Satellite tagging of female hawksbill sea turtles (Eretmochelys imbricata) nesting on Groote Eylandt, Northern Territory

Brief description

Hawksbill turtles are classified Critically Endangered by the IUCN following intense commercial exploitation that decimated global stocks. Despite Australia supporting one of the largest breeding aggregations worldwide, hawksbill turtle biology and ecology remains poorly documented, especially for populations nesting in the Northern Territory. This study focused on the internationally significant hawksbill turtle population breeding in Groote Eylandt in the Gulf of Carpentaria, and aimed at providing high resolution information for managing this critically endangered species. By using multiple state-of-the-art analytical frameworks and combining satellite telemetry, hydrological modelling, and tag recapture data, we (i) assessed habitat utilisation during the inter-nesting and foraging periods, (ii) quantified migratory behaviour for better understanding of navigational strategies , and (iii) simulated post-hatchling dispersal patterns, which we subsequently compared to the location of adult foraging grounds.

This metadata record, represents several different datasets listed hereafter, which can all be accessed through a multi-WFS service.

CTD - Data parameters measured by the instruments include time, temperature, and depth. The data represented by this record are presented in delayed mode.

GPS - Location data parameters measured by the instruments include time, longitude, latitude, location quality, along with other diagnostic information. The Fastloc GPS data represented by this record are presented in delayed mode.

Argos - Location data parameters measured by the instruments include time, longitude, latitude, location quality, along with other diagnostic information provided by Argos (http://www.argos-system.org/). The Argos data represented by this record are presented in delayed mode.

Haulout - A haulout begins when the SRDL has been continuously dry for a specified length of time (usually 10 minutes). It ends when continuously wet for another interval (usually 40 seconds). Haulout data parameters measured by the instruments include haulout start and end dates and longitude/latitude, and haulout number. The haulout data represented by this record are presented in delayed mode.

Diving - Diving data parameters measured by the instruments include start and end time and longitude/latitude of each individual dive, post-dive surface duration, dive duration, maximum dive depth, intermediate dive depths and times. The diving data represented by this record are presented in delayed mode.

Summary - As well as sending records of individual events such as dives and haulouts, the SRDL also calculates summary statistics of those events over a specified time period (usually 3, 4 or 6 hours). Summary statistics computed by the instruments include the proportion of time spent diving, at the surface and hauled-out, the number of dives, and the average, standard deviation and maximum dive duration and dive depth during each summary period. These statistics are based on all the data recorded by the SRDL and so are not prone to distortion by variations in the efficiency of transmission via Argos. The summary data represented by this record are presented in delayed mode. Note that it is impossible to subset this particular dataset using a bounding box as there is no latitude, longitude coordinates associated with each entry.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: The Aboriginal owned Groote Eylandt (136º 30´ E, 14º S) archipelago is located in the western part of the Gulf of Carpentaria (Northern Territory), a large shallow embayment (maximum depth ≈ 70 m) situated between northern Australia, Indonesia and Papua New Guinea, connected to the West to the Arafura Sea and to the East to the Coral Sea through Torres Strait (Torgersen et al. 1983, Somers & Long 1994). After oviposition, we equipped seven adult female hawksbill turtles with satellite transmitters on North East Island (13°38.4 S, 136°56.6 E ), a 4.4 km2 remote and uninhabited island 30 km off Groote Eylandt, Northern Territory, Australia, where over 100 breeding females nest annually (Limpus et al. 2000). When available, we used an ultrasound scanner (Easi-Scan, BCF Pty Ltd) prior to deployment to confirm the presence of mature follicles and ensure that animals would collect data between nesting events. All turtles were measured and weighed prior to satellite transmitter attachment using standard procedures (i.e. minimum curved carapace length (CCL) and maximum curved carapace width (CCW), measurement error = ± 0.5 cm; weighing error = ± 0.25 kg) and tagged with two numbered titanium tags (Stockbrands®, Australia) applied at a proximal location in each front flipper (Limpus 1992a, Balazs 1999, Bolten 1999). We attached seven satellite relay data loggers (SRDLs, Sea Mammal Research Unit, St. Andrews, U.K.). SRDLs relayed both highly accurate Fastloc GPS locations (95th percentile error < 140 m) (Fedak et al. 2002, Bryant 2007, Hazel 2009a, Shimada et al. 2012) and animal haulout records. To maximise communication efficiency between units and satellites we mounted satellite transmitters onto wedges (SRDL wedges: base = 102 mm, width = 5 mm, height = 30 mm; PTT wedges: base = 73 mm, width = 4 mm, height = 4 mm) (McMahon et al. 2007). We glued units and wedges with quick-setting two-part epoxy resin (Sika AnchorFix®-3+, Sika Australia Pty Ltd) onto the two anterior central scutes of hawksbills’ carapace. As the satellite transmitters we used were hydrodynamic and represented less than 1.5 % of hawksbill turtles’ weight, we presumed they had minimal effects on marine turtle behaviour (SRDL: 700 g, PTT: 430 g, average weight of adult female hawksbill turtles: 48.7 kg). Temperature-depth profiles were relayed, based on continuous water temperature recordings throughout dives by a CTD instrument, and reconstructed using an 11 point broken-stick algorithm (Fedak et al., 2002, McMahon et al., 2007). For details about the tag: http://www.smru.st-and.ac.uk/Instrumentation/GPSArgosTag/

Statement: This dataset collection combines the following datastreams: CTD, GPS, Argos, Haulout, Diving, Summary Statistics.

Prior to October 2015, these datastreams were described and served separately but with new developments of the portal 1-2-3, they have been combined in a single collection for ease of discovery and data access.

Notes

Credit
Australian Government under the Caring for Country initiative

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Anindilyakwa Land Council

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Northern Territory Government – Marine Biodiversity Group, Department of Natural Resources, Environment, the Arts and Sport

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Charles Darwin University (CDU)

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ANZ Trustees Foundation – Holsworth Wildlife Research Endowment