Orientation and navigation in elasmobranchs: Which way forward?

Elasmobranchs possess a multiplicity of mechanisms controlling posture and short distance orientation. Visual-vestibular contributions to posture and locomotion are well documented. So too, are the contributions of vision, ol faction and the octavolateralis senses to short distance orientation, parti cularly orientation to specific environmental stimuli such as those generat ed by prey. Less well understood are the mechanisms guiding orientation ove r longer distances. Anecdotal and systematic observations of behaviour show tidal, daily, repeat long distance, and even seasonal movement patterns. T rue navigation has not been demonstrated in elasmobranchs and the sensory m echanisms underlying the above movement patterns remain largely speculative . However, they are likely to include responses to water currents, and phys ical parameters such as temperature, pressure, and the geomagnetic field. O f particular interest in elasmobranchs is that geomagnetic orientation coul d be mediated directly via a magnetite based sensory system, or indirectly via the electrosensory system. Systematic studies of movement patterns and experimental studies of the underlying mechanisms of orientation are requir ed to gain an increased understanding of orientation and navigation in this intriguing group.