Little is known about the sleeping patterns of our underwater friends but a new study has shown that dolphins and whales sleep with half their brain switched on.
The University of Canterbury study shows that whales, dolphins and porpoises sleep with only half the brain on at a time, an unusual behaviour trait also seen in migrating birds.
University of Canterbury researcher Andrew Wright says the research raises the possibility that animals sleeping underwater might be more susceptible to being entangled in nets.
Dr Wright said if fishermen avoided setting nets at the depth that dolphins slept, they could make a big difference to saving endangered dolphins lives.
"Although the dives make up less than 10 per cent of all the activities for each animal, even small reductions in fisheries bycatch can make a big difference to the long-term survival of many endangered cetacean species," he said.
The study also has implications for how scientists measure dolphins activity as dolphins use very little echolocation clicks when they are sleeping.
"The existence of quiet dives mean that not all animals will necessarily be detected. This means the finding also has implications for industries that rely on passive acoustic monitoring to protect marine mammals for harmful effects, such as the oil and gas industry," Dr Wright said.