A fish aggregating (or aggregation) device (FAD) is a man-made object used to attract ocean going pelagic fish such as marlin, tuna and mahi-mahi (dolphin fish). They usually consist of buoys or floats tethered to the ocean floor with concrete blocks. Over 300 species of fish gather around FADs. FADs attract fish for numerous reasons that vary by species.

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Fish tend to move around FADs in varying orbits, rather than remaining stationary below the buoys. Both recreational and commercial fisheries use FADs.

Before FADs, commercial tuna fishing used purse seining to target surface-visible aggregations of birds and dolphins, which were a reliable signal of the presence of tuna schools below. The demand for dolphin-safe tuna was a driving force for FADs.

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Source: Wikipedia

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