Behavioural plasticity in the use of a neritic foraging area by loggerhead sea turtles: insights from 37 years of capture–mark–recapture in the Adriatic Sea (Mediterranean Sea)

Abstract

Assessing sea turtle movements and connectivity among different areas is pivotal to understanding their biology and implementing efficient conservation actions. In the Adriatic Sea, one of the most important sea turtle foraging areas in the Mediterranean, a total of 311 capture–mark–recapture (CMR) records (mostly bycatch) from 294 loggerhead turtles (Caretta caretta) in the period 1984–2021 were analysed. A general fidelity pattern to Adriatic subareas was indicated by a significantly shorter CMR distance than the potential dispersal distance and by the significantly higher proportion of re-encounters in the same area of release than expected. No seasonal pattern was detected between subareas, and shorter re-encounter distances were observed in turtles released and re-encountered in the same season, suggesting different winter and summer residential areas. Results suggest that turtles frequenting the Adriatic can go anywhere in the Mediterranean basin and may exhibit a wandering behaviour regardless of their size. A substantial connectivity with nesting sites in Greece was observed, confirming with empirical evidence that this is the most important breeding area for turtles foraging in the Adriatic Sea. This study highlights the value of cooperation among different groups and shows a main behavioural pattern of fidelity to neritic foraging grounds.

Diet of loggerhead turtles in the Gulf of Manfredonia, South Adriatic Sea: evidence of winter feeding and anthropogenic impacts

“…In the GoM, loggerhead turtles generally showed fidelity to the area (Casale and Simone 2017;Baldi et al 2023), therefore dietary items identified in our sample can be considered representative of the prey available in the GoM. Most taxa can be found between 0 and 100 m depth, but some have a deeper range.…”

“…The Adriatic Sea is a semi-closed basin with a wide latitudinal range. It is frequented only by loggerhead turtles of Mediterranean origin, especially from breeding sites in Greece (Tolve et al 2018;Baldi et al 2023). Here, turtles show a degree of fidelity to subareas (Casale and Simone 2017;Baldi et al 2023) that may differ in trophic resources.…”

“…It is frequented only by loggerhead turtles of Mediterranean origin, especially from breeding sites in Greece (Tolve et al 2018;Baldi et al 2023). Here, turtles show a degree of fidelity to subareas (Casale and Simone 2017;Baldi et al 2023) that may differ in trophic resources. So far, diet of loggerhead turtles in the Adriatic has been reported from the Central Adriatic (Mariani et al 2023) and from the North Adriatic (Lazar et al 2011), although limited to mollusks in the latter.…”

The tale of the sea turtle flipper tagging technique, a global environmental impact assessment

“…These identification procedures can be considered minimally invasive for sea turtles as they moderately disrupt the integrity of the skin at the tag insertion point. Sea turtle flipper and PIT tags have been applied in the context of capture–mark–recapture (CMR) monitoring, an essential technique to study the elusive highly migratory marine megafauna that are sea turtles, allowing to assess the life parameters and life history of sea turtle populations since the inception of sea turtle research and conservation in the 1920s (e.g., Baldi et al, 2022; Bjorndal et al, 2017; Carr et al, 1978; Van de Crommenacker et al, 2022; Eckert & Beggs, 2006; Horrocks et al, 2011, 2016; Meylan et al, 2011; Moncada & Prieto, 1999; Moorhouse, 1933; Omeyer et al, 2019; Prince, 1993; Prince et al, 2012; Syed & Syed, 2002). The identification of sea turtles by unique carapace and flipper tags has been performed since 1920s in Queensland Australia along the Great Barrier Reef (Carr et al, 1978; Diamond, 1976; Hendrickson, 1958; Hirth & Carr, 1970; Limpus, 1992; Moorhouse, 1933), PIT tags have been additionally applied since 1990s (e.g., Wyneken et al, 2010) to complement the biometric data of flipper tags that might be lost at sea (e.g., Bjorndal et al, 1996; Meylan et al, 2011; Omeyer et al, 2019).…”

“…The identification of sea turtles by unique carapace and flipper tags has been performed since 1920s in Queensland Australia along the Great Barrier Reef (Carr et al, 1978; Diamond, 1976; Hendrickson, 1958; Hirth & Carr, 1970; Limpus, 1992; Moorhouse, 1933), PIT tags have been additionally applied since 1990s (e.g., Wyneken et al, 2010) to complement the biometric data of flipper tags that might be lost at sea (e.g., Bjorndal et al, 1996; Meylan et al, 2011; Omeyer et al, 2019). Sea turtle flipper tags recovery has been a pilar research technique in marine science universally applied since a century, triggering strong international cooperations and significantly leading to the development of transboundary protected areas based on the analysis of the migratory geographical connectivity of sea turtle species across Sovereign States (e.g., Ahmed et al, 2006; Baldi et al, 2022; Barreto et al, 2021; Bjorndal et al, 2017; Chacón‐Chaverri et al, 2015; Van de Crommenacker et al, 2022; Dalleau et al, 2012; Van de Geer et al, 2022; Hart et al, 2015; Rees et al, 2012; Sanchez et al, 2020). The migratory tracks data of satellite‐tagged sea turtles covering a more reduced timeline, may also be integrated to recovered sea turtle flipper tags datasets to understand species distribution and behavior (e.g., Perez et al, 2022; Shimada et al, 2021a).…”