The first physiological evidence that sharks take a break from tracking prey to catch a few winks has been uncovered by a researcher who specializes in sleep among aquatic creatures, from sharks to crocodiles. The comparative sleep physiologist studied the metabolic signatures of sleep and behavioral sleep indicators among New Zealand's draughtsboard sharks. His research found that they produced a lower metabolic rate and recumbent body posture when inactive for longer than five minutes, supporting the idea that they were conserving energy by sleeping.