Southeast Fisheries Science Center, National Marine Fisheries Service, 75 Virginia Beach Drive, Miami, FL 33149, USA.
Southeast Fisheries Science Center, National Marine Fisheries Service, 75 Virginia Beach Drive, Miami, FL 33149, USA; Department of Biology, University of Central Florida, Orlando, FL 32816, USA.
Curr Biol. 2015 May 4;25(9):1221-7. doi: 10.1016/j.cub.2015.03.014. Epub 2015 Apr 9.
Although oceanic dispersal in larval and juvenile marine animals is widely studied, the relative contributions of swimming behavior and ocean currents to movements and distribution are poorly understood [1-4]. The sea turtle "lost years" [5] (often referred to as the surface-pelagic [6] or oceanic [7] stage) are a classic example. Upon hatching, young turtles migrate offshore and are rarely observed until they return to coastal waters as larger juveniles [5]. Sightings of small turtles downcurrent of nesting beaches and in association with drifting organisms (e.g., Sargassum algae) led to this stage being described as a "passive migration" during which turtles' movements are dictated by ocean currents [5-10]. However, laboratory and modeling studies suggest that dispersal trajectories might also be shaped by oriented swimming [11-15]. Here, we use an experimental approach designed to directly test the passive-migration hypothesis by deploying pairs of surface drifters alongside small green (Chelonia mydas) and Kemp's ridley (Lepidochelys kempii) wild-caught turtles, tracking their movements via satellite telemetry. We conclusively demonstrate that these turtles do not behave as passive drifters. In nearly all cases, drifter trajectories were uncharacteristic of turtle trajectories. Species-specific and location-dependent oriented swimming behavior, inferred by subtracting track velocity from modeled ocean velocity, contributed substantially to individual movement and distribution. These findings highlight the importance of in situ observations for depicting the dispersal of weakly swimming animals. Such observations, paired with information on the mechanisms of orientation, will likely allow for more accurate predictions of the ecological and evolutionary processes shaped by animal movement.
尽管海洋幼体和幼年期海洋动物的扩散过程已被广泛研究，但游泳行为和海流对运动和分布的相对贡献仍知之甚少[1-4]。海龟的“失落岁月”[5]（通常称为海面浮游[6]或海洋[7]阶段）就是一个经典的例子。幼龟孵化后会向近海迁徙，在它们作为较大的幼龟返回沿海水域之前，很少被观察到[5]。在筑巢海滩下游和与漂流生物（例如马尾藻）一起发现小海龟，导致人们将这个阶段描述为“被动迁移”，在此期间海龟的运动受海流支配[5-10]。然而，实验室和模型研究表明，扩散轨迹也可能受到定向游泳的影响[11-15]。在这里，我们采用了一种实验方法，通过在小绿海龟（Chelonia mydas）和肯普氏丽龟（Lepidochelys kempii）野生捕获的海龟旁边同时部署一对表面漂流器，直接测试被动迁移假说，通过卫星遥测跟踪它们的运动。我们明确证明这些海龟并没有表现出被动漂移的行为。在几乎所有情况下，漂流器的轨迹都与海龟的轨迹不同。通过从模型海洋速度中减去轨迹速度推断出的特定物种和位置相关的定向游泳行为，对个体运动和分布有很大贡献。这些发现强调了进行现场观测对于描述弱游泳动物扩散的重要性。这种观测与定向机制的信息相结合，可能会更准确地预测动物运动所塑造的生态和进化过程。
