission phase rather than the receiving phase of a sonar cycle. We find that the amplitude of the dolphins' echolocation signals are highly range dependent; this amplitude increases with increasing target range, R, in a 20 log(R) fashion to compensate for propagation loss. If the echolocation target is a fish school with many sound scatterers, the echoes from the school will remain nearly constant with range as the dolphin closes in on it. This characteristic has the same effect as time-varying gain in bats and technological sonar when considered from a sonar system perspective.

DIRECTIONALITY IN THE WHISTLES OF HAWAIIAN SPINNER DOLPHINS (STENELLA LONGIROSTRIS): A SIGNAL FEATURE TO CUE DIRECTION OF MOVEMENT?

AbstractDolphins produce frequency modulated (FM) whistles that are thought to promote the synchrony and coordination of behavior between members of a group. How whistles are used in this regard remains poorly understood. One possibility is that whistles have directionality and thereby convey the orientation and direction of movement of the signaler to nearby listeners. To explore this possibility, whistles from free‐ranging Hawaiian spinner dolphins (Stenella longirostris) were obtained using a towed, three‐hydrophone line array and examined for the presence of directionality. Both the estimated source level and harmonic content of whistles produced by animals traveling with or toward the array were greater than those of animals moving ahead or away from it. In addition, signals produced by animals near the array (within 20 m) were received differently on the three hydrophones spaced 11.5 m apart. These differences were greater than would be expected from transmission loss disparities alone. The results indicate that directivity is present in the transmission pattern of whistles. To infer the form of this directivity, a theoretical whistle beam pattern was established based on the assumption that the dolphin's sound source is approximated by a circular piston transducer (Au 1993). The resulting beam indicates that spinner dolphin whistles become increasingly directional with frequency, especially with respect to harmonics. The orientation‐dependent harmonic structure of whistles thus presents a potential cue that listening animals could interpret to infer the direction of movement of signalers. Harmonics are present in the whistles of many dolphin species and may represent an inherent signal design feature that promotes coordination between animals.

Source levels of clicks from free-ranging white-beaked dolphins (Lagenorhynchus albirostris Gray 1846) recorded in Icelandic waters.

This study reports the source levels of clicks recorded from free-ranging white-beaked dolphins (Lagenorhynchus albirostris Gray 1846). A four-hydrophone array was used to obtain sound recordings. The hydrophone signals were digitized on-line and stored in a portable computer. An underwater video camera was used to visualize dolphins to help identify on-axis recordings. The range to a dolphin was calculated from differences in arrival times of clicks at the four hydrophones, allowing for calculations of source levels. Source levels in a single click train varied from 194 to 211 dB peak-to-peak (p-p) re: 1 microPa. The source levels varied linearly with the log of range. The maximum source levels recorded were 219 dB (p-p) re: 1 microPa.

MAXIMUM SWIM SPEEDS OF CAPTIVE AND FREE‐RANGING DELPHINIDS: CRITICAL ANALYSIS OF EXTRAORDINARY PERFORMANCE

AbstractResearch into dolphin swimming historically was guided by false assumptions pertaining to maximum speed. Accurate measurements on swimming speed and duration of effort of free‐ranging dolphins are rare. To examine the variance of maximum swimming speeds, nearly 2,000 speed measurements were obtained for both captive and free‐ranging dolphins, including Tursiops truncatus, Pseudorca crassidens, Delphinus capensis, and Delphinus delpbis. Measurements were made from videotapes of dolphins trained to swim fast around a large pool or jumping to a maximum height, videotapes of captured wild dolphins immediately after release, and sequential aerial photographs of a school of free‐ranging dolphins startled by a passing airplane. Maximum horizontal speeds for trained animals were 8.2 m/sec for T. truncatus, 8.0 m/sec for D. delphis, and 8.0 m/sec for P. crassidens. Maximum speeds for T. truncatus swimming upwards, prior to vertical leaps ranged from 8.2 to 11.2 m/sec. Wild T. truncatus demonstrated a maximum speed of 5.7 m/sec. Maximum swimming speed of free‐ranging D. capensis responding to multiple passes by a low flying airplane was 6.7 m/sec. There was no evidence that the freeranging dolphins have superior swimming capabilities to captive animals. The results of this study imply that realistic maximum swimming speeds for dolphins are lower than previous reports which were based on sparse data and imprecise measurement techniques.

