Hydromechanics and biology

Summary To exemplify relations between biology and hydrodynamics the Reynolds number range and the effects of viscosity and inertia in swimming and flying organisms is discussed. Comparing water beetles and penguins it is shown, that the technical drag coefficient is an adequate means to describe flow adaptation in animals. Compared to technical systems, especially the penguins' drag coefficient is astonishingly low. Furthermore, the question, why comparatively thick bodies in penguins and dolphins show rather low drag is discussed. Distributed boundary layer damping in dolphins and secretion of special high molecular slimes in fishes help to keep flow characteristics laminar. As an example of one easily understood thrust mechanism, the drag inducing pair of rowing legs in water beetles is morphologically and hydrodynamically analysed. Fish swimming is discussed as a locomotion principle using lift components. Thrust generation by the moving tail fin of a fish is analysed in detail. Coming back to the influence if Reynolds number, it is finally shown, how very small, bristle bearing swimming legs and wings of insects make use of viscosity effects for locomotion.     

Simulated and experimental estimates of hydrodynamic drag from bio-logging tags

Drag force acting on swimming marine mammals is difficult to measure directly. Researchers often use simple modeling and kinematic measurements from animals, or computational fluid dynamics (CFD) simulations to estimate drag. However, studies that compare these methods are lacking. Here, computational simulation and physical experiments were used to estimate drag forces on gliding bottlenose dolphins (Tursiops truncatus). To facilitate comparison, variable drag loading (no-tag, tag, tag + 4, tag + 8) was used to increase force in both simulations and experiments. During the experiments, two dolphins were trained to perform controlled glides with variable loading. CFD simulations of dolphin/tag geometry in steady flow (1–6 m/s) were used to model drag forces. We expect both techniques will capture relative changes created by experimental conditions, but absolute forces predicted by the methods will differ. CFD estimates were within a calculated 90% confidence interval of the experimental results for all but the tag condition. Relative drag increase predicted by the simulation vs. experiment, respectively, differed by between 21% and 31%: tag, 4% vs. 33%; tag + 4, 47% vs. 68%; and tag + 8, 108% vs. 77%. The results from this work provide a direct comparison of computational and experimental estimates of drag, and provide a framework to quantify uncertainty.     

Impact of different groups of swimmers on dolphins in swim-with-the-dolphin programs in two settings

Abstract

In recent years, dolphin-assisted therapy has become very popular, and an increasing number of facilities worldwide are offering therapy programs that incorporate dolphins. We observed 83 sessions with five dolphins at “Dolphins Plus,” USA, and 37 sessions with 13 dolphins at “Dolphin Reef.” Israel, during unstructured swim-with-the-dolphin programs. Both facilities are fenced sea pens with ocean water. Our detailed observations focused on contact and distance behaviors between dolphins and amongst dolphins with different groups of human swimmers: adults, children and children with mental and physical disabilities at “Dolphins Plus,” and adults only at “Dolphin Reef.” The dolphins at “Dolphins Plus” showed some signs of stress such as avoidance, speed increase, higher metabolism and intensification of a subgroup. These signs were most evident when the dolphins were with adult swimmers. In contrast, the dolphins at “Dolphin Reef” seemed to be attracted to adult swimmers. We will discuss these opposing findings with reference to the different housing conditions. Our results indicate that limited space results in a reduction of the dolphins' attraction for swimmers.     

The Mechanism of Drag Reduction around Bodies of Revolution Using Bionic Non-Smooth Surfaces

Bionic non-smooth surfaces （BNSS） can reduce drag. Much attention has been paid to the mechanism of shear stress reduction by riblets. The mechanism of pressure force reduction by bionic non-smooth surfaces on bodies of revolution has not been well investigated. In this work CFD simulation has revealed the mechanism of drag reduction by BNSS, which may work in three ways. First, BNSS on bodies of revolution may lower the surface velocity of the medium, which prevents the sudden speed up of air on the cross section. So the bottom pressure of the model would not be disturbed sharply, resulting in less energy loss and drag reduction. Second, the magnitude of vorticity induced by the bionic model becomes smaller because, due to the sculpturing, the growth of tiny air bubbles is avoided. Thus the large moment of inertia induced by large air bubble is reduced. The reduction of the vorticity could reduce the dissipation of the eddy. So the pressure force could also be reduced. Third, the thickness of the momentum layer on the model becomes less which, according to the relationship between the drag coefficient and the momentum thickness, reduces drag.     

