Sink fast and swim harder! Round-trip cost-of-transport for buoyant divers
Sink fast and swim harder! Round-trip cost-of-transport for buoyant divers
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DOI：
10.1242/jeb.070128
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发表时间：
2012-10-01
影响因子：
2.8
通讯作者：
Fedak, Mike A.
中科院分区：
文献类型：
--
作者：
Miller, Patrick J. O.;Biuw, Martin;Fedak, Mike A.
在深海猎物资源和水面氧气之间的高效移动对于屏住呼吸的潜水员来说至关重要，这样才能最大限度地延长在觅食层的时间，从而提高净能量摄入率。潜水员的身体密度随身体状况的变化而变化，决定了潜水员的表观重量（浮力），这可能会影响到水面与深度之间的往返运输成本（COT）。我们评估了外部功和驱动盘理论对非中性浮力如何影响往返COT到深度的预测，以及稳态垂直运输的最小COT速度。不出所料，模型预测当浮力辅助（阻碍）单向运输时，单向COT会减少（增加）。在极端偏离中性浮力的情况下，在有浮力辅助的方向上，以终端速度滑行是最小的COT策略。在受浮力阻碍的运输方向上，外功模型预测，当偏离中性浮力较大时，最小COT速度不会改变，但在执行器盘模型下，预计最小COT速度会增加。正如之前关于灰海豹的文献所述，我们发现36只象海豹的垂直穿越率在两个方向上都增加了，因为身体密度偏离了中性浮力，这表明执行器圆盘理论可能比外部工作模型更能准确地预测受重力影响的潜水员的动力需求。对于这两种模型，中性浮力的微小偏差不影响最小COT速度或往返COT本身。然而，在极端体密度情况下，两种模型都预测辅助方向的减排量并不能完全抵消阻碍方向所需的更大推力所带来的COT增加。
Efficient locomotion between prey resources at depth and oxygen at the surface is crucial for breath-hold divers to maximize time spent in the foraging layer, and thereby net energy intake rates. The body density of divers, which changes with body condition, determines the apparent weight (buoyancy) of divers, which may affect round-trip cost-of-transport (COT) between the surface and depth. We evaluated alternative predictions from external-work and actuator-disc theory of how non-neutral buoyancy affects round-trip COT to depth, and the minimum COT speed for steady-state vertical transit. Not surprisingly, the models predict that one-way COT decreases (increases) when buoyancy aids (hinders) one-way transit. At extreme deviations from neutral buoyancy, gliding at terminal velocity is the minimum COT strategy in the direction aided by buoyancy. In the transit direction hindered by buoyancy, the external-work model predicted that minimum COT speeds would not change at greater deviations from neutral buoyancy, but minimum COT speeds were predicted to increase under the actuator disc model. As previously documented for grey seals, we found that vertical transit rates of 36 elephant seals increased in both directions as body density deviated from neutral buoyancy, indicating that actuator disc theory may more closely predict the power requirements of divers affected by gravity than an external work model. For both models, minor deviations from neutral buoyancy did not affect minimum COT speed or round-trip COT itself. However, at body-density extremes, both models predict that savings in the aided direction do not fully offset the increased COT imposed by the greater thrusting required in the hindered direction.