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The false killer whale (Pseudorca crassidens (Owen, 1846)) is a globally distributed delphinid that shows geographical differentiation in its skull morphology. We explored cranial morphological variation in a sample of 85 skulls belonging to a mixed sex population stranded in the Moray Firth, Scotland, in 1927. A three-dimensional digitizer (Microscribe 2GX) was used to record 37 anatomical landmarks on the cranium and 25 on the mandible to investigate size and shape variation and to explore sexual dimorphism using geometric morphometric. Males showed greater overall skull size than females, whereas no sexual dimorphism could be identified in cranial and mandibular shape. Allometric skull changes occurred in parallel for both males and females, supporting the lack of sexual shape dimorphism for this particular sample. Also, fluctuating asymmetry did not differ between crania of males and females. This study confirms the absence of sexual shape dimorphism and the presence of a sexual size dimorphism in this false killer whale population. Key words: toothed whale, morphology, asymmetry, partial least squares, Pseudorca crassidens, false killer whale. Le faux-orque (Pseudorca crassidens (Owen, 1846)) est un delphinidé de répartition planétaire dont la morphologie crânienne présente une différentiation géographique. Nous avons examiné les variations morphologiques du crâne au sein d'un échantillon de 85 crânes provenant d'une population mixte sur le plan du sexe échouée dans le Moray Firth (Ecosse) en 1927. Un numériseur tridimensionnel (Microscribe 2GX) a été utilisé pour enregistrer 37 repères anatomiques sur les crânes et 25 sur les mâchoires afin d'examiner les variations de taille et de forme et d'explorer le dimorphisme sexuel à l'aide de la morphométrie géométrique. Si la taille des crânes de mâles est généralement plus grande que celle des crânes de femelles, aucun dimorphisme sexuel n'est relevé en ce qui concerne la forme du crâne ou de la mâchoire. Des changements allométriques parallèles sont observés pour les crânes mâles et femelles, ce qui appuie l'interprétation de l'absence de dimorphisme sexuel sur le plan morphologique pour cet échantillon. En outre, il n'y a pas de différence en ce qui concerne l'asymétrie fluctuante entre les crânes de mâles et de femelles. L'étude confirme l'absence d'un dimorphisme sexuel de la forme et la présence d'un dimorphisme sexuel de la taille au sein de cette population de faux-orques. [Traduit par la Rédaction] Mots-clés: cétacé à dents, morphologie, asymétrie, moindres carrés partiels, Pseudorca crassidens, faux-orque., Introduction The false killer whale (Pseudorca crassidens (Owen, 1846)) is a large cetacean with a cosmopolitan distribution that ranges mainly between 50[degrees]N and 50[degrees]S in latitude (Baird 2009a). Adults can [...]

Reproductive biology was assessed in 106 female common dolphins (Delphinus delphis) examined post-mortem from stranding and bycatch events along the New Zealand coastline between 1997 and 2019. The average age (ASM) and length (LSM) at sexual maturity was estimated at 7.5 years and 183.5 cm, respectively. The total number of corpora in mature individuals increased with age and appeared to persist throughout life. Ovarian asymmetry was apparent, with the left ovary displaying higher rates of ovulation, and a maximum of 19 corpora recorded for a 24-year-old female. The estimated ovulation and annual pregnancy rates for mature females were 0.39 year.sup.-1 and 30%, respectively. Conception and calving occurred year-round, with a weak seasonal increase observed in late austral spring and early austral summer. As these data did not clearly show whether seasonality was present, the gestation, lactation, and resting periods were calculated as either 12.6 or 12.8 months based on the presence/absence of seasonality, respectively. Similarly, calving interval ranged from 3.15 to 3.2 years, depending upon whether seasonality was considered. The estimated LSM of the New Zealand population aligns with other populations globally, although the estimated ASM is younger by approximately 6 months. Other reproductive parameters align with Northern Hemisphere populations, although demonstrate variation, which may reflect adaptations to local conditions such as water temperature and prey availability. As the species is subject to anthropogenic impacts including pollution and bycatch, we suggest our findings be used as a baseline with which to monitor trends in population parameters., Author(s): Emily I. Palmer [sup.1] , Emma L. Betty [sup.1] , Sinéad Murphy [sup.2] , Matthew R. Perrott [sup.3] , Adam N. H. Smith [sup.4] , Karen A. Stockin [sup.1] [...]

