Little penguin (IMAGE) Swansea University Caption Little penguins travel beneath the zone of highest wave drag close to the surface. Many air-breathing marine vertebrates optimise their swim depth when transiting and not feeding, travelling just deep enough to avoid wave creation on the surface. Credit Phillip Island Nature Parks. Usage Restrictions None License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.