Ascension Island green turtles migrations
Paolo Luschi, University of Pisa, Italy; Graeme Hays, Swansea University, UK; and Susanne Akesson, und University, Sweden
Luschi, P. 2013. Ascension Island green turtles migrations. Data downloaded from OBIS-SEAMAP (http://seamap.env.duke.edu/dataset/994) on yyyy-mm-dd.
Halpin, P.N., A.J. Read, E. Fujioka, B.D. Best, B. Donnelly, L.J. Hazen, C. Kot, K. Urian, E. LaBrecque, A. Dimatteo, J. Cleary, C. Good, L.B. Crowder, and K.D. Hyrenbach. 2009. OBIS-SEAMAP: The world data center for marine mammal, sea bird, and sea turtle distributions. Oceanography. 22(2):104-115.
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.
Luschi, P., G.C. Hays, C. Del Seppia, R. Marsh and F. Papi. 1998. The navigational feats of green sea turtles migrating from Ascension Island investigated by satellite telemetry. Proceedings of the Royal Society: Biological Sciences. 265: 2279-2284.
Attributes described below represent those in the original dataset provided by the provider.
This section explains attributes included in the original dataset. OBIS-SEAMAP restricts the attributes available to the public to date/time, lat/lon and species names/counts only. Should you need other attributes described here, you are encouraged to contact the data provider.
Attributes in dataset provided
|Rays and sharks||0|
|Latitude||-12.76 - -5.16|
|Longitude||-38.17 - -12.45|
|Coord. prec.||3 decimal digits|
|Data type||Telemetry location|
|Tracklines||YES (ID: 995)|
|Sharing policy||CC-BY (Minimum)|
|Also availalbe from||iOBIS|
|See metadata in static HTML|
|See metadata in FGDC XML|
|See download history / statistics|