Studies using teeth to estimate age in marine mammals presume that the neonatal line (NNL) develops at birth. This study of Indo-Pacific bottlenose dolphins (Tursiops aduncus (Ehrenberg, 1833)) is the first to investigate when the NNL appears in odontocete dentine. Two to four teeth were prepared by decalcification, thin-sectioning, and staining for 103 dolphins, including 7 dolphins of known age. Tooth length, prenatal and postnatal dentine and NNL widths were measured. Developmental class (foetus, young neonate, older neonate, Key words: Indo-Pacific bottlenose dolphin, Tursiops aduncus, neonatal line, tooth dentine, incremental layers, birth, developmental class. Les etudes qui utilisent les dents pour estimer l'age de mammiferes marins partent de l'hypothese que la ligne neonatale (LNN) se forme a la naissance. La presente etude de dauphins indiens (Tursiops aduncus (Ehrenberg, 1833)) est la premiere a se pencher sur le moment de l'apparition de la LNN dans la dentine d'odontocetes. De deux a quatre dents ont ete preparees par decalcification, preparation de lames minces et coloration pour 103 dauphins, dont 7 dauphins d'age connu. La longueur de la dent, ainsi que les largeurs de la dentine prenatale et postnatale et de la LNN ont ete mesurees. Le stade du developpement (fcetus, jeune nouveau-ne, nouveau-ne plus vieux, delphineau de moins de 1 an, delphineau de 1 an) a ete determine sur la base d'elements externes de la carcasse. La presence ou absence de LNN a ete categorisee pour chaque dauphin. La LNN etait absente chez un fcetus presque a terme et chez tous les jeunes nouveau-nes sauf un et elle etait entierement formee chez 50% des nouveau-nes plus vieux, d'ages estimes allant d'une semaine a deux mois. Elle etait absente chez un dauphin d'age connu de4a7semaines. La largeur de la LNN etait plus grande chez les dauphins de moins de 1 an que chez ceux de 1 an. Les facteurs qui declenchent la formation de la LNN sont inconnus. L'etude porte a croire que la LNN pourrait ne pas etre reliee a la croissance comme telle chez les dauphins, comme cela a clairement ete demontre chez les humains. Des processus physiologiques modules par des changements comportementaux et du regime alimentaire durant les premiers mois de la vie postnatale pourraient etre d'importants facteurs intervenant dans la formation de la LNN chez les odontocetes. [Traduit par la Redaction] Mots-cles: dauphin indien, Tursiops aduncus, ligne neonatale, dentine, couches successives, naissance, stade du developpement., Introduction Calcified structures such as bones, teeth, and horns have been used to determine age and reconstruct life-history events for individuals and populations of vertebrates (Klevezal 1996). Also known as [...]

Skin and muscle from 43 bottlenose dolphins (38 juveniles/adults, 5 calves) stranded in NW Spain were analysed to determine whether stable isotope ratios ([delta].sup.13C and [delta].sup.15N) could be used to assess dietary variation, habitat segregation and population substructure. Results were compared with published stomach contents data. Stable isotope ratios from 17 known prey species were also determined. Isotope ratios of the main prey (blue whiting, hake) varied significantly in relation to fish body size. Dolphin calves showed significant heavy isotope enrichments compared to adult females. Excluding calves, [delta].sup.15N decreased with increasing dolphin body size, probably related to an ontogenetic shift in diet towards species at lower trophic levels, e.g. on blue whiting as suggested by stomach content results. Bottlenose dolphins were divided into two putative populations (North, South) based on previous genetic studies, and values of [delta].sup.13C and [delta].sup.15N differed significantly between these two groups, confirming the existence of population structuring., Author(s): Ruth Fernández [sup.1] [sup.2] , Susana García-Tiscar [sup.3] , M. Begoña Santos [sup.4] , Alfredo López [sup.2] , Jose A. Martínez-Cedeira [sup.2] , Jason Newton [sup.5] , Graham J. [...]

