Environmental predictors of foraging and transit behaviour in flatback turtles Natator depressus (original) (raw)
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Marine and Freshwater Research, 2012
Large marine vertebrates are particularly susceptible to anthropogenic threats because they tend to be long-lived, late to mature and wide-ranging. Loggerhead sea turtles (Caretta caretta) are characterised by such life history traits and are listed as ‘Endangered’ by The World Conservation Union. Although juvenile movements and at-sea behaviour of adult females are relatively well studied, little is known about the movements of males and their subsequent exposure to threats. Shark Bay, Western Australia, is home to the largest breeding population of loggerhead turtles in Australia. We assessed the large-scale movements of nine adult male loggerhead turtles, with the goal of aiding conservation and management policies. During 7 months outside the breeding season, all nine turtles stayed within the Shark Bay World Heritage Area, with most showing fidelity to small coastal foraging areas. Several turtles, however, showed relatively large movements between core foraging areas. None of ...
2011
Leatherback turtles are the largest and widest ranging turtle species, and spend much of their time in the offshore pelagic environment. However, the high seas have thus far received little management attention to protect their ecosystems and biodiversity. We tagged 46 female leatherback turtles with satellite transmitters at Playa Grande, Costa Rica from 2004 to 2007. In the present study, we analyzed the vertical and horizontal habitat preferences of these leatherback turtles in the South Pacific Ocean. The turtles exhibited short, shallow dives during their migration southward (mean depth: 45 m; mean duration: 23.6 min), followed by deeper, longer dives (mean depth: 56.7 m; mean duration: 26.4 min) in the South Pacific Gyre that probably indicated searching for prey. We integrated the horizontal movements with remotely sensed oceanographic data to determine the turtles' response to the environment, and applied this information to recommendations for conservation in the pelagic environment. A generalized additive mixed model applied to the daily turtle travel rates confirmed that slower travel rates occurred at cooler sea surface temperatures, higher chlorophyll a concentration and stronger vertical Ekman upwelling, all of which are considered favorable foraging conditions. The southern terminus (35 to 37°S) of the leatherback tracks was also in an area of increased mesoscale activity that might act as a physical mechanism to aggregate their prey, gelatinous zooplankton. However, this could also act as a thermal limit to their distribution. This characterization of leatherback habitat use could aid the development of management efforts within the South Pacific Ocean to reduce mortality of leatherback turtles from fisheries interactions.
The western Pacific leatherback turtle (Dermochelys coriacea), one of three genetically distinct stocks in the Indo-Pacific region, has declined markedly during past decades. This metapopulation nests year-round at beaches of several western Pacific island nations and has been documented through genetic analysis and telemetry studies to occur in multiple regions of the Pacific Ocean. To provide a large-scale perspective of their movements, high-use areas, and habitat associations, we report and synthesize results of 126 satellite telemetry deployments conducted on leatherbacks at western Pacific nesting beaches and at one eastern Pacific foraging ground during 2000–2007. A Bayesian switching state-space model was applied to raw Argos-acquired surface locations to estimate daily positions and behavioral mode (either transiting or area-restricted search) for each turtle. Monthly areas of high use were identified for postnesting periods using kernel density estimation. There was a clea...
Spatial site fidelity of Sea Turtles at a foraging ground in Mabul Island, Sabah, Malaysia
International Journal of Fisheries and Aquatic Studies, 2017
Mabul Island, located on the east coast of Sabah, Malaysia, has a population of resident green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles, however little is known about them. This report highlights the spatial site fidelity of sea turtles at a foraging ground in this region. A mark-recapture study was conducted between August 2010 through November 2015 and there were 109 individual turtles of various size classes repeatedly captured at seven established dive sites where they ranged from 4 to 40 occurrences (mean ± s.d. = 16 ± 14). The results demonstrated that the turtles significantly (p<0.000) favored some dive sites mainly due to the availability of shelter under rocky outcrops and on reef ledges. Further analysis showed that juveniles were the most abundant (78.9%) (p = 0.0021), indicating a healthy recruitment into this population. Green turtles were the dominant species with a ratio of 6:1 (p = 0.0326).
2012
Interactions with fisheries are believed to be a major cause of mortality for adult leatherback turtles (Dermochelys coriacea), which is of particular concern in the Pacific Ocean, where they have been rapidly declining. In order to identify where these interactions are occurring and how they may be reduced, it is essential first to understand the movements and behavior of leatherback turtles. There are two regional nesting populations in the East Pacific (EP) and West Pacific (WP), comprising multiple nesting sites. We synthesized tracking data from the two populations and compared their movement patterns. A switching state-space model was applied to 135 Argos satellite tracks to account for observation error, and to distinguish between migratory and area-restricted search behaviors. The tracking data, from the largest leatherback data set ever assembled, indicated there was a high degree of spatial segregation between EP and WP leatherbacks. Area-restricted search behavior mainly occurred in the southeast Pacific for the EP leatherbacks, whereas the WP leatherbacks had several different search areas in the California Current, central North Pacific, South China Sea, off eastern Indonesia, and off southeastern Australia. We also extracted remotely sensed oceanographic data and applied a generalized linear mixed model to determine if leatherbacks exhibited different behavior in relation to environmental variables. For the WP population, the probability of area-restricted search behavior was positively correlated with chlorophyll-a concentration. This response was less strong in the EP population, but these turtles had a higher probability of search behavior where there was greater Ekman upwelling, which may increase the transport of nutrients and consequently prey availability. These divergent responses to oceanographic conditions have implications for leatherback vulnerability to fisheries interactions and to the effects of climate change. The occurrence of leatherback turtles within both coastal and pelagic areas means they have a high risk of exposure to many different fisheries, which may be very distant from their nesting sites. The EP leatherbacks have more limited foraging grounds than the WP leatherbacks, which could make them more susceptible to any temperature or prey changes that occur in response to climate change.
