Evaluation of Argos Telemetry Accuracy in the High-Arctic and Implications for the Estimation of Home-Range Size

Animal tracking through Argos satellite telemetry has enormous potential to test hypotheses in animal behavior, evolutionary ecology, or conservation biology. Yet the applicability of this technique cannot be fully assessed because no clear picture exists as to the conditions influencing the accuracy of Argos locations. Latitude, type of environment, and transmitter movement are among the main candidate factors affecting accuracy. A posteriori data filtering can remove “bad” locations, but again testing is still needed to refine filters. First, we evaluate experimentally the accuracy of Argos locations in a polar terrestrial environment (Nunavut, Canada), with both static and mobile transmitters transported by humans and coupled to GPS transmitters. We report static errors among the lowest published. However, the 68^th error percentiles of mobile transmitters were 1.7 to 3.8 times greater than those of static transmitters. Second, we test how different filtering methods influence the quality of Argos location datasets. Accuracy of location datasets was best improved when filtering in locations of the best classes (LC3 and 2), while the Douglas Argos filter and a homemade speed filter yielded similar performance while retaining more locations. All filters effectively reduced the 68^th error percentiles. Finally, we assess how location error impacted, at six spatial scales, two common estimators of home-range size (a proxy of animal space use behavior synthetizing movements), the minimum convex polygon and the fixed kernel estimator. Location error led to a sometimes dramatic overestimation of home-range size, especially at very local scales. We conclude that Argos telemetry is appropriate to study medium-size terrestrial animals in polar environments, but recommend that location errors are always measured and evaluated against research hypotheses, and that data are always filtered before analysis. How movement speed of transmitters affects location error needs additional research.     

Enhancing the use of Argos satellite data for home range and long distance migration studies of marine animals

Accurately quantifying animals' spatial utilisation is critical for conservation, but has long remained an elusive goal due to technological impediments. The Argos telemetry system has been extensively used to remotely track marine animals, however location estimates are characterised by substantial spatial error. State-space models (SSM) constitute a robust statistical approach to refine Argos tracking data by accounting for observation errors and stochasticity in animal movement. Despite their wide use in ecology, few studies have thoroughly quantified the error associated with SSM predicted locations and no research has assessed their validity for describing animal movement behaviour. We compared home ranges and migratory pathways of seven hawksbill sea turtles (Eretmochelys imbricata) estimated from (a) highly accurate Fastloc GPS data and (b) locations computed using common Argos data analytical approaches. Argos 68(th) percentile error was <1 km for LC 1, 2, and 3 while markedly less accurate (>4 km) for LC ≤ 0. Argos error structure was highly longitudinally skewed and was, for all LC, adequately modelled by a Student's t distribution. Both habitat use and migration routes were best recreated using SSM locations post-processed by re-adding good Argos positions (LC 1, 2 and 3) and filtering terrestrial points (mean distance to migratory tracks ± SD = 2.2 ± 2.4 km; mean home range overlap and error ratio = 92.2% and 285.6 respectively). This parsimonious and objective statistical procedure however still markedly overestimated true home range sizes, especially for animals exhibiting restricted movements. Post-processing SSM locations nonetheless constitutes the best analytical technique for remotely sensed Argos tracking data and we therefore recommend using this approach to rework historical Argos datasets for better estimation of animal spatial utilisation for research and evidence-based conservation purposes.     

ASSESSMENT OF ARGOS LOCATION ACCURACY FROM SATELLITE TAGS DEPLOYED ON CAPTIVE GRAY SEALS

The Argos satellite system is commonly used to track and relay behavioral data from marine mammals, but their underwater habit results in a high proportion of locations of non-guaranteed accuracy (location classes (LC) O, A, and B). The accuracy of these locations is poorly documented in marine mammals. We assessed the accuracy of all LCs on four juvenile gray seals fitted with Argos satellite relay data loggers and held in captivity in an outdoor tank for a total of 61 seal-days. Four hundred and twenty-six locations were obtained from seals in captivity, and their latitude and longitude error was assessed before and after filtering, following MConnell et al. (1992). There was significantly more error in longitude than latitude in all LCs except I. C A. The ratio of the standard deviations of longitude : latitude ranged from 1.77 (LC 3) to 2.58 (LC 1). Filtering had very little effect on errors in LCs 3-1, but in the remaining LCs filtering resulted in error reductions ranging from 8% to 63%. In LCs O, A, and B, error reduction was greater in the 95th percentile errors, especially in longitude. The averages of the latitude and longitude 68th percentile errors and those predicted by Argos (in brackets) were 226 (150), 372 (350), and 757 (1000) m for LCs 3, 2, and 1 respectively. Both latitude and longitude errors of LCs > O were normally distributed. Both filtered and unfiltered LC A locations were of a similar accuracy to LC 1 locations, and considerably better than LC O locations.     

