When I was Station Fire officer at Seletar (1967-68) we were sometimes asked for spare drums of foam compound by blokes who were going shark fishing. Apparently they trickled it into the water behind the boat and the theory was it would attract every shark for miles around. Nobody ever presented us with a shark, though, so I have no idea how effective it was.
Actually it made very good thick foam which didn't disperse quickly, unlike the chemical foam compound which came along later.