INSEAD Annual Report 2023-20143 test - Flipbook - Page 34
32
Bertarelli Foundation
In 1873, Charles Darwin marvelled at the ability of
sea turtles to find isolated island breeding sites,
but the details of how sea turtles and other animals
navigate during these migrations remains perplexing.
To help solve this long-standing enigma, this study
tracked 22 critically endangered hawksbill turtles
(Eretmochelys imbricata) after they had finished
nesting in the Chagos Archipelago all the way to
their foraging grounds in other parts of the Indian
Ocean. The team considered the likely resolution of
any mapping sense used in migration, based on the
navigational performance across different scales
(tens to thousands of kilometres).
Travel routes to
remote ocean targets
reveal the map sense
resolution for a
marine migrant
Hays, G.C., Atchison-Balmond, N., Cerritelli, G.,
Laloë, J.O., Luschi, P., Mortimer, J.A., Rattray,
A., and Esteban, N., ‘Travel routes to remote ocean
targets reveal the map sense resolution for a marine
migrant’ – Journal of the Royal Society Interface
https://doi.org/10.1098/rsif.2021.0859
The studies found that these turtles often followed
circuitous paths when migrating short distances. For
example, one turtle travelled 1,306.2 km, seven times
the beeline distance to the target foraging ground of
only 176.4 km. When off the beeline to their target,
turtles sometimes corrected their course both in
the open ocean and when encountering shallow
water. The results provide compelling evidence that
hawksbill turtles only have a relatively crude map
sense in the open ocean, almost certainly using a
geomagnetic map that only corrects them when they
are a long way off route. The existence of widespread
foraging and breeding areas on isolated oceanic
sites points to target searching being common in sea
turtles in the final stages of migration.
Hawksbill turtles typically migrate much shorter
distances than green turtles, around 150 km
compared to up to 5,000 km. An earlier paper about
tagged green turtles in 2020 by the authors provided
some of the best evidence to date for the ability of
turtles to reorient in the open ocean, but similarly
only at a crude level. Sea turtles therefore locate
isolated targets through a roughly target-oriented
ocean crossing, open ocean course corrections and
then localised search closer to the target. Sea turtle
navigational abilities are therefore far from perfect
but may simply be as good as possible within the
constraints of their sensory ability.
