Assessing reliance on vector navigation in the long-distance oceanic migrations of green sea turtles
Authored by Giulia Cerritelli, Giuseppe Bianco, Giacomo Santini, Annette C Broderick, Brendan J Godley, Graeme C Hays, Paolo Luschi, Susanne Akesson
Date Published: 2019
DOI: 10.1093/beheco/ary166
Sponsors:
Swedish Research Council
Platforms:
R
Model Documentation:
Other Narrative
Model Code URLs:
Model code not found
Abstract
We modeled the oceanic migration of turtles nesting in the remote
Ascension Island to gain insights into the unknown mechanisms of open
sea navigation. We show that a simple strategy of maintaining a single
heading for a given amount of time can account for the turtles'
postnesting migrations directed to targets along the Brazilian coast,
while for prebreeding migrations aimed at reaching the isolated
Ascension Island, reliance on more complex, map-like systems seems
crucial.
Abstract Vector navigation, i.e., maintaining a constant heading for a
given amount of time, is hypothesized to provide a viable basis for the
navigational feats of a number of long-distance animal migrants. Since
animals following this strategy are subject to drift by wind or by ocean
current, performing long migrations relying on vector navigation is
particularly challenging. We tested whether vector navigation could be
involved in the migrations of green turtles (Chelonia mydas) that
migrate between the remote Ascension Island and Brazil. To this aim, a
novel approach was followed using individual-based numerical models to
simulate migratory trajectories of virtual turtles that were compared to
actual routes reconstructed by satellite. Simulated postnesting
migrations from Ascension revealed that weak currents enabled modeled
turtles to reach the Brazilian coast, but only for a limited range of
headings around due West. This conclusion was corroborated by comparing
modeled trajectories with the actual routes of previously tracked
turtles, with a beeline vector navigation strategy providing the best
fit, although a true-navigation strategy directed to the landfall site
produced similar results. Finally, we tested if a vector navigational
strategy was feasible for the prebreeding migration from Brazil towards
Ascension, but modeled routes mostly failed to reach the island or a
larger area around it, with individuals drifting away under the
influence of currents. We conclude that Ascension turtles can take
advantage of vector navigation when migrating towards a wide target like
the Brazilian coast, while the demanding prebreeding migration likely
requires more complex navigational systems.
Tags
individual-based models
Migration
movements
Animal behavior
Dispersal
Orientation
Fidelity
Population-structure
Chelonia-mydas
Clock and compass
Navigational
strategies
Ascension island
Satellite
tracking
Marine predator