title: Passive drift or active swimming in marine organisms?
abstract: Predictions of organismal movements in a fluid require knowing the fluid's velocity and potential contributions of the organism's behaviour (e.g. swimming or flying). While theoretical aspects of this work are reasonably well-developed, field-based validation is challenging. A much-needed study recently published by Briscoe and colleagues in Proceedings of the Royal Society B compared movements and distribution of satellite-tracked juvenile sea turtles to virtual particles released in a data-assimilating hindcast ocean circulation model. Substantial differences observed between turtles and particles were considered evidence for an important role of active swimming by turtles. However, the experimental design implicitly assumed that transport predictions were insensitive to (i) start location, (ii) tracking duration, (iii) depth, and (iv) physical processes not depicted in the model. Here, we show that the magnitude of variation in physical parameters between turtles and virtual particles can profoundly alter transport predictions, potentially sufficient to explain the reported differences without evoking swimming behaviour. We present a more robust method to derive the environmental contributions to individual movements, but caution that resolving the ocean velocities experienced by individual organisms remains a problem for assessing the role of behaviour in organismal movements and population distributions.
authors.affiliation: Cooperative Institute for Marine and Atmospheric Studies, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA nathan.putman@gmail.com.|Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, Miami, FL 33149, USA.
authors.forename: Nathan F
authors.identifier: 0000-0001-8485-7455
authors.initials: NF
authors.lastname: Putman
authors.affiliation: Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, Miami, FL 33149, USA.
authors.forename: Rick
authors.initials: R
authors.lastname: Lumpkin
authors.affiliation: Department of Biology, University of Central Florida, Orlando, FL 32816, USA.
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Sacco
authors.affiliation: Department of Biology, University of Central Florida, Orlando, FL 32816, USA.
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Mansfield
mesh_terms: D063147:Animal Distribution; D000818:Animals; D008962:Models, Theoretical; D009068:Movement; D009792:Oceans and Seas; D013550:Swimming; D013686:Telemetry; D014426:Turtles / Q000502:physiology*; D014872:Water Movements
keywords: ocean circulation model; ocean currents; passive drift; satellite telemetry; sea turtle; swimming