The evolutionary forces that drive fitness variation in species are of considerable interest. Despite this, the relative importance and interactions of genetic and social factors involved in the evolution of fitness traits in wild mammalian populations are largely unknown. To date, a few studies have demonstrated that fitness might be influenced by either social factors or genes in natural populations, but none have explored how the combined effect of social and genetic parameters might interact to influence fitness. Drawing from a long-term study of wild bottlenose dolphins in the eastern gulf of Shark Bay, Western Australia, we present a unique approach to understanding these interactions. Our study shows that female calving success depends on both genetic inheritance and social bonds. Moreover, we demonstrate that interactions between social and genetic factors also influence female fitness. Therefore, our study represents a major methodological advance, and provides critical insights into the interplay of genetic and social parameters of fitness. animal model | gene-culture coevolution | social learning | reproductive success | relatedness doi/ 10.1073/pnas.1007997107

Several cetacean species exhibit fine-scale population structure despite their high dispersal capacities and the apparent continuity of the marine environment. In dolphins, most studies have focused on coastal areas and continental margins, and they revealed differentiated populations within relatively small geographic areas, sometimes in conjunction with a specialisation for different habitats (ecotypes). We analysed the population genetic structure of short-beaked common dolphins (Delphinus delphis) and Atlantic spotted dolphins (Stenella frontalis) in the Azores and Madeira, the two most isolated archipelagos of the North Atlantic. The archipelago of the Azores is divided into three groups of islands and stands 900 km away from Madeira. It is not known whether individuals migrate between groups of islands and archipelagos, nor whether distinct ecotypes are present. These questions were investigated by genetic analyses of 343 biopsy samples collected on free-ranging dolphins. The analyses consisted in sequencing part of the mitochondrial hyper-variable region, screening up to 14 microsatellite loci, and molecular sexing. Results did not unravel any population structure at the scale of the study area. Lack of differentiation matches expectations for spotted dolphins, which are transient in both archipelagos, but not for common dolphins, which are present year-round in the Azores and potentially resident. Absence of genetic structure over hundreds and even thousands of kilometres implies the existence of gene flow over much larger distances than usually documented in small delphinids, which could be achieved through individual movements. This finding indicates that population structure in oceanic habitat differs from that observed in coastal habitat., Author(s): Sophie Quérouil [sup.1] [sup.2] [sup.5] , Luís Freitas [sup.3] , Irma Cascão [sup.1] , Filipe Alves [sup.3] , Ana Dinis [sup.3] , Joana R. Almeida [sup.1] , Rui Prieto [...]

Blubber is a critical component of thermoregulation for marine mammals, particularly for cetaceans. However, the cost of overcoming blubber's buoyant force during descent could constrain blubber deposition. One- to 12-year-old healthy, free-ranging common bottlenose dolphins (Tursiops truncatus) were studied in Sarasota Bay, Florida, during summer (mean water temperature: 29.7[degrees]C [+ or -] 0.1 SE) and winter (mean water temperature: 19.2 [+ or -] 0.4[degrees]C) to examine ontogenetic and seasonal trends in morphology and blubber deposition. Surface-area-to-volume ratio decreased significantly with age. During summer, yearlings had significantly thicker blubber than 2- to 12-year-old animals but this difference diminished by winter because blubber deposition in response to the colder water temperature was smaller in yearlings (2-mm increase) compared to 2- to 12-year-old animals (3- to 6-mm increase). During summer, buoyancy was highest in yearlings (6.24 N [+ or -] 0.41 SE), compared to a buoyant force of -0.98 [+ or -] 0.90 N (neutrally buoyant) for 12-year-old animals. Conversely, all dolphins converged upon a similar buoyant force (8.01 [+ or -] 0.56 N) in winter. The elevated buoyancy of yearlings in summer presumably limits seasonal blubber adjustments, because all yearlings (regardless of season) converged upon a similar calculated mass-specific cost of descent that was greater than all other age classes. Balancing energetic demands of thermoregulation and locomotion may limit the flexibility of yearlings to adjust blubber deposition in response to fluctuating water temperatures. Key words: blubber, buoyancy, cetacean, cost of descent, development, dolphin, marine mammal, morphology, thermoregulation, surface-area-to-volume ratio

