PORTLAND, OREGON—A dolphin’s body is optimized for fast, streamlined movement. So much so that even a high-tech prosthetic tail can’t match a real dolphin fluke in terms of propulsion efficiency, researchers reported here last week at the annual meeting of the American Physical Society Division of Fluid Dynamics. Engineers and biologists studied Winter, a bottlenose dolphin who lost her tail after becoming entangled in a crab trap line. When Winter started showing early signs of scoliosis after repeatedly twisting side to side to propel herself forward, scientists trained her to wear an artificial fluke—the first of its kind for a dolphin. However, even with her new fluke, Winter wasn’t as efficient in the water as her able-bodied pool mates, the team found. Her stride length—how far she moved relative to her body length in one flapping motion of her fluke—was only about 0.35; healthy dolphins have stride lengths of 0.80–0.90. By modeling Winter’s movements in 3D and studying the wake patterns she created while wearing her prosthetic, the researchers found that only the downstroke of Winter’s fluke helped propel her forward; the upward motion of her fluke generated mostly drag. This decreased efficiency is likely caused by Winter's curved body profile because of her scoliosis, the researchers hypothesize, something that future generations of dolphin prosthetics may be able to compensate for. Tail or no tail, Winter still delights visitors every day in the Florida aquarium she calls home.