Interactions between marine predators: dolphin food intake is related to number of sharks

Dolphins and sharks feed at times on the same food; however, the influence of these interactions on the feeding success of either predator has not been measured. I employed underwater video to record bottlenose dolphins Tursiops truncatus and silky sharks Carcharhinus falciformis feeding on the same school of fish, and for the first time measured food intake of free-ranging dolphins. Regression analyses showed that dolphin food intake diminished as the number of feeding sharks increased, but was unrelated to the number of dolphins feeding, size of the prey clump or duration of feeding events. The number of dolphins increased at the beginning of a feeding event in the presence of sharks but not in their absence. This increase apparently provided a benefit to dolphins since the number of sharks feeding was negatively related to the number of dolphins feed- ing. Other studies have indicated that risk of shark predation influences dolphin group size and habi- tat use. This study indicates that interspecific contests over food influence dolphin food intake and perhaps also dolphin group size.

Canine distemper infections, with special reference to South Africa, with a review of the literature.

Canine distemper virus is a member of the genus Morbillivirus of the family Paramyxoviridae that causes severe disease in dogs and a range of wild mammals. The clinical signs relate essentially to the respiratory, gastrointestinal and central nervous systems. In South Africa, infection with Ehrlichia canis and canine parvovirus may present similarly Many dogs will initially present with a wide range of central nervous system signs without any history of systemic disease. A recent South African study evaluating ante mortem diagnosis highlighted the importance of recognising clinical signs, cerebrospinal fluid IgG titres, serum IgM titres and immunocytochemistry of epithelial tissue. A 2-year retrospective evaluation of cerebrospinal fluid samples collected from dogs presented to the Onderstepoort Veterinary Academic Hospital indicates that distemper infection is common, and this disease should routinely be suspected in cases of diverse neurological disease in dogs. The South African dog population is specifically at high risk for the disease because of the large pool of unvaccinated, reproductively-active dogs that expose the wildlife resources of the country to risk of fatal disease. Outbreaks of disease in dogs continue to occur in developed and developing communities in both vaccinated and unvaccinated dogs worldwide, and have also been described in a wide range of free-ranging wildlife, including seals, dolphins and lions, and in endangered zoo animals. Modified live virus vaccines have contributed markedly to disease control in the dog population but have caused mortality in some wild carnivores. New recombinant vaccines are being developed that will be safe in wild animals. The pathogenesis of CNS demyelination has been compared to various important demyelinating diseases in humans and, amongst other things, relates to down-regulation of the oligodendrocyte gene coding for myelin synthesis and non-immunocyte CNS cell expression of type II major histocompatibility receptors. Early CNS lesions are characterised by demyelination and later lesions by perivascular round cell cuffing. Treatment is supportive.

Organochlorine compounds in common dolphins ( Delphinus delphis) from the Atlantic and Mediterranean waters of Spain

