SCHULTZ, W. W.*; WEBB, P. W.*: Power requirements of swimming: Do new methods resolve the old questions?

A recurring question in the study of fish biomechanics and energetics is the mechanical power required for swimming at the high speeds seen among aquatic vertebrates. The quest for answers has been driven by conceptual advances in fluid dynamics, starting with ideas on the boundary layer and drag initiated by Prandtl, and in measurement techniques starting with force balances. Elongated slender-body theory gave results for power needs for thrust production which were generally consistent with physiological performance. Slender-body and blade-element theories provided frameworks that explained many of the functional consequences of differences in morphology. Predictions from elongated slender body theory were supported by several apparently discriminatory experiments, but as a result of recent advances in stability and maneuverability, the results prove to be subject to different explanations. Advances in flow visualization and computational fluid dynamics are for the first time permitting more direct observation and measurement of flow phenomena that affect the resistance and rates of working. These and a more sophisticated force balance measurements are being used to revisit questions of mechanical power requirements for swimming, but do not fully resolve the issues. Although results of these studies have been expressed historically in terms of drag, the mingling of thrust and resistance elements suggests other measures are desirable.