Diversity and Distributions, 2010
Aim Resources can shape patterns of habitat utilization. Recently a broad foraging dichotomy between oceanic and coastal sites has been revealed for loggerhead sea turtles (Caretta caretta). Since oceanic and coastal foraging sites differ in prey availability, we might expect a gross difference in home-range size across these habitats. We tested this hypothesis by equipping nine adult male loggerhead sea turtles with GPS tracking devices.Location National Marine Park of Zakynthos (NMPZ) Greece, central and eastern Mediterranean (Adriatic, Ionian and Aegean seas).Methods In 2007, 2008 and 2009, Fastloc GPS-Argos transmitters were attached to nine male loggerheads. In addition, a Sirtrack PTT unit was attached to one male in 2007. Four of the turtles were tracked on successive years. We filtered the GPS data to ensure comparable data volumes. Route consistency between breeding and foraging sites of the four re-tracked turtles was conducted. Foraging site home range areas and within site movement patterns were investigated by the fixed kernel density method.Results Foraging home range size ranged between circa 10 km2 at neritic habitats (coastal and open-sea on the continental shelf) to circa 1000 km2 at oceanic sites (using 90% kernel estimates), the latter most probably reflecting sparsely distributed oceanic prey. Across different years individuals did not follow exactly the same migration routes, but did show fidelity to their previous foraging sites, whether oceanic or neritic, with accurate homing in the final stages of migration.Main conclusions The broad distribution and diverse life-history strategies of this population could complicate the identification of priority marine protected areas beyond the core breeding site.
Marine Ecology Progress Series, 2016
Home range analysis is a powerful tool for identifying priority areas for conservation, but estimating the home range for many species is still challenging. In particular, highly mobile species may use different areas at different times (e.g. summer or winter), so temporally biased location data may only partially represent their home range. We investigated the temporal patterns in habitat use of green turtles Chelonia mydas (n = 52) and loggerhead turtles Caretta caretta (n = 20) at longer (>1 yr) and shorter (<1 yr) scales. The study was conducted in subtropical and tropical foraging habitats along the Queensland coast of Australia between 1991 and 2015. Each turtle was tracked by a satellite-linked tag for the effective life of the device; 3 turtles were tracked twice. Mark−recapture studies were also conducted intermittently. Single satellite-tag deployments confirmed site fidelity to a foraging habitat for up to 2.5 yr in green turtles and 2.7 yr in loggerhead turtles. Further, combining satellite telemetry and mark−recapture records indicated much longer periods of foraging residency, up to 17 yr for green turtles and 23 yr for loggerhead turtles. No tracked turtles made substantial changes in their foraging range between years. Within the long-term home range, subtropical turtles tended to shift their foraging areas seasonally. Consequently, for many turtles, the existing conservation legislation provided protection in some seasons but not others. Our results emphasise the importance of protecting areas according to the turtles' use of space, with careful consideration given to identify temporal trends in their habitat selection.
Remote Sensing, 2021
Western Australia’s remote Kimberley coastline spans multiple Traditional Owner estates. Marine turtle nesting distribution and abundance in Indigenous Protected Areas and newly declared Marine Parks were assessed by aerial photogrammetry surveys for the Austral summer and winter nesting seasons. Images of nesting tracks were quantified in the lab and verified by ad hoc ground patrols. The rankings of log-scaled plots of track abundance and density give guidance to regional co-management planning. Spatial and temporal differences were detected in that remoter islands had higher nesting usage and few terrestrial predators. The surveys found year-round green turtle nesting peaking in summer, as well as spatial boundaries to the summer and winter flatback stocks. Summer surveys recorded 126.2 island activities per km and 17.7 mainland activities per km. Winter surveys recorded 65.3 island activities per km and quantified a known winter mainland rookery with 888 tracks/km. The three hig...
Does behaviour affect the dispersal of flatback post-hatchlings in the Great Barrier Reef?
Royal Society open science, 2017
The ability of individuals to actively control their movements, especially during the early life stages, can significantly influence the distribution of their population. Most marine turtle species develop oceanic foraging habitats during different life stages. However, flatback turtles (Natator depressus) are endemic to Australia and are the only marine turtle species with an exclusive neritic development. To explain the lack of oceanic dispersal of this species, we predicted the dispersal of post-hatchlings in the Great Barrier Reef (GBR), Australia, using oceanographic advection-dispersal models. We included directional swimming in our models and calibrated them against the observed distribution of post-hatchling and adult turtles. We simulated the dispersal of green and loggerhead turtles since they also breed in the same region. Our study suggests that the neritic distribution of flatback post-hatchlings is favoured by the inshore distribution of nesting beaches, the local wate...