Some effects of shark nets in the Natal nearshore environment

Synopsis Protective gillnets (shark nets) have been successful in reducing the frequency of shark attacks on the coast of Natal, South Africa. This is achieved primarily through a reduction in numbers of large sharks. The nets also take a by catch of dolphins, sea turtles, batoids and teleosts. Concern has been expressed over the direct effect of mortalities on the various stocks and also the broader, indirect effects on the inshore system. Catch rates of most shark species declined initially but have shown no trend since the mid-1970s. A first estimate of the reduction in total shark numbers is provided, and factors such as stock identity and net avoidance are discussed. Turtle and teleost stocks do not appear to be threatened by net mortalities but marine mammalogists are investigating the sustainability of catches of two dolphin species. Certain batoids may have declined despite a high release rate, but more data are needed. A published contention that shark netting has resulted in a proliferation of small sharks through reduced predation is re-examined and considered to be exaggerated. Reduced predation on dolphins, as a result of shark netting, is estimated.     

The influence of competing-risks setting on the choice of hypothesis test for treatment effect

There is considerable debate regarding the choice of test for treatment difference in a randomized clinical trial in the presence of competing risks. This question arose in the study of standard and new antiepileptic drugs (SANAD) trial comparing new and standard antiepileptic drugs. This paper provides simulation results for the log-rank test comparing cause-specific hazard rates and Gray's test comparing cause-specific cumulative incidence curves. To inform the analysis of the SANAD trial, competing-risks settings were considered where both events are of interest, events may be negatively correlated, and the degree of correlation may differ in the 2 treatment groups. In settings where there are effects in opposite directions for the 2 event types, a likely situation for the SANAD trial, Gray's test has greater power to detect treatment differences than log-rank analysis. For the epilepsy application, conclusions were qualitatively similar for both log-rank and Gray's tests.     

Historical and current records of aquarium cetaceans in China

The number of cetaceans housed in aquariums in China is increasing. Detailed information on the historical and current population status has not been reported, despite its importance for successful breeding and population management. Questionnaires were conducted between December 2006 and May 2009, and the information was used to construct studbooks. Our survey showed that 10 species had been introduced to aquariums since 1978, including 26 (with 15 in the current population) finless porpoises (Neophocaena phocaenoides), 5 (5) false killer whales (Pseudorca crassidens), 94 (80) common bottlenose dolphins (Tursiops truncatus), 48 (30) Indo-Pacific bottlenose dolphins (Tursiops aduncus), 36 (32) beluga whales (Delphinapterus leucas), 10 (10) pantropical spotted dolphins (Stenella attenuata), 8 (8) Risso's dolphins (Grampus griseus), 2 (2) short-finned pilot whales (Globicephala macrorhynchus), 2 (2) Pacific white-sided dolphins (Lagenorhynchus obliquidens), and 5 (0) baiji dolphins (Lipotes vexillifer). The number of cetaceans has increased markedly in the past 32 years, especially since 1995. Currently, 184 individuals are under human care throughout China, a number larger than any other country with an International Species Information System membership. In addition, the Annual Survival Rates of bottlenose dolphins (0.959) and beluga whales (0.968) were found higher than those reported previously (0.93-0.951 and 0.94-0.954, respectively).     

