Why do tuna boats use live bait and water sprays during pole-and-line fishing?

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A worker in dark clothing inspects large frozen tuna lined up on the floor at Tsukiji fish market in Tokyo, Japan, using a tool to check the fish. — commercial fishing Worker in the Tsukiji fish market, Tokyo.

In pole-and-line fishing, tuna boats utilize live bait and water sprays to effectively attract and maintain schools of tuna near the vessel.1

Live Bait: Fishermen throw live bait overboard—a process known as chumming—to entice the fish and keep them close to the boat. Because this bait must be kept alive in circulating seawater tanks, it represents a significant operational cost, requiring approximately 100 kilograms of bait fish for every ton of tuna caught.1
Water Sprays: Spraying water serves two primary purposes. First, it acts as an additional attractant for the tuna. Second, it creates a visual disturbance on the surface that camouflages the shadows of the boat and the crew, preventing the fish from being spooked by the vessel's presence.1

When the tuna are particularly eager to feed, they may strike at artificial lures or even naked hooks, allowing the crew to maximize their catch rate during limited fishing windows.1