Satellite tracking reveals unusual diving characteristics for a marine reptile, the olive ridley turtle : Lepidochelys olivacea

The movements, diving behaviour and thermal environment occupied by 4 adult female olive ridley turtles Lepidochelys olivacea in northern Australia were determined through satellite telemetry. Patterns of behaviour recorded were rather unusual compared to other sea turtles in that dives were mainly deep, largely benthic and exceptionally long (>2 h) in some cases, characteristics typical of over-wintering turtles in colder environments. One individual occupied shallow coastal foraging zones, while the others foraged far from land (probably on the seabed) in relatively deep water (>100 m). Individuals performed long dives (frequently >100 min), but from the short post-dive intervals we suggest that these dives were mainly aerobic. Maximum dive depth recorded was 200 ± 20 m (mean maximum depths ranged from 20.1 to 46.7 m across individuals; n = 17328 dives in total; depths ≥3 m were considered ‘dives’) and the maximum duration was 200 ± 20 min (mean durations ranged from 24.5 to 48.0 min across individuals). Temperature profiles indicate that turtles experienced temperatures ranging from 23 to 29°C at the surface, with the lowest temperature recorded (18.7°C) at a depth of 98 m. Only 6.9% of the dives were in water <20°C. From time-allocation at depth (TAD) scores, we demonstrated that many dives reaching the known or inferred sea bottom were U-shaped, but there was no apparent diel signal in dive depth. This suggests that many benthic dives were not associated exclusively with resting behaviour and likely had a foraging component as well. The ability to perform long benthic dives allows this species to exploit deeper benthic environments in addition to the shallow coastal areas more generally occupied by adult hard-shelled sea turtles (e.g. green and hawksbill turtles). Deep benthic dives also occur in certain marine mammals (e.g. narwhals) and sea birds (e.g. rockhopper penguins) and therefore seem to be a general foraging strategy exploited by animals that can perform long dives.

Accuracy of ARGOS locations of pinnipeds at-sea estimated using Fastloc GPS

Background: ARGOS satellite telemetry is one of the most widely used methods to track the movements of free-ranging marine and terrestrial animals and is fundamental to studies of foraging ecology, migratory behavior and habitat-use. ARGOS location estimates do not include complete error estimations, and for many marine organisms, the most commonly acquired locations (Location Class 0, A, B, or Z) are provided with no declared error estimate.
Methodology/Principal Findings: We compared the accuracy of ARGOS locations to those obtained using Fastloc GPS from the same electronic tags on five species of pinnipeds: 9 California sea lions (Zalophus californianus), 4 Galapagos sea lions (Zalophus wollebaeki), 6 Cape fur seals (Arctocephalus pusillus pusillus), 3 Australian fur seals (A. p. doriferus) and 5 northern elephant seals (Mirounga angustirostris). These species encompass a range of marine habitats (highly pelagic vs coastal), diving behaviors (mean dive durations 2–21 min) and range of latitudes (equator to temperate). A total of 7,318 ARGOS positions and 27,046 GPS positions were collected. Of these, 1,105 ARGOS positions were obtained within five minutes of a GPS position and were used for comparison. The 68^th percentile ARGOS location errors as measured in this study were LC-3
0.49 km, LC-2 1.01 km, LC-1 1.20 km, LC-0 4.18 km, LC-A 6.19 km, LC-B 10.28 km.
Conclusions/Significance: The ARGOS errors measured here are greater than those provided by ARGOS, but within the range of other studies. The error was non-normally distributed with each LC highly right-skewed. Locations of species that make short duration dives and spend extended periods on the surface (sea lions and fur seals) had less error than species like elephant seals that spend more time underwater and have shorter surface intervals. Supplemental data (S1) are provided allowing the creation of density distributions that can be used in a variety of filtering algorithms to improve the quality of ARGOS tracking data.

