The Implications of Lung-Regulated Buoyancy Control for Dive Depth and Duration

Abstract

Among air‐breathing divers, control of buoyancy through lung volume regulation may be most highly developed in marine turtles. In short, the turtle lung may serve a dual role as both an oxygen store and in buoyancy control. A simple model is developed to show that, for turtles diving up to the maximum depth at which they can still use their lungs to attain neutral buoyancy, the total oxygen store will increase greatly with dive depth, and hence a corresponding increase in dive duration is predicted. Time–depth recorders attached to free‐living green turtles (Chelonia mydas) at Ascension Island confirmed a marked increase in dive duration with depth, with the gradient of this relationship being >10 times that seen in diving birds and mammals. Consistent with the prediction that the lungs serve a dual role, we found that, when lead weights were added to some turtles to increase their specific gravity, the mean depth of dives decreased, but for dives to the same depth, weighted animals dived for longer. The depth distribution of green turtles seems to be generally constrained by the maximum depth at which they can still attain close to neutral buoyancy.

Trading shallow safety for deep sleep: juvenile green turtles select deeper resting sites as they grow

“…The duration of a turtle's dive is dependent on both the size of a breath taken at the surface and the energy expenditure during a dive. The size of the breath can also influence turtle dive depth as it impacts the depth of neutral buoyancy (Hays et al 2004); turtles modulate the size of their breath based on the intent of the dive (Okuyama et al 2014). Accordingly, we modeled the effect of dive depth and activity level (i.e.…”

Inspiration by Magellanic penguins: reduced swimming effort when under pressure

“…The change in flipper angular velocity over the course of the dive can be attributed to changes in buoyancy that occur as a result of changing pressure with depth (Lovvorn et al 1991, 1999, Williams et al 2000, Hays et al 2004). Having inhaled a particular amount of air, and having a fixed amount of air in the plumage (Wilson et al 1992), a descending penguin must work against the upthrust in order to descend although, at constant speed, the power associated with this will decrease with increasing depth, as the air volume will be compressed, resulting in reduced upthrust.…”

“…An analogous situation has been reported for turtles, where those lying on the seabed can only do so motionless, and therefore with minimum energy expenditure, if they are negatively buoyant. This means that their lung volumes must be regulated, giving them less air at shallower depths (Hays et al 2004). However, turtles are essentially benthic and move comparatively slowly, therefore inspired air volume is not expected to vary greatly from dive to dive, whereas Magellanic penguins, with their pelagic diving behaviour (Peters et al 1998) may change the depth of the bottom phase substantially on a dive to dive basis and must correct accordingly.…”

Hyperbaric computed tomographic measurement of lung compression in seals and dolphins

“…Paulev showed that rapid, repetitive breath holding in human divers results in DCS (Paulev, 1965). The paradox of marine mammals, birds and reptiles diving routinely to substantial depths without apparent acute or chronic symptoms of DCS has aroused the curiosity of many scientists (Costa et al, 2004;Fossette et al, 2010;Hays et al, 2004;Kooyman, 2006;Ridgway and Howard, 1979;Scholander, 1940;Wilson et al, 1992). Anatomical adaptations thought to be important include: lung collapse, the atelectic collapse of alveoli to shunt blood away from gas exchange surfaces; tracheobronchial compliance changes (Bostrom et al, 2008); and blood redistribution into the rete mirabile in cetaceans and blood sinuses in pinnipeds.…”