Thursday, December 04, 2008
For an animal in the ocean, the ability to leap out the water for a short period can enhance its survival, navigation and foraging capabilities. Parker the sea lion is learning how to demonstrate this ability as he is being trained by our staff to porpoise out of the water. Porpoising is when an animal jumps clear out of the water at an angle so as to travel horizontally over the surface as dolphins (at one time inaccurately called “porpoises”) do regularly while traveling.
The mammalogists use a target pole that Parker is trained to place his nose on when asked to teach him the porpoise behavior. As his nose gets close to touching the pole it is brought up out of the water and arched in a half circle. By following the target Parker soon learns that the mammalogists want him to leap clear out of the water in an arch. They also use the pole to teach the sea lion where to porpoise by hitting the water with the end of the pole approximately where they want Parker to leap. In this manner the sea lion is taught to make a series of porpoise behaviors.
What allows Parker to perform this behavior? I’ll attempt to explain how by using a couple of aeronautical principles that I was first introduced to back during my days as a flight test photographer in the high desert. Unlike a flying fish that uses its unique airplane-like fin configuration to create a favorable Lift to Drag Ratio (like an an aircraft wing) that allows it to glide above the surface of the water, Parker uses another physics principle to become airborne. When Parker leaves the water, he does so using a favorable Thrust to Weight Ratio. In other words, he goes ballistic using sheer power and body streamlining that allows him to overcome the gravity and drag on his body to obtain a trajectory that can send him several feet above the water and have him travel several feet horizontally.
In the wild, there are advantages for a predator that is able to porpoise out of the water. While down in Puerto Vallarta several years ago I watched a flying fish being pursued by a dorado. The flying fish thought it was safe from the predator once it left the water and glided above the surface but the dorado followed the flying fish by porpoising as it pursued it; tracking its prey during its leaps. For the dorado, the ability to porpoise allowed it to have greater success in hunting its prey. The flying fish soon became a meal for the dorado.
Another advantage of porpoising is that it allows a marine mammal like a sea lion or dolphin to travel more efficiently. Air has less resistance (drag) than water thus a marine mammal uses less energy when traveling at high speeds by using a series of porpoises than it would by swimming underwater only. The energy efficiency of porpoising goes down at slower speeds. Because of their highly favorable Thrust to Weight Ratio, a sea lion or dolphin is able to sustain the force necessary to porpoise continuously over a distance. These series of porpoises also allows the mammal to breath without having to slow down.
By demonstrating this ability, Parker is showing how marine animals adapt to the challenges of their environment.
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