Performance and accuracy of Argos transmitters for wildlife monitoring in Southern Russia

Satellite telemetry is a powerful tool for monitoring animal movements, and Argos transmitters have been widely used. Unfortunately, only few studies have systematically evaluated the performance of Argos satellite collars for wildlife monitoring. We tested Argos satellite telemetry transmitters at two power levels in Southern Russia (five transmitters at 0.5 W and three at 1 W). Performance metrics were derived from the number and accuracy of location estimates and the number of days on which collars transmitted or failed to transmit data. Our results suggest that the performance of Argos collars in our study region was poor. At the power level of 0.5 W, 55% of the sessions resulted in at least one transmission, but only 21% provided a location estimate. The percentage of successful sessions did not increase much after setting the power level to 1.0 W (63%), but the increase in the number of location estimates was considerable (54%). At either power level, the majority of the location estimates were in the low quality classes though (80% nonstandard locations with 0.5 W and 45% with 1 W). Positional accuracies were 0.5, 0.7, 1.5, and 4.6 km for location classes 3, 2, 1, and 0, respectively. For nonstandard location classes A and B, positional accuracies were 2.1 and 18.3 km. Careful testing of transmitters is recommended before deployment, as the location of the study area can seriously affect performance.

     

Satellite tracking of kereru (

Satellite transmitters (PTTs) were attached to four kereru (New Zealand pigeon, Hemiphaga novaeseelandiae) in Invercargill, Southland, New Zealand, during 2005?06. The transmitters were used to monitor the birds? locations, movements and home ranges. Attachment of the transmitters affected the behaviour and body condition of one of the kereru; no other negative effects, such as skin abrasion, were noticed. Fifty-four percent of locations recorded were of Argos location classes 1, 2 or 3 (accuracy of ?1 km), and were used to determine the birds? movements and home range areas. Three of the kereru made flights across Foveaux Strait (a minimum distance of 33 km) to Stewart Island; the other remained around Invercargill. The maximum distance between their locations ranged from 11.4 to 101.9 km. Home ranges, as determined by cluster analysis, ranged from 619 ha to 31,732 ha, 100?1000 times greater than kereru home range areas estimated in previous studies. Given the long-distance movements kereru make, often to locations distant from roads and tracks, satellite telemetry is probably the most reliable and cost-effective method of determining their locations.     

Assessing the accuracy of small satellite transmitters on free‐living flying‐foxes

Satellite telemetry using ARGOS platform transmitter terminals (PTTs) is widely used to track the movements of animals, but little is known of the accuracy of these systems when used on active terrestrial mammals. An accurate estimate of the error, and therefore the limitations of the data, is critical when assessing the level of confidence in results. ARGOS provides published 68th percentile error estimates for the three most accurate location classes (LCs), but studies have shown that the errors can be far greater when the devices are attached to free‐living animals. Here we use data from a study looking at the habitat use of the spectacled flying‐fox in the wet tropics of Queensland to calculate these errors for all LCs in free‐living terrestrial mammals, and use these results to assess what level of confidence we would have in habitat use assignment in the study area. The results showed that our calculated 68th percentile errors were larger than the published ARGOS errors for all LCs, and that for all classes the error frequency had a very long tail. Habitat use results showed that the size of the error compared with the scale of the habitat the study was conducted in makes it unlikely that our data can be used to assess habitat use with great confidence. Overall, our results show that while satellite telemetry results are useful for assessing large scale movements of animals, in complex landscapes they may not be accurate enough to be used for finer scale analysis including habitat use assessment.     

