Hugh's Aquarium Views Video Number 54
The circulation grates at the bottom of the seal and sea lion exhibit are part of the water quality system. The circulation of the water creates a mild vortex above the grate. When the Aquarium of the Pacific first opened to the public visitors would be entertained by the antics of a playful young seal that was spinning within the invisible vortex. 20 years later the pup of that same seal, Shelby, is having fun doing the exact same thing.
Check out the video of a pup playing Spin-the-Seal.