Hierarchical state-space estimation of leatherback turtle navigation ability

Remotely sensed tracking technology has revealed remarkable migration patterns that were previously unknown; however, models to optimally use such data have developed more slowly. Here, we present a hierarchical Bayes state-space framework that allows us to combine tracking data from a collection of animals and make inferences at both individual and broader levels. We formulate models that allow the navigation ability of animals to be estimated and demonstrate how information can be combined over many animals to allow improved estimation. We also show how formal hypothesis testing regarding navigation ability can easily be accomplished in this framework. Using Argos satellite tracking data from 14 leatherback turtles, 7 males and 7 females, during their southward migration from Nova Scotia, Canada, we find that the circle of confusion (the radius around an animal's location within which it is unable to determine its location precisely) is approximately 96 km. This estimate suggests that the turtles' navigation does not need to be highly accurate, especially if they are able to use more reliable cues as they near their destination. Moreover, for the 14 turtles examined, there is little evidence to suggest that male and female navigation abilities differ. Because of the minimal assumptions made about the movement process, our approach can be used to estimate and compare navigation ability for many migratory species that are able to carry electronic tracking devices.     

Navigational challenges in the oceanic migrations of leatherback sea turtles

The open-sea movements of marine animals are affected by the drifting action of currents that, if not compensated for, can produce non-negligible deviations from the correct route towards a given target. Marine turtles are paradigmatic skilful oceanic navigators that are able to reach remote goals at the end of long-distance migrations, apparently overcoming current drift effects. Particularly relevant is the case of leatherback turtles (Dermochelys coriacea), which spend entire years in the ocean, wandering in search of planktonic prey. Recent analyses have revealed how the movements of satellite-tracked leatherbacks in the Indian, Atlantic and Pacific Oceans are strongly dependent on the oceanic currents, up to the point that turtles are often passively transported over long distances. However, leatherbacks are known to return to specific areas to breed every 2–3 years, thus finding their way back home after long periods in the oceanic environment. Here we examine the navigational consequences of the leatherbacks'' close association with currents and discuss how the combined reliance on mechanisms of map-based navigation and local orientation cues close to the target may allow leatherbacks to accomplish the difficult task of returning to specific sites after years spent wandering in a moving medium.     

Acinetobacter sp. HM746599 isolated from leatherback turtle blood

A newly described bacterial isolate, Acinetobacter sp. HM746599, has been obtained from leatherback sea turtle hatchling blood. The implication is that the hatchling was infected during development in the egg, which is substantiated by other studies to be reported by us in the future. The 16S rRNA gene sequence of the bacterium (GenBank accession number: HM746599) showed the greatest similarity to the identified species, Acinetobacter beijerinckii (97.6-99.78%) and Acinetobacter venetianus (99.78%). Acinetobacter sp. HM746599 are gram-negative, rod-shaped coccobacilli and are hemolytic/cytotoxic to human and sea turtle red blood cells (RBCs). Hemolysis is not the result of any detectable soluble toxin. Acinetobacter beijerinckii and A. venetianus hemolyze sheep RBCs while Acinetobacter sp. HM746599 does not, and unlike A. venetianus, the growth of Acinetobacter sp. HM746599 and A. beijerinckii is not supported by l-arginine. Many Acinetobacter species, especially hemolytic ones, are pathogenic to immunologically compromised humans and it is possible that, in addition to sea turtles, this bacterium might also be a danger to susceptible humans who handle infected hatchlings. The bacteria are available from CCUG (Culture Collection, University Gothenburg, G?teborg, Sweden) and from NRRL (Agricultural Research Service Culture Collection, Peoria, IL).     

Long-term monitoring of leatherback turtle diving behaviour during oceanic movements

The diving behaviour of four leatherback turtles (Dermochelys coriacea) was recorded for periods of 0.5-8.1 months during their postnesting movements in the Indian and Atlantic Oceans, when they covered 1569-18,994 km. Dive data were obtained using satellite-linked transmitters which also provided information on the dive depths and profiles of the turtles. Turtles mainly dove to depths < 200 m, with maximum dive durations under 30-40 min and exhibited diel variations in their diving activity for most part of the routes, with dives being usually longer at night. Diurnal dives were in general quite short, but cases of very deep (> 900 m) and prolonged (> 70 min) dives were however recorded only during daytime. The three turtles that were tracked for the longest time showed a marked change in behaviour during the tracking, decreasing their dive durations and ceasing to dive deeply. Moreover, diel variations disappeared, with nocturnal dives becoming short and numerous. This change in turtle diving activity appeared to be related to water temperature, suggesting an influence of seasonal prey availability on their diving behaviour. The turtle diving activity was independent on the shape of their routes, with no changes between linear movements in the core of main currents or looping segments in presence of oceanic eddies.     

