What We Know, Don’t Know, and Want to Know About Semi-aquatic Turtles
All of our curriculum projects begin by asking participants questions and engaging in discussion. We ask participants to share their experiences with and knowledge about turtles. We encourage participants to think broadly. For example, we ask them to describe actual experiences with wild turtles, seeing turtles on television or at an aquarium, reading stories about turtles, having turtles as pets, or even stories about people who eat turtles. This conversation should reveal what they know and do not know about turtles, their interests in turtles and their misconceptions about turtles. We suggest that instructors value all responses and not be critical or judgmental about any of the stories shared. This conversation provides instructors with a place to start the semi-aquatic turtles curriculum.
You can help to focus student thinking by asking, “What are the differences between terrestrial, aquatic, and semi-aquatic turtles?” Possible answers include
- Terrestrial turtles spend their lives on land.
- Aquatic turtles have shells that have highly hydrodynamic shapes. They spend most of their lives in the water (e.g. soft shelled turtles, sea turtles), except under special circumstances, like when they lay eggs.
- Semi-aquatic turtles live most of their lives in the water but, in some cases, can spend considerable time on land. Their shells are sometimes more boxy-shaped than aquatic turtles, though there are many exceptions.
Since turtles are reptiles, leaders can also ask about and then discuss the defining features of reptiles:
- Drier skin (than amphibians) with scales
- Internal fertilization
- Leathery shelled eggs that are laid on land
- Lung breathers
Once students are engaged in the process of learning more about semi-aquatic turtles, they can examine the similarities and differences among turtle shells.
External Anatomy of Turtles
Provide students with sample turtle shells, replicas, or homemade Styrofoam shells (see Appendix B for directions on how to make these). Teach participants basic anatomical features of the shells, and have them identify features on their own shell. Have them study turtle shells and make sketches in their notebooks. Remind them of the importance of accuracy.
The shell of the turtle is made up of bony plates. A scute is the keratinized material that covers each bony plate. The scutes continually peel off the shell. Have each participant find the cervical scute (the cervical scute is the small scute right over the neck of a turtle, which separates the turtle into left and right sides). Then, have participants count the vertebral scutes on the turtle shell that they are holding. Most turtles have five vertebral scutes but there is some variation. Next, have students count the marginal scutes, checking themselves in various ways (by starting with the cervical scute and going right, then starting with the cervical scute and going left and then counting marginal scutes on each half of the shell from head to tail. Usually, turtles have 24 marginal scutes; 12 on each side, but again, this is variable.
Have participants label their turtle shell sketches with features such as marginal scutes, vertebral scutes, lateral or pleural scutes, and cervical scute (on the carapace), and the names of the various plates on the plastron (if this much detailed is desired). It is good to locate at least the gular scutes on the plastron as these are useful in turtle identification.
Video Parts of the Turtle Shell: http://vimeo.com/109017644
The carapace of a Florida cooter
Common Snapping turtle plastron
If beginning in the classroom, have students locate information about the types of semi-aquatic turtles that are common in their area. Field guides or internet sites will be useful. When the guides or websites include range maps, participants could generate their own list of species that might likely be found in the study area. Students should focus on determining at least three or four physical characteristics that can be used to distinguish each turtle species.
Once turtle shell activities have been completed, students can begin the process of checking turtle traps that were set the night before. Instructors can set the traps or participants can be involved in the trap setting process. Instructors typically set traps the first night of our program, and students are involved in re-baiting and re-setting traps on future days of the program.
We typically bait traps with canned sardines packed in water. Bait holders (bait buckets) are made for each trap to hold the partially opened can of sardines out of reach of the captured turtles. This allows some of the bait to remain unconsumed so the trap will continue catching turtles. Bait buckets can be hung anywhere in the trap but should be under water once the trap is set. Each trap also needs to have empty (air-filled) sealed containers to make sure there is no danger of the trap sinking. We cut pieces of PVC pipe to hold the traps open and tie the end of the trap to a solid object such as a tree trunk or dock post. Traps are typically placed near areas where turtles bask, but participants may suggest other placements for experimental purposes. It is important to indicate on a map or sketch of the area where traps are located and how they are numbered (in a clockwise or counterclockwise sequence).
Lift trap from both ends to check for captures.
Students select and put on waders based on shoe size. Two or three participants can work together to remove traps from the water. Two students should walk to either side of the trap and lift the trap by the metal hoops, not by the PVC pipes which are structural components. If picked up by the PVC pipes, the trap could collapse and the PVC pipes fall out and sink. The two students carefully walk with the trap back to the shoreline. The third person can pull the rope that is tied to the trap.
The group should survey the animals that are in the trap before removing anything. Smaller turtles can be removed by reaching into the throat of the trap and pulling them out, posterior end first. Keep hands away from turtles’ mouths and claws. Other participants should be prepared to take the turtles that are being removed from the trap. If a large collection container (like a 10-gallon bucket) is available, turtles can be placed in this. For large turtles, such as snapping turtles, it may be necessary to untie the end of the trap that was previously tied to the stationary object. Once this end of the trap is open, fold back the net and place the trap near the water’s edge so that the turtle can walk out on its own. This is safer for people and for the turtle. In our project, we do not handle large snapping turtles. Sometimes traps will catch other animals such as fish. Reach into the throat of the trap and remove fish and return them to the water.
