How does body size influence movement in marine fish?

C.A. Griffiths (1,2), P.G. Blackwell (1), D. Righton (3), J. Pitchford (4), R. Law (4), J. Leis (2), T. Patterson (5), J.L. Blanchard (2)

1 School of Mathematics & Statistics, University of Sheffield, Sheffield UK.

2 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia.

3 Centre for Environment, Fisheries & Aquaculture Science (CEFAS), Lowestoft, UK.

4 Department of Mathematics, University of York, York, UK.

5 Commonwealth Scientific & Industrial Research Organisation (CSIRO), Hobart, Australia.

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An organism’s physical capabilities are governed by its body size. Power laws are a useful means of describing allometric movement rates, metabolism and predator-prey interactions. However, the generality of how body size scales with movement across a wide range of taxa or life-stages has never been empirically tested in marine fish. Here we analyse data from ~900 individuals across 25 different species and over 4 orders of magnitude (body lengths ranging from 0.005m to 4.8m). We show that three-dimensional movement rates scale with body length according to an exponent of approximately 0.4, irrespective of taxa. Preliminary investigations however contradict such findings, illustrating that as individuals transit through variable habitats, shift behavioural modes or deal with differing temperature regimes the exponent can change. Understanding how power laws stand up to empirical tests is essential for the development of robust and biological realistic population and community models.