Anguillid eels grow in freshwater but spawn in the open ocean. The cues that guide eels over long distances to the spawning area are unknown. The Earth's magnetic field can provide directional and positional information and is likely used by catadromous eels during their spawning migration; as magnetosensitivity and compass orientation have been reported in eels. To test whether this is theoretically possible, we compared the migratory routes of five species of temperate eels that undertake long migrations with the geomagnetic field of their distribution/spawning areas. We found that, regardless of the species and although routes are different between life stages, larvae of those species always drift along paths of increasing magnetic inclination and intensity, while adults follow reverse gradients. This is consistent with an imprinting/retracing hypothesis. We propose a general navigation mechanism based on larvae imprinting on a target magnetic intensity (or inclination) at the hatching area and on the intensity (or inclination) gradient during larval drift. Years later, adults retrace the magnetic route by following the gradient of decreasing total intensity (or inclination) values that occurs towards lower latitudes. As they reach the target value, adults switch to compass orientation to stay on the target isoline and reach the spawning area. The proposed mechanism fits for all temperate eels examined. Knowledge about navigational strategies of eels is important to evaluate the effectiveness of management strategies that involve stocking of juveniles displaced from one area to another to rebuild local populations.

中文翻译：

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温带鳗鲡产卵迁徙的统一假设

鳗鲡在淡水中生长，但在开阔的海洋中产卵。引导鳗鱼长距离到达产卵区的线索尚不清楚。地球磁场可以提供方向和位置信息，并且很可能在产卵迁徙期间被落水鳗鱼使用；因为已经在鳗鱼中报道了磁敏性和指南针方向。为了测试这在理论上是否可行，我们比较了五种温带鳗鱼的迁徙路线，这些鳗鱼进行了长时间的迁徙，并与它们分布/产卵区的地磁场进行了比较。我们发现，无论物种如何，尽管生命阶段之间的路线不同，但这些物种的幼虫总是沿着磁倾角和强度增加的路径漂移，而成虫则遵循反向梯度。这与印记/追溯假设一致。我们提出了一种通用的导航机制，该机制基于幼虫在孵化区的目标磁强度（或倾角）和幼虫漂移期间的强度（或倾角）梯度上的印记。多年后，成年人通过遵循向低纬度地区发生的总强度（或倾角）值递减的梯度来回溯磁路。当它们达到目标值时，成虫会切换到指南针方向以停留在目标等值线上并到达产卵区。所提出的机制适用于所有检查过的温带鳗鱼。关于鳗鱼航行策略的知识对于评估管理策略的有效性非常重要，这些管理策略涉及放养从一个地区到另一个地区的幼鱼以重建当地人口。我们提出了一种通用的导航机制，该机制基于幼虫在孵化区的目标磁强度（或倾角）和幼虫漂移期间的强度（或倾角）梯度上的印记。多年后，成年人通过遵循向低纬度地区发生的总强度（或倾角）值递减的梯度来回溯磁路。当它们达到目标值时，成虫会切换到指南针方向以停留在目标等值线上并到达产卵区。所提出的机制适用于所有检查过的温带鳗鱼。关于鳗鱼航行策略的知识对于评估管理策略的有效性非常重要，这些管理策略涉及放养从一个地区到另一个地区的幼鱼以重建当地人口。我们提出了一种通用的导航机制，该机制基于幼虫在孵化区的目标磁强度（或倾角）和幼虫漂移期间的强度（或倾角）梯度上的印记。多年后，成年人通过遵循向低纬度地区发生的总强度（或倾角）值递减的梯度来回溯磁路。当它们达到目标值时，成虫会切换到指南针方向以停留在目标等值线上并到达产卵区。所提出的机制适用于所有检查过的温带鳗鱼。关于鳗鱼航行策略的知识对于评估管理策略的有效性非常重要，这些管理策略涉及放养从一个地区到另一个地区的幼鱼以重建当地人口。