There are basically two ways the radio transmitter can be attached to the turtle.
Bolt attachment method
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Epoxy glueing method
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Telemetry tracking protocol
The most accurate method to determine the location of a turtle with a transmitter is by using a canoe and going to the vicinity of the turtle or by triangulation from several points at a distance (see below).
• Turtles equipped with transmitters are located via homing to their position either by estimating the location from the shore or from water by boat (marking GPS location where the strongest, most consistent signal is received) using a portable receiver (e.g., Wildlife Elements) and 3-element (e.g., YAGI) antenna.
• Visual observations of tagged turtles during the day are also be recorded; a test of transmitter functioning should be conducted with visual observations.
• Observers may estimate the turtle's position from land when the turtle is near the shoreline. Using a boat for these detections may be biased if turtles are disturbed by the researcher's activities or movements. When the turtle is not visible, locations are estimated by moving the antenna back and forth, detecting where the signal drops and where it is the strongest, then picking the direction of the strongest, most consistent signal. Observers should obtain directions from at least two sites until confident that the true location can be estimated and that any inconsistences in signal strength are not due to movements of the turtle (e.g., coming closer to the water surface).
• GPS coordinates from which turtle locations are estimated from the shore are recorded, along with the estimated distance to the turtle and a description of the location. These can then be used to determine the GPS coordinates of the turtle more accurately via plotting on GPS mapping software (e.g., Map Source). In cases when this methoc is not be sufficient to derive an accurate location, a single person can ‘triangulate’ as described below.
• The method of using a boat to acquire locations is appropriate for daily detections far from the shore; an adaptation of the shore method of locating turtles may be used at night due to safety concerns.
An alternative tracking method consists of triangulation to determine the turtle's location; this requires two people simultaneously determining the strongest direction of the radio signal and recording an angle (using a compass) from two different localities on land(A and B in Figure 2), while being in constant radio contact with each other. To minimize error observers need to position themselves so as to create as close to a 90 degree angle as possible with the turtle's location. Locations of turtles can be estimated using GPS software (such as Map Source) by inputing each observers' location (marked via GPS) and the angle of the strongest signal strength. The point of intersection between the two lines of the angles is used to estimate turtle location (Figure 2). However, for this method an additional receiver unit, GPS, and compass are needed.
Figure 2. Triangulation method for determining turtle location using radio-telemetry.
Turtle with a radio-transmitter bolted on to the edge of the carapace.
Turtle with a transmitter epoxied onto the carapace.
Overwintering area can be determined after the turtle’s tracked location has been in approximately the same place for three tracking sessions at the appropriate overwintering time (late fall/early winter).
To assess habitat use by turtles, habitat is described both at locations of tracked turtles and random sites within movement capabilities of the turtle. Comparisons are then made between multiple variables that are recorded for the habitat plots (see below for examples) to determine if significant differences exist between the areas turtles are using and random locations. Please refer to the Western Painted Turtle Monitoring at Alaksen National Wildlife Area (NWA)- Final Report March 2011 by Vanessa Kilburn and Aimee Mitchell of the South Coast Western Painted Turtle Recovery Project for an example and details on habitat analysis and results (PDF)
• To compare habitat use daily and seasonally, habitat is described at tracking locations that are >10m apart (average error of locations). See Datasheets for sample on recording data.
• In addition, habitat plots can be placed within the estimated overwintering area to characterize that habitat.
• The following aquatic habitat charateristics will be measured/recorded as soon as possible to the tracking of each location:
- Air temperature
- Surface water temperature
- Water column temperature (mid-way)
- Bottom water temperature
- Nearest basking location temperature (during summer only)
- Water depth (using pre-marked rope with weight)
- General habitat description: habitat type (i.e., edge, open, basking), degree of cover (i.e., shaded, clear of canopy), degree of woody emergents and submergents in 2 m radius, other fish, wildlife, plant species visibly present in immediate area
• General habitat features are identified as follows: Edge Habitat (ED) refers to the area within 10 m of shore which can be shaded by riparian vegetation (including trees) and generally has more woody emergents/submergents because of dead fall from the surrounding areas. This usually means most ED is also basking habitat (BA), but BA can also exist in open water. Open water habitat (OP) is the area outside of the 10 m zone on edges of a water body that is typically clear of vegetation and woody emergent/submergents.
Example of Edge Habitat (ED) (with basking habitat also)
Example of Open Water Habitat (OP)
• In addition, an aquatic sediment/vegetation sample to examine the substrate composition can be collected: organic (e.g., leaf litter, woody debris) and inorganic (e.g., silt, sand, clay) , which may be accessed using a paddle dipped at the plot location.
• A selection of random points equal in number to tracked locations (excluding overlapping locations) should also have habitat plots placed throughout the available aquatic habitat for comparisons. Random plot locations were generated by CWS staff while tracking at Alaksen National Wildlife Area in Delta, BC via Hauth’s Analysis Tools for ArcGIS (source: http://www.spatialecology.com/htools/rndpnts.php)
• Any locations on land would be categorized via habitat categories (or landscape composition categories) already described in the Site Management Plans as part of The South Coast Turtle Recovery Project Final Report (Kilburn and Mitchell, 2011) and outlined by Marchand and Litvaitis, 2004 (Reference 16).
- Kayak, paddle, and life jacket
- Chest waders
- Receiver and antenna (x 2 for triangulation)
- GPS unit (x 2 for triangulation)
- Notebook and pencil
- Temp/Cond/pH meter
- Glass thermometer
- Weighted rope with depths pre-marked
Examples of Datasheets
Locations form boat
- ↑ Bowne, D.R., M.A. Bowers, and J.E. Hines. 2006. Connectivity in an agricultural landscape as reflected by interpond movements of a freshwater turtle. Conserv. Biol. 20(3):780-791.
- ↑ Springer, J. T. 1979. Some sources of bias and sampling error in radio triangulation. J.Wildlife Mgmnt 43:926-935.
- ↑ Rowe, J.W. and S.J. Dalgran. 2009. Effects of Sex and Microhabitat Use on Diel Body Temperature Variation in Midland Painted Turtles (Chrysemys picta marginata). Copeia, 1:85-92
- ↑ Marchand, M.N and J.A. Litvaitis. 2004. Effects of habitat features and landscape composition on the population structure of a common aquatic turtle in a region undergoing rapid development. Conserv. Biol. 18(3):758-767.