Blubber of free-ranging common dolphins ( Delphinus delphis) from the northwestern coast of Spain (Atlantic), sampled in 1984 and 1996, and of common dolphins entangled in fishing nets in the southwestern Mediterranean, sampled during 1992–1994, was analysed for organochlorine pollutants. In the Atlantic, concentration of all pollutants was significantly higher in males than in females. The overall tPCB/tDDT ratio in this area was 3.35, which indicates a predominance of industrial inputs over those associated with agriculture. Individuals sampled in 1996 showed significantly lower DDT concentrations but a higher ppDDE/tDDT ratio than those sampled in 1984, which reflects the aging of the environmental load. In the same period, tPCB concentration remained constant and, as a consequence, the tPCB/tDDT ratio more than doubled. In the Mediterranean, the reduced sample size of adult individuals precluded proper statistical investigation of sex-related variation. The overall tPCB/tDDT ratio was 1.12, suggesting a higher contribution of pollutants of agricultural origin. Individuals had significantly higher levels of all DDT forms and a higher ppDDE/tDDT ratio than their counterparts from the Atlantic, but similar PCB concentrations. However, the relative frequency of the different congeners in relation to the total PCB load was different in the two areas. This indicates that the two populations do not mix, at least in the short- or medium-term. Organochlorine levels in both areas are at the mid to low end of the range of concentrations detected in other common dolphin populations and in that of other Delphinidae species from the same region. Although the impact of the organochlorine concentrations on the common dolphin populations surveyed cannot be assessed, it is considered unlikely that they have played a significant role in the decline that the species has suffered in recent decades in the western Mediterranean.

イルカのソナー能力

Dolphins have highly developed sonar abilities and have been studied extensively in captivity. The use of sonar by dolphins and porpoises in the wild is thought to be related to the underwater navigation and searching behavior. Here we report a new and simple method to archive continuous click events individually. Echolocation click events and swimming speed of finless porpoises (Neophocaena phocaenoides) were recorded with data loggers attached on the animals. The echolocation range converted from sonar pulse intervals in open waters ranged up to 130 m. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging. Silent swim distance, calculated by the swim speed multiplied by the duration of the non-echolocating periods, was smaller than the echolocation range. Finless porpoises are believed to examine their frontal area acoustically using echolocation. In other words, the observed finless porpoises swam without echolocation only in an already inspected area.

DIFFERENCES IN THE EXTERNAL MORPHOLOGY OF TWO SYMPATRIC SPECIES OF BOTTLENOSE DOLPHINS (GENUSTURSIOPS) IN THE WATERS OF CHINA

Clear genetic and osteological characters exist to distinguish 2 sympatric species of bottlenose dolphins (genus Tursiops) in the waters of China. However, these characters are not useful for the identification of free-ranging dolphins. To determine if these species could be differentiated by external morphology, a discriminant analysis was performed on 8 external morphometric characters of 57 specimens, 40 of which were classified a priori as T. truncatus and 17 as T. aduncus using genetic, osteological, and other information. External morphological separation of the 2 species was highly significant. Furthermore, discriminant scores were nonoverlapping, and classification functions were successful in classifying several new specimens from the waters of China and Indonesia. Rostrum length as an absolute measure and as a proportion of total body length or snout-to-eye length revealed nonoverlapping distributions for the 2 species in the waters of China and thus offered useful field characters for classifying fresh carcasses, stranded individuals, captive specimens, photographs, and in some cases free-ranging individuals.

Changing occurrence of epidermal lesions in wild bottlenose dolphins

There are increasing concerns that human activities promote the development of nat- ural diseases in aquatic organisms. Of these, diseases concerning small cetaceans have received increasing attention. Most studies have focused on dead animals and provided information on pathogens, contaminant exposure and probable causes of death. However, our understanding of dis- eases in living populations, particularly with respect to prevalence during the lives of individuals, and for whole populations in different years, remains limited. This study was designed to provide such information on epidermal lesions (abnormalities not directly attributable to physical trauma that may indicate disease) in a wild population of bottlenose dolphins Tursiops truncatus. An 8 yr time series of photographs of 82 free-ranging dolphins from NE Scotland was used to investigate the occurrence and dynamics of epidermal lesions in 7 age classes of young dolphins (from their 1st to their 7th sum- mer of life) and for an adult group. Lesions were found at high prevalence (90 to 100%) in both young and adult dolphins, with 1st-summer calves having the lowest levels. Lesions of different appearance showed 2 patterns of occurrence, either being restricted to young individuals or becoming more com- mon with age. When severity was compared between calves (in their 2nd summer of life) born in 8 different years, a significant decline over time was observed (p < 0.005). Comparison of this change with environmental and anthropogenic factors may help identify which factors may be promoting the ubiquitous epidermal lesions in these dolphins.

