Thursday, March 28, 2013

Dolphins: Sentinels of the Sea

by kellyc, This post originally appeared at the Future Science Leaders blog.

Imagine staying awake for 15 continuous days! It seems impossible to us, yet scientists have learned that dolphins are able to stay alert for 15 days or more due to their ability to sleep with one half of their brain at a time. Previous research has shown that dolphins have this unique sleeping capacity, known as unihemispheric sleep, yet this characteristic and its direct implications on dolphins were largely unknown and unstudied. New research from Brian Branstetter and his team at the National Marine Mammal Foundation has shown that this trait allows dolphins to stay alert for many continuous days without showing fatigue, and that dolphins are able to accomplish precise tasks such as echolocation in order to identify targets and monitor their environment, with astonishing precision, for up to 15 days in a row.

Branstetter’s team in California team studied 2 bottlenose dolphins, one of each gender, and tested their ability to echolocate for extended periods of time, a feat that certainly would have left other animals incapacitated, sleep-deprived and exhausted. In their tests, the dolphins were required to swim around a pen while locating eight phantom sonar targets, which sent back phantom echoes after detecting dolphin sound pulses. When a dolphin activated a target and heard its echo, it responded by pushing a paddle. Correct detection was signalled by a tone, and the successful dolphin received a fish. False alarms resulted in no tone or reward. The researchers repeated this 5-day experiment 3 times with accuracy rates around 99%.

As a result of these experiments, the researchers discovered the dolphins’ capacity to maintain alertness and awareness of their surroundings with no signs of fatigue for 5 days. The female dolphin was more successful, a result that researchers attributed to the female’s more motivated personality, often producing victory squeals upon successful detection of a sonar target. Further experimentation showed that she was able to maintain this ability for 15 days. Unfortunately, due to a storm, the experiment was cut short and the potential to continue was not fully studied.
Branstetter notes: ”From an anthropomorphic viewpoint, the ability of the dolphin to continuously monitor its environment for days without interruption seems extreme.”
However, it is believed that dolphins evolved with the ability to sleep using only one half of the brain because it is vital to the dolphins’ survival, as it allows them to continuously breathe at the surface of the water, even while half-asleep. Branstetter comments, “If dolphins sleep like terrestrial animals, they might drown,” so this seemingly extreme capability is “quite normal, unspectacular, and necessary for survival from the dolphin’s perspective.” Branstetter’s new findings also suggest that the need to remain observant and aware of one’s environment, such as the need to avoid predators may also have played a factor in developing this ability for unihemispheric sleep.

“These majestic beasts are true unwavering sentinels of the sea. The demands of ocean life on air breathing dolphins have led to incredible capabilities, one of which is the ability to continuously, perhaps indefinitely, maintain vigilant behavior through echolocation,” says Branstetter.
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About this contributor: Kelly is an ocean lover and high school student, and is particularly fascinated by whales. She enjoys being outdoors, writing, traveling and meeting new people.

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