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Watanabe K.K.,University of Tokyo | Watanabe K.K.,Japan National Institute for Land and Infrastructure Management | Hatase H.,University of Tokyo | Kinoshita M.,Kyoto University | And 10 more authors.
Marine Ecology Progress Series | Year: 2011

Knowledge of detailed population genetic structure is crucial to conserve and manage endangered species effectively. Size-related variation in feeding-habitat use (neritic vs. oceanic) by adult loggerhead turtles Caretta caretta has been reported within several populations, and sympatric population subdivision was suspected. In the present study, genetic differences between the 2 feeding-habitat groups within 2 Japanese nesting sites were assessed, using 5 microsatellite loci and mitochondrial (mt) DNA sequences. There were no genotypic or haplotype differences between the feeding-habitat groups, which were defined by egg-yolk stable isotope ratios and body size, at both nesting sites, suggesting that both neritic and oceanic individuals belong to the same genetic population. Differences in feeding-habitat use are unlikely to be a limiting factor for gene flow between feeding-habitat groups and were thought to be the result of phenotypic plasticity rather than population subdivision. Gene flow among 5 nesting sites was assessed by pooling these feeding-habitat groups at each nesting site. Significant genetic structure by female natal homing was observed at the mtDNA level. However, no significant structure was found at the microsatellite DNA level, suggesting male-mediated gene flow caused by migration through courtship areas. Although nesting beaches are connected by male-mediated gene flow, which might have evolved as a mechanism to avoid genetic fragmentation by natal homing, extirpated beaches would not be easily recolonized from other nesting populations due to female philopatry. Therefore, conservation of individual nesting beaches is still needed to maintain the overall genetic diversity of Japanese loggerheads. © Inter-Research 2011.


Yoshikawa N.,Center for Molecular Biodiversity Research | Kamezaki N.,Okayama University of Science | Kawazu I.,Okinawa Churashima Foundation | Hirai S.,Sea Turtle Association of Japan | Taguchi S.,Akita
Current Herpetology | Year: 2016

We determined sequences of mitochondrial control region of 16 specimens of the leatherback turtles, Dermochelys coriacea, collected in the vicinity of Japan, and estimated stock origin of Japanese migrants. As a result, we found three haplotypes (JD1, 2, and 3) in these specimens, and 14 specimens possessed JD1. In comparison with previously reported sequences, JD1 and 2 were identical to a single haplotype endemic to West Pacific stock in New Guinea and Solomon Islands, whereas JD3 was identical to a haplotype nearly endemic to Malaysian stock. Our results indicate that most of the leatherbacks foraging around Japan originate in West Pacific stock, and a few may migrate from the Malaysian nesting population. © 2016 by The Herpetological Society of Japan.


Hamabata T.,Kyoto University | Hikida T.,Kyoto University | Okamoto K.,Orido | Watanabe S.,Sea Turtle Association of Japan | And 2 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2015

To understand the life histories and ontogenetic habitat utilization of green turtles along the coasts of the western Japanese main islands, we collected size frequency and genetic data of green turtles captured by pound nets in three foraging grounds (FG): Nomaike (n=38), Muroto (n=93), and Kumano-nada (n=31), and compared their natal origins among different size classes. Population genetic analyses based on an 820-bp fragment of mitochondrial DNA showed that the three FG were part of a single multiple-coast FG. Although turtles from all size classes originated mainly from rookeries in the Ogasawara Group, the size distributions clearly exhibited bimodality, with low occurrences of turtles in the 50-70-cm straight carapace length (SCL) range. The bimodal size distributions could not be attributed to demographic shifts in rookeries, because the number of female green turtles in Ogasawara has exhibited an increasing trend since 1979. We also examined whether factors such as seasonality and predation risk could have caused the size bimodality. There were, however, no strong relationships between sea-surface temperatures when turtles were captured and the sizes of the turtles (r2<0.2), and it appeared that predation risk could not result in the size modality observed in the FG. Our results strongly suggest that after switching from a pelagic to a neritic lifestyle, the green turtles in the neritic FG along the western Japanese main islands undergo another ontogenetic habitat shift upon reaching ~50-cm SCL. Here, we explore the possibility that developmental growth might stimulate a habitat shift, resulting in habitat differentiations by size and growth phase in the long-lived green turtle. © 2014 Elsevier B.V.