Serum α- and γ-tocopherols, retinol, retinyl palmitate, and carotenoid concentrations in captive and free-ranging bottlenose dolphins ( Tursiops truncatus)

Concentrations of retinol, retinyl palmitate, β-carotene, α-carotene, cryptoxanthin, lutein, lycopene, α-tocopherol, and γ-tocopherol were measured in blood samples collected from 15 captive and 55 free-ranging bottlenose dolphins ( Tursiops truncatus). From June 1991 to June 1994, blood samples were collected from captive animals residing at two locations; at Seven Seas (Brookfield Zoo, Brookfield, IL) and Hawk’s Cay (Marathon Key, FL). Blood samples were collected from free-ranging animals from June 1991 to June 1996. Retinol levels were not significantly different between captive dolphin groups. However, Seven Seas animals had higher ( P<0.01) serum retinol concentrations compared to free-ranging animals (0.061 vs 0.041 μg/ml). Retinyl palmitate was not detected in the serum of captive or free-ranging dolphins. Alpha-tocopherol levels were significantly ( P<0.05) higher for Seven Seas dolphins (16.4 μg/ml) than for Hawk’s Cay (13.0 μg/ml) and free-ranging dolphins (12.5 μg/ml). Gamma-tocopherol concentrations were similar among captive and free-ranging dolphins. Free-ranging dolphins showed levels of circulating carotenoids (lutein and β-carotene) while the captive animals did not. Additional carotenoids (lycopene, α-carotene and cryptoxanthin) were analyzed but not detected in any samples. Serum vitamin differences between captive and free-ranging dolphins may reflect the natural diet or indicate some potential biological or nutritional status significance.

Decreased lymphocyte responses in free-ranging bottlenose dolphins (Tursiops truncatus) are associated with increased concentrations of PCBs and DDT in peripheral blood.

Since 1987, large-scale mortalities of dolphins have been reported along the Atlantic coast of North America, in the Gulf of Mexico, and in the Mediterranean Sea. Autopsied bottlenose dolphins, Tursiops truncatus, which were collected from the large-scale mortality along the Atlantic coast in 1987 to 1988, exhibited opportunistic infections indicative of immune dysfunction. Further, these animals had high levels of chlorinated hydrocarbons, such as PCBs and DDT, that can suppress immune functions. The purpose of this study was to determine whether there is a relationship between chemical contaminant exposure and immune response in free-ranging dolphins. In June of 1991, peripheral blood was obtained from members of a bottlenose dolphin population that resides along the west coast of Florida. Peripheral blood lymphocyte responses to Concanavalin A (Con A) and phytohemagglutinin (PHA) were determined in vitro and compared by regression analysis with contaminant concentrations in whole blood from a small subset of these animals (n = 5). These data indicate that a reduced immune response in these bottlenose dolphins was correlated with increasing whole blood concentrations of several contaminants. Specifically, inverse correlations were found between Con A-induced lymphocyte proliferation and tetrachlorinated to octachlorinated biphenyls (r2 values ranged from 0.70 to 0.87). Con A-induced lymphocyte responses also correlated inversely with p,p'DDT (r2 values of 0.73 and 0.79); o.p'-DDE (r2 values of 0.93 and 0.96); and p,p'-DDE (r2 values of 0.73 and 0.81).

Human Interactions with Free-Ranging and Captive Bottlenose Dolphins

ABSTRACTThe popular demand for encounters with dolphins has resulted in organized encounters around the world involving in-water interactions with both captive and free-ranging dolphins. Many concerns about these interactions have been raised with regard to the well-being of human and dolphin participants (e.g. Capaldo 1989; Iannuzzi and Rowan 1991). In this paper we (a) review existing information on human/dolphin interactions, (b) provide a qualitative comparison of such interactions in the captive and in the wild with the same species of dolphin (Tursiops truncatus), and (c) make suggestions regarding future research needs regarding the wellbeing of dolphins and humans in interactive programs.This study found that the free-ranging dolphin/human interactions consisted primarily of basic elements of intraspecific interactions among free-ranging dolphins. Interactive dolphin behaviors in the captive environment consisted primarily of actions that had been signaled and then reinforced by humans. Potential ...

