Sea Mammal Research Unit, Scottish Oceans Institute, University of Saint Andrews, Saint Andrews, Fife KY16 8LB, UK.
J Exp Biol. 2011 Sep 1;214(Pt 17):2973-87. doi: 10.1242/jeb.055137.
Many diving animals undergo substantial changes in their body density that are the result of changes in lipid content over their annual fasting cycle. Because the size of the lipid stores reflects an integration of foraging effort (energy expenditure) and foraging success (energy assimilation), measuring body density is a good way to track net resource acquisition of free-ranging animals while at sea. Here, we experimentally altered the body density and mass of three free-ranging elephant seals by remotely detaching weights and floats while monitoring their swimming speed, depth and three-axis acceleration with a high-resolution data logger. Cross-validation of three methods for estimating body density from hydrodynamic gliding performance of freely diving animals showed strong positive correlation with body density estimates obtained from isotope dilution body composition analysis over density ranges of 1015 to 1060 kg m(-3). All three hydrodynamic models were within 1% of, but slightly greater than, body density measurements determined by isotope dilution, and therefore have the potential to track changes in body condition of a wide range of freely diving animals. Gliding during ascent and descent clearly increased and stroke rate decreased when buoyancy manipulations aided the direction of vertical transit, but ascent and descent speed were largely unchanged. The seals adjusted stroking intensity to maintain swim speed within a narrow range, despite changes in buoyancy. During active swimming, all three seals increased the amplitude of lateral body accelerations and two of the seals altered stroke frequency in response to the need to produce thrust required to overcome combined drag and buoyancy forces.
许多潜水动物的身体密度会发生显著变化，这是它们在每年的禁食周期中脂质含量变化的结果。由于脂质储存量的大小反映了觅食努力（能量消耗）和觅食成功（能量同化）的综合情况，因此测量身体密度是一种很好的方法，可以跟踪在海上的自由放养动物的净资源获取情况。在这里，我们通过远程拆卸重量和浮标，同时使用高分辨率数据记录仪监测它们的游泳速度、深度和三轴加速度，实验性地改变了三只自由放养的象海豹的身体密度和质量。从自由潜水动物的水动力滑翔性能估算身体密度的三种方法的交叉验证与通过同位素稀释体成分分析获得的身体密度估算值之间具有很强的正相关性，其密度范围在 1015 至 1060 千克/立方米之间。所有三种水动力模型都在 1%以内，但略高于同位素稀释确定的身体密度测量值，因此有可能跟踪各种自由潜水动物的身体状况变化。当浮力操作有助于垂直迁移的方向时，滑翔在上升和下降期间明显增加，而划水率降低，但上升和下降速度基本不变。海豹调整划水强度以保持游泳速度在狭窄范围内，尽管浮力发生了变化。在主动游泳时，所有三只海豹都增加了侧向身体加速度的幅度，其中两只海豹改变了划水频率，以应对克服阻力和浮力合力所需的推力。
