Is the Shark Just Drifting, or Does It Take a Quick Nap?

Abstract

It is unknown if resting sharks can sleep, which is also true for gliding ones.Here, a videotaped bull shark is presented that drifted in an uncontrolled manner for 120 seconds while sinking with 0.1 m/second. Several aspects are discussed to determine if the shown behavior reflects the commonly accepted definition of sleep. Additionally, the idea is also discussed if this state might reflect a "quiet waking state" instead of where the shark still maintained some vigilance despite its general appearance.

Behavioural sleep in two species of buccal pumping sharks (Heterodontus portusjacksoni and Cephaloscyllium isabellum)

“…As the Port Jackson sharks were smaller in size, this orientation did not provide them with the same level of contact with the tank corners, which may explain the difference in behavioural choices between the two species. Although anecdotes of increased arousal thresholds have been described in sharks (Clark, 1973;Kelly et al, 2019;Ritter, 2020;Weber, 1961), this is the first quantitative evidence of this phenomenon in any cartilaginous fish.…”