Echolocating bottlenose dolphins (Tursiops truncatus) discriminate between objects on the basis of the echoes reflected by the objects. However, it is not clear which echo features are important for object discrimination. To gain insight into the salient features, the authors had a dolphin perform a match-to-sample task and then presented human listeners with echoes from the same objects used in the dolphin's task. In 2 experiments, human listeners performed as well or better than the dolphin at discriminating objects, and they reported the salient acoustic cues. The error patterns of the humans and the dolphin were compared to determine which acoustic features were likely to have been used by the dolphin. The results indicate that the dolphin did not appear to use overall echo amplitude, but that it attended to the pattern of changes in the echoes across different object orientations. Human listeners can quickly identify salient combinations of echo features that permit object discrimination, which can be used to generate hypotheses that can be tested using dolphins as subjects. Keywords: echolocation, bottlenose dolphins, human listening, acoustic features, match-to-sample

As part of an examination of the population structure of short-beaked common dolphins (Delphinus delphis) in the North Atlantic, I tested if there were systematic differences in cranial morphology, in relation to geographic location, for common dolphins both within the western North Atlantic (wNA; n = 141) and between the wNA and eastern North Atlantic (eNA; n = 106). Cranial specimens from the wNA were obtained between Nova Scotia, Canada, and Florida. Those from the eNA came from the Irish Sea and the coasts of Ireland and the United Kingdom. A Wilks' [lambda] canonical discriminant analysis (CDA) was performed on the within-groups covariance matrix to test whether significant differences in group centroids (multivariate means) existed between putative population units separately for males and females. In addition, the CDA was used to reclassify each dolphin into a geographic group based on the discriminant function. The CDA of 35 cranial variables found no evidence (males: Wilks' [lambda] = 0.603, P = 0.286; females: Wilks' [lambda] 0.145, P = 0.08) of population structure below the species level within the wNA. Thus, the 1-population model for this region was supported. CDAs revealed significant differences between the eNA and wNA for both males and females (males: Wilks' [lambda] = 0.371, P < 0.0001; females: Wilks' [lambda] = 0.260, P < 0.0001). Cross-validated reclassification rates for males were 78.8% (eNA) and 87.6% (wNA) and for females were 90.6% (eNA) and 81.4% (wNA). Measurements associated with the rostrum were important discriminating variables that might reflect differences in feeding habits between these areas. Key words: common dolphin, cranial morphology, Delphinus delphis, discriminant analysis, morphometrics, North Atlantic

Hector's dolphin (Cephalorhynchus hectori) is a small New Zealand delphinid with a coastal distribution. Within a strip of 1 km from shore, the present study quantified the habitat used by the dolphins (n = 461 groups) over a 19-month period (216 field days with 966 survey hours) by recording the abiotic factors sea surface temperature (SST), water depth and water clarity. Resource selection functions were used to distinguish the properties of 461 'used' sites (dolphins present) from 425 'unused' sites (no dolphins present) in six different study areas. Most dolphins were encountered in waters < 39 m depth, with < 4 m Secchi disk visibility and > 14[degrees]C temperature. The preference of Hector's dolphins for warm and turbid waters was tested using eight models. Water depth, water clarity, SST and the study area explained dolphin presence to a very significant degree (p < 0.001), and the model allowed the creation of probability plots for a variety of combinations of the variables. Habitat selection by dolphins differed between study areas, particularly between east and west coasts, in summer (December-February) and winter (June-August). Dolphin abundance appeared to change seasonally in some study areas, possibly due to a more offshore distribution of their prey in the winter, with its lower SSTs. This was so especially in summer (the main reproductive season), when dolphins (frequently with calves) occupied shallow and turbid waters, whereas in winter less use was made of this habitat.

