Large-scale movements in the oceanic environment identify important foraging areas for loggerheads in central Mediterranean Sea

Abstract

Loggerhead sea turtles (Caretta caretta) are known to display a wide range of movement patterns during the different stages of their life cycle, but empirical information to document this extensive behavioural plasticity is still limited. This is especially true for large, adultsized individuals, that are thought to mainly forage in neritic areas. In the present paper, eight adult-sized loggerhead turtles were tracked using satellite telemetry to identify the location of their foraging grounds in the seas along the western coast of the Italian peninsula. Tracked turtles mostly stayed in the region between the Italian peninsula and the islands of Sicily and Sardinia, that was reached following quick, directed movements by the turtles from a release site to the north. In this area, two turtles took up residence in spatially-limited neritic sites along the coast, while the remaining six alternated circumscribed coastal stays with long-distance, circuitous movements in the oceanic environment. An utilization distribution analysis clearly identified an area, mostly comprising oceanic waters, that was continuously used by turtles in different seasons and years. The present results contribute to the still-limited knowledge of the spatial ecology of loggerheads frequenting the Western Mediterranean Sea and highlight the presence of a potentially important oceanic region in the Southern Tyrrhenian Sea where adult-sized turtles forage for extended periods. These findings increase our knowledge of complex life history traits of loggerhead turtles and provide important information to be considered for evidence-based conservation measures.

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

“…In the Tyrrhenian Sea, juveniles and adult-sized turtles foraging on pelagic prey frequent the oceanic waters around the Aeolian Archipelago, north of Sicily (Blasi & Mattei 2017). Moreover, a recent satellite-tracking study has revealed a high use area in the southern Tyrrhenian Sea (Luschi et al 2018), so this basin may be of importance for loggerhead turtles foraging in the oceanic realm. Other areas where satellite-tracked turtles have taken up residence, presumably for foraging, are the Algerian Sea (Hays et al 2014a), the deep waters of the Sicilian Strait (Bentivegna 2002, Casale et al 2012c, the western Ionian (Mingozzi et al 2016) and the central Ionian (Zbinden et al 2008.…”

Turtles on the trash track: loggerhead turtles exposed to floating plastic in the Mediterranean Sea

“…The higher SPUE of the southern Tyrrhenian Sea compared to that of the Adriatic Sea was rather unexpected, since the Tyrrhenian Sea has thus far not received much consideration as an important marine habitat (see also Casale & Mariani 2014 for a discussion on this topic). Only recently, Luschi et al (2018) identified a high-use area in the north-central Tyrrhenian, derived from satellite tracking results on 8 adult-sized loggerhead turtles. Our results could not confirm this finding, because no effort was made through this part of the Tyrrhenian Sea.…”

“…In brief, while loggerhead turtles and especially their juveniles can be found in virtually all oceanic areas in the Mediterranean Sea, data derived from fishery by-catch rates indicate relatively high abundances in the westernmost part of the basin, the southern Sicily Channel, and the northern Ionian/southern Adriatic Sea (Casale et al 2018). In the Tyrrhenian Sea, catch rates are lower, but nonetheless, recent studies have also highlighted the Tyrrhenian Sea as an important oceanic area for this species (Blasi & Mattei 2017, Luschi et al 2018. Unfortunately, no comparable by-catch rates are available for other areas in the eastern Mediterranean, although high turtle abundances could be expected there because of the proximity of its oceanic areas to known nesting beaches (Casale et al 2018).…”

Contrasted habitats and individual plasticity drive the fine scale movements of juvenile green turtles in coastal ecosystems

“…Although some behavioural similarities can be observed between individuals from the same species, a wide variation in plasticity responses is commonly evidenced in sea turtles [25][26][27][28][29][30][31][32], and is revealed by contrasting diet [33][34][35], diving behaviour [25,26], spatial dynamics [20,28,31] or habitat used [25,36]. For example, adult female green, loggerhead and leatherback turtles explore different habitats during their postnesting migration, using both neritic and oceanic environments [27,31,37]. Similarly, juvenile green turtles from the Atlantic spread in different directions to reach distinct foraging grounds [32].…”