Shift in demographic structure and increased reproductive activity of loggerhead turtles in the French Mediterranean Sea revealed by long-term monitoring

Abstract

Climate-induced environmental changes are profoundly impacting marine ecosystems and altering species distribution worldwide. Migratory organisms, including sea turtles, are expected to be particularly sensitive to these variations. Here, we studied changes in the size structure and reproductive activity of loggerhead turtles in the French Mediterranean over 30 years. Overall, there was a significant increase in the size of observed loggerheads between 1990 and 2020. However, this increase was only significant during the breeding/nesting season (May to September) and was driven by the increased presence of adults. Furthermore, nesting activity along the French coast was detected in 2002 for the first time in more than 50 years, and has become frequent after 2014, with nests discovered every year. The number of eggs laid as well as incubation duration and success varied among sites but fell within the range reported at established Mediterranean nesting sites. These observations, along with recent reports of breeding activity and evidence of significant sea surface warming, suggest that the north-western Mediterranean basin has become increasingly suitable to loggerhead turtles. We postulate that this range expansion is the result of climate change and propose that emerging nesting activity in France should be closely monitored and guarded against human activities.

Adaptation of sea turtles to climate warming: Will phenological responses be sufficient to counteract changes in reproductive output?

“…It might be that several other processes need to take place for sea turtles to be able to adapt to climate change. Other behavioral adaptations may include changes in the spatial distribution of sea turtle nesting sites, as well as changes in their nest‐site choice on nesting beaches (Cardona et al., 2022; Girard et al., 2021; Hochscheid et al., 2022; Mancino et al., 2022; Tomillo et al., 2022). Since spatial and temporal adaptations may occur simultaneously (Chuine, 2010), future studies should develop a multi‐faceted framework to explore the adaptive potential of sea turtles in response to contemporary climate change.…”

Toward a common approach for assessing the conservation status of marine turtle species within the european marine strategy framework directive

“…In the case of loggerheads, the Adriatic and Aegean-Levantine Seas are mostly frequented by individuals from the Mediterranean sub-population, while three sub-populations (Mediterranean, Northwest and Northeast Atlantic RMUs, Figure 3) co-occur in the Western and Central basins, with the abundances of individuals of Atlantic origin decreasing eastward (Maffucci et al, 2005;Carreras et al, 2006;Clusa et al, 2014;Loisier et al, 2021). Even though the number of sporadic nesting events in the western Mediterranean Sea has been increasing in the last few years (Maffucci et al, 2016;Carreras et al, 2018;Girard et al, 2021), nesting is almost entirely confined to the eastern Mediterranean basin (Margaritoulis et al, 2003;Casale et al, 2020b).…”

Reproduction in Sea Turtles, a Review

“…In response to increased global temperatures, sea turtles have shown several adaptations to maximize reproductive success under increasingly adverse conditions. These include earlier nesting (Weishampel et al ., 2004, 2010; Mazaris et al ., 2013) and a shift of preferred nesting sites to cooler climates (Stewart et al ., 2011; Girard et al ., 2021; Cardona et al ., 2022; Mancino et al ., 2022). These changes suggest that sea turtles may be able to combat climate change, to a point, by altering some aspects of their life history traits.…”