title: Scaling of swim speed and stroke frequency in geometrically similar penguins: they swim optimally to minimize cost of transport.
abstract: It has been predicted that geometrically similar animals would swim at the same speed with stroke frequency scaling with mass(-1/3). In the present study, morphological and behavioural data obtained from free-ranging penguins (seven species) were compared. Morphological measurements support the geometrical similarity. However, cruising speeds of 1.8-2.3 m s(-1) were significantly related to mass(0.08) and stroke frequencies were proportional to mass(-0.29). These scaling relationships do not agree with the previous predictions for geometrically similar animals. We propose a theoretical model, considering metabolic cost, work against mechanical forces (drag and buoyancy), pitch angle and dive depth. This new model predicts that: (i) the optimal swim speed, which minimizes the energy cost of transport, is proportional to (basal metabolic rate/drag)(1/3) independent of buoyancy, pitch angle and dive depth; (ii) the optimal speed is related to mass(0.05); and (iii) stroke frequency is proportional to mass(-0.28). The observed scaling relationships of penguins support these predictions, which suggest that breath-hold divers swam optimally to minimize the cost of transport, including mechanical and metabolic energy during dive.
authors.affiliation: International Coastal Research Center, Ocean Research Institute, The University of Tokyo, 2-106-1 Akahama, Otsuchi, Iwate 028-1102, Japan. katsu@ori.u-tokyo.ac.jp
authors.forename: Katsufumi
authors.initials: K
authors.lastname: Sato
authors.forename: Kozue
authors.initials: K
authors.lastname: Shiomi
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Watanuki
authors.forename: Akinori
authors.initials: A
authors.lastname: Takahashi
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Ponganis
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D001696:Biomechanical Phenomena; D049628:Body Size; D004242:Diving / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology*; D008954:Models, Biological; D046429:Spheniscidae / Q000033:anatomy & histology / Q000502:physiology*; D013550:Swimming / Q000502:physiology*