Stroke frequency, but not swimming speed, is related to body size in free-ranging seabirds, pinnipeds and cetaceans.
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.
Sato
Katsufumi
K
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
Watanuki
Yutaka
Y
Takahashi
Akinori
A
Miller
Patrick J O
PJ
Tanaka
Hideji
H
Kawabe
Ryo
R
Ponganis
Paul J
PJ
Handrich
Yves
Y
Akamatsu
Tomonari
T
Watanabe
Yuuki
Y
Mitani
Yoko o
Yo
Costa
Daniel P
DP
Bost
Charles-André
CA
Aoki
Kagari
K
Amano
Masao
M
Trathan
Phil
P
Shapiro
Ari
A
Naito
Yasuhiko
Y
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*