Diverse Activity Rhythms in Sharks (Elasmobranchii).

Sharks are an interesting group of vertebrates, as many species swim continuously to "ram" oxygen-rich seawater over their gills (ram ventilators), whereas other species "pump" seawater over their gills by manipulating buccal cavity volume while remaining motionless (buccal pumpers). This difference in respiratory physiology raises the question: What are the implications of these differences in lifestyle for circadian rhythms? We investigated the diel activity patterns of 5 species of sharks, including 3 ram ventilating species: the school shark (), the spotted estuary smooth-hound (), and the spiny dogfish (); and 2 buccal pumping species: the Port Jackson () and draughtsboard () sharks. We measured the amount, duration, and distance traveled while swimming over multiple days under a 12:12 light:dark light regime for all species and used modified light regimes for species with a clear diel rhythm in activity.