Sato George, Adachi Taiki, Guinet Christophe, Miller Patrick
Sea Mammal Research Unit, University of St Andrews, St Andrews KY16 8LB, Scotland, UK.
National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan.
J Exp Biol. 2025 May 15;228(10). doi: 10.1242/jeb.249659. Epub 2025 May 23.
The role of diving respiratory air volume (DRAV) in deep-diving phocid seals remains poorly understood, largely because of the lack of methods for measuring DRAV in free-ranging divers that exhale before diving. We developed a method to estimate DRAV using a hydrodynamic glide model applied to descent glides recorded using multi-sensor data loggers. We estimated dive-by-dive DRAV for six negatively buoyant female southern elephant seals (Mirounga leonina). During shallow descent glides, rapid compression of DRAV influenced net buoyancy and gliding speed, making this phase suitable for estimating DRAV. Our results revealed dive-by-dive variation in DRAV, which was positively correlated with root mean square (RMS) sway acceleration (a proxy for per-stroke effort) and the depth at which gliding began during the initial descent. DRAV increased with both tissue density and maximum dive depth, suggesting that seals adjusted their DRAV to stay closer to neutral buoyancy through their dives. However, the observed level of adjustment did not result in neutral buoyancy at half of the maximum dive depth, as predicted to minimise round-trip locomotion costs. Instead, the seals typically adjusted DRAV to reach neutral buoyancy at ∼30 m depth, <10% of their mean maximum dive depth. This indicates that strong negative tissue density imposes transit costs that cannot be fully compensated for by DRAV adjustment alone. Future work should explore whether other breath-hold divers show similar patterns of DRAV adjustment and quantify the associated physiological and ecological benefits.
潜水呼吸空气量（DRAV）在深潜的海豹中的作用仍未得到充分了解，这主要是因为缺乏在自由潜水且潜水前呼气的动物身上测量DRAV的方法。我们开发了一种方法，利用流体动力学滑行模型来估计DRAV，该模型应用于使用多传感器数据记录器记录的下降滑行过程。我们估计了六只负浮力雌性南象海豹（Mirounga leonina）每次潜水的DRAV。在浅下降滑行过程中，DRAV的快速压缩影响了净浮力和滑行速度，使得这个阶段适合估计DRAV。我们的结果揭示了DRAV在每次潜水中的变化，它与均方根（RMS）摇摆加速度（每划动努力程度的一个指标）以及初始下降过程中开始滑行的深度呈正相关。DRAV随着组织密度和最大潜水深度的增加而增加，这表明海豹在潜水过程中调整它们的DRAV以更接近中性浮力。然而，观察到的调整水平并没有如预期的那样在最大潜水深度的一半时达到中性浮力，以最小化往返运动成本。相反，海豹通常将DRAV调整到在约30米深度达到中性浮力，这不到它们平均最大潜水深度的10%。这表明强烈的负组织密度带来了运输成本，仅靠DRAV调整无法完全补偿。未来的工作应该探索其他屏气潜水动物是否表现出类似的DRAV调整模式，并量化相关的生理和生态益处。