Lack of Association between Magnetic Patterns and the Distribution of Free-Ranging Dolphins

While free-ranging dolphins ( Delphinus sp.) have been shown to be associated with bottom topography (depth contours of the sea floor), stranded dolphins have been shown to be associated with magnetic topography. Association with magnetic patterns that may be useful for orientation and navigation by free-ranging dolphins has not been demonstrated. Evaluation of the same 140 locations of free-ranging Delphinus delphis that demonstrate an association with bottom topography patterns shows no association with magnetic intensity gradients or directional orientation with magnetic patterns. Dolphins may be able to detect cues from both bottom topography and magnetic patterns, but the free-ranging dolphins analyzed here are associated with only bottom topography.

Sexing beluga whales (Delphinapterus leucas) by means of DNA markers

Few methods are available for determining the sex of free-ranging individual whales, dolphins, and porpoises of species that are not obviously sexually dimorphic. We have developed a technique for sexing beluga whales (Delphinapterus leucas) by using a Y-chromosome-specific DNA restriction fragment. Genomic DNA was extracted from liver samples of 18 beluga whales (9 males, 9 females) sexed at dissection. DNA from males and females was digested with five restriction enzymes, electrophoresed, and transferred to membranes by Southern blotting. When probed with the labelled human Y-chromosome zinc finger protein gene probe pDP1007, male-specific bands and bands common to both sexes, but more intense in females than in males, were observed. The DNA digested with EcoRI provided the clearest sex-discriminating banding pattern. Even when DNA of various qualities digested with EcoRI was used, all the males showed a 3.4-kilobase (kb) band, presumably from the Y-chromosome, as well as a 2.1-kb band. Females showed the 2.1-kb band, but all lacked the 3.4-kb band. This 3.4-kb EcoRI male-specific band permits unambiguous sex determination, which will facilitate examination of sex-related differences in population structure and habitat use of belugas, which have important implications for management decisions.

Surfacing Behavior and Ventilation in Free-Ranging Dolphins

Journal Article Surfacing Behavior and Ventilation in Free-Ranging Dolphins Get access Clifford A. Hui Clifford A. Hui Code 521, Naval Ocean Systems Center, San Diego, CA 92152 Search for other works by this author on: Oxford Academic Google Scholar Journal of Mammalogy, Volume 70, Issue 4, 27 November 1989, Pages 833–835, https://doi.org/10.2307/1381722 Published: 27 November 1989 Article history Received: 23 June 1988 Accepted: 01 February 1989 Published: 27 November 1989

Brain lesions in a Pacific white-sided dolphin (Lagenorhynchus obliquidens).

A young, male, free-ranging Pacific white-sided dolphin (Lagenorhynchus obliquidens) was found disoriented and died after being held in captivity for several months. Malacic lesions in several areas of the brain were associated with helminth eggs. The appearance and location of these eggs suggested they were of the genus Nasitrema.

Cortisol, Aldosterone, and Leucocytes in the Stress Response of Bottlenose Dolphins, Tursiops truncatus

The activity associated with capturing, restraining, and removing bottlenose dolphins, Tursiops truncatus, from water stimulates a stress response as reflected by circulating cortisol, aldosterone, and eosinophils. Serum cortisol increased from resting levels of about 30 to 110 nmol/L within 1 h, aldosterone rose from less than 280 pmol/L to up to 1880 pmol/L within 3 h, and circulating eosinophils were depressed to less than 40% of their initial numbers within 7 h after the animals were removed from water (calm-capture). This basic response was not enhanced when the capture procedure was prolonged for 3 h (chase-capture) or when the dolphins were given adrenocorticotropic hormone and was similar to that observed in free-ranging dolphins after they had been held in a net for up to 5 h. Eosinophil numbers appear to be a consistent and practical indicator of stress in dolphins.