Platform Transmitter Terminals Research Articles

Remote-sensing systems and seabirds: their use, abuse and potential for measuring marine environmental variables

We examined how seabirds might be used to study marine environmental variables, which necessitates knowing location and the value of the variable to be studied. Five systems can potentially be used for determination of location: VHF (Very High Frequency) telemetry, PTT (Platform Terminal Transmitters) telemetry, GLS (Global Location Service) geolocation methods, dead reckoning and GPS (Global Positioning System), each with its own advantages with respect to accuracy, potential number of fixes and size. Temperature and light were used to illustrate potential difficulties in recording environmental variables. Systems currently used on seabirds for measurement of temperature respond slowly to environmental changes; thus, they may not measure sea surface temperature adequately when contact periods with water bodies are too short. Light can be easily measured for light extinction studies, but sensor orientation plays a large role in determining recorded values. Both problems can be corrected. The foraging behaviour of seabirds was also examined in order to identify those features which would be useful for determination of marine environmental variables at a variety of spatial and temporal scales. Area coverage by birds is highly dependent on breeding phase and tends to be concentrated in areas where prey acquisition is particularly enhanced. The identification of these sites may be of particular interest to marine biologists. 'Plungers' and 'divers' are potentially most useful for assessment of variables deeper within the water column, with some divers spending up to 90% of their time sub-surface. Few seabirds exploit the water column deeper than 20 m, although some divers regularly exceed 50 m (primarily penguins and auks), while 2 species dive in excess of 300 m. The wide-ranging behaviour of seabirds coupled, in many instances, with their substantial body size makes them potentially excellent carriers of sophisticated environmental measuring technology; however, the ethical question of how much the well-being of birds can, and should, be compromised by such an approach needs to be carefully considered.

Autonomous Pinniped Environmental Samplers: Using Instrumented Animals as Oceanographic Data Collectors

Data-recording tags applied to marine animals store data for later retrieval and can return valuable information on animal behavior and ecology, including habitat preference, physiology, and movement patterns, as well as environmental data. If properly instrumented, calibrated, and archived, data from these tags can add to the oceanographic datastream for parts of the ocean where data are sparse or lacking. Such data, from northern elephant seals instrumented with time‐temperature‐depth recorders (TTDR) and ARGOS platform terminal transmitters, is examined in this study. Northern elephant seals range widely over the northeastern Pacific on long foraging trips. The seals dive continuously on these trips to depths of 400‐600 m. Between March 1998 and March 1999, six female and three male elephant seals were tagged in central California and data were collected during subsequent foraging trips. Temperature and depth were measured and stored every 30 s and retrieved after the animals returned to the rookery months later. Portions of the track where both ARGOS and TTDR data were available from these nine animals averaged 4634 km over 67 days with 2.4 ARGOS positions per day. Mean dive duration was 20 min and mean dive depth was 428 m. A comparison of temperature profiles from seal TTDR with Global Temperature‐Salinity Profile Program (GTSPP) subsurface data showed very good agreement, as did surface temperatures to other sources of SST. Quality control of the data and entry into the World Ocean Database (WOD) is described. A total of 75 665 autonomous pinniped bathythermograph (APBT) profiles over the 41 702 km of seal trackline were added to the WOD. Biological autonomous sampling systems have immense potential to contribute oceanographic data in a costeffective manner. The northern elephant seal represents but one species covering portions of the northeast Pacific Ocean. Research programs presently exist on a variety of species, including southern elephant seals and other pinnipeds, tunas and billfish, sharks, seabirds, marine turtles, and whales. With improving technology, such tags will be applied to even more marine animals and the approach described here can be applied to other species to improve ocean data availability.