Shimada T.,University of Tokyo | Aoki S.,University of Tokyo | Kameda K.,Sea Turtle Association of Japan | Hazel J.,James Cook University | And 3 more authors.
Endangered Species Research | Year: 2014

Incomplete knowledge about local foraging ecology of green turtles hampers their conservation management in Japan, where stocks have only partially recovered from heavy exploitation in previous centuries. We used stable isotope ratios of δ13C and δ15N for turtle carapace scutes, where successive layers contain a chronological record of diet assimilated over a period of years. Turtles were sampled at 2 geographically separate foraging grounds in Japan: the temperate Main Islands (n=32) and the sub-tropical Nansei Islands (n=42). Site fidelity was inferred for the majority of turtles at each site (81 and 64% resident turtles) because isotope data indicated diets consistent with food taxa at the respective sites. Immigrant turtles (previous diet outside their current site) were few (n=4) at the Main Islands site but numerous (n=14) at the Nansei Islands site, where they were significantly smaller than residents. An ontogenetic shift (Main Islands to Nansei Islands) was inferred for many of the immigrants on the basis of isotope evidence and body size. These immigrants corresponded to a size cohort that was relatively scarce in Main Islands foraging grounds according to previous studies. Bayesian mixing models, used to estimate proportional components of diet, showed varying degrees of imbalance between seagrass and algae and indicated that hypothetical consumption of non-trivial amounts of animal matter was plausible. The latter represented a hypothetical diet component for study turtles since animal matter was rarely found in stomach contents. Potential ambiguity and other issues that constrained inference from mixing models are discussed. © Inter-Research 2014.


Pfaller J.B.,University of Florida | Pfaller J.B.,Caretta Research Project | Alfaro-Shigueto J.,ProDelphinus | Alfaro-Shigueto J.,University of Exeter | And 8 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2014

Studying how host characteristics and ecology affect the mating systems of symbiotic crustaceans offers an opportunity to understand how ecological factors contribute to the evolution of different animal mating systems. In theory, symbiotic crustaceans should display social monogamy with long-term heterosexual pairing when hosts are relatively small in body size and structurally simple, and when hosts have relatively low abundance in habitats where the risk of mortality for symbionts (e.g., predation) away from hosts is high. We test this prediction in the mating system of the flotsam crab (Planes major) and its facultative association with loggerhead sea turtles (Caretta caretta). First, we found that the overall population and sex distributions were non-random and crabs inhabited host turtles as heterosexual pairs more frequently than expected by chance, which supports the hypothesis that P. major is socially monogamous on C. caretta. Second, we found that male crabs pair with females regardless of their reproductive state, male-female pairs do not display size-assortative pairing, crab body size and host turtle body size are not correlated, and crabs display reverse sexual dimorphism in body size and conventional sexual dimorphism in weaponry. These results do not support the hypothesis that social monogamy in P. major is always long term. Instead, our results suggest that the duration of social monogamy in P. major is likely variable and may involve some degree of host switching and intra-sexual (mostly male-male) competition. Our results were only partially consistent with theoretical considerations for how host characteristics and ecology affect the mating systems of symbiotic crustaceans, and future studies should focus on quantifying the degree and direction of host switching to better understand the factors that affect the duration of monogamous pairing when P. major associates with C. caretta. © 2014 Elsevier B.V.


Pfaller J.B.,University of Florida | Pfaller J.B.,Caretta Research Project | Alfaro-Shigueto J.,ProDelphinus | Alfaro-Shigueto J.,University of Exeter | And 8 more authors.
Marine Biology | Year: 2014

Studies that incorporate information from habitat-specific ecological interactions (e.g., epibiotic associations) can reveal valuable insights into the cryptic habitat-use patterns and behavior of marine vertebrates. Sea turtles, like other large, highly mobile marine vertebrates, are inherently difficult to study, and such information can inform the implementation of conservation measures. The presence of epipelagic epibionts, such as the flotsam crab Planes major, on sea turtles strongly suggests that neritic turtles have recently occupied epipelagic habitats (upper 200 m in areas with >200 m depth) and that epipelagic turtles spend time at or near the surface. We quantified the effects of turtle species, turtle size, and habitat (neritic or epipelagic) on the frequency of epibiosis (F 0) by P. major on sea turtles in the Pacific Ocean. In neritic habitats, we found that loggerhead (F 0 = 27.6 %) and olive ridley turtles (F 0 = 26.2 %) host crabs frequently across a wide range of body sizes, and green turtles almost never host crabs (F 0 = 0.7 %). These results suggest that loggerheads and olive ridleys display variable/flexible epipelagic-neritic transitions, while green turtles tend to transition unidirectionally at small body sizes. In epipelagic habitats, we found that loggerheads host crabs (F 0 = 92.9 %) more frequently than olive ridleys (F 0 = 50 %) and green turtles (F 0 = 38.5 %). These results suggest that epipelagic loggerheads tend to spend more time at or near the surface than epipelagic olive ridleys and green turtles. Results of this study reveal new insights into habitat-use patterns and behavior of sea turtles and display how epibiont data can supplement data from more advanced technologies to gain a better understanding of the ecology of marine vertebrates during cryptic life stages. © 2014 Springer-Verlag Berlin Heidelberg.