The Argos-CLS Kalman Filter: Error Structures and State-Space Modelling Relative to Fastloc GPS Data

Understanding how an animal utilises its surroundings requires its movements through space to be described accurately. Satellite telemetry is the only means of acquiring movement data for many species however data are prone to varying amounts of spatial error; the recent application of state-space models (SSMs) to the location estimation problem have provided a means to incorporate spatial errors when characterising animal movements. The predominant platform for collecting satellite telemetry data on free-ranging animals, Service Argos, recently provided an alternative Doppler location estimation algorithm that is purported to be more accurate and generate a greater number of locations that its predecessor. We provide a comprehensive assessment of this new estimation process performance on data from free-ranging animals relative to concurrently collected Fastloc GPS data. Additionally, we test the efficacy of three readily-available SSM in predicting the movement of two focal animals. Raw Argos location estimates generated by the new algorithm were greatly improved compared to the old system. Approximately twice as many Argos locations were derived compared to GPS on the devices used. Root Mean Square Errors (RMSE) for each optimal SSM were less than 4.25km with some producing RMSE of less than 2.50km. Differences in the biological plausibility of the tracks between the two focal animals used to investigate the utility of SSM highlights the importance of considering animal behaviour in movement studies. The ability to reprocess Argos data collected since 2008 with the new algorithm should permit questions of animal movement to be revisited at a finer resolution.     

AN ALGORITHM TO IMPROVE GEOLOCATION POSITIONS USING SEA SURFACE TEMPERATURE AND DIVING DEPTH

The at-sea movement of marine mammals is an important component of their foraging ecology, but has been difficult to study. Geolocation timed-data recorders (GLTDRs) estimate positions using measured light level to calculate day length and local noon. It is well known that these location estimates are imprecise (mean error of > 1°). Satellite telemetry generally provides a more accurate, but also more expensive means of monitoring movement. We evaluated the accuracy and precision of geolocation positions by comparing these locations with satellite data from Service Argos for eight free-ranging gray seals ( Halichoerns grypus ) equipped with both a satellite-linked data recorder (SDR) and a GLTDR. Geolocation positions differed by 1,026.0 ± 292.28 km from the corresponding Argos locations. We developed an algorithm to correct geolocation positions by comparing surface water temperature (ST) and dive depth collected by GLTDRs with existing sea-surface temperature and bathymetry databases. The corrected positions were significantly closer (P < 0.025) to the Argos locations of these seals (94.2 ± 8.22 km). The original geolocation positions would have led to incorrect conclusions about the use of space by gray seals; however, the corrected positions can be reliably used to study the large-scale spatial distribution of individuals.     

A THREE-STAGE ALGORITHM FOR FILTERING ERRONEOUS ARGOS SATELLITE LOCATIONS

Several methods have been used to identify erroneous animal locations based on Argos satellite data. Using 15,987 satellite locations for 37 gray seals ( Haliockoerus grypus ), we tested a three-stage filtering algorithm designed to address shortcomings of other filters. In stage 1, for each location, four rates of travel were calculated—the rate to each of the two previous locations and the two subsequent locations. If all four rates exceeded 2 m/sec (95th percentile of our data), the location was removed (7.25% of total locations). Stage 2 incorporated the filtering algorithm developed by McConnell et al. (1992) resulting in the rejection of 22.75% of total locations based on reasonable assumptions of straight-line travel. At stage 3, the remaining data were evaluated against a distance threshold, defined as the 99th percentile of realized distance traveled over a period of seven days. Locations exceeding this threshold-were rejected (0.69% of total locations). Overall, the three-stage filter eliminated fewer locations (30.7 ± 1.62%), than the stage 2 filter alone. Most standard locations were retained, but 85.7% of location class 0, 76.6% of A, and 41.9% of B were also retained. These location classes account for most of data routinely collected but not used.     

Evaluation of fast-acquisition GPS in stationary tests and fine-scale tracking of green turtles

