Tracing sea turtle origins using their genetic fingerprints
Leatherback hatchling on nesting beach, St. Croix, USVI
Credit: Kelly Stewart, NOAA
Sea turtles spend the majority of their lives in the open ocean and underwater, but each one belongs to a specific nesting population.
When turtles feed and migrate, they generally mix with turtles from several nesting populations. To be able to properly assess threats from fisheries or other anthropogenic dangers, we need to know which nesting populations these turtles came from.
Where do turtles out in the ocean originate?
We had an opportunity to investigate this question for leatherback turtles (Dermochelys coriacea) in Canadian waters. We used a combination of tools to trace the origins (home nesting beach) of individual turtles:
- genetic techniques
- satellite tracking
- traditional flipper tags (used for identifying individuals)
Leatherback turtles are wide-ranging. In the northwest Atlantic, they nest throughout the Caribbean and Florida, heading to cold northern waters off Canada and the Northeast U.S. following nesting each summer to feed on jellyfish. In the Atlantic, there are 9 nesting populations:
- Costa Rica
- St. Croix
- French Guiana
- South Africa
From 2001 to 2012, the Canadian Sea Turtle Network collected samples from 288 leatherback turtles off the coast of Nova Scotia and Cape Breton. In addition, they flipper-tagged each turtle and tracked some using satellite telemetry to see where they went to nest the following spring.
Sea turtle fingerprints
To determine a home nesting beach for each of these individuals, we first assigned each turtle to a source nesting population using genetic information. Each turtle has a unique genetic "fingerprint" and may be assigned to a nesting population based on how closely the individual's genetic fingerprint matches the genetic signature of the nesting population.
We already knew the origin for 83 of the Canadian turtles--after being tagged in Canada, they were observed nesting on a specific beach in the Caribbean. Collaborators in many countries shared information about when and where they had seen tagged turtles, illustrating the value of building networks of sea turtle biologists and conservationists. Using information from the network on turtle sightings, we were able to ground-truth our genetic assignments to see how accurately the genetic information matched the actual nesting beach chosen by the turtle.
We found that the genetic assignments matched the nesting beach chosen by the turtles very well. We found that the majority of the Canadian turtles belong to the biggest nesting populations in the western Atlantic:
- French Guiana
With this method now in place, and having shown it to be accurate and useful, we are now able to expand the analysis to look at other turtle samples taken from fisheries bycatch or strandings along the coast to see what populations are being affected in which region of the Atlantic.
Results from this study were published in the Journal of Animal Ecology:
- Stewart, KR, MC James, S Roden and PH Dutton. 2013. Assignment tests, telemetry and tag-recapture data converge to identify natal origins of leatherback turtles foraging in Atlantic Canadian waters. Journal of Animal Ecology 82(4): 791-803.
Updated: June 13, 2014