Behavioural and neural correlates of hydrostatic pressure sensing in sharks

• Main Author: Smith, Lauren E.
• Published: University of Aberdeen 2008
• Subjects: 591.5; Sharks
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499728

The normal depth usage of the juvenile lemon shark, <i>Negaprion brevirostris </i>was determined using data storage tags which logged pressure and temperature.  Sharks were found to predominantly occupy water depths between the surface and 1m.  A diel rhythm and a tidal rhythm were found for the pressure data.  Simultaneous acoustic tracking showed shallow water use despite the availability of deeper areas within the sharks’ home ranges.  All sharks mainly occupied a narrow range of temperatures (29°C - 31°C) at the high end of their range.  Temperature data showed mainly diel rhythms with slight tidal influence.  Pressures and temperatures used by the sharks seemed to be affected by size of home range, individual preference and predator avoidance.  The behaviour of the lesser spotted dogfish <i>Scyliorhinus canicula </i>was investigated during controlled small steps of pressure inside a hypobaric chamber.  Swimming occurred in response to decreasing pressure with increased swimming speed and duration suggesting enhanced sensitivity of the shark pressure sensor within  a narrow range between 39mbar above and down to 195mbar below barometric pressure.  Further studies using a novel tidal tank system showed that <i>Scyliorhinus </i>synchronised their activity with a 12.5 hour tidal cycle but not with a 9  hour cycle.  When different resting depths were made available, they were utilised by dogfish, suggesting an individual preference independent of environmental cues or the presence of the opposite sex.  Isolated vestibular systems were challenged over a range of pressures. Hair cell afferent activity showed responses to sinuosoidal cycles and step changes of pressure.  Temperature effects are complex but were small compared with pressure effects.  Knowledge of the pressure sensor and vertical range used by sharks is essential in the present development of marine protected areas in an attempt to ultimately aid the conservation of sharks.