FORAGING ECOLOGY OF NORTHERN ELEPHANT SEALS

Sexual segregation in foraging is predicted from the great size disparity of male and female northern elephant seals, Mirounga angustirostris. Our aim was to test this prediction by measuring diving and foraging behavior, foraging locations, and distribution of the sexes during biannual migrations in the northeastern Pacific Ocean. Daily movements of 27 adult males and 20 adult females, during 56 migrations from Afio Nuevo, California, USA, were determined by Argos satellite telemetry via head-mounted platform transmitter terminals. Diving records were obtained with archival time-depth-speed recorders attached to the backs of seals that were recovered when the seals returned to the rookery. Pronounced sex differences were found in foraging location and foraging pattern, as reflected by hor- izontal transit speed and diving behavior. Males moved directly north or northwest at a mean speed of 90 ? 27 km/d to focal foraging areas along the continental margin ranging from coastal Oregon (534 km away) to the western Aleutian Islands (4775 km away). Males remained in these areas (mean size = 7892 ki2) for 21-84% of their 4-mo stays at sea. The predominance of flat-bottom dives in these areas suggests concentrated feeding on benthic prey. Migration distance and estimated mass gain were positively correlated with male size, and individual males returned to the same area to forage on subsequent migrations. In contrast, females ranged across a wider area of the northeastern Pacific, from 380 to 600 N and from the coast to 172.5? E. Focal foraging areas, indicated by a reduction in swim speed to <0.4 m/s, were distributed over deep water along the migratory path, with females remaining on them a mean of 3.5 d before moving to another one. Jagged-bottom dives that tracked the deep scattering layer prevailed in these areas, suggesting that females were feeding on pelagic prey in the water column. Females took roughly similar initial paths in subsequent migrations, but large deviations from the previous route were observed. We conclude that there is habitat segregation between the sexes. Females range widely over deep water, apparently foraging on patchily distributed, vertically migrating, pelagic prey, whereas males forage along the continental margin at the distal end of their migration in a manner consistent with feeding on benthic prey.

Movements and distribution of polar bears in the Beaufort Sea

We fitted 173 satellite radio collars (platform transmitter terminals) to 121 adult female polar bears in the Beaufort Sea and relocated the bears 44 736 times between 1985 and 1995. We regularly resighted many instrumented bears so that we could ascertain whether changes in movements or distribution were related to reproductive status. Mean short-term movement rates were less than 2 km/h for all classes of bears. Maximum movement rates occurred in winter and early summer. In the southern Beaufort Sea (SBS), net geographic movements from the beginning to the end of each month were smaller for females with cubs of the year than for solitary females, and larger in November than in April, May, or July. In May, June, July, and August, radio-collared bears in the SBS moved north. They moved south in October. In the northern Beaufort Sea (NBS), bears moved north in June and south in March and September. Total annual movements ranged from 1406 to 6203 km. Mean total distances moved each month ranged from 79 to 420 km. Total monthly movements by SBS bears were largest in early winter and smallest in early spring. In the NBS, movements were largest in summer and smallest in winter. In the SBS, females with cubs moved less each month than other females. Annual activity areas ranged from 7264 to 596 800 km2. Monthly activity areas ranged from 88 to 9760 km2. Seasonal fidelity to activity areas of bears captured in all parts of the Beaufort Sea was strongest in summer and weakest in spring.

Performance and Accuracy Evaluation of Small Satellite Transmitters

Recent technological advances have resulted in small (30 g) satellite platform transmitter terminals (PTTs) that can be used to track animals with masses as little as 900-1,000 g. While larger PTTs (>80 g) often yield locations accurate to within hundreds of meters, the location accuracy of smaller PTTs has not been tested. We did these tests while using the PTTs to document migration routes and nonbreeding areas of American peregrine falcons (Falco peregrinus anatum). We PTT-tagged 42 female peregrines from 2 breeding areas (upper Yukon River in eastcentral Alaska and Lake Powell on the Colorado Plateau in southern Utah and northern Arizona) late in the breeding seasons of 1993-95. Only 2 of the PTTs failed prematurely (4.7% failure rate). Active PTTs (i.e., PTTs on live birds that eventually stopped transmitting due to battery exhaustion) averaged 280 transmission hours for 1993-94 (n = 3), 380 transmission hours for 1994-95 (n = 7), and 430 transmission hours for 1995-96 (n = 15). Using an estimate of maximum ground speed of peregrines (104 km/ hr) based on empirical observations and aerodynamic calculations, we determined that 4.48% of all locations provided to us by Argos (n = 2.323) were biologically implausible. We also received many poor-quality locations (68% of records were in Argos location classes 0, A. and B) typical of small, relatively underpowered PTTs. To estimate location accuracy of these poor-quality locations, we compared Argos-estimated locations with known locations of 11 rock doves (Columba livia) tagged with PTTs. The location types with the highest precision averaged 4 km from the true location, while the location types with the lowest precision averaged 35 km from the true location. These results indicate the PTT locations were sufficient to document animal movements over broad spatial scales such as identifying migration routes and nonbreeding areas of birds. This technology is more efficient and less biased than the current approaches used to obtain this information (mark-resighting of banded animals or standard radiotelemetry techniques). However, the PTTs currently available are not suitable when position accuracy <35 km is needed.