Factors influencing the winter haulout behaviour of Weddell seals : consequences for satellite telemetry

An understanding of pinniped haulout behaviour can provide information on how animals interact with their environment, their foraging strategies and the behaviour of their prey. For Weddell seals Leptonychotes weddelli, knowledge of haulout patterns and the environmental drivers of haulout is comprehensive for the austral spring and summer, but is poorly described outside this period. Pinniped behaviour is commonly examined using satellite telemetry; however, it is unclear whether the behavioural state of the seal can itself influence data acquisition. We examined haulout behaviour of female Weddell seals in eastern Antarctica over 3 winters (March to August, 2006–2008) using satellite-linked data loggers. Haulout behaviour followed a diel cycle with predominantly nocturnal haulouts. The environmental variables wind speed and temperature were influential on haulout, with seals tending to haul out more in lower winds and at higher temperatures. Haulout duration decreased across the winter, as did the number of satellite uplinks, suggesting that haulout duration played a role in data acquisition. There was no evidence of a decline in tag condition over this period, indicating that the decrease in uplinks was primarily the result of the winter behaviour of the seals. Overall, the number of haulout locations in the data set was over-represented, with more uplinks per hour occurring when the seals were hauled out than when they were at sea. For Weddell seals and other ice seals, tracking data that include haulout locations can bias spatial representations of foraging behaviour (e.g. haulout sites may be mistaken for regions of area-restricted search).

Conservation hotspots : implications of intense spatial area use by breeding male and female loggerheads at the Mediterranean’s largest rookery

The implementation of appropriate protection measures for endangered species in protected areas requires knowledge of their fine-scale habitat use. In May and June of 2006 and 2007, we used GPS loggers (some linked to the Argos system) and a conventional Argos transmitter to track male and female loggerhead turtles Caretta caretta in the vicinity of the breeding area of Laganas Bay within the National Marine Park of Zakynthos, Greece. We obtained (1) 9681 useable locations (mean: 1383 locations ind.–1; range: 519 to 2198 locations) from Tracktag GPS loggers attached to 7 females for a mean duration of 34 d (range: 17 to 52 d); (2) 1245 useable locations (mean: 311 locations ind.–1; range: 38 to 1110 locations) from 4 males fitted with Fastloc Argos tags for a mean duration of 29 d (range: 3 to 51 d) and (3) 100 locations from 1 male fitted with a conventional Argos satellite tag tracked for 128 d. GPS data indicated that before the onset of nesting, both males and females primarily used an area within 500 m of the shore along a core 9 km stretch of coastline, where existing protective legislation requires strengthening. Our observations suggest that a 76.7% female-biased operational sex ratio, measured previously from in-water surveys, may represent a realistic sex ratio estimate in the period before nesting starts. In the first month following the onset of nesting, female spatial distribution remained similar, whereas most males departed for distant areas presumably to forage. Our study provides quantitative evidence of the need to improve the management planning and conservation measures to protect sea turtles in a coastal breeding area, and new insights on male turtle migration.

A biologist's guide to assessing ocean currents : a review

We review how ocean currents are measured (in both Eulerian and Lagrangian frameworks), how they are inferred from satellite observations, and how they are simulated in ocean general circulation models (OGCMs). We then consider the value of these ‘direct’ (in situ) and ‘indirect’ (inferred, simulated) approaches to biologists investigating current-induced drift of strong-swimming vertebrates as well as dispersion of small organisms in the open ocean. We subsequently describe 2 case studies. In the first, OGCM-simulated currents were compared with satellite-derived currents; analyses suggest that the 2 methods yield similar results, but that each has its own limitations and associated uncertainty. In the second analysis, numerical methods were tested using Lagrangian drifter buoys. Results indicated that currents simulated in OGCMs do not capture all details of buoy trajectories, but do successfully resolve most general aspects of current flows. We thus recommend that the errors and uncertainties in ocean current measurements, as well as limitations in spatial and temporal resolution of the surface current data, need to be considered in tracking studies that incorporate oceanographic data. Whenever possible, cross-validation of the different methods (e.g. indirect estimates versus buoy trajectories) should be undertaken before a decision is reached about which technique is best for a specific application.

