Body density affects stroke patterns in Baikal seals
Body density affects stroke patterns in Baikal seals
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DOI：
10.1242/jeb.02402
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发表时间：
2006-09-01
影响因子：
2.8
通讯作者：
Miyazaki, Nobuyuki
中科院分区：
文献类型：
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作者：
Watanabe, Yuuki;Baranov, Eugene A.;Miyazaki, Nobuyuki
浮力是作用于吸气式潜水员的主要外力之一，它会影响他们的游泳能量学。由于海洋哺乳动物的身体组成（即低密度脂质和高密度瘦肉组织的相对数量）随个体和季节而变化，因此它们的浮力也波动很大，人们预计在潜水期间会相应地调整其划水模式。为了验证这一预测，我们将加速度数据记录器连接到贝加尔湖的四只自由活动的贝加尔海豹Phoca sibirica，并监测鳍状肢的划动活动以及游泳速度，深度和身体轴的倾斜度（俯仰）。除记录器外，一只海豹（个体4）还配备了铅锤，铅锤在预定时间段后被丢弃，以便我们对具有不同身体密度的同一个体进行一组观察。这四组数据揭示了贝加尔湖海豹的一般潜水模式，也提供了直接了解浮力对这些模式的影响。海豹反复进行潜水，平均持续时间为7.0分钟（最大）。15.4潜水深度平均为66米，但变化很大，最大深度为324米。海豹个体之间表现出不同的中风模式;一些海豹在下降过程中的中风率低于上升，而另一些海豹在下降过程中的中风率高于上升。当铅块与个体4分离时，海豹通过将游泳模式从长时间滑行转变为更多的划水和滑行游泳来增加其下降时的划水率，并通过将连续划水转变为划水和滑行游泳来降低其上升时的划水率。我们的结论是，海豹采取不同的中风模式，根据其个人的浮力。我们还表明，个人4在下降过程中长时间滑翔达到的终端速度取决于其总浮力和间距，在加权条件下，在陡峭的间距达到更高的速度。一个简单的物理模型使我们能够从速度和音高估计海豹的身体密度（1027-1046 kg m（-3），大致相当于32-41%的脂质含量，对于加权条件; 1014-1022 kg m（-3），43 - 47%的脂质含量，对于未加权条件）。
Buoyancy is one of the primary external forces acting on air-breathing divers and it can affect their swimming energetics. Because the body composition of marine mammals (i.e. the relative amounts of lower-density lipid and higher-density lean tissue) varies individually and seasonally, their buoyancy also fluctuates widely, and individuals would be expected to adjust their stroke patterns during dives accordingly. To test this prediction, we attached acceleration data loggers to four free-ranging Baikal seals Phoca sibirica in Lake Baikal and monitored flipper stroking activity as well as swimming speed, depth and inclination of the body axis ( pitch). In addition to the logger, one seal ( Individual 4) was equipped with a lead weight that was jettisoned after a predetermined time period so that we had a set of observations on the same individual with different body densities. These four data sets revealed the general diving patterns of Baikal seals and also provided direct insights into the influence of buoyancy on these patterns. Seals repeatedly performed dives of a mean duration of 7.0 min (max. 15.4 min), interrupted by a mean surface duration of 1.2 min. Dive depths were 66 m on average, but varied substantially, with a maximum depth of 324 m. The seals showed different stroke patterns among individuals; some seals stroked at lower rates during descent than ascent, while the others had higher stroke rates during descent than ascent. When the lead weight was detached from Individual 4, the seal increased its stroke rate in descent by shifting swimming mode from prolonged glides to more stroke- and- glide swimming, and decreased its stroke rate in ascent by shifting from continuous stroking to stroke and glide swimming. We conclude that seals adopt different stroke patterns according to their individual buoyancies. We also demonstrate that the terminal speed reached by Individual 4 during prolonged glide in descent depended on its total buoyancy and pitch, with higher speeds reached in the weighted condition and at steeper pitch. A simple physical model allowed us to estimate the body density of the seal from the speed and pitch (1027-1046 kg m(-3), roughly corresponding to 32-41% lipid content, for the weighted condition; 1014-1022 kg m(-3), 43 - 47% lipid content, for the unweighted condition).