But, some turtle monitoring projects focus on younger turtles at their in-water feeding grounds.  Several such in-water studies are on-going in Seychelles -- the most notable being the long-term study of foraging immature hawksbill and green turtles at Aldabra, conducted by Seychelles Islands Foundation (SIF) since 1986.  Juvenile hawksbill and green turtles encountered (mostly inside the lagoon) at Aldabra are captured, tagged, measured, weighed, and released. 

Since 1986, about 500 immature hawksbills have been tagged at Aldabra, and about a third of those were later recaptured and re-measured at the atoll -- some individuals up to a dozen times.  These data provide information on growth rates and migrations of the turtles in the vicinity of Aldabra.  They show that the young hawksbills don’t move around much while they are at Aldabra. 

They also show that most of these Aldabra hawksbills are between 30 and 55 cm in shell length; and they grow at a rate of about 1.5 to 3.2 cm per year.   But, adult hawksbills measure between 75 and 90 cm in shell length, and there are relatively few hawksbills bigger than 55 cm at Aldabra. In fact, relatively few hawksbills (only a couple of dozen) nest at Aldabra each year.  So, it appears that once their shells reach lengths of about 55-60 cm most of these turtles depart Aldabra. 

Where do they go?   

The western Indian Ocean is a vast territory.  So, once an immature hawksbill departs Aldabra, the odds of seeing it again are low.  Remarkably, however, we now have two confirmed re-sightings of tagged juvenile animals that demonstrate long distance migrations away from Aldabra.  This information may help us begin to answer another question:  Where do they come from in the first place? 

Turtle 1. In November 2006, off Anse Mondon, Silhouette Island, an observant diver with a camera provided the Nature Protection Trust of Seychelles (NPTS) with photographs of a tagged hawksbill that show a side view of the entire animal and also a close-up of the tag itself (SEY1756).  SIF tagging records show the turtle had been tagged 9.6 years earlier (in April 1997) by Jeanne Mortimer and Tony Jupiter in shallow waters near Ile Esprit, Aldabra -- 1,150 km away.  Using the photos to compare the size of the turtle relative to the tag, its shell was calculated to have grown from 56.4 cm in 1997 to about 70 cm in 2006 -- an average of about 1.4 cm per year.  From the size of its tail, it was clearly a sub-adult male in 2006.

Turtle 2. In December 2009, at Desroches Island in the Amirantes, Phil Summerton of Island Conservation Society (ICS) found a nesting female bearing tag numbers SEY1151 and SEY1152, and took digital photos of both tags.  The photos and SIF tagging data confirm that the turtle was tagged 13.2 years earlier (in October 1996) by Jeanne Mortimer and France Sophola at Passe Hoareau, Aldabra -- 900 km away.  Between 1996 and 2009 she grew 29 cm in shell length (from 57.2 to 86.2 cm) -- indicating a minimum growth rate of about 2.2 cm per year.  She is now an adult, having laid 111 eggs at Desroches.

What these records tell us

These exciting tag records are instructive, and tell us:  
1.  Photographic evidence is valuable. Had either of these records not been supported by photographic evidence they would have been plagued by uncertainty.  Identification codes of turtle tags typically comprise six to eight characters, and if any one of them is misread or misrecorded the identity of the turtle will be wrong and the data misleading.  But, in the case of these two turtles, there is no doubt about their identity and the veracity of the data.   We encourage anyone who encounters a nesting turtle with unusual tags (i.e., tags with a code series not used at their study site) to photograph them if possible.  And we recommend photographing the tag numbers of any tagged turtles encountered underwater.

2.   Sea turtles are highly migratory. Immature hawksbills can travel vast distances during the 30-40 years it takes them to reach maturity, and those at Aldabra likely originate from nesting beaches throughout the region. Our data suggest that some Aldabra hawksbills come from the Amirantes and maybe even the granitic islands. 
 
3.   It is important to protect and monitor turtles throughout their range -- at Aldabra, in the outer islands, and indeed throughout Seychelles.  Individual turtles are shared by many islands in Seychelles and throughout the region.  No island -- not even magnificent Aldabra Atoll -- is a closed system when it comes to sea turtles. 

by Jeanne A. Mortimer, Justin Gerlach, & Philip Summerton

Forrás: http://www.nation.sc/index.php?art=18623