Fastloc GPS (FGPS) is a variant of Global Positioning System (GPS) technology that offers important new utility for investigating fine-scale movements of marine animals like green turtles that surface too briefly for effective use of standard GPS. I report here on the accuracy and efficiency of this novel technology, compare it with two alternative methods, namely boat-based ultrasonic tracking and Argos Platform Transmitter Terminals (PTTs), and provide new data on the vagility and habitat selection of green turtles in shallow coastal foraging habitat. I used a combined FGPS receiver and PTT transmitter (Sirtrack, Havelock North, New Zealand) mounted together with an ultrasonic transmitter and time-depth recorder in a tether-attached housing that allowed automatic detachment and subsequent retrieval of the equipment without the requirement to recapture turtles. With this equipment I conducted short deployments (4.5 to 16.8 d) on 3 free-living adult-size green turtles in coastal foraging habitat in Queensland, Australia. In addition, stationary tests in air and afloat were conducted at the same site. FGPS location error (mean ± SD) increased as the number of satellites used in each computation decreased, from 26 m ± 19.2 (8 satellites) to 172 m ± 317.5 (4 satellites). During live tracking the frequency of FGPS locations greatly exceeded Argos PTT, such that screened data comprised about 50 times more FGPS locations despite a much tighter screening threshold for FGPS (250 m) than for Argos PTT (1000 m). FGPS locations showed the three study turtles used modest short-term activity ranges with Minimum Convex Polygon area mean ± SD 662 ha ± 293.9. They all remained within < 4.7 km of their capture-release locations and favoured shallow water, with 86% of locations at charted depths ≤ 3 m and the deepest location at 5.9 m. Fine-scale movements of each turtle varied from day to day with respect to tortuosity and areas traversed. Statistically significant day-night differences were evident in average rates of movement (greater by day) and in habitat selection, where diurnal locations had greater seagrass density while nocturnal locations featured deeper bathymetry. Individual turtles revisited some of their centres of activity (identified from 50% fixed kernel utilisation distributions) on multiple occasions but none of the study turtles travelled consistently between the same day-night pair of sites as has been reported elsewhere. Such disparity and the day-to-day variation in movements revealed by these short-term findings highlight the need for detailed tracking over longer periods at multiple locations. Fastloc GPS technology proved an effective new tool for this area of research.     

A simple new algorithm to filter marine mammal Argos locations

During recent decades satellite telemetry using the Argos system has been used extensively to track many species of marine mammals. However, the aquatic behavior of most of these species results in a high number of locations with low or unknown accuracy. Argos data are often filtered to reduce the noise produced by these locations, typically by removing data points requiring unrealistic swimming speeds. Unfortunately, this method excludes a considerable number of good‐quality locations that have high traveling speeds that are the result of two locations being taken very close in time. We present an alternative algorithm, based on swimming speed, distance between successive locations, and turning angles. This new filter was tested on 67 tracks from nine different marine mammal species: ringed, bearded, gray, harbor, southern elephant, and Antarctic fur seals, walruses, belugas, and narwhals. The algorithm removed similar percentages of low‐quality locations (Argos location classes [LC] B and A) compared to a filter based solely on swimming speed, but preserved significantly higher percentages of good‐quality positions (mean ± SE% of locations removed was 4.1 ± 0.8%vs. 12.6 ± 1.2% for LC 3; 6.8 ± 0.6%vs. 15.7 ± 0.9% for LC 2; and 11.4 ± 0.7%vs. 21.0 ± 0.9% for LC 1). The new filter was also more effective at removing unlikely, conspicuous deviations from the track's path, resulting in fewer locations being registered on land and a significant reduction in home range size, when using the Minimum Convex Polygon method, which is sensitive to outliers.     

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.     

HARBOR SEAL TRACKING AND TELEMETRY BY SATELLITE

We tested a satellite Platform Transmitter Terminal (PTT) in the laboratory (on a float and on captive seals) and on a free-ranging harbor seal in the Southern California Bight to investigate the utility of satellite telemetry in documenting seals'at-sea behavior and movements. We used records from a microprocessor-based time-depth recorder (TDR) to interpret location and diving records from the PTT. For the free-ranging harbor seal, we obtained at least one uplink during 70% (while the seal was at sea) to 82% (while she was ashore) of satellite passes and at least one location each day. Of 62 locations determined by Service Argos for the free-ranging seal, 20 were verified from TDR records to have been at sea; these indicated that the seal may have ranged up to 48 km from the haul-out site, although most locations were within 5 km. The accuracies of locations calculated when the seal was at sea (±15 km) were substantially less than when it was ashore (±1.5 km), thus limiting at-sea tracking of seals by satellite to rather gross movements. Fewer transmissions were detected and locations calculated when the seal was actively diving than when it was swimming near the surface as it departed from or returned to the haul-out site. Consequently, average dive durations indicated by the PTT were substantially shorter than those calculated from TDR records. Documentation of foraging areas and detailed at-sea movements using satellite technology may not be possible for pinnipeds unless PTT-transmission rates are increased substantially from the 1 per 45 set maximum rate now permitted by Service Argos.     

