Data from: A model for simulating the active dispersal of juvenile sea turtles with a case study on western Pacific leatherback turtles

Oceanic currents are known to broadly shape the dispersal of juvenile sea turtles during their pelagic stage. Accordingly, simple passive drift models are widely used to investigate the distribution at sea of various juvenile sea turtle populations. However, evidence is growing that juveniles do not drift purely passively but also display some swimming activity likely directed towards favorable habitats. We therefore present here a novel Sea Turtle Active Movement Model (STAMM) in which juvenile sea turtles actively disperse under the combined effects of oceanic currents and habitat-driven movements. This model applies to all sea turtle species but is calibrated here for leatherback turtles (Dermochelys coriacea). It is first tested in a simulation of the active dispersal of juveniles originating from Jamursba-Medi, a main nesting beach of the western Pacific leatherback population. Dispersal into the North Pacific Ocean is specifically investigated. Simulation results demonstrate that, while oceanic currents broadly shape the dispersal area, modeled habitat-driven movements strongly structure the spatial and temporal distribution of juveniles within this area. In particular, these movements lead juveniles to gather in the North Pacific Transition Zone (NPTZ) and to undertake seasonal north-south migrations. More surprisingly, juveniles in the NPTZ are simulated to swim mostly towards west which considerably slows down their progression towards the American west coast. This increases their residence time, and hence the risk of interactions with fisheries, in the central and eastern part of the North Pacific basin. Simulated habitat-driven movements also strongly reduce the risk of cold-induced mortality. This risk appears to be larger among the juveniles that rapidly circulate into the Kuroshio than among those that first drift into the North Equatorial Counter Current (NECC). This mechanism might induce marked interannual variability in juvenile survival as the strength and position of the NECC are directly linked to El Niño activity.已知大洋环流在幼年海龟的远洋阶段对其扩散范围具有广泛的塑造作用。因此，简易被动漂流模型被广泛用于探究各类幼年海龟种群的远洋分布情况。然而，越来越多的证据表明，幼年海龟并非完全被动漂流，还会展现出一定的游泳行为，且该行为大概率朝向适宜栖息地。为此，本文提出了一种全新的海龟主动运动模型（Sea Turtle Active Movement Model, STAMM），该模型中幼年海龟会在大洋环流与栖息地驱动运动的共同作用下主动扩散。此模型适用于所有海龟物种，但本次研究针对棱皮龟（Dermochelys coriacea）进行了参数校准。研究首先针对西太平洋棱皮龟种群的主要筑巢海滩——雅穆尔斯巴-梅迪（Jamursba-Medi）所产出的幼年个体的主动扩散过程开展模拟验证，并专门探究了其向北太平洋的扩散情况。模拟结果显示，尽管大洋环流广泛塑造了扩散区域的范围，但模型所模拟的栖息地驱动运动极大地结构化了该区域内幼年个体的时空分布特征。具体而言，这些运动驱使幼年海龟聚集于北太平洋过渡带（North Pacific Transition Zone, NPTZ），并开展季节性的南北洄游。更值得注意的是，模拟结果显示北太平洋过渡带内的幼年海龟大多向西游动，这显著减缓了它们向美国西海岸推进的速度，延长了其在北太平洋中东部海域的停留时间，进而增加了其与渔业活动发生交互的风险。模拟得到的栖息地驱动运动还显著降低了低温致死风险。相较于先漂流进入北赤道逆流（North Equatorial Counter Current, NECC）的幼年个体，那些快速流经黑潮（Kuroshio）的幼龟面临的低温致死风险更高。由于北赤道逆流的强度与位置直接与厄尔尼诺（El Niño）活动相关，这一机制可能会导致幼年海龟存活率出现显著的年际波动。