Ascension Island green turtles migrations

Paolo Luschi, University of Pisa, Italy; Graeme Hays, Swansea University, UK; and Susanne Akesson, und University, Sweden

Previous tagging studies of the movements of green turtles (Chelonia mydas) nesting at Ascension Island have shown that they shuttle between this remote target in the Atlantic Ocean and their feeding grounds on the Brazilian coast, a distance of 2300 km or more. Since knowledge of sea turtle migration routes might allow inferences on the still unknown navigational mechanisms of marine animals, we tracked the postnesting migration of six green turtle females from Ascension Island to Brazil. Five of them reached the proximity of the easternmost stretch of the Brazilian coast, covering 1777-2342 km in 33-47 days. Their courses were impressively similar for the first 1000 km, with three turtles tracked over different dates following indistinguishable paths for the first 300 km. Only the sixth turtle made some relatively short trips in different directions around Ascension. The tracks show that turtles (i) are able to maintain straight courses over long distances in the open sea; (ii) may perform exploratory movements in different directions; (iii) appropriately correct their course during the journey according to external information; and (iv) initially keep the same direction as the west-south-westerly flowing current, possibly guided by chemical cues.

Luschi et al. (1998) reconstructed the routes followed by turtles leaving the island for their postnesting migration, to evaluate their navigational performance. This would then allow a re-examination of the hypotheses so far proposed about the navigational
system used by these turtles to pinpoint Ascension, assuming that the same mechanisms guide the postnesting migration as well. Results show that Ascension turtles use information picked up en route to adjust their migratory course, and suggest that current-borne cues, probably of a chemical nature, may be involved in this process for at least part of the journey.

Papi et al. (2000) reports the results of an experiment aimed to test the geomagnetic hypothesis by applying a magnetic disturbance to Ascension turtles returning to Brazil. If this disturbance were to impair the orientation of the turtles, this interesting hypothesis would receive its first experimental
support. However, the results obtained show that magnetic cues are not essential for oceanic navigation by adult
turtles migrating to Brazil.

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Overview

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Attributes described below represent those in the original dataset provided by the provider.
Only minimum required attributes are visible and downloadable online. Other attributes may be obtained upon provider's permission.

Attributes in dataset

Attribute (table column)	Description
oid	Unique ID (created by OBIS-SEAMAP)
recid	Record ID
tag_id	Tag ID
fixno
obs_count	Number of animals
sp_obs	Species observed
sp_tsn	Species ITIS TSN
year	Year of observation
datetime1	Original date and time
obs_date	Date of observation
obs_time	Time of observation
lc	Location class
latitude	Latitude of observation
longitude	Longitude of observation
sex	Sex of animal
age_class	Age class of animal (adult or juvenile)
country	Country where sea turtle was tagged
beach	Nesting beach where sea turtle was tagged
notes	Notes
cite1	Citation 1
cite2	Citation 2