The estuarine dolphin (Sotalia guianensis) is common along most of the Brazilian coast, but little is known about its reproduction. We analyzed the gonads of 50 individuals incidentally caught in fishing nets on the coast of Parana, southern Brazil, between 1997 and 1999. Testes of adult males were [less than or equal to] 31.9 cm in length and [less than or equal to] 11.6 cm in width and [less than or equal to] 3.3% of the total body mass. Relative size of testes suggests a multimale mating system with sperm competition. Females ovulate in both ovaries, although the left ovary matures earlier than the right. Males reached sexual maturity at 7 years and at body lengths estimated at 170-175 cm. Females matured at 5-8 years of age and at body lengths of 164-169 cm. The reproductive cycle was estimated at 2 years, with no marked seasonality in ovulation or timing of birth. Gestation was about 12 months, fetal growth rate was 9 cm/month, and length at birth was estimated at 92.2 cm. Females older than 25 years had senescent ovaries. Key words: Brazil, estuarine dolphin, reproduction, Sotalia guianensis

The understanding of fish maneuvering and its application to underwater rigid bodies are considered. The goal is to gain insight into stealth. The recent progress made in NUWC is reviewed. Fish morphology suggests that control fins for maneuverability have unique scalar relationships irrespective of their speed type. Maneuvering experiments are carried out with fish that are fast yet maneuverable. The gap in maneuverability between fish and small underwater vehicles is quantified. The hydrodynamics of a dorsal fin based brisk maneuvering device and a dual flapping foil device, as applied to rigid cylindrical bodies, are described. The role of pectoral wings in maneuvering and station keeping near surface waves is discussed. A pendulum model of dolphin swimming is presented to show that body length and tail flapping frequency are related. For nearly neutrally buoyant bodies, Froude number and maneuverability are related. Analysis of measurements indicates that the Strouhal number of dolphins is a constant. The mechanism of discrete and deterministic vortex shedding from oscillating control surfaces has the property of large amplitude unsteady forcing and an exquisite phase dependence, which makes it inherently amenable to active control for precision maneuvering. Theoretical control studies are carried out to demonstrate the feasibility of maneuverability of biologically inspired bodies under surface waves. The application of fish hydrodynamics to the silencing of propulsors is considered. Two strategies for the reduction of radiated noise are developed. The effects of a reduction of rotational rate are modeled. The active cambering of blades made of digitally programmable artificial muscles, and their thrust enhancement, are demonstrated. Next, wake momentum filling is carried out by artificial muscles at the trailing edge of a stator blade of an upstream stator propulsor, and articulating them like a fish tail. A reduction of radiated noise, called blade tonals, is demonstrated theoretically.

A study of cranial shape in dolphins of genus Sotalia was done using 104 specimens (92 from localities along the Brazilian coast and 12 from the Amazon River basin). Twenty-two cranial landmarks, assumed to be homologous, were selected for analysis. The first 2 principal components of aligned coordinates explained 40.6% of the total variation in cranial shape. Although no sexual dimorphism was detected (P = 0.811), shape differences among populations of Sotalia were highly significant (P < 0.000001). The 1st and 2nd principal components of shape showed that the Sotalia population from the Amazon basin differed in cranial shape from marine populations. Based on differences in geometric shape, a discriminant analysis of 3 linear measurements between landmarks provided an equation that classified skulls as belonging to Amazonian or marine populations. Based on these results and evidence from several other divergent character systems and life history attributes, we suggest the use of Sotalia guianensis for marine dolphins and S. fluviatilis for Amazonian dolphins. Key words: dolphins, geographic variation, geometric morphometrics, skull shape, Sotalia

