Mediterranean sea turtles: current knowledge and priorities for conservation and research

Abstract

The available information regarding the 2 sea turtle species breeding in the Mediterranean (loggerhead turtle Caretta caretta and green turtle Chelonia mydas) is reviewed, including biometrics and morphology, identification of breeding and foraging areas, ecology and behaviour, abundance and trends, population structure and dynamics, anthropogenic threats and conservation measures. Although a large body of knowledge has been generated, research efforts have been inconsistently allocated across geographic areas, species and topics. Significant gaps still exist, ranging from the most fundamental aspects, such as the distribution of major nesting sites and the total number of clutches laid annually in the region, to more specific topics like age at maturity, survival rates and behavioural ecology, especially for certain areas (e.g. southeastern Mediterranean). These gaps are particularly marked for the green turtle. The recent positive trends of nest counts at some nesting sites may be the result of the cessation of past exploitation and decades of conservation measures on land, both in the form of national regulations and of continued active protection of clutches. Therefore, the current status should be considered as dependent on such ongoing conservation efforts. Mitigation of incidental catch in fisheries, the main anthropogenic threat at sea, is still in its infancy. From the analysis of the present status a comprehensive list of re search and conservation priorities is proposed.

Spatial ecology of loggerhead turtles: Insights from stable isotope markers and satellite telemetry

“…Satellite‐tracked females from North Cyprus had mean CCL of 0.73 ± 0.06 m (range: 0.65 to 0.85 m), while turtles from Greece had mean CCL of 0.84 ± 0.04 m (range: 0.76–0.89 m). These CCL values are within the ranges recorded for nesting females at each representative site, showing satellite‐tracked females represent the parent population well (Casale et al, ; Omeyer, Godley, & Broderick, ).…”

“…In the Mediterranean Sea, bycatch is one of the most important threats to marine turtles and the Tunisian Plateau has some of the highest rates (Casale, ; Casale et al, ; Casale, Cattarino, Freggi, Rocco, & Argano, ). In Alagadi and Zakynthos, nest counts are not increasing as rapidly as expected (Casale et al, ), suggesting that alternative conservation approaches are needed. This study supports the need to focus site‐specific conservation strategies to key marine habitats, such as the Tunisian Plateau, which may dramatically increase the survival of individuals in this foraging ground and aid in the recovery of many loggerhead rookeries across the Mediterranean.…”

“…This study supports the need to focus site‐specific conservation strategies to key marine habitats, such as the Tunisian Plateau, which may dramatically increase the survival of individuals in this foraging ground and aid in the recovery of many loggerhead rookeries across the Mediterranean. Potential future conservation management approaches to reduce bycatch in important foraging areas, such as the Tunisian Plateau, have been reviewed in Casale et al (). The review highlights the need of monitoring and reporting bycatch, the enforcement of changes to less detrimental fishing gears, as well as mitigation measures such as the use of turtle excluder devices by bottom trawlers or “circle hooks” by longliners (Casale et al, and references therein).…”

“…Nest counts in Mediterranean rookeries are generally not increasing as rapidly as expected despite intensive conservation efforts on the nesting beaches (Casale et al, ). A more comprehensive picture of where Mediterranean loggerhead turtles are foraging would help target conservation strategies (Casale et al, ). Combining satellite telemetry and SIA, Bradshaw et al () described in detail the foraging grounds of a large proportion of nesting green turtles ( Chelonia mydas ) from an important rookery in North Cyprus.…”

“…The large geographical range over which marine turtles migrate and forage means that turtles are under high threat from fisheries so require a more diverse approach to conservation (Wallace et al, ). Bycatch is one of the key threats to marine turtles in the Mediterranean Sea resulting in high levels of mortality (conservatively 44,000 deaths per year, Casale, ; Casale et al, ). Consequently, working towards the conservation of critical marine regions, including foraging grounds and migratory routes, is considered a research priority in Mediterranean marine turtle ecology (Casale et al, ).…”