Etude des facteurs écologiques et écotoxicologiques impliqués dans la réussite d’incubation chez la tortue luth, Dermochelys coriacea, de Guyane Française

Leatherback turtles, Dermochelys coriacea, have relatively low hatching success in
comparison to other marine turtle species. This low hatching rate is largely a result of high embryonic
mortality rather than infertility, but the specific causes remain unknown. Leatherbacks are vulnerable
to excessive adult mortality (resulting in population decline) because they are long-lived species.
However, low hatching success and corresponding low juvenile recruitment could also result in long
term declines of leatherbacks. On the Yalimapo beach, in French Guiana, hatching success is lower for
this species than on other nesting sites, emphasising the problem of recruitment for the population.
Understanding the causes of low hatching success is therefore an important conservation step towards
preventing extinction in this population.
During my thesis, I investigated the role of ecological (predation and nest site location) and
ecotoxicological factors (blood and egg contamination by trace elements and organochlorine
compounds) on the hatching success of leatherback nests. Firstly, nest location was shown to have an
important effect on predation and inundation rate that decreased hatching success. Secondly, a
maternal transfer of contaminants from females to their eggs was confirmed, raising the issue of the
deleterious effects of environmental contaminants on embryos development, a developmental stage
very sensitive to contaminants. Dose-effect relationships between contaminants and hatching success
need to be assessed to establish the risk of environmental pollution for leatherback reproduction.
Moreover, the use of stable isotope analysis for females differing in the number of years between two
reproductive seasons revealed that they used different feeding areas. These feeding grounds differed in
their geographical location, but also in the quality of the available prey in terms of their level of
contamination by environmental pollutants, highlighting the issue of adult contamination.
This thesis confirmed the importance of ecological factors for hatching rate and highlighted
the existence of ecotoxicological factors, which have not yet been studied for the leatherback turtle.