Bottom or midwater: alternative foraging behaviours in adult female loggerhead sea turtles

Abstract

Intrapopulational polymorphism in habitat use is widely reported in many animal species. The phenomenon has recently also been recognized in adult female loggerhead sea turtles Caretta caretta, with small females tending to inhabit oceanic areas (where water depths are 4200 m) while presumably feeding pelagically and large females tending to inhabit neritic areas (where depths are o200 m) while presumably feeding benthically. In this study, dive recording satellite telemetry units were used to verify their foraging and diving behaviours in these habitats. Two females that nested on Yakushima Island, Japan, were tracked for 124 and 197 days. The small female wandered in the oceanic Pacific, and spent most of the time at 0-25 m depths regardless of day or night, implying that she foraged pelagically at the surface and shallow depths. Her mean dive durations were significantly longer at night than during the day. The large female moved into the neritic East China Sea, and spent most of the time over the continental shelf at 100-150 m depths during the day and at 0-25 m depths at night, suggesting that she alternated between diurnal benthic foraging and nocturnal resting within the depths where she could attain neutral buoyancy. Her mean dive durations were not significantly different between day and night. The increase in dive duration for both turtles coincided with a seasonal decrease in water temperature. The small female sometimes showed midwater dormancy at 0-25 m depths with a duration of 45 h that was in contrast with bottom dormancy by sea turtles inhabiting other regions. The diving behaviours observed during this study were consistent with their estimated main feeding habits, which demonstrated resource polymorphism in a marine reptile.

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…Papi et al 1997;Limpus & Limpus 2001), where females stay for long periods feeding on benthic prey and to which they show fidelity in successive reproductive seasons ). The most recent results have, however, revealed numerous exceptions to this general pattern, including the possible prolonged residence of females in the oceanic habitat (Hatase et al 2002;Hawkes et al 2006;Hatase et al 2007;Rees et al 2010), suggesting the possibility of epipelagic feeding in adults (Reich et al 2010), the presence of seasonal migrations between different feeding and wintering areas (Hawkes et al 2007;Zbinden et al 2008Zbinden et al , 2011 or convoluted segments in the migratory routes (Dodd & Byles 2003;Hatase et al 2007;Hawkes et al 2007) of uncertain biological significance.…”

Shorter telomere length with age in the loggerhead turtle: a new hope for live sea turtle age estimation

“…This simple, rapid, non-invasive technique has the potential to advance our understanding of the enigmatic ecology of sea turtles. For example, although size-related differences in the use of feeding habitats (neritic vs. oceanic) by adult female loggerhead turtles have been reported within several populations (Hatase et al, 2002(Hatase et al, , 2007Hawkes et al, 2006), the mechanisms that produce and maintain this phenomenon are still unknown. Relative age information obtained with this method may become a key to help solve this phenomenon, which is closely related to facultative habitat shifts during ontogeny and alternative life histories in animals (Hatase et al, 2006;McClellan and Read, 2007).…”

Genetic composition of loggerhead turtle feeding aggregations: migration patterns in the North Pacific

“…As the females appear to have high site fidelity to feeding areas , it may indicate that adults go back to the Sanriku coastal area after their breeding migration. According to tag-recapture data (Kamezaki et al 1997), the post-nesting females that nest in Yakushima migrate mainly to Japanese coastal areas and the East China Sea, whereas, according to satellite telemetry (Hatase et al 2007), some small adults migrate following the Kuroshio Current to the pelagic Pacific after nesting. These adult-sized loggerhead turtles migrating along the Kuroshio Current after their breeding migration may recruit to the Sanriku coastal area.…”

“…As there are no genetic differences between neritic foragers and oceanic foragers within Minabe and Ya kushima rookeries, the difference in feeding strategy is assumed to indicate phenotypic plasticity (Watanabe et al 2011). Juveniles that use the oceanic feeding strategy after the transoceanic migration, originating from the southern rookeries and possibly from the northern rookeries, are considered to migrate along the Kuroshio Current, as do some oceanic postnesting adults nesting in Japan (Hatase et al 2002b(Hatase et al , 2007, analogous to the juveniles in the Atlantic migrating along the Gulf Stream (Mansfield et al 2009). When juveniles that are transported to the north in the Kuroshio Current encounter the Sanriku coastal area, they settle or at least opportunistically forage in this area because of its high productivity.…”