There’s been lots of interesting anthro news this past week which as yet I haven’t had the time to write up, and it might be a day or two yet before I catch up. In the meantime I hope readers will find this freely accessible paper of interest, which investigates the remarkable way in which leatherback turtles, amongst others, are able to return to specific geographical locations many years after their prior visit. Although this phenomena has long been observed, nobody as yet has been able to determine the processes and navigational capabilities by which turtles are able to achieve these feats. It has taken humans hundreds if not thousands of years to be able to navigate with confidence around the world’s vast oceanic spaces, and yet the turtle appears to have an inbuilt capacity for long distance navigation over many years without recourse to invented technologies. This paper examines ocean currents, magnetic cues and visual clues, in an attempt to unravel the mystery of the ocean-going turtle.
The open-sea movements of marine animals are affected by the drifting action of currents that, if not compensated for, can produce non-negligible deviations from the correct route towards a given target. Marine turtles are paradigmatic skilful oceanic navigators that are able to reach remote goals at the end of long-distance migrations, apparently overcoming current drift effects. Particularly relevant is the case of leatherback turtles (Dermochelys coriacea), which spend entire years in the ocean, wandering in search of planktonic prey. Recent analyses have revealed how the movements of satellite-tracked leatherbacks in the Indian, Atlantic and Pacific Oceans are strongly dependent on the oceanic currents, up to the point that turtles are often passively transported over long distances.
However, leatherbacks are known to return to specific areas to breed every 2–3 years, thus finding their way back home after long periods in the oceanic environment. Here we examine the navigational consequences of the leatherbacks’ close association with currents and discuss how the combined reliance on mechanisms of map-based navigation and local orientation cues close to the target may allow leatherbacks to accomplish the difficult task of returning to specific sites after years spent wandering in a moving medium.
It is suggested that some turtles showed an ability to respond to the Earth’s magnetic field, and that this ability was compromised in some turtles who had small magnets attached to their heads by researchers; an interesting paper which suggests that in addition to the proposed factors prevalent in the turtles’ abilities to achieve long term navigational goals, other elements also play a part.
An olfactory factor might be present as described in this abstract, and note is also made of the sun, moon and stars as other possible factors present in aiding turtle navigation; in the linked paper we learn that turtles have been tracked on their voyages by satellites in space, a technology developed by humans only made possible in the last few hundred years as we began to appreciate the movements and dynamics of our own solar system. Whether turtles have a map of the skies and are able to chart the relative positions of moving objects therein, isn’t covered in this study, but such an awareness is surely a potential contender for explaining how turtles are able to keep track of their global positioning status at all times.
Reference: Navigational Challenges in the Oceanic Migrations of Leatherback Sea Turtles by Alessandro Sale and Paolo Lusch
Published online before print July 22, 2009, doi: 10.1098/rspb.2009.0965 rspb20090965
image: Leatherback turtle from ‘Why would a Leatherback Turtle Dive 1000m Deep?’ at Deep Sea News