Overwintering behaviour in sea turtles : dormancy is optional

Thirteen loggerhead turtles Caretta caretta were released (10 from Naples, Italy, 2 from Monastir, Tunisia, 1 from Gallipoli, South Italy) with satellite relay data loggers (SRDL) to elucidate their overwintering behaviour. Nine turtles were successfully tracked throughout the winter, while 4 SRDLs failed to transmit after short deployment periods. Of these 9, 4 remained within 80 km of the release site, 3 travelled to a distant overwintering site, and 2 continued to move and did not remain within 80 km of a specific site. Apart from these differences, all turtles stayed near the coast and dedicated most of their time to dives lasting 3 h and longer. Maximum dive durations ranged from 270 to 480 min and were highly correlated with water temperatures, which fell below the supposed 15°C threshold for sea turtle hibernation in all overwintering sites. Median dive depths were between 4 and 24 m and were, thus, well within the mixed layer, as revealed by temperature profiles, which also were relayed by the SRDLs. No evidence was found that the turtles preferred warmer temperatures to overwinter in, because the range of temperature was very narrow on both the horizontal and the vertical scale of their movements. Despite the long resting phases and the low temperatures (minimum = 11.8°C) all turtles retained activity to some degree, at least to commute between the depth of resting and the surface to breathe. While the degree of winter dormancy is certainly affected by temperature, turtles were by no means obligatory hibernators, and their ability to move and even forage during the winter may be important for their growth and maturation rates, as well as their reproductive output.

The behaviour of a hawksbill turtle data-logged during the passage of hurricane Georges through the Caribbean

Recent severe hurricanes in the Caribbean and south-east United States have had devastating socio-economic effects, and there is a pressing need to learn how animals are impacted by such events. We serendipitously deployed a multi-channel data logger onto a hawksbill turtle (Eretmochelys imbricata) during the breeding season in 1998 and logged various aspects of her behaviour before, during and after passage of hurricane Georges. As Georges passed by, the turtle made shorter dives, became more active and spent less time at the surface between dives compared with its baseline, non-storm activity. However, after passage of the hurricane the turtle quickly resumed its pre-hurricane behaviour and nested successfully a few days later. These results show that, in this case, the hurricane had a minor impact on the submerged animal presumably because of the dampening effect of depth on high winds over water.

Do leatherback turtles Dermochelys coriacea forage during the breeding season? A combination of data-logging devices provide new insights

Animals which undertake migrations from foraging grounds to suitable breeding areas must adopt strategies in these new conditions in order to minimise the rate at which body condition deteriorates (which will occur due to oogenesis or provisioning for young). For some animals this involves continuing foraging, whereas for others the optimal strategy is to fast during the breeding season. The leatherback turtle undertakes long-distance migrations from temperate zones to tropical breeding areas, and in some of these areas it has been shown to exhibit diving behaviour indicative of foraging. We used conventional time–depth recorders and a single novel mouth-opening sensor to investigate the foraging behaviour of leatherback turtles in the southern Caribbean. Diving behaviour suggested attempted foraging on vertically migrating prey with significantly more diving to a more consistent depth occurring during the night. No obvious prey manipulation was detected by the mouth sensor, but rhythmic mouth opening did occur during specific phases of dives, suggesting that the turtle was relying on gustatory cues to sense its immediate environment. Patterns of diving in conjunction with these mouth-opening activities imply that leatherbacks are attempting to forage during the breeding season and that gustatory cues are important to leatherbacks.

Model based analysis of fMRI/EEG data

This thesis addresses two major topics in neuroscience literature and drawbacks from existing literature are addressed by utilising state space models and Bayesian estimation techniques. Particle filter-based joint estimation of the physiological model for time-series analysis of fMRI data is demonstrated first in the thesis and secondly the Granger causality-based effective connectivity analysis of EEG data is investigated.