Dispersal pathways of American eel larvae from the Sargasso Sea

At the end of their life cycle, American eel ( Anguilla rostrata ) migrate to the Sargasso Sea from freshwater habitats along the east coast of North America in order to spawn planktonic eggs. The eggs develop into larvae that then have to reach estuarine and freshwater nursery habitats along the North American coast within approximately their first year of life. A coupled biological—physical model was used to study how potential behavioral adaptations influence the ability of American eel larvae to reach near‐coastal waters. Specifically, several larval swimming behaviors were investigated, including passive drift, random walk swimming, and directional navigation with and without a preferred swimming direction. Directional swimming with a randomly chosen direction improved the success rates of larvae reaching the continental shelf by more than two orders of magnitude compared to passive drift, and swimming primarily to the northwest further tripled these success rates. Success rates also substantially increased for larvae with swimming abilities even slightly above an estimated average. Notably, directional swimming resulted in a reasonable distribution of larvae along the North American shelf break, whereas other swimming scenarios left distinct gaps where no simulated larvae reached the shelf, including near the Gulf of Maine where juvenile eels are abundant. Additionally, directional swimming yielded transit times of ∼ 1 yr, in agreement with observations. Finally, the model supported the southwestern Sargasso Sea as the probable spawning area for American eel.