Annual distribution of hooded seals (Cystophora cristata) in the Greenland and Norwegian seas

Nineteen hooded seals (Cystophora cristata) were tagged with satellite-linked platform terminal transmitters (PTT) on the sea ice near Jan Mayen. Fifteen were instrumented after completion of the mouly in July 1992 (five males, ten females, at 71°N, 12°W), and four during breeding in March 1993 (four females, at 69°N, 20°W). Sixteen of the seals were tagged with Satellite-Linked Time-Depth-Recorders (SLTDR), yielding location, dive depth and dive duration data. The average (±SD) longevity of all PTTs was 199±84 days (n=19; range: 43–340 days), and they yielded 12,834 location fixes. Between tagging in July 1992 and pupping in March 1993, two seals remained in or near the ice off the east coast of Greenland for most of the tracking period. However, most of the seals made one or several trips away from the ice edge, mostly to distant waters. These excursions had an average (±SD) duration of 47±22 days (n=46; range: 4–99 days). Eight seals travelled to waters off the Faeroe Islands, three to the continental shelf break south of Bear Island, and three to the Irminger Sea southwest of Iceland. Eleven seals were tracked in the period between breeding (March/April) and moulting (July). Several of these spent extended periods at sea west of the British Isles, or in the Norwegian Sea.

THE USE OF SATELLITE SYSTEMS FOR THE STUDY OF BIRD MIGRATION

ABSTRACT The Argos satellite system, with two or more polar-orbiting satellites, provides the basis for receiving radio signals from transmitters and for estimating locations of those transmitters anywhere around the earth. We briefly relate the development of platform-transmitter terminals small enough to be placed on birds, but powerful enough to send signals to the satellites. We review the use of this recent technology in avian studies, including several applications to bird migration. We also describe the type of information we are obtaining from three of our current studies of migratory birds.

Comparison of 3 Methods for Evaluating Activity of Dall's Sheep

Validation of the reliability of remote-sensing data is critical to subsequent analyses, yet is often neglected. Thus, we assessed the efficacy of 3 methods of collecting information on activities of captive and free-ranging Dall's sheep (Ovis dalli) in Alaska. Conventional very high frequency (VHF) radio-telemetry transmitters and platform transmitter terminals that transmit to satellites, eacj wotj motion-sensitive tipswitches, were compared with simultaneous direct observation Both VHF (98% agreement) and satellite telemetry (98% agreement) reliably distinguished active from inactive behaviors for free-ranging females

Tracking of marine animals by satellite

Abstract Systems developed for tracking marine animals including fish, reptiles, mammals and birds using the.ARGOS system are described. Platform Terminal Transmitters (PTTs) attachable to animals now weigh less than 150 g and can be used on larger species of birds. Simultaneous remote sensing and location of animals using the NOAA satellites is described. Marine animals can only be tracked if they surface during a satellite overpass. New developments which permit animal location using fewer messages greatly increase the probability of successful tracking. Only satellite tracking can provide long-term ocean-wide coverage necessary for management and conservation of many important species.

Satellite Telemetry: Performance of Animal-Tracking Systems

We used 10 Telonics ST-3 platform transmitter terminals (PTT's) configured for wolves and ungulates to examine the performance of the Argos satellite telemetry system. Under near-optimal conditions, 68 percentile errors for location qualities (NQ) 1, 2, and 3 were 1,188 903, and 361 m, respectively. Errors (r E ) exceeded expected values for NQ=2 and 3, varied greatly among PTT's, increased as the difference (H E ) between the estimated and actual PTT elevations increased, and were correlated nonlinearly with maximum satellite pass height (P H ). We present a model of the relationships among r E , H E , and P H . Errors were bimodally distributed along the east-west axis and tended to occur away from the satellite when H E was positive. A southeasterly bias increased with H E , probably due to the particular distribution of satellite passes and effects of H E on r E . Under near-optimal conditions, ≥1 sensor message was received for up to 64% of available (P H ≥5°) satellite passes, and a location (NQ≥1) was calculated for up to 63% of such passes. Sampling frequencies of sensor and location data declined 13 and 70%, respectively, for PTT's in a valley bottom and 65 and 86%, respectively, for PTT's on animals that were in valley bottoms. Sampling frequencies were greater for ungulate than for wolf collars

HARBOR SEAL TRACKING AND TELEMETRY BY SATELLITE

AbstractWe 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.