The spawning area and oceanic migratory cues for American and European eels have long remained enigmatic. Because young eel larvae are concentrated immediately to the south of the North Atlantic Subtropical Convergence in the Sargasso Sea, it is hypothesized that mature eels cease migration and spawn near this front and use physical or biological features of the front for orientation. This research will directly test (1) whether maturing adult American eels are concentrated in, or immediately to the south of, the frontal zone, and (2) how the fine-scale vertical and horizontal distributions of adults are related specifically to characteristics of the frontal zone and adjacent waters. Quantitative hydroacoustic sampling will be used to identify echoes of appropriate strength to be eels and to map their distributional patterns and densitites. Aimed midwater trawling, video from a remotely operated vehicle, traps baited with mature captive eels, and fine-scale sampling of eggs and newly hatched larvae will be used to verify whether targets are actually eels. Hydroacoustic data, midwater trawling, and profiles of temperature and salinity will be used to characterize the biological and physical features of the front. This research links open-ocean spawing of a physiologically unique, long-distance migrating fish to a specific oceanographic feature.