Experiment about Drag Reduction of Bionic Non-smooth Surface in Low Speed Wind Tunnel

The body surface of some organisms has non-smooth structure, which is related to drag reduction in moving fluid. To imitate these structures, models with a non-smooth surface were made. In order to find a relationship between drag reduction and the non-smooth surface, an orthogonal design test was employed in a low speed wind tunnel. Six factors likely to influence drag reduction were considered, and each factor tested at three levels. The six factors were the configuration, diameter/bottom width, height/depth, distribution, the arrangement of the rough structures on the experimental model and the wind speed. It was shown that the non-smooth surface causes drag reduction and the distribution of non-smooth structures on the model, and wind speed, are the predominant factors affecting drag reduction. Using analysis of variance, the optimal combination and levels were obtained, which were a wind speed of 44 m/s, distribution of the non-smooth structure on the tail of the experimental model, the configuratio     

Seroprevalence of Toxoplasma gondii antibodies in wild dolphins from the Spanish Mediterranean coast

Although Toxoplasma gondii infection has been found occasionally in cetaceans, little is known of the prevalence of antibodies to T. gondii in wild dolphins. Antibodies to T. gondii were determined in serum samples from 58 dolphins stranded in the Spanish Mediterranean coast. Modified agglutination test was used to determine T. gondii antibodies, and a titer of 1:25 was considered indicative of T. gondii infection. Antibodies to T. gondii were found in 4 of 36 striped dolphins (Stenella coeruleoalba), in 2 of 4 common dolphins (Delphinus delphis), in 4 of 7 bottlenose dolphins (Tursiops truncatus), and in 1 harbour porpoise (Phocoena phocoena). Antibodies were not found in 9 Risso's dolphins (Grampus griseus) and in 1 long-finned pilot whale (Globicephala melas) surveyed. The results indicate that T. gondii infection is frequent in at least 3 dolphin species from the Mediterranean Sea.     

Skin-friction drag analysis from the forced convection modeling in simplified underwater swimming

This study deals with skin-friction drag analysis in underwater swimming. Although lower than profile drag, skin-friction drag remains significant and is the second and only other contribution to total drag in the case of underwater swimming. The question arises whether varying the thermal gradient between the underwater swimmer and the pool water may modify the surface shear stress distribution and the resulting skin-friction drag acting on a swimmer's body. As far as the authors are aware, such a question has not previously been addressed. Therefore, the purpose of this study was to quantify the effect of this thermal gradient by using the integral formalism applied to the forced convection theory. From a simplified model in a range of pool temperatures (20-30 degrees C) it was demonstrated that, whatever the swimming speeds, a 5.3% reduction in the skin-friction drag would occur with increasing average boundary-layer temperature provided that the flow remained laminar. However, as the majority of the flow is actually turbulent, a turbulent flow analysis leads to the major conclusion that friction drag is a function of underwater speed, leading to a possible 1.5% reduction for fast swimming speeds above 1m/s. Furthermore, simple correlations between the surface shear stress and resulting skin-friction drag are derived in terms of the boundary-layer temperature, which may be readily used in underwater swimming situations.     

Morphology of the subdermal connective tissue sheath of dolphins: a new fibre-wound, thin-walled, pressurized cylinder model for swimming vertebrates

The subdermal connective tissue sheath (SDS) of dolphins is a fibre-reinforced membrane connected to other locomotor tissues, including blubber, axial muscles and tendons, and vertebral column. The complicated connections between the SDS and other locomotor tissues suggest that the SDS acts as a peripheral skeletal element for the axial locomotor muscles and as an anchor for a de novo dermal appendage, the dorsal fin. The morphology of the SDS suggests that the dolphin can be modelled as a fibre-wound, thin-walled, pressurized cylinder. Existing cylinder models predict that the SDS functions to resist torsional forces, prevent aneurysms, and limit wrinkling when the dolphin bends in locomotion. I present a new functional model that more accurately represents the morphology of the dolphin cylinder wrapped by the SDS. The new model predicts that the SDS: (1) acts as a retinaculum for the terminal tendons of the axial locomotor muscles; and (2) plays a role in maintaining the laterally flattened cross-sectional shape of the caudal peduncle. The model is based on external morphological features of dolphins shared by other steady swimming aquatic vertebrates, such as carangiform and thunniform fishes. These features, which include a streamlined body shape and narrow necking of the caudal peduncle have been identified as adaptions to reduce drag. The new model offers insight into some of the structural features of the body wall required to maintain the hydrodynamicallytuned, external morphology of steady-swimming vertebrates.     