Research has been conducted on the high-energy-demand tunas and dolphin fish. The Na (super)+ -K (super)+ ATPase activity has been measured in homogenates of the frozen samples taken from the gills and intestines of these fish in investigating the effect of salt rates and water transfer on the fish gills and intestines.

There have been few studies of brain growth in cetaceans despite their potential importance for understanding cetacean, and generally mammalian, brain-behavior relationships. Among terrestrial mammals, and notably primates, high encephalization levels and long juvenile periods of dependency are associated with a prolonged period of brain development. I examined brain-growth patterns in the harbor porpoise (Phocoena phocoena) and Pacific white-sided dolphin (Lagenorhynchus obliquidens). The brain of P. phocoena is substantially more mature throughout development than that of L. obliquidens, and brain-growth patterns are related generally to adult encephalization levels in these two species. Various factors, such as habitat type and body size, are likely to play an interrelated role in brain development in cetaceans. Key words: Pacific white-sided dolphin, Lagenorhynchus obliquidens, harbor porpoise, Phocoena phocoena, cetacean, brain growth

How do male cetaceans and seals keep their testes cool without a scrotum? It turns out to be the same mechanism that keeps the fetus cool in a pregnant female [...]

Zoologist Randall S. Wells is the chief scientist of the Dolphin Biology Research Institute and a conservation biologist with the Chicago Zoological Society. Wells is based at Sarasota, FLA's Mote Marine Laboratory and began his study of dolphins in 1970, at age 16. A quarter century of research have added to human understanding of Tusrsiops truncatus. It is now known that the life span is twice as long as science once thought. For male dolphins it is about 40 years, while females live into their fifties. The dolphins on Florida's Gulf coast live in established communities, where migration is negligible.

Increased blood oxygen reserves facilitate diving in marine mammals. Previous studies show that pinnipeds require a developmental period for blood oxygen stores to reach adult capacities. We investigated if a developmental period for the blood also occurs in cetaceans which unlike pinnipeds, are exposed to diving immediately after birth. Blood samples were collected from bottlenose dolphins aged 0-12 years from wild and captive populations to determine red blood cell number cell number (RBC), hemoglobin content (Hb), hematocrit (Hct), mean corpuscular volume (MCV), mean cell hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). We found that during postnatal development, RBC, Hb, and Hct decrease from 0-1.5 months and then increase significantly from 1.5-6 months, reaching adult levels by 3 years. MCV and MCH significantly increase from birth until 2 months of age at which time they approximate adult values. MCHC significantly decreases from 0-3.2 months, then increases and approximates adult values by 6 months. Because weaning occurs at 1.5 years for bottlenose dolphins, the development of the blood oxygen store is not complete with the initiation of independent foraging. The lower oxygen storage capacity of immature dolphins undoubtedly limits dive capabilities as indicated by aerobic dive limits (ADL) calculated from our blood data. ADLs of 0-3 year olds (1.9-4.8 min) are lower than the ADLs of 4-8 and 9-12 year olds (5.1 and 5.4 min, respectively). Increases in ADL from 0 to 3 years are attributed to increases in body mass and mass specific oxygen stores while body mass alone explains the increases in ADL for dolphins 3 to 9 years.

