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We investigated how trophic polymorphism observed at a loggerhead sea turtle (Caretta caretta) rookery affected the interannual variability of clutch frequency (the number of clutches laid by a female during a nesting season) and of the number of total located nests, based on comprehensive nighttime and daytime field surveys conducted at Yakushima Island, Japan, over a non‐consecutive eight‐year period. Taking into account the fact that lower trophic‐level sea turtles show greater variability in these parameters, we anticipated clutch frequency and the number of total located nests to vary more in low trophic‐level oceanic planktivores (secondary consumers) than in high trophic‐level neritic benthivores (tertiary consumers). Oceanic planktivores and neritic benthivores were classified by stable isotope ratios in egg yolks. Neritic foragers had higher clutch frequencies than oceanic foragers in any year. Contrary to our anticipation, however, both types of foragers showed similarly low interannual variability in clutch frequencies. No significant correlations were found between mean clutch frequencies and the estimated number of nests made by either oceanic or neritic foragers and the number of total located nests. Interannual fluctuations in the total number of nests made by loggerhead turtles, whether trophically monomorphic or polymorphic, seem to be driven more by the number of females than by clutch frequency; this suggests that the number of total located nests can be a good proxy for the population size of iteroparous animals at relatively high trophic levels. [ABSTRACT FROM AUTHOR]

Abstract: Among species without parental care, nest sites selected by mothers determine their fitness via the survival of offspring. We examined nest site selection in oceanic (>200 m water depth) and neritic (<200 m water depth) foraging loggerhead sea turtles Caretta caretta that differ greatly in reproductive output to assess a trade‐off between quantity and quality of offspring. Nest sites selected by oceanic and neritic foragers, which were classified based on differences in stable isotope ratios, on two adjacent beaches at Yakushima Island, Japan, were compared. Both oceanic and neritic foragers preferred a wider beach where they could nest further from the sea, with no significant differences being found in beach sections used for nesting between the two foragers. On the wider beach, nests of both foragers tended to be clumped on open sand close to vegetation. Oceanic foragers nested significantly closer to the sea than did neritic foragers, although significance was lost with adjusted beach width. These results, together with similarities in morphology, emergence success and activity levels of hatchlings, suggested comparable offspring survival rate on land between the two foragers. Thus, low fecundity of oceanic foragers would not be offset by differences in offspring survival via nest site selection. These support unbalanced fitness between the two foragers and environmental maintenance of their alternative life histories. [ABSTRACT FROM AUTHOR]

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 >200 m) while presumably feeding pelagically and large females tending to inhabit neritic areas (where depths are <200 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 >5 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. [ABSTRACT FROM AUTHOR]

There are size-related differences in the use of feeding habitats (planktonic or benthic; oceanic or neritic) by adult female loggerhead sea turtles (Caretta caretta) within Japanese populations. We thus hypothesized that the differences may be reflected in their remigration and growth patterns, and investigated the relationships between body size and remigration intervals, growth rates, and remigration percentages, for female loggerheads nesting on a Japanese beach between 1991 and 2001. Although remigration intervals, growth rates, and remigration percentages were not significantly different among females, there were trends for longer remigration intervals and lower remigration percentages in smaller females. All females grew little. Considering these results along with previous findings, we speculated on the life-history strategy of female Japanese loggerheads. [ABSTRACT FROM AUTHOR]

Nucleotide sequences from the control region of the mitochondrial (mr) DNA were analyzed for Japanese loggerhead turtles (Caretta caretta) to elucidate population genetic structure and phylogeography. Three haplotypes were detected among 259 females sampled from four nesting sites in 1994-1999. Within nesting colonies, haplotype frequencies were not significantly different between sampling years, whereas among nesting colonies, they were significantly different and fixation indices (F[sub st]) were significantly >0 in most comparisons. These findings indicate that nesting colonies of Japanese loggerheads are genetically distinct and that Japanese females show precise natal homing on an ecological time scale. There were no obvious latitudinal variations in the mtDNA diversity among Japanese nesting populations in contrast with those of the USA, where a series of colonization bottlenecks on northern nesting populations accompanied by postglacial expansion are supposed to be the cause of the trend. Since (1) the mtDNA diversity of Pacific loggerheads consists of a small number of divergent haplotypes and (2) their population size is smaller than those of loggerheads inhabiting other regions, the Pacific loggerheads might have experienced more critical bottlenecks than the others. The discovery of a female with the haplotype that had previously been detected in the nesting colonies of the South Pacific but not the North Pacific made us reconsider the stock composition of loggerheads observed in the North Pacific; that is, all loggerheads inhabiting the North Pacific are derived from Japanese beaches. [ABSTRACT FROM AUTHOR]