Genetic differentiation between parapatric 'nearshore' and 'offshore' populations of the bottlenose dolphin.

The existence of nearshore and offshore populations of the bottlenose dolphin has been documented throughout its range. In several cases the two regional forms have been shown to be morphologically distinct, although there is considerable overlap for most characters. The populations off the eastern coast of North America have been the subject of a long-term programme of research on their distribution and movements. In this study, we compare mitochondrial and nuclear genetic markers between dolphins classified as either nearshore or offshore type. These putative populations were found to be distinct at both nuclear and mitochondrial genetic markers. Further, the level of variation among the nearshore dolphins was reduced compared with the offshore population. A broader geographical comparison suggests a shared lineage between offshore dolphins from the western North Atlantic and both offshore and nearshore dolphins from the eastern Atlantic. These results are consistent with local differentiation based on habitat or resource specialization in the western North Atlantic, and suggest differences in the character of the nearshore/offshore distinction in different parts of the world.     

Long-term viability and differentiation of bovine oviductal monolayers: Bidimensional versus three-dimensional culture

Different in vitro models have been developed to study the interaction of gametes and embryos with the maternal tract. In cattle, the interaction of the oviduct with gametes and embryos have been classically studied using oviductal explants or monolayers (OMs). Explants are well differentiated but have to be used within 24 h after collection, whereas OMs can be used for a longer time after cell confluence but dedifferentiate during culture, losing cell polarity and ciliation. Herein, OMs were cultured either in M199 plus 10% fetal calf serum or in a semidefined culture medium (Gray's medium), in an immersed condition on collagen-coated coated microporous polyester or polycarbonate inserts under air-liquid interface conditions. The influence of culture conditions on long-term viability and differentiation of OMs was evaluated through scanning electron microscopy, localization of centrin and tubulin at the confocal laser scanning microscope, and assessment of maintenance of viability of sperm bound to OMs. Findings demonstrated that OMs cultured in an immersed condition with Gray's medium retain a better morphology, do not exhibit signs of crisis at least until 3 wks postconfluence, and maintain the viability of bound sperm significantly better than parallel OMs cultured in M199 plus 10% fetal calf serum. OM culture with Gray's medium in air-liquid interface conditions on porous inserts promotes cell polarity, ciliation, and maintenance of bound sperm viability at least until 3 wks postconfluence. In conclusion, oviduct culture in Gray's medium in an immersed or air-liquid condition allows long-term culture and, in the latter case, also ciliation of bovine OMs, and may represent in vitro systems that mimick more closely the biological processes modulated by the oviduct in vivo.     

Effects of fresh and seawater ingestion on osmoregulation in Atlantic bottlenose dolphins (Tursiops truncatus)

Bottlenose dolphins (Tursiops truncatus) are marine mammals with body water needs challenged by little access to fresh water and constant exposure to salt water. Osmoregulation has been studied in marine mammals for a century. Research assessing the effects of ingested fresh water or seawater in dolphins, however, has been limited to few animals and sampling times. Nine 16- to 25-h studies were conducted on eight adult dolphins to assess the hourly impact of fresh water, seawater, and seawater with protein ingestion on plasma and urine osmolality, urine flow rate (ufr), urinary and plasma solute concentrations, and solute clearance rates. Fresh water ingestion increased ufr. Fresh water ingestion also decreased plasma and urine osmolality, sodium and chloride urine concentrations, and solute excretion rates. Seawater ingestion resulted in increased ufr, sodium, chloride, and potassium urine concentrations, sodium excretion rates, and urine osmolality. Seawater with protein ingestion was associated with increased ufr, plasma osmolality, sodium excretion, and sodium, chloride, potassium, and urea urine concentrations. In conclusion, bottlenose dolphins appear to maintain water and plasma solute balance after ingesting fresh water or seawater by altering urine osmolality and solute clearance. Ingestion of protein with seawater appears to further push osmoregulation limits and urine solute concentrations in dolphins.     