生物多样性保护主流化的新机遇

<正>生物多样性是人类赖以生存和发展的物质基础。不断加剧的人类活动,致使生物多样性受到严重威胁,引起国际社会的广泛关注。生物多样性保护必须实现主流化,与社会经济可持续发展紧密结合,否则很难奏效。在全球尺度上,统领发展的最重要的理念即可持续发展(World Commission on Environment and Development,1987)。1992年联合国环境与发展大会通过了《21世纪议程》,被称为世界范围内可持续发展行动计划;2000年联合国世界首脑会议通过了     

On the dispersal of leatherback turtle hatchlings from Mesoamerican nesting beaches

So little is known about the early life history of leatherback turtles (Dermochelys coriacea) from hatchling to adulthood that this period has been termed the 'lost years'. For critically endangered eastern Pacific leatherback populations, continued and rapid declines underscore the urgent need to develop conservation strategies across all life stages. We investigate leatherback hatchling dispersal from four Mesoamerican nesting beaches using passive tracer experiments within a regional ocean modelling system. The evolution of tracer distribution from each of the nesting beaches showed the strong influence of eddy transport and coastal currents. Modelled hatchlings from Playa Grande, Costa Rica, were most likely to be entrained and transported offshore by large-scale eddies coincident with the peak leatherback nesting and hatchling emergence period. These eddies potentially serve as 'hatchling highways', providing a means of rapid offshore transport away from predation and a productive refuge within which newly hatched turtles can develop. We hypothesize that the most important leatherback nesting beach remaining in the eastern Pacific (Playa Grande) has been evolutionarily selected as an optimal nesting site owing to favourable ocean currents that enhance hatchling survival.     

Vibrio damsela infection in a stranded leatherback turtle (Dermochelys coriacea)

Necropsy of a stranded adult leatherback turtle (Dermochelys coriacea) determined that the animal died as a result of valvular endocarditis and septicemia. Vibrio damsela was isolated from the endocardial thrombus. The route of entry for infection probably was through the gastrointestinal tract.     

Expanded thermal niche for a diving vertebrate: A leatherback turtle diving into near-freezing water

The global distribution of extant reptiles is more limited than that of mammals or birds, with low reptilian species diversity at high latitudes. Central to this limited geographical distribution is the ectothermic nature of reptiles, which means that they generally become torpid at cold temperatures. However, here we report the first detailed telemetry from a leatherback turtle (Dermochelys coriacea) diving in cold water at high latitude. An individual equipped with a satellite tag that relayed temperature-depth profiles dived continuously for many weeks into sub-surface waters as cold as 0.4 °C. Global warming will likely increase the foraging range of leatherback turtles further into temperate and boreal waters.     

Post-mortem investigations on a leatherback turtle Dermochelys coriacea stranded along the Northern Adriatic coastline

Leatherback sea turtles Dermochelys coriacea are regularly reported in the Mediterranean Sea but rarely reach the northern Adriatic Sea. In the summer of 2009, a well-preserved carcass of an adult female of this species was found dead along the coast of Lido di Venezia. A complete necropsy was carried out, along with evaluation of levels of tissue trace elements. The the post-mortem revealed acute severe bacterial gastroenteritis caused by Photobacterium damselae ssp. piscicida, an opportunistic agent that infected an apparently debilitated animal weakened by ingested plastic debris. High levels of heavy metals (Hg, Pb, Cd and As) found in the liver and kidneys might have contributed to the animal's demise. These findings support previous indications that marine debris is one of the major threats to marine animals, particularly for critically endangered species such as the leatherback turtle.     

