title: Stroke frequency, but not swimming speed, is related to body size in free-ranging seabirds, pinnipeds and cetaceans.
abstract: It is obvious, at least qualitatively, that small animals move their locomotory apparatus faster than large animals: small insects move their wings invisibly fast, while large birds flap their wings slowly. However, quantitative observations have been difficult to obtain from free-ranging swimming animals. We surveyed the swimming behaviour of animals ranging from 0.5 kg seabirds to 30 000 kg sperm whales using animal-borne accelerometers. Dominant stroke cycle frequencies of swimming specialist seabirds and marine mammals were proportional to mass(-0.29) (R(2)= 0.99, n = 17 groups), while propulsive swimming speeds of 1-2 m s(-1) were independent of body size. This scaling relationship, obtained from breath-hold divers expected to swim optimally to conserve oxygen, does not agree with recent theoretical predictions for optimal swimming. Seabirds that use their wings for both swimming and flying stroked at a lower frequency than other swimming specialists of the same size, suggesting a morphological trade-off with wing size and stroke frequency representing a compromise. In contrast, foot-propelled diving birds such as shags had similar stroke frequencies as other swimming specialists. These results suggest that muscle characteristics may constrain swimming during cruising travel, with convergence among diving specialists in the proportions and contraction rates of propulsive muscles.
authors.affiliation: International Coastal Research Centre, 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: Yutaka
authors.initials: Y
authors.lastname: Watanuki
authors.forename: Akinori
authors.initials: A
authors.lastname: Takahashi
authors.forename: Patrick J O
authors.initials: PJ
authors.lastname: Miller
authors.forename: Hideji
authors.initials: H
authors.lastname: Tanaka
authors.forename: Ryo
authors.initials: R
authors.lastname: Kawabe
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Ponganis
authors.forename: Yves
authors.initials: Y
authors.lastname: Handrich
authors.forename: Tomonari
authors.initials: T
authors.lastname: Akamatsu
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Yoko o
authors.initials: Yo
authors.lastname: Mitani
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Costa
authors.forename: Charles-André
authors.initials: CA
authors.lastname: Bost
authors.forename: Kagari
authors.initials: K
authors.lastname: Aoki
authors.forename: Masao
authors.initials: M
authors.lastname: Amano
authors.forename: Phil
authors.initials: P
authors.lastname: Trathan
authors.forename: Ari
authors.initials: A
authors.lastname: Shapiro
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Naito
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001717:Birds / Q000033:anatomy & histology / Q000502:physiology*; D049628:Body Size; D010872:Caniformia / Q000033:anatomy & histology / Q000502:physiology*; D002591:Cetacea / Q000033:anatomy & histology / Q000502:physiology*; D013550:Swimming / Q000502:physiology*