Simulating transoceanic migrations of young loggerhead sea turtles: merging magnetic navigation behavior with an ocean circulation model

Abstract

SUMMARYYoung loggerhead sea turtles (Caretta caretta) from eastern Florida, USA, undertake a transoceanic migration in which they gradually circle the Sargasso Sea before returning to the North American coast. Loggerheads possess a ʻmagnetic mapʼ in which regional magnetic fields elicit changes in swimming direction along the migratory pathway. In some geographic areas, however, ocean currents move more rapidly than young turtles can swim. Thus, the degree to which turtles can control their migratory movements has remained unclear. In this study, the movements of young turtles were simulated within a high-resolution ocean circulation model using several different behavioral scenarios, including one in which turtles drifted passively and others in which turtles swam briefly in accordance with experimentally derived data on magnetic navigation. Results revealed that small amounts of oriented swimming in response to regional magnetic fields profoundly affected migratory routes and endpoints. Turtles that engaged in directed swimming for as little as 1-3h per day were 43-187% more likely than passive drifters to reach the Azores, a productive foraging area frequented by Florida loggerheads. They were also more likely to remain within warm-water currents favorable for growth and survival, avoid areas on the perimeter of the migratory route where predation risk and thermal conditions pose threats, and successfully return to the open-sea migratory route if carried into coastal areas. These findings imply that even weakly swimming marine animals may be able to exert strong effects on their migratory trajectories and open-sea distributions through simple navigation responses and minimal swimming. Supplementary material available online at

Fish navigation of large dams emerges from their modulation of flow field experience

“…By cueing on acceleration phenomena and their duration at multiple scales, fish could be sensitive to analogous phenomena implicated in sediment motion (61) that elicit invertebrate drift. In ocean currents, turtles (62) and fish (63,64) could use acceleration phenomena as cues in navigation. Behaviors B{1-3}, or their inverted forms, could be used to position fish within the moving media at locations that confer the greatest advantage for their life stage.…”

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“…Formally, drifters are organisms/particles that simply float and are convected by currents: certain studies assume this if active movement is smallish (e.g. [12]), yet it must be considered carefully since even small amounts of oriented swimming can alter overall behaviour [10,11]. A navigator corresponds to an organism that actively swims, periodically assessing its environment and biasing its active direction accordingly.…”

“…Lagrangian-based particle models are often employed for the IBM, with each individual indexed by its instantaneous position and velocity: navigation can be incorporated via a directional bias according to orienteering cues. Currents can be obtained from widely available datasets and models based on these principles have been applied to understand movement dynamics across aquatic and airborne populations: the advection-dominated movement of fish larvae [8]; the role of current-directed movement in jellyfish blooms [9]; the influence of directed movement on turtle drifting within ocean currents [10,11]; the Atlantic movements of eel larvae [12]; how wind influences the choice of staging sites during red knot migration [13]; the exploitation of favourable winds by high-flying insects [14]. For many further references and examples, see [15,16].…”

Finding the ‘lost years’ in green turtles: insights from ocean circulation models and genetic analysis

“…As additional information on the biology of oceanic species becomes available, such factors can be readily incorporated into the existing model framework (e.g. [1,9,22]), and thus refine the quantitative estimates for the ecological and evolutionary processes driven by organismal movements.…”

“…To simulate sub-grid scale turbulent processes, horizontal dispersion was also included in the advection process [19]. The HYCOM-ICHTHYOP system accurately predicts the movement of surface-drifting buoys [20] and is well established for studying sea turtle dispersal [6,9,[20][21][22][23]. Young turtles are relatively weak swimmers and divers, and although even minimal swimming can influence the distribution of marine organisms [9,24], these turtles' net movement is largely driven by ocean currents [6,12,15].…”