Institute of Marine Science, University of California, Santa Cruz, 115 McAllister Way, Santa Cruz, CA 95060, USA
Hopkins Marine Station, Stanford University, 120 Ocean View Blvd, Pacific Grove, CA 93950, USA.
J Exp Biol. 2020 Jun 11;223(Pt 11):jeb224402. doi: 10.1242/jeb.224402.
Whale sharks () - the largest extant fish species - reside in tropical environments, making them an exception to the general rule that animal size increases with latitude. How this largest fish thrives in tropical environments that promote high metabolism but support less robust zooplankton communities has not been sufficiently explained. We used open-source inertial measurement units (IMU) to log 397 h of whale shark behavior in Yucatán, Mexico, at a site of both active feeding and intense wildlife tourism. Here we show that the strategies employed by whale sharks to compensate for the increased drag of an open mouth are similar to ram feeders five orders of magnitude smaller and one order of magnitude larger. Presumed feeding constituted 20% of the total time budget of four sharks, with individual feeding bouts lasting up to 11 consecutive hours. Compared with normal, sub-surface swimming, three sharks increased their stroke rate and amplitude while surface feeding, while one shark that fed at depth did not demonstrate a greatly increased energetic cost. Additionally, based on time-depth budgets, we estimate that aerial surveys of shark populations should consider including a correction factor of 3 to account for the proportion of daylight hours that sharks are not visible at the surface. With foraging bouts generally lasting several hours, interruptions to foraging during critical feeding periods may represent substantial energetic costs to these endangered species, and this study presents baseline data from which management decisions affecting tourist interactions with whale sharks may be made.
鲸鲨（）——现存最大的鱼类物种——生活在热带环境中，这是一个例外，因为一般来说，动物的体型会随着纬度的增加而增大。这种最大的鱼类是如何在促进新陈代谢但支持不太健壮的浮游动物群落的热带环境中茁壮成长的，还没有得到充分的解释。我们使用开源惯性测量单元（IMU）在墨西哥尤卡坦的一个既有积极觅食又有密集野生动物旅游的地点记录了 397 小时的鲸鲨行为。在这里，我们表明，鲸鲨为了补偿张开的嘴带来的更大阻力而采用的策略与五倍数量级更小、一倍数量级更大的吞食者相似。据推测，进食构成了四条鲨鱼总时间预算的 20%，单次进食持续长达 11 小时。与正常的、水面下的游泳相比，三只鲨鱼在水面进食时增加了划水频率和幅度，而一只在深水区进食的鲨鱼并没有表现出能量消耗的大幅增加。此外，根据时间-深度预算，我们估计，对鲨鱼种群的空中调查应该考虑包括一个 3 的修正因子，以说明鲨鱼在水面下不可见的白天时间比例。由于觅食时间通常持续数小时，在关键觅食期中断觅食可能会对这些濒危物种造成巨大的能量成本，本研究提供了基线数据，可据此做出影响游客与鲸鲨互动的管理决策。