Being born directly into an aquatic environment creates unique challenges for the breathing muscles of neonatal cetaceans. Not only must these muscles be active at the instant of birth to allow for gas exchange, but their activities must also be coordinated such that breathing takes place at the surface. Thus, we hypothesize that the breathing muscles of bottlenose dolphins, represented in this study by the diaphragm, will demonstrate adult morphologies at birth, as measured by the histochemical (myosin ATPase) and biochemical activities of their component muscle fibers. The fiber-type profiles of adult (64% slow-twitch) and neonatal (33% slow-twitch) dolphin diaphragms are found to be statistically different (F=48.02, p=0.002, df=5, n=6). In addition, there is a strong positive correlation (R-sq=0.98) between the fiber-type profile (percent slow-twitch fibers) of the dolphin diaphragm and total body length (TBL), a character that is used as a relative measure of age in dolphins. The results of the biochemical analyses support the correlation between fiber-type profile and TBL, demonstrating an increase in the expression of slow (type I) myosin heavy chain isoform with increasing body length. Thus, the diaphragms of neonatal dolphins are not well developed at birth (92-132 TBL). However, as the dolphin grows and increases its swimming and diving activities, the diaphragm matures and achieves adult morphology. Therefore, unlike dolphin locomotor muscles, which are well developed at birth, the diaphragm requires an extended period of postnatal development to achieve the adult fiber-type profile.

Actively swimming dolphins exhale and inhale in 0.3 seconds, exchanging 80% or more of their tidal volume. Although dolphins possess typical mammalian respiratory muscles (intercostals, diaphragm, rectus abdominus, etc.), the muscles responsible for their unique respiratory behavior are poorly understood. This study assessed the significance of contractions of the diaphragm, the main inspiratory muscle of terrestrial mammals, in the respiratory mechanics of bottlenose dolphins. Histochemical analyses revealed the adult fiber-type profile to be 67% slow-twitch fibers, similar to the profiles of diaphragms in other mammals, like horses (66%) and cattle (76%). The diameters of the dolphin's muscle fibers are much smaller than those of large mammals and of their own axial locomotor muscles. The small size of the fibers, their high oxidative capacity (NADH), and the slow-twitch fiber-type profile suggest a fatigue-resistant, slow-contracting diaphragm, a muscle profile that does not fit with the model of respiratory mechanics of dolphins. We ask if the diaphragm plays a major role in inspiration in dolphins.

The coastal migratory stock of Atlantic Bottlenose dolphins experienced a mass mortality event in 1987. In response, this study was designed to address a number of ecological issues relevant to this poorly described migratory dolphin stock. The evaluation of habitat usage along the Virginia coast may yield insights into the natural resources critical to these dolphins. Data on a range of environmental factors has been collected during dolphin sightings over two seasons. It has been determined that human impact on the dolphins is relatively low in this area, with only 15% of the sightings coinciding with human activity in the immediate area. There is also evidence to support the importance of this area for foraging since 17% of the sightings have included observations of probable or confirmed feeding. What is not yet clear is the duration of residence of an individual or group of dolphins in this area. Additional data, particularly uniquely identifiable dorsal fin images for tracking individuals, is needed before the overall ecological importance of this particular area can be determined.

The spinner dolphin (Stenella longirostris) performs spectacular leaps from the water while rotating around its longitudinal axis up to seven times. Although twisting of the body while airborne has been proposed as the mechanism to produce the spin, the morphology of the dolphin and basic physics precludes the spinning maneuver. A mathematical, physics-based model was developed to determine the causal mechanisms for the spinning maneuver. The model demonstrated that the angular momentum to induce the spin was generated underwater, prior to the leap. Underwater rotation would be initiated by canting the flippers at an angle to the direction of travel. The lateral drag on the flukes, flippers, and dorsal fin with their high moment of inertia restrict high rotation rates, when the dolphin is submerged. As the dolphin leaps clear of the water, the effective drag is reduced as is the moment of inertia. The rotation rate in the aerial phase increases by 2.85 times due to conservation of angular momentum as calculated from the model. Data collected from video of spinner dolphins showed a rotation rate increase of 2.65. Although there is no definitive reason for performing aerial spins, the model indicates that the high rotation rates and orientation of the dolphins body during re-entry into the water could dislodge hydrodynamically-parasitic remoras.