Trade-off between current reproductive effort and delay to next reproduction in the leatherback sea turtle

The trade-off between current and future reproduction plays an important role in demographic analyses. This can be revealed by the relationship between the number of years without reproduction and reproductive investment within a reproductive year. However, estimating both the duration between two successive breeding season and reproductive effort is often limited by variable recapture or resighting effort. Moreover, a supplementary difficulty is raised when nonbreeder individuals are not present sampling breeding grounds, and are therefore unobservable. We used capture–recapture (CR) models to investigate intermittent breeding and reproductive effort to test a putative physiological trade-off in a long-lived species with intermittent breeding, the leatherback sea turtle. We used CR data collected on breeding females on Awa:la-Ya:lima:po beach (French Guiana, South America) from 1995 to 2002. By adding specific constraints in multistate (MS) CR models incorporating several nonobservable states, we modelled the breeding cycle in leatherbacks and then estimated the reproductive effort according to the number of years elapsed since the last nesting season. Using this MS CR framework, the mean survival rate was estimated to 0.91 and the average resighting probability to 0.58 (ranged from 0.30 to 0.99). The breeding cycle was found to be limited to 3 years. These results therefore suggested that animals whose observed breeding intervals are greater than 3 years were most likely animals that escaped detection during their previous nesting season(s). CR data collected in 2001 and 2002 allowed us to compare the individual reproductive effort between females that skipped one breeding season and females that skipped two breeding seasons. These inferences led us to conclude that a trade-off between current and future reproduction exists in leatherbacks nesting in French Guiana, likely linked to the resource provisioning required to invest in reproduction.     

Thermal and trophic habitats of the leatherback turtle during the nesting season in French Guiana

Understanding environmental cues determining behaviour and habitat use of species of conservation concern is crucial if one aims at implementing sustainable management of these natural resources. In this way, here, we investigate the thermal and trophic conditions encountered by the critically endangered leatherback sea turtle Dermochelys coriacea during its nesting season in French Guiana where high bycatch rates have been reported.Mean sea water temperatures obtained in situ by animal-borne recorders were 26.6 ± 0.7 °C in the water column, with all but one turtle remaining in water > 25 °C during the inter-nesting interval. In terms of prey availability, regular jellyfish stranding events were recorded during the nesting season, on a 1.25-km long section of the nesting beach. The occurrence of jellyfish was supported by benthic trawls performed on the continental shelf, with a total of 45.4 kg of jellyfish collected in 3.5 h exclusively in coastal waters 10 to 20 m deep where water transparency was between 0.8 and 3 m. This is consistent with the at sea distribution area of gravid leatherbacks during their inter-nesting intervals, as they spent almost 70% of their time diving in shallow (< 20 m deep) waters in front of the Maroni River estuary. In French Guiana, leatherback's gelatinous prey are thus present in very shallow water close to the nesting site and may be easily exploited by active gravid leatherbacks. This suggests that French Guiana female leatherbacks may be influenced by local trophic conditions and actively prospect productive areas overlapping with local fisheries ground.     

Embryonic death is linked to maternal identity in the leatherback turtle (Dermochelys coriacea)

Leatherback turtles have an average global hatching success rate of ~50%, lower than other marine turtle species. Embryonic death has been linked to environmental factors such as precipitation and temperature, although, there is still a lot of variability that remains to be explained. We examined how nesting season, the time of nesting each season, the relative position of each clutch laid by each female each season, maternal identity and associated factors such as reproductive experience of the female (new nester versus remigrant) and period of egg retention between clutches (interclutch interval) affected hatching success and stage of embryonic death in failed eggs of leatherback turtles nesting at Playa Grande, Costa Rica. Data were collected during five nesting seasons from 2004/05 to 2008/09. Mean hatching success was 50.4%. Nesting season significantly influenced hatching success in addition to early and late stage embryonic death. Neither clutch position nor nesting time during the season had a significant affect on hatching success or the stage of embryonic death. Some leatherback females consistently produced nests with higher hatching success rates than others. Remigrant females arrived earlier to nest, produced more clutches and had higher rates of hatching success than new nesters. Reproductive experience did not affect stage of death or the duration of the interclutch interval. The length of interclutch interval had a significant affect on the proportion of eggs that failed in each clutch and the developmental stage they died at. Intrinsic factors such as maternal identity are playing a role in affecting embryonic death in the leatherback turtle.     

The effects of nest environment on calcium mobilization by leatherback turtle embryos (Dermochelys coriacea) during development.

