宽吻海豚（ Tursiops truncatus ）游泳时，速度约每小时9.7公里，冲刺时速度则可以再快一倍。海豚们要和水的阻力作斗争，游得越努力，阻力就越强。
美国加州大学圣克鲁兹分校的海洋生物学家诺尔（Shawn R. Noren）决定做一个研究，分析成年母海豚怀孕末期时所体验到的额外阻力。
海豚就和奶牛一样是远古有蹄类动物的后代，它们一次生一个孩子，孕期12个月。在怀孕过程中，雌海豚的腹部隆起，腰围增加约50%。
体型变化的结果是阻力急剧增大。《实验生物学期刊》（The Journal of Experimental Biology）12月刊上发布的这篇论文发现，产前几周时，雌海豚在4英里/小时（6.44公里/小时）速度游动时，受到的阻力相当于平常以8英里/小时（12.9公里/小时）游动时的阻力。
怀孕也对海豚游泳能力有其他方面的影响，怀孕的动物会更胖，而赘肉的脂类含量更高，这让海豚更容易漂浮，难以下潜捕食。怀孕的海豚游泳方式也不一样，她们的推水动作时间更短也更频繁。
Pregnancy is a drag: hydrodynamics, kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops truncatus)
Shawn R. Noren, Jessica V. Redfern, Elizabeth F. Edwards
Constraints on locomotion could be an important component of the cost of reproduction as carrying an increased load associated with eggs or developing fetuses may contribute to decreased locomotor performance for females across taxa and environments. Diminished performance could increase susceptibility to predation, yet the mechanism(s) by which gravidity and pregnancy affect locomotion remains largely unexplored. Here we demonstrate that morphology, hydrodynamics and kinematics were altered during pregnancy, providing a mechanism for diminished locomotor performance in two near-term pregnant (10 days pre-parturition) bottlenose dolphins (Tursiops truncatus). Near-term pregnancy resulted in a 51±14% increase in frontal surface area, coinciding with dramatic increases in drag forces while gliding. For example, pregnant females encountered 80 N of drag at 1.7 m s–1 whereas that magnitude of drag was not encountered until speed doubled for females 18 months post-parturition. Indeed, drag coefficients based on frontal surface area were significantly greater during pregnancy (Cd,F=0.22±0.04) than at 18 months post-parturition (Cd,F=0.09±0.01). Pregnancy also induced a gait change as stroke amplitude and distance per stroke were reduced by 13 and 14%, respectively, compared with non-pregnant periods (1–24 months post-parturition). This was concomitant with a 62 and 44% reduction in mean and maximum swim speeds, respectively, during the pregnancy period. Interestingly, attack speeds of known predators of dolphins surpass maximum speeds for the pregnant dolphins in this study. Thus, pregnant dolphins may be more susceptible to predation. This study demonstrates unequivocally that changes in morphology, hydrodynamics and kinematics are associated with diminished performance during pregnancy in dolphins.
文献链接：https://jeb.biologists.org/content/214/24/4151.abstract?sid=a6f39b8f-0878-4fc1-8817-1c82bd56bbf4