Kobayashi D.R.,National Oceanic and Atmospheric Administration | Cheng I.-J.,National Taiwan Ocean University | Parker D.M.,University of Hawaii at Manoa | Polovina J.J.,National Oceanic and Atmospheric Administration | And 2 more authors.
ICES Journal of Marine Science | Year: 2011

Satellite tags were attached to 34 non-reproductive loggerhead turtles (Caretta caretta) caught as bycatch in the Taiwanese coastal poundnet fishery from 2002 to 2008. Transmission durations ranged from 6 to 503 d (median 172 d), with 5860 d tracked in total. Horizontal track data were processed using the Bayesian state-space modelling to extract the most likely daily positions, taking into account ARGOS data quality and other forms of statistical error. A region of high occupancy in the East China Sea, covering 433 549 km2 of coastal and pelagic area next to Taiwan, China, Japan, and South Korea, was characterized from the tracking data. Various attributes of this hotspot are described using satellite tracks and remotely sensed data. The tracks were merged with oceanographic data, emphasizing a new global dataset characterizing mesoscale eddies from satellite altimetry data. A proximity-probability approach coupled with odds ratio testing was used to infer orientation to eddy features. Comparisons against random points, simulated particle tracks, and drifter buoys were used to demonstrate turtle differential responses to eddies inside and outside the hotspot, depending on eddy features (i.e. cyclonic vs. anticyclonic, edges vs. centres). Turtles inside the hotspot utilize fewer strong cyclonic eddy edges than those outside. © United States Government, Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service 2011. Published by Oxford Journals. All rights reserved.


Ishihara T.,University of Tokyo | Kamezaki N.,University of Tokyo | Matsuzawa Y.,Sea Turtle Association of Japan | Iwamoto F.,Sea Turtle Association of Japan | And 4 more authors.
Current Herpetology | Year: 2011

We measured the straight carapace length (SCL) of 1392 loggerhead turtles of the Japanese aggregation that were incidentally captured between July 2002 and November 2009 by pound nets set near the eastern coast of Cape Muroto, Kochi Prefecture, Japan. Each specimen was categorized as adult, subadult, or juvenile on the basis of their maturity status inferred from SCL. In the present sample, SCL exhibited a unimodal distribution with the mode located in the 740-749 mm class (x4±SD: 757±67 mm; range: 563-1050 mm). The majority of loggerhead turtles composing the Japanese aggregation was subadult (75.9%). The SCL of smaller specimens suggested that reentery into Japanese waters of individuals once flown to the northeastern Pacific occurs in the later juvenile stage. A unimodal histogram implies that the major size classes in SCL of turtles reentering Japanese waters range from 560-749 mm. A comparison between the Japanese aggregation and the Mexican aggregation indicates that turtles at the later juvenile stage start to migrate westward, taking only a few years to cross the North Pacific to Japanese waters. © 2011 by The Herpetological Society of Japan.


Hamabata T.,Kyoto University | Kamezaki N.,Sea Turtle Association of Japan | Kamezaki N.,University of Tokyo | Hikida T.,Kyoto University
Marine Biology | Year: 2014

Several green turtle (Chelonia mydas) nesting populations have been reported in the northwestern Pacific region, the northernmost limit of its distribution range. However, the population history in this region as a whole is not well understood. To clarify how the green turtle nesting populations have evolved in the northwestern Pacific region, the genetic composition of mitochondrial DNA control region sequences in the northwestern Pacific was compared with that of the other Pacific populations. We analyzed 302 samples from the northwestern Pacific rookeries, including 78 newly collected samples from rookeries in the Ryukyu Archipelago, Japan (from 24.27°N, 123.76°E to 28.45°N, 129.61°E). Our results revealed that the northwestern Pacific populations consisted of one highly endemic lineage (Clade IV) in the northwestern Pacific rookeries and two other lineages (Clades I and V) which were widely observed in other Pacific populations. We concluded that the highly endemic lineage indicated that a refugial population existed in this region during the Last Glacial Maximum, and the other two lineages indicated that colonization from populations at lower latitudes occurred during interglacial periods. The green turtle nesting populations in the present periphery of their distribution range had been thought to have their origin in colonization from lower latitudes, which served as refugia during glacial periods. However, the present results indicated that the northwestern Pacific peripheral populations have been maintained on the evolutionary timescale of this species and should be treated as long-term conservation resources. © 2013 Springer-Verlag Berlin Heidelberg.


Nishizawa H.,Kyoto University | Asahara M.,Kyoto University | Kamezaki N.,Sea Turtle Association of Japan | Arai N.,Kyoto University
Current Herpetology | Year: 2010

Skull morphology was compared between juvenile and adult green turtles by geometric morphometrics. The size of the orbit and length of the supraoccipital in relation to the centroid size were larger in juveniles than in adults, while the relative sizes of the infratemporal fossae and parietal were larger in the latter than in the former. The difference in the relative length of the supraoccipital did not predict the maintenance of functional equivalence of trophic structures, probably reflecting a functional trophic change with growth. © 2010 by The Herpetological Society of Japan.

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