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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

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. Source

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

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. Source

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

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. Source

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

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. Source

Pfaller J.B.,University of Florida | Pfaller J.B.,Caretta Research Project | Alfaro-Shigueto J.,ProDelphinus | Alfaro-Shigueto J.,University of Exeter | And 7 more authors.
Marine Biology

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. Source

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