Movements Of Sharks Research Articles

Movements of blue sharks (Prionace glauca) in depth and course

Acoustic telemetry was used to follow 22 blue sharks,Prionace glauca (Linnaeus), over the continental shelf and slope in the region between George's Bank and Cape Hatteras between 1979 and 1986. The sharks frequently made vertical excursions between the surface and depths of several hundred meters. The oscillations, which were repeated every few hours, were largest in the daytime and were smaller in amplitude and confined to depths near the thermocline at night. This behavior was prominent in trials from August through March, but was not seen from June through July. Diving is discussed in terms of a hunting tactic and behavioral thermoregulation. Most of the sharks moved in a southeasterly direction from the release point and many maintained a constant course day and night for several days. The sharks may orient to the earth's magnetic field, or to the ocean's electric fields, allowing them to swim on a constant heading in the absence of celestial cues. These possibilities are discussed in the appendix.

A basking shark ( Cetorhinus maximus) tracked by satellite together with simultaneous remote sensing

Tracking movements of marine animals for extended periods at sea is very expensive and labour intensive. The only method that shows promise for world-wide tracking in long-term studies is satellite tracking. The purpose of this study was to test this technique under operational conditions on basking sharks in the North Atlantic Ocean. These fish feed on plankton near the surface, and the long-term objective is to investigate the foraging and migratory movements in relation to sea surface temperature and plankton distribution patterns. A basking shark equipped with a special UHF radio transmitter was tracked for 17 days off the West Coast of Scotland using the ARGOS satellite data collection and location system. The shark surfaced during warm sunny weather and its movements were rather localised. Swimming speed was estimated as 0.106 body lengths per second between locations on successive satellite orbits. Simultaneous infrared imagery using the NOAA 7 AVHRR indicated the shark's movements relative to sea surface temperature variations. This preliminary experiment clearly demonstrates the feasibility of satellite-based monitoring of movements of marine animals using currently available operational satellite systems.

Juvenile denticles of the swell shark Cephaloscyllium ventriosum: function in hatching

The swell shark Cephaloscyllium ventriosum is an oviparous scyliorhinid. The young possess two longitudinal, dorsolateral rows of denticles, designated juvenile denticles, which are larger and different in form from the surrounding ones. Observations of the hatchings of five sharks and analysis of films taken of one indicate that these specialized denticles interact with the edge of the egg-case opening in the manner of a pawl and ratchet during the shark's emergence, thus serving as a mechanical aid which increases the efficiency of the shark's movements in hatching. These specialized denticles are found on the young of a variety of oviparous sharks and chimaeroids, and disappear from the young soon after hatching.