2024-12-16 スウォンジー大学
A green turtle comes up for air. Like many air-breathing marine megafauna, green turtles optimise their swim depth during migration to minimise the cost of transport, travelling at around three body-depths beneath the surface in order to avoid creating waves whilst maximising horizontal distance travelled (Picture © R. D. and B. S. Kirkby).
<関連情報>
- https://www.swansea.ac.uk/press-office/news-events/news/2024/12/new-study-finds-marine-animals-save-energy-by-swimming-in-a-depth-sweet-spot-.php
- https://www.pnas.org/doi/10.1073/pnas.2413768121
多様な分類群における水平移動時の遊泳深度の最適化 Optimization of swim depth across diverse taxa during horizontal travel
Kimberley L. Stokes, Nicole Esteban, Paolo Casale, +6, and Graeme C. Hays
Proceedings of the National Academy of Sciences Published:December 16, 2024
DOI:https://doi.org/10.1073/pnas.2413768121
Significance
Three-dimensional tracking of animals has become an integral part of the study of their movement ecology, but the top few meters of depth data for diving animals are often routinely disregarded and so shallow diving is rarely recorded. We show that near-surface travel may be a conservative trait across diverse marine taxa and follows an allometric pattern with body size across various reptilian, avian, and mammalian species. We match theory with empirical data from animal tracking to present a common principle of energetic optimization during oceanic travel, with implications for the protection and conservation of migratory species.
Abstract
Semiaquatic taxa, including humans, often swim at the air–water interface where they waste energy generating surface waves. For fully marine animals however, theory predicts the most cost-efficient depth-use pattern for migrating, air-breathing species that do not feed in transit is to travel at around 2 to 3 times the depth of their body diameter, to minimize the vertical distance traveled while avoiding wave drag close to the surface. This has rarely been examined, however, due to depth measurement resolution issues at the surface. Here, we present evidence for the use of this strategy in the wild to the nearest centimeter and document the switch to shallow swimming during naturally occurring long-distance migrations. Using high-resolution depth-accelerometry and video data for little penguins (Eudyptula minor) and loggerhead turtles (Caretta caretta), satellite-relayed data for green turtles (Chelonia mydas), and literature data for further sea turtle, penguin, and whale species, we show that near-surface swimming is likely used broadly across nonforaging diving animals to minimize the cost of transport.
