[OANNES Foro] Scaling of swim speed in breath-hold divers (diving birds, mammals and turtles)

[Mario Cabrejos]

Journal of Animal Ecology
Article first published online: 14 OCT 2010
DOI: 10.1111/j.1365-2656.2010.01760.x

Scaling of swim speed in breath-hold divers
Yuuki Y. Watanabe1,*, Katsufumi Sato2, Yutaka Watanuki3, Akinori Takahashi1, Yoko Mitani4, Masao Amano5, Kagari Aoki2, Tomoko Narazaki2, Takashi Iwata1, Shingo Minamikawa6, Nobuyuki Miyazaki7
1 National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan2 International Coastal Research Center, Atmosphere and Ocean Research Institute, The University of Tokyo, Otsuchi, Iwate 028-1102, Japan3 Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan4 Field Science Center for Northern Biosphere, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan5 Faculty of Fisheries, Nagasaki University, Nagasaki-shi, Nagasaki 852-8521, Japan6 National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Yokohama, Kanagawa 236-8648, Japan
7 Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-8564, Japan.*Correspondence: Yuuki Y. Watanabe, E-mail: watanabe.yuuki en nipr.ac.jp
Summary
1. Breath-hold divers are widely assumed to descend and ascend at the speed that minimizes energy expenditure per distance travelled (the cost of transport (COT)) to maximize foraging duration at depth. However, measuring COT with captive animals is difficult, and empirical support for this hypothesis is sparse.

2. We examined the scaling relationship of swim speed in free-ranging diving birds, mammals and turtles (37 species; mass range, 0·5-90 000 kg) with phylogenetically informed statistical methods and derived the theoretical prediction for the allometric exponent under the COT hypothesis by constructing a biomechanical model.

3. Swim speed significantly increased with mass, despite considerable variations around the scaling line. The allometric exponent (0·09) was statistically consistent with the theoretical prediction (0·05) of the COT hypothesis.

4. Our finding suggests a previously unrecognized advantage of size in divers: larger animals swim faster and thus could travel longer distance, search larger volume of water for prey and exploit a greater range of depths during a given dive duration.

5. Furthermore, as predicted from the model, endotherms (birds and mammals) swam faster than ectotherms (turtles) for their size, suggesting that metabolic power production limits swim speed. Among endotherms, birds swam faster than mammals, which cannot be explained by the model. Reynolds numbers of small birds (<2 kg) were close to the lower limit of turbulent flow (?3 × 105), and they swam fast possibly to avoid the increased drag associated with flow transition.

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