Satellite Tracking Project, 2000

Up to 10,000 juvenile loggerhead sea turtles (Caretta caretta) inhabit Chesapeake Bay each summer (Byles, 1988; Keinath et al., 1987; Keinath and Musick, 1991; Lutcavage, 1981; Lutcavage and Musick, 1985; Musick, 1988; Musick et al., 1985). However, nesting female loggerheads are rare north of Cape Hatteras, with typically two to ten nests occurring annually in Virginia (Byles and Musick, 1981; Jones and Musick, 1989; Musick et al., 1985). The first nighttime study of turtles nesting in Virginia occurred in 1989 with seven nests found. According to flipper tags, it appeared that two turtles deposited multiple nests. Flipper-tagging has traditionally been the most common method used to study movements of free ranging sea turtles, but this technique suffers from loss of tags, and only reveals point to point movements. Despite drawbacks, flipper tagging has revealed the greatest amount of information on movements and philopatry of free ranging sea turtles. Other methods have been employed to track sea turtles: Balloons (Carr, 1963; 1972), floats (Carr et al., 1974, Meylan, 1982, Mortimer, 1981, Mortimer and Portier, 1989), and dye (Witham et al., 1973) were used to track movements of sea turtles off the nesting beaches, but these experiments were of limited duration and had some drawbacks (Carr, 1963). Carr (1963) suggested electronic tracking would be ideal to monitor sea turtles in their natural environment.

Radio, sonic, and satellite telemetry has recently been used successfully to monitor wild sea turtle movements. In addition, other behavioral data can also be gathered with modern transmitters. Both radio and sonic telemetry require expensive vessel support to stay in contact with the transmitters. This limits duration of tracks from days up to a few weeks (Keinath, 1986, 1991). Satellite telemetry demands a large initial investment, but may provide months of data. The Sea Turtle Project at the Virginia Institute of Marine Science (VIMS) has developed relatively inexpensive satellite transmitters, and VIMS has monitored over 25 sea turtles of three species with satellite telemetry since 1985 (Keinath et al., 1992; Keinath, 1993).

Satellite telemetry utilizes radio transmitters which relay signals to satellites which in turn relay data to earth stations (Byles and Keinath, 1990; Keinath, 1991, 1993). Movements of Kemp's ridley, Lepidochelys kempii (Byles, 1989; Keinath, 1993), leatherback, Dermochelys coriacea (Duron-Dufrenne, 1987; Keinath and Musick, 1993), and loggerhead sea turtles (Byles, 1988; Byles and Dodd, 1989; Keinath et al., 1989; Stoneburner, 1982; Timko and Kolz, 1982) have been successfully studied via satellite. Satellite telemetry systems allow collection of data that have included water temperature and precise diving/surfacing parameters. Diving behavior data from satellite transmitters have been reported for Kemp's ridley (Byles, 1989; Keinath, 1993) and loggerhead sea turtles (Byles and Dodd, 1989; Keinath et al., 1989; Keinath, 1993), and the VIMS research team was the first to successfully study leatherback diving behavior via satellite (Keinath and Musick, 1993).

Loggerhead sea turtles usually nest several times during a nesting season. Adult female loggerhead sea turtles have been observed to utilize the Chesapeake Bay as an internesting habitat and are estimated to compose five percent of the total turtle population within the Bay (Musick and Limpus, 1997). Based on previous VIMS tracking studies, nesting female loggerheads have been found to use estuarine areas as internesting feeding habitats. Three turtles satellite tagged by the Army Corps of Engineers Sea Turtle Nesting and Tracking Study have migrated to the Delaware Bay and/or Chesapeake Bay between nesting events within Back Bay National Wildlife Refuge (BBNWR) (Bartol and Musick, 1997, 1998).

MATERIALS AND METHODS:

Satellite telemetry uses UHF transmitters that transmit signals to a satellite. The satellite in turn relays the signals to an earth station. The ARGOS satellite telemetry system utilizes NOAA Tiros satellites to calculate transmitter location by doppler shift of the transmitter's radio frequency (Kenward, 1987). A salt-water switch was used to turn off the transmitter while underwater (UHF radio waves do not travel through seawater) to extend the battery life from 25 - 30 days to up to a year of operation. Data are accessed via the internet and email. Location, day and time of reception, and probability of location accuracy are among the data received.

In contrast to radio and sonic telemetry which can provide continuous data, the ARGOS system provides only a limited number of daily fixes, depending on latitude (Kenward, 1987). Since Tiros satellites are polar orbiting, more fixes are possible at higher latitudes (up to 15 per day) than at the equator (up to seven per day), and since the transmitter is below the surface most of the time, probability of receiving a location is decreased further. Several fixes are received per day, although there may be occasions when no positions may be recorded for days (Keinath, 1993).

Personnel and volunteers from the Back Bay National Wildlife Refuge (BBNWR) and the Virginia Marine Science Museum conduct a combination of daytime and nighttime sea turtle nesting patrols on the beaches from the northern limit of Sandbridge Beach to the southern limit of BBNWR at the North Carolina border. Any nesting turtle encountered by BBNWR personnel is restrained until VIMS personnel can access the refuge and attach a satellite transmitter to the nesting turtle.

A satellite transmitter (Telonics model ST-14) was affixed to the carapace of the turtle with epoxy and fiberglass resin, a non-invasive procedure. We have utilized this method successfully on over 25 turtles (Keinath, 1993). The turtle was then immediately released at the same location, and movements and behavior will monitored until positions are no longer received.

Facts about the Satellite Turtle:

Species: Loggerhead (Caretta caretta)
Gender: Adult female
Carapace Length: 93.1 cm (curved length)
Date Found: July 11, 2000
What she was doing when found: Nesting on the beach at Back Bay NWR; first observed at 10:25 pm
Eggs Laid: 119
Flipper Tag: XXF-853 applied to front left flipper
Satellite Tag Applied: Early morning, July 12, 2000; tag was placed on the second and third vertebral scutes on the turtle's carapace. Tag was applied after the turtle had completed her nesting event. She was released on the beach the same night.

LITERATURE CITED

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