We have a new paper out, published in Endangered Species Research, on juvenile green turtles from Dry Tortugas National Park.
Using accelerometers, we assessed both depth and ‘overall dynamic body acceleration’ for the turtles. These two factors showed activity during the day and resting at night, whether or not the turtles stayed in shallow water or traveled to deeper water.
From this, it appeared that traveling to deeper waters at night (as some turtles did) was all about resting. So why do some turtles rest in shallow water and some in deep? Well, it turns out the turtles resting in deeper water got more bang for their buck – they were able to get longer resting dives.
Living in an underwater world means considering sleep differently than you or I might. They need to balance out their bouyancy, which changes depending on how much air is taken in. A larger animal can take a larger breath to fill larger lungs, which mean the animal must go deeper to reach neutral buoyancy. Once there, they can rest longer with all that oxygen stored up.
As a growing young turtle, rest is important. It seems that as they get larger, these turtles are willing to expend more energy to travel to deeper waters AND face potential risks associated with that – sharks are in the area for example – in order to get better sleep.
The full citation is:
Hart KM, White CF, Iverson AR, Whitney N (2016) Trading shallow safety for deep sleep: juvenile green turtles select deeper resting sites as they grow. Endangered Species Research 31: 61-73.