A comparison of pectoral fin contact between two different wild dolphin populations

Contact behaviour involving the pectoral fin has been documented in a number of dolphin species, and various explanations about its function have been offered. Pectoral fin contact can take a variety of forms, and involves a number of body parts and movements, likely differing depending upon social or ecological context. For this study, we compare the pectoral fin contact behaviour of two species of wild dolphins: Indo-Pacific bottlenose dolphins (Tursiops aduncus) from around Mikura Island, Japan, and Atlantic spotted dolphins (Stenella frontalis) from The Bahamas. The two study populations exhibit surprising similarity in the ways in which pectoral fin contacts are used, despite differences in species and environmental conditions at the two sites. Differences in contact rates for calves between the two sites suggest that calf-focused aggression from adult dolphins is more prevalent at Mikura than in The Bahamas. Our results suggest that pectoral fin contact behaviour seems to be driven primarily by social pressures, and may be similar in function to allogrooming described in primates.     

Captive environment influences the composition and diversity of fecal microbiota in Indo-Pacific bottlenose dolphins,Tursiops aduncus

Captive environments impact the microbiota of captive animals; however, the comparison of microbiota between wild and captive dolphins has been poorly investigated. To explore the impact of a captive environment, we characterized the fecal microbiota of nine wild and four captive Indo-Pacific bottlenose dolphins, Tursiops aduncus, using a next-generation sequencing and revealed differences in the fecal microbiota between the analyzed groups. Statistical differences in abundances of the phyla Firmicutes and Proteobacteria were found between the wild and captive dolphins. Thirty-six genera (22.9% of the total genera detected in all dolphins) were shared between the groups, whereas 79 (50.3%) and 42 (26.8%) genera were found only in the wild or captive dolphins, respectively. Several pathogenic bacterial genera, including Morganella and Mycoplasma, were detected only in the captive dolphins, and the genus Lactobacillus was found only in the wild dolphins. LefSe and SIMPER analyses revealed that the genus Clostridium sensu stricto 1 was significantly more abundant in the captive dolphins than in the wild ones and contributed the most to the dissimilarity of fecal microbiota between the groups. Our results indicate that the captive environment impacts the fecal microbiota of dolphins and reinforces the importance of monitoring potentially pathogenic bacteria in captivity.     

"PUSHY" BEHAVIOR IN A WILD DOLPHIN FEEDING PROGRAM AT TANGALOOMA, AUSTRALIA

A program where wild bottlenose dolphins (Tursiops truncatus) are fed by tourists in shallow water adjacent to a wharf has been established at Tangalooma, Queensland, Australia. Up to nine dolphins attend the nightly feedings, and between 60 and 80 resort guests are permitted to hand feed these dolphins each night. Since this program began in 1992, the dolphins have increased in confidence and have started, at times, to make forceful contact with guests who enter the water to feed them. This paper categorizes such behavior as "pushy" and reports on a study which quantifies the "pushiness" of the dolphins which feed at Tangalooma. The study examines ecological variables which may determine how pushy the dolphins are at different feeding sessions. The number of dolphins attending a particular feeding significantly increases the pushiness. In addition, the presence of adult males at a feeding is likely to increase pushing. Tidal state also influences how pushy the dolphins are. At low tide, when the dolphins'mobility is restricted by the water depth, they are less likely to be pushy. Given the problems experienced in a number of other situations where wild animals are fed by humans, it is important to monitor carefully the escalation of pushy behavior in this dolphin feeding program, as it may be a precursor to more aggressive actions on the part of the dolphins.     