Satellite tracking of grey seals (Halichoerus grypus)

Three types of Argos satellite transmitter were attached to grey seals ( Halichoerus grypus ) at Donna Nook (South Humberside, UK) between 1985 and 1989 in order to investigate their movements. With the first two transmitters (A and B) the entire package was attached to the seal's back. Seal A was tracked for 29 days but although it was located on sandbanks up to 150 km south-east of Donna Nook, no locations were obtained at sea. Transmitters B and C used a submergence sensor to regulate transmissions. Seal B was tracked for 51 days and remained within 40 km of Donna Nook. A few locations were obtained at sea but all within 10 km of Donna Nook. Transmitter C incorporated a head-mounted aerial in order to increase the number of location fixes when the seal was at sea. This seal was tracked for 111 days, producing an average of 9·1 location fixes per day while at sea. It used two sites 265 km apart and undertook three transits between them. On the second visit to the northern site it made several trips up to 55 km out to sea. The majority of the remainder of the time was spent within 10 km of the haulout sites. Estimates of swimming speed were consistent with values required for minimum cost of transport.     

Long-Term GPS Tracking of Ocean Sunfish Mola mola Offers a New Direction in Fish Monitoring

Satellite tracking of large pelagic fish provides insights on free-ranging behaviour, distributions and population structuring. Up to now, such fish have been tracked remotely using two principal methods: direct positioning of transmitters by Argos polar-orbiting satellites, and satellite relay of tag-derived light-level data for post hoc track reconstruction. Error fields associated with positions determined by these methods range from hundreds of metres to hundreds of kilometres. However, low spatial accuracy of tracks masks important details, such as foraging patterns. Here we use a fast-acquisition global positioning system (Fastloc GPS) tag with remote data retrieval to track long-term movements, in near real time and position accuracy of <70 m, of the world''s largest bony fish, the ocean sunfish Mola mola. Search-like movements occurred over at least three distinct spatial scales. At fine scales, sunfish spent longer in highly localised areas with faster, straighter excursions between them. These ‘stopovers’ during long-distance movement appear consistent with finding and exploiting food patches. This demonstrates the feasibility of GPS tagging to provide tracks of unparalleled accuracy for monitoring movements of large pelagic fish, and with nearly four times as many locations obtained by the GPS tag than by a conventional Argos transmitter. The results signal the potential of GPS-tagged pelagic fish that surface regularly to be detectors of resource ‘hotspots’ in the blue ocean and provides a new capability for understanding large pelagic fish behaviour and habitat use that is relevant to ocean management and species conservation.     

Performance of a satellite-linked GPS on Pacific walruses (<Emphasis Type="Italic">Odobenus rosmarus divergens</Emphasis>)

We evaluated the utility of a satellite-linked GPS in obtaining location data from Pacific walruses (Odobenus rosmarus divergens). A unit was attached to one of the tusks of each of three adult male walruses in Bristol Bay, Alaska. The units were designed to relay GPS positions through the Argos Data Collection and Location System. The GPS was only minimally effective in obtaining location data. An average of only 5% of the attempts yielded a position, and only a small number of these were locations at sea. The paucity of successful attempts was probably due to infrequent and brief surfacings of the GPS, the proximity of cliffs to predominant haul-out sites in the study region, and the packing of animals when they were hauled out in herds. Argos was effective in relaying GPS positions in this study, but as GPS technology advances, and its application to marine mammal studies becomes more prevalent, it seems that the greatest challenge to the study of many species will be in data retrieval.     

