Seasonal encounter rate, life stages and main threats to the loggerhead sea turtle (Caretta caretta) in the Aeolian Archipelago (southern Thyrrenian Sea)

Abstract

1. Annual and seasonal encounter rates, life stages and the main threats to loggerhead sea turtles (Caretta caretta) in the Aeolian Archipelago (southern Italy) were studied. 2. Dedicated boat surveys resulted in 258 surface observations and 138 captures of healthy (n = 309), ailing (n = 66) and dead (n = 21) turtles from 2009 to 2013.3. Loggerheads were encountered at the sea water surface while resting (87%) or feeding on pelagic prey (13%).4. The loggerhead encounter rate (observations per km surveyed) was higher during the autumn, suggesting the presence of potential foraging/overwintering habitats in the area.5. The mean (± SD) curved carapace length (CCL) was 48.8 ± 10.7 cm, with 65% of the individuals ranging from 40-70 cm in size. Smaller turtles were encountered more frequently during the spring months, probably as a result of the abundant pelagic prey within the coastal area. During the colder season, larger turtles were more common in the afternoon than in the morning, suggesting that the time needed for rewarming might increase with turtle size.6. Ingestion of anthropogenic debris was reported in 48.5% of the rescued turtles. Individual mortality was mainly related to longline fishing (70.6%), with debris entanglements/ingestion frequently associated with these records. Longline bycatch and boat collisions were higher in summer, whereas debris ingestion was highest in spring. Different threats might affect particular life stages because the longline bycatch was more frequent for larger turtles, whereas boat collisions were more frequent with smaller individuals. 7. Migratory patterns, habitat characteristics and seasonal changes in sea temperature and currents might influence the seasonal occurrence of loggerhead turtles in this area.8. These results increase the current ecological knowledge of the factors driving loggerhead turtle life and are important for implementing management plans for its conservation in the Mediterranean Sea.

Antibiotic Resistance of Gram-Negative Bacteria from Wild Captured Loggerhead Sea Turtles

“…First, larger turtles, which are known to feed at higher trophic levels [15,33], might preferentially feed on prey items in neritic waters and, consequently, be more exposed to anthropogenic contaminations. Indeed, in our study, the mean CCL of weak individuals was higher than that of healthy ones as the adult turtles are known to be more frequently injured by different anthropogenic threats [25,26]. Secondly, variations in diet (i.e., trophic differences) and/or food opportunity could take place among individuals in different areas, since loggerhead sea turtles are migratory species and opportunistic predators [26,49,50].…”

“…Indeed, in our study, the mean CCL of weak individuals was higher than that of healthy ones as the adult turtles are known to be more frequently injured by different anthropogenic threats [25,26]. Secondly, variations in diet (i.e., trophic differences) and/or food opportunity could take place among individuals in different areas, since loggerhead sea turtles are migratory species and opportunistic predators [26,49,50]. These considerations suggest caution in the interpretation of the results on the gut microbial communities, when animals with different health conditions are compared.…”

“…The cloacal samples were collected by dedicated boat surveys from March to December 2014 as previously described [25,26]. The loggerhead turtles (33 individuals) were temporarily captured by hand in their foraging grounds to take body measurements using standard methods [33] and to collect cloacal samples [12], and then released at sea or brought in the rescue centre if severe injuries, diseases or problems were detected.…”

“…The Aeolian Archipelago, located in Southern Tyrrhenian Sea (Sicily, Italy) (Figure 1), is a volcanic area with adjacent extensive neritic and oceanic habitats within short distances [24]. Although it is not a usual nesting site for loggerhead sea turtles, it is considered an important foraging and over-wintering ground [25,26]. To date, a few studies investigated the microbial community associated with Caretta caretta by using culture-dependent methods [9,10,[27][28][29] or metagenomic analysis [30][31][32], and even fewer studies were carried out on the antibiotic resistance of isolates [9,10,13,28].…”

Incidental catch of loggerhead sea turtles (Caretta caretta) along the Sicilian coasts by longline fishery

“…One of the primary causes of loggerhead sea turtle stranding is incidental capture by fishing gear with particular reference to longline fishing ( Camiñas & De La Serna, 1995 ; Laurent et al, 2001 ; Lewison, Freeman & Crowder, 2004 ; Camiñas-Hernández et al, 2006 ; Casale, Freggi & Rocco, 2008 ; Di Bello et al, 2013 ; Blasi & Mattei, 2017 ). Other threats in the Mediterranean Sea include the destruction of reproductive habitats ( Casale & Margaritoulis, 2010 ), collisions with boats, and intentional killing ( Tomás et al, 2008 ; Casale et al, 2010 ; Casale, 2011 ).…”