Isolation and characterization of a Helicobacter sp. from the gastric mucosa of dolphins, Lagenorhynchus acutus and Delphinus delphis

Gastric ulcerations in dolphins have been reported for decades. Some of these lesions were associated with parasitic infections. However, cases of nonparasitic gastric ulcers with no clearly defined etiology also have been reported in wild and captive dolphins. Considerable speculation exists as to whether dolphins have Helicobacter-associated gastritis and peptic ulcer disease. The stomachs of seven stranded Atlantic white-sided dolphins, Lagenorhynchus acutus, and 1 common dolphin, Delphinus delphis, were assessed for the presence of Helicobacter species. Novel Helicobacter species were identified by culture in the gastric mucosa of two of the eight dolphins studied and by PCR in seven of the eight dolphins. The gram-negative organisms were urease, catalase, and oxidase positive. Spiral to fusiform bacteria were detected in gastric mucosa by Warthin Starry staining. Histopathology revealed mild to moderate diffuse lymphoplasmacytic gastritis within the superficial mucosa of the main stomach. The pyloric stomach was less inflamed, and bacteria did not extend deep into the glands. The lesions parallel those observed in Helicobacter pylori-infected humans. Bacteria from two dolphins classified by 16S rRNA analysis clustered with gastric helicobacters and represent a novel Helicobacter sp. most closely related to H. pylori. These findings suggest that a novel Helicobacter sp. may play a role in the etiopathogenesis of gastritis and gastric ulcers in dolphins. To our knowledge this represents the first isolation and characterization of a novel Helicobacter sp. from a marine mammal and emphasizes the wide host distribution and pathogenic potential of this increasingly important genus.     

Bionic Research on Fish Scales for Drag Reduction

To reduce friction drag with bionic method in a more feasible way,the surface microstructure of fish scales was analyzed attempting to reveal the biologic features responding to skin friction drag reduction.Then comparable bionic surface mimicking fish scales was fabricated through coating technology for drag reduction.The paint mixture was coated on a substrate through a self-developed spray-painting apparatus.The bionic surface with micron-scale caves formed spontaneously due to the interfacial convection and deformation driven by interfacial tension gradient in the presence of solvent evaporation.Comparative experiments between bionic surface and smooth surface were performed in a water tunnel to evaluate the effect of bionic surface on drag reduction,and visible drag reduction efficiency was obtained.Numerical simulation results show that gas phase develops in solid-liquid interface of bionic surface with the effect of surface topography and partially replaces the solid-liquid shear force with gas-liquid shear force,hence reducing the skin friction drag effectively.Therefore,with remarkable drag reduction performance and simple fabrication technology,the proposed drag reduction technique shows the promise for practical applications.     

Features of the structural organization of the dolphin (Phocaena phocaena) lateral geniculate body in comparison to other dolphins]

The work describes a new for dolphins type of the cytoarchitectonic organization and topographo-anatomical features of the dorsal nucleus of the external geniculate body found in the dolphin Phocaena phocaena. In dolphins only the alveolar type of organization of the formation in question had been known which was principally different from the laminar and nuclear types characteristic of the terrestrial mammals. The Phocaena phocaena proved to have the nuclear type of organization of the external geniculate body, as well as in certain mammals. In addition, a fact of a sharp quantitative diminution of the external geniculate body as compared with other dolphins has been revealed which is of interest for the physiology of vision. This fact is of significance showing the total amount of nerve cells in the dorsal nucleus of the external geniculate body of the Phocaena phocaena to be equal to 6,6% as compared with the white-sided dolphin. Since the above diminution proved to be selective and did not take place in the anterior tuber of the quadrigeminum, the author puts forward the idea that a considerably less afferentation comes to the visual cortex of the Phocaena phocaena than to that of other dolphins, due to some, yet unknown, restriction of the visual function.