These are skin grafts from the light colored plastron to the darker colored carapace, usually performed at the hatchling stage. This grafting process is basically a surgery, making it somewhat laborious and logistically challenging. The turtles must be held in captivity for some time to allow the graft to "take hold," after which they can be released. The idea is that the light colored "spot" from the graft will be always visible throughout the life of the turtle. This technique has been used in different places including the USA, Mexico and the Cayman Islands. Although there is little information on the retention success of these tags, or of the likelihood that they will be recognized at adulthood, there are examples of nesting females being recognized with living tags (click on the links below):

• http://www.seaturtle.org/mtn/archives/mtn98/mtn98p5.shtml
• http://www.seaturtle.org/mtn/archives/mtn82/mtn82p1b.shtml

For photos of living tags, visit the Image Library of SEATURTLE.ORG