Dolphin sympatric ecology

Interspecific associations between two or more species of the family Delphinidae have been reported by many scientists, but the sympatric ecology of such dolphin associations has not been studied in great detail. A few field investigations have been conducted on this subject in different parts of the world on species such as bottlenose dolphins (Tursiops spp.), short-beaked common dolphins (Delphinus delphis), and killer whales (Orcinus orca). Sympatric dolphins seem to use different strategies to co-exist when resources appear to be limited, including dietary divergence (different prey preference, slightly diverse diet, different feeding time) and/or different habitat use (shallow versus deep waters, flat areas versus submarine canyons and escarpments, different travel routes). This paper presents a review of some well-studied dolphin species found in sympatry and discusses the nature of habitat and resource partitioning as well as studies on aggressive behaviour displayed by species living in the same habitat.     

Dolphin swimming–a review

Research into dolphin swimming has historically been guided by false assumptions of 'effortless', 'high-speed' swimming. These assumptions have instigated the development of drag-reduction hypotheses but tests of these hypotheses have generally had little success. The autecological approach has dominated recent efforts and has been more successful. In this review we summarize results of decades of research efforts to study these creatures. (1) Drag is minimized primarily by the streamlined shape of the body and appendages, with no known contributions from compliant dampening, dermal ridges, secretions, boundary layer heating, or skin folds. All indications are that the boundary layer is turbulent. (2) Muscles for the upstroke and downstroke of swimming dolphins provide approximately equal power. (3) Output force is enhanced by insertions occurring on the long processes of the vertebrae and on the subdermal connective tissue sheath. (4) Measured swimming speeds are lower than previously believed, with maximum reported routine speeds being approximately 3 m/s. (5) Porpoising behaviour appears to be the most energetically conservative manner in which to breathe when swimming at high speed. (6) Riding surf and wind waves involves the balance between the wave slope and the weight of the animal whereas riding the bow wave involves the interaction of the pressure wave in front of a ship and the drag of the dolphin.     

Dolphin sonar--modelling a new receiver concept

Observations suggest that dolphin sonars function well in the very shallow, reverberant, near-shore region of the ocean, and significantly out-perform man-made systems under such conditions. The echolocation characteristics of many small cetaceans have been measured directly and the high performance of biosonar systems is not in question, but explanations for their resolution, target detection, localization and tracking abilities are inadequate and deserve further investigation. The dolphin's lower jaw has been identified as part of an echo-receptor, and several hypotheses have been proposed to explain this. In one of these, the regularity of dolphin teeth was considered as a sonar array. This paper explores the physics of such systems with models based on established radar and sonar principles, and using data from various dolphin species. The insights gained from this modelling then lead to speculative proposals for new sonar receiver concepts that may have advantages over more conventional designs in shallow water operation.     

Dolphin skin as a natural anisotropic compliant wall

Although the success of compliant walls in mimicking dolphin skin is well known, the drag-reducing properties of a dolphin's skin are still unclear. Moreover, little is known about the relation between the 3D structure of the skin and the local flow conditions. To study the role of a dolphin's skin in reducing the drag the skin morphology parameters were compared with the parameters of an anisotropic compliant wall and a possible flow-skin interface was considered. The 3D structure of skin from different locations was modelled using serial histological sections of the skin. The hydrodynamics of the dorsal fin of the harbour porpoise was studied by means of computer simulation of the flow around virtual models of the fin. It was found that the distribution of the skin morphology parameters is correlated with the local flow parameters on the fin surface. The skin structure appears to allow the flow-skin interface to behave similar to an anisotropic compliant wall in the regions of favourable and adverse pressure gradients on the fin. The relation founded between the skin morphology and the local flow parameters could be useful in the design of multipanel anisotropic compliant walls.     

A Quantitative Analysis of the Sounds of Hector's Dolphin

We developed an automatic, computer-based system in which digital signal processing techniques were used to measure 31 variables from digitized Hector's dolphin (Cephalorhynchus hectori) sounds. Principal component analyses of these data were used to investigate the relationships between sounds. Hector's dolphins make only a very few types of pulsed “clicks”, most of which are centred around 125 kHz. None of these had an average frequency of less than 82 kHz, and the only audible sounds were made up of high-frequency clicks repeated at such high rates that the repetition rate was audible to us as a tonal “cry” or “squeal”. In comparison to signal levels recorded from other cetaceans, all the Hector's dolphin signals were low-level; the maximum received sound pressure level was 163 dB (re 1μPa).     

永远的“淇淇”

<正>1 978年,中国科学院水生生物研究所成立白鱀豚研究组,正式开始科学研究。同年,国务院颁布了《水资源繁殖保护条例》、《 关于严格保护珍贵稀有野生动物通令》,也将其列为重点保护对象。随着对白鱀豚"琪琪"的人工饲养成功,白鱀豚逐渐被科学家揭开了神秘的面纱,并且引起了国内外的高度关注。但人们并不知道,在这一过程中还有那些未曾饲养成功的白鱀豚,为科     

Dolphin natures, human virtues: MacIntyre and ethical naturalism

Can biological facts explain human morality? Aristotelian 'virtue' ethics has traditionally assumed so. In recent years Alasdair MacIntyre has reintroduced a form of Aristotle's 'metaphysical biology' into his ethics. He argues that the ethological study of dependence and rationality in other species--dolphins in particular--sheds light on how those same traits in the typical lives of humans give rise to the moral virtues. However, some goal-oriented dolphin behaviour appears both dependent and rational in the precise manner which impresses MacIntyre, yet anything but ethically 'virtuous'. More damningly, dolphin ethologists consistently refuse to evaluate such behaviour in the manner MacIntyre claims is appropriate to moral judgement. In light of this, I argue that virtues--insofar as they name a biological or ethological category--do not name a morally significant one.     

Social cognition

Social cognition concerns the various psychological processes that enable individuals to take advantage of being part of a social group. Of major importance to social cognition are the various social signals that enable us to learn about the world. Such signals include facial expressions, such as fear and disgust, which warn us of danger, and eye gaze direction, which indicate where interesting things can be found. Such signals are particularly important in infant development. Social referencing, for example, refers to the phenomenon in which infants refer to their mothers' facial expressions to determine whether or not to approach a novel object. We can learn a great deal simply by observing others. Much of this signalling seems to happen automatically and unconsciously on the part of both the sender and the receiver. We can learn to fear a stimulus by observing the response of another, in the absence of awareness of that stimulus. By contrast, learning by instruction, rather than observation, does seem to depend upon awareness of the stimulus, since such learning does not generalize to situations where the stimulus is presented subliminally. Learning by instruction depends upon a meta-cognitive process through which both the sender and the receiver recognize that signals are intended to be signals. An example would be the 'ostensive' signals that indicate that what follows are intentional communications. Infants learn more from signals that they recognize to be instructive. I speculate that it is this ability to recognize and learn from instructions rather than mere observation which permitted that advanced ability to benefit from cultural learning that seems to be unique to the human race.