Movements of two Svalbard polar bears recorded using geographical positioning system satellite transmitters

Until recently, studies on polar bear (Ursus maritimus) movements and space use have used data collected by satellite telemetry collars that provided positions infrequently (typically weekly) and with low precision (by Doppler Shift method). A new generation of transmitters incorporated into collars use the Global Positioning System (GPS) to provide highly accurate positions, and have the ability to provide many positions per day. We used data from two GPS collars fitted to female polar bears, that attempted to collect six positions per day (4-h apart) for 546 days (from April 2000 to September 2001) and 413 days (from April 2000 to May 2001) to estimate how estimated speed of movement and home range size increase with increasing number of data points. Using all the positions, we estimated that the bears moved a minimum of 14.3 and 15.8 km per day on average. The fractal dimension (D) of the movement pathways for the two bears were D = 1.28 and 1.31, respectively, indicating low tortousity of the movements. Their minimum estimated annual home range areas were 20,794 and 112,183 km². Simulations showed that a commonly used sampling regime of one location every 6th day would have significantly underestimated the movement rates and the home range sizes compared to our estimates. We also used the high accuracy of GPS positions to look at distances moved within 4-h periods. Maximum movement rate during a 4-h period for the two bears was 4.21 and 4.58 km/h, respectively. Variation in median values by month was significant (0.01 km/h in November for N23476 to 1.48 km/h in December for N7955). Diurnal variation was observed to differ between defined periods.     

The effects of interpolation error and location quality on animal track reconstruction

The Global Positioning System (GPS) gives precise estimates of location. However, the investigation of animal movement and behavior often requires interpolation to examine events between such fixes. We obtained 6,288 GPS locations from an electronic tag deployed for 170 d on an adult male gray seal ( Halichoerus grypus ) that ranged freely off the east coast of Scotland, and interpolated between subsamples of these data to investigate the growth of uncertainty within the intervals between observations. Average uncertainty over the path increased linearly as the interval between interpolating locations increased, reaching 12 km in longitude and 6 km in latitude at 2-d separation. The decrease in precision caused by duty-cycling, only collecting data in part of the day, was demonstrated. Adding noise to the GPS locations to simulate data from the ARGOS satellite system had little effect on the total errors for observations separated by more than 12 h. While the rate of growth in interpolation error is likely to vary between species, these results suggest that frequent, and preferably evenly spaced, location fixes are required to take full advantage of the precision of GPS data in the reconstruction of animal tracks.     

Global positioning system and associated technologies in animal behaviour and ecological research

Biologists can equip animals with global positioning system (GPS) technology to obtain accurate (less than or equal to 30 m) locations that can be combined with sensor data to study animal behaviour and ecology. We provide the background of GPS techniques that have been used to gather data for wildlife studies. We review how GPS has been integrated into functional systems with data storage, data transfer, power supplies, packaging and sensor technologies to collect temperature, activity, proximity and mortality data from terrestrial species and birds. GPS ‘rapid fixing’ technologies combined with sensors provide location, dive frequency and duration profiles, and underwater acoustic information for the study of marine species. We examine how these rapid fixing technologies may be applied to terrestrial and avian applications. We discuss positional data quality and the capability for high-frequency sampling associated with GPS locations. We present alternatives for storing and retrieving data by using dataloggers (biologging), radio-frequency download systems (e.g. very high frequency, spread spectrum), integration of GPS with other satellite systems (e.g. Argos, Globalstar) and potential new data recovery technologies (e.g. network nodes). GPS is one component among many rapidly evolving technologies. Therefore, we recommend that users and suppliers interact to ensure the availability of appropriate equipment to meet animal research objectives.     

DIVE DATA FROM SATELLITE TAGS AND TIME-DEPTH RECORDERS: A COMPARISON IN WEDDELL SEAL PUPS

The diving behavior of juvenile Weddell seals, Leptonychotes weddellii , was monitored simultaneously with time-depth recorders (TDRs) and satellitelinked time-depth recorders (SLTDRs). Recovered TDRs provided a complete record of the depth and duration of all dives, while data received from SLTDR tags via the ARGOS satellite system were compressed into the number of dives in each of six depth or duration bins. The dive information from the two types of tags was compared to determine if data compression, processing, and transmission influenced the data received.
While only half of the dive data collected by TDRs was also received from the SLTDR tags, the chance of receiving SLTDR data was independent of when diving occurred, when data was transmitted, and the subsequent dive activity. In addition, the number of dives in each depth and duration bin was an accurate representation of the actual dive behavior. Therefore, SLTDR tags were judged to provide data qualitatively similar to that provided by TDRs. The accuracy of seal locations provided by Service ARGOS was estimated by comparison to Global Positioning System (GPS) locations, and the average position error found to be significantly greater than predicted by Service ARGOS or reported in other studies (LCO locations ± 11.4 km, LC1 ± 5.0 km).