Physics: Cavitation

Cavitation is when vapor bubbles form in a liquid when the liquid pressure drops below the vapor pressure.

Cavitation can occur on ship and submarine propellers. Because the faster a fluid move the less pressure it has. The water moving past the propeller can reach pressures bellow the vapor pressure and cavitation occurs.

Just as cavitation bubbles form on a fast-spinning boat propeller, they may also form on the tails and fins of aquatic animals. The effects of cavitation are especially important near the surface of the ocean, where the ambient water pressure is relatively low and cavitation is more likely to occur.

For powerful swimming animals like dolphins and tuna, cavitation may be detrimental, because it limits their maximum swimming speed. Even if they have the power to swim faster, dolphins may have to restrict their speed because collapsing cavitation bubbles on their tail are too painful. Cavitation also slows tuna, but for a different reason. Unlike dolphins, these fish do not feel the painful bubbles, because they have bony fins without nerve endings. Nevertheless, they cannot swim faster because the cavitation bubbles create an air film around their fins that limits their speed. Lesions have been found on tuna that are consistent with cavitation damage.

Sources: Wikipedia