We investigated the effect of sand moisture content and sand temperature on developmental success and the mobilization of calcium during development using laboratory incubated eggs (n=251) collected from leatherbacks nesting at Parque Nacional Marino Las Baulas, Costa Rica. Calcium concentrations of egg components [eggshell, yolk plus albumen (Y+A) and embryo] changed significantly through incubation for both viable and undeveloped eggs. In developed eggs, eggshell calcium content decreased 42.9% by day 60 of incubation. The Y+A calcium decreased by 20.8% until the last quarter of incubation, and then increased to 0.99% above initial Y+A calcium concentrations just prior to hatching. In undeveloped eggs, eggshell calcium content decreased by 25.7%, with the rate of decrease slowing significantly beyond day 30 of incubation. In contrast, Y+A calcium increased steadily through the 60-day incubation period. Embryos incorporated a higher proportion of calcium when incubated at a lower sand moisture content (5% H(2)O>12% H(2)O) and at lower sand temperatures (28.5 degrees C, 29.5 degrees C>31.0 degrees C). The total wet mass of freshly oviposited eggs was negatively correlated with calcium concentration per gram of eggshell (r=-0.569; P<0.001). Thus, each yolked egg, regardless of initial wet mass, had an average of 1.23 g (+/-0.43 g) of calcium per egg (Mean egg mass: 76.24+/-1.21 g). Both developmental success (24.1%) and hatching success (7.4%) of laboratory-incubated eggs were dependent to a greater extent on temperature than on moisture, with an increase in mortality as sand temperature increased. For natural nests on Playa Grande, developmental success (37.4%) and hatching success (19.8%) were similar in magnitude to the results obtained from the laboratory. The recent ENSO (El Ni?o Southern Oscillation) event and increased tidal activity may be responsible for the high embryonic mortality measured during the 1997-1998 nesting season.     

Tropical biologists, local people and conservation: new opportunities for collaboration

Tropical biologists need help. Examples show that local people can be trained to be effective parataxonomists, greatly assisting efforts to document and assess tropical biodiversity. Local collaborations also offer promising ways with which to improve natural resource management and conservation. However, for several reasons, most biologists remain slow to approve and implement these approaches. The challenges and potentials need evaluation and neglect means that opportunities are being missed. Here, we consider experiences of local collaborations and discuss obstacles to their wider implementation. We urge tropical biologists to recognize and embrace the opportunities provided by working with local people.     

Movement patterns for a critically endangered species, the leatherback turtle (Dermochelys coriacea), linked to foraging success and population status

Foraging success for pelagic vertebrates may be revealed by horizontal and vertical movement patterns. We show markedly different patterns for leatherback turtles in the North Atlantic versus Eastern Pacific, which feed on gelatinous zooplankton that are only occasionally found in high densities. In the Atlantic, travel speed was characterized by two modes, indicative of high foraging success at low speeds (<15 km d(-1)) and transit at high speeds (20-45 km d(-1)). Only a single mode was evident in the Pacific, which occurred at speeds of 21 km d(-1) indicative of transit. The mean dive depth was more variable in relation to latitude but closer to the mean annual depth of the thermocline and nutricline for North Atlantic than Eastern Pacific turtles. The most parsimonious explanation for these findings is that Eastern Pacific turtles rarely achieve high foraging success. This is the first support for foraging behaviour differences between populations of this critically endangered species and suggests that longer periods searching for prey may be hindering population recovery in the Pacific while aiding population maintenance in the Atlantic.     

Phenotypically linked dichotomy in sea turtle foraging requires multiple conservation approaches

Marine turtles undergo dramatic ontogenic changes in body size and behavior, with the loggerhead sea turtle, Caretta caretta, typically switching from an initial oceanic juvenile stage to one in the neritic, where maturation is reached and breeding migrations are subsequently undertaken every 2-3 years. Using satellite tracking, we investigated the migratory movements of adult females from one of the world's largest nesting aggregations at Cape Verde, West Africa. In direct contrast with the accepted life-history model for this species, results reveal two distinct adult foraging strategies that appear to be linked to body size. The larger turtles (n = 3) foraged in coastal waters, whereas smaller individuals (n = 7) foraged oceanically. The conservation implications of these findings are profound, with the population compartmentalized into habitats that may be differentially impacted by fishery threats in what is a global fishing hotspot. Although the protection of discrete areas containing coastal individuals may be attainable, the more numerous pelagic individuals are widely dispersed with individuals roaming over more than half a million square kilometers. Therefore, mitigation of fisheries by-catch for sea turtles in the east Atlantic will likely require complex and regionally tailored actions to account for this dichotomous behavior.