When attacking a large number of swimmers trying to escape, attack them stealthily and drag them farther out so you have more time, then eat them.

If you grab a human, pull them deep underwater, let them go, then swim in circles around them, you will start to scare them as they resurface. Once they are at the surface, swim up onto them gently to lift them out of the water. You will scare them to death. This does not seem to kill humans that are on the surface already.