Students retrieving turtles from the hoop trap
A fish caught in the hoop trap
Video Trapping Turtles in a Hoop Trap: http://vimeo.com/109018471
Identifying Turtles in the Field
If there are multiple turtles in the trap, students can work in pairs to identify their assigned turtle. Students may create a dichotomous key for turtles or use their field guide, looking at pictures and reading the text and then comparing the information in the text to the turtle in their possession. We ask students to provide a minimum of three field characteristics to identify a turtle. A learner may say that their turtle is a Yellow-bellied Slider (Trachemys scripta) because it has yellow on its belly, but this could describe multiple turtles in our area, so we ask them for a second distinguishing characteristic. They may then say that the turtle has yellow stripes on its leg. This still describes multiple local turtles, so we ask for a third characteristic. They may finally refer to a yellow blotch or bar behind the eye linking a pair of yellow stripes on each side of the neck. Only after giving three field characteristics do we allow a student group to arrive at an identification. We might also ask for a fourth characteristic (pair of dark spots on the gular scutes) just to be sure.
Some of the more common turtles where we conduct our project include
- Eastern Mud Turtle (Kinosternon subrubrum)—no distinct head stripes, double hinged plastron, pectoral scutes meet only narrowly on the midline of the plastron forming a triangle
- Eastern Musk Turtle (Sternotherus odoratus)—also commonly called the stinkpot, from the odor it releases, two pairs of barbels on the chin and throat, single, weakly hinged plastron, pectoral scutes rectangular in shape, light yellowish line above and below the eye
- Common Snapping Turtle (Chelydra serpentine)—large head, long and tapering tail armed above with large scales, small cross-shaped plastron, carapace with three longitudinal keels (more prominent in young turtles) (If large snapping turtles are caught in a trap, they should never be handled or removed by students. See suggestions above for how to safely release these large animals)
- Painted Turtle (Chrysemys picta)—pale transverse seams between the dorsal scutes, two yellow spots in line behind the eye, conspicuous red markings around the edges of the shell, legs with red and yellow stripes
Once participants have identified the turtle to species, we ask them to attempt to determine if the turtle is male, female, or too young to tell. Again, students will need to go back to their field guides to be able to do this. Depending on the number of different species caught, student groups can share with the entire group their turtle’s identification and its distinguishing features, sex, and selected other information (for example, how many eggs a female of the species might lay or what kind of food it prefers).
Nails on the forelimbs of males are longer than those of females.
Typically, male turtle tails have vents outside the edge of the carapace while females have vents inside the edge of the carapace.
If submitting data to The HERP Project or another database, take the following
measurements for each turtle:
- Straight carapace length (midline, notch to notch)
- Width at widest point
- Shell height at tallest point (carapace to plastron)
- Midline straight plastron length
Information about our aquatic turtle project and The HERP Project can be found at http://theherpproject.uncg.edu/research/herpetology-studies/aquatic-turtles/. A sample of our data sheet can be found in Appendix A. Another option is to download the free HERP Project data collection app from http://theherpproject.uncg.edu/apps-collecting-data/.
The size of the caliper used depends on the size of the turtle. The smallest caliper possible is generally best. We typically measure in millimeters.
- To measure minimum straight carapace length, put one end of the caliper at the most anterior position of the cervical scute and the other at the farthest position on the posterior end of the carapace, notch to notch.
- To measure width at widest point, determine the widest point on the shell and measure from one side to the other. Make sure the caliper is perpendicular to an imaginary line drawn from the middle of the head of the turtle to the middle of the tail.
- To measure shell height, determine the tallest point of the shell from plastron to carapace. This measurement is important to describe the size of the dome on the turtle shell. Slide one end of the caliper under the turtle next to the plastron and bring down the other end at the tallest point on the carapace. For some turtles, dome shape may give an indication of the sex of the turtle
- To measure plastron length, put one end of the caliper at the most anterior position of the plastron and the other end at the farthest position on the posterior end of the plastron.
Using a digital caliper to measure the carapace length of a Painted Turtle.
Using a digital caliper to measure the plastron length of a Yellow-bellied Slider.
- If using a platform scale, place container on the platform, tare (zero) the scale, and then add the turtle. We measure mass in grams.
- If using a spring scale, the size of the spring scale depends on the mass of the turtle. The smallest scale possible is generally best. Make sure that the spring scale begins at zero.
- Tie loops at both ends of a small piece of rope to make a saddle for weighing turtles. The rope’s length and thickness depends on the size of the turtles.
- Hold the turtle low to the ground and wrap the saddle around the shell of the turtle. Insert one loop into another, tighten so the animal is secure, attach the other loop to the spring scale, and read the mass. Remove the turtle from the saddle to determine the saddle’s mass; subtract this from the first measurement.
Massing the turtle with a spring scale.
The HERP Project is conducting mark-recapture studies. This is indicated on the data sheets by “turtle code” and “new or recapture.” Mark-recapture population studies are conducted to determine the types and numbers of animals that are in a particular area, providing baseline data so that population changes can be monitored over time and over environmental changes that occur.
Filing the carapace so that this Painted Turtle will be recognized if caught again.
Metadata are data that provide information about other data. If a biological inventory or population study is being conducted, document the site location, trap location(s), and the day and time of each capture event. Also record total trap captures. Here is an example of the information that would need to be collected:
On June 15, 2017, we set 5 baited (sardines) traps in the Country Park Lake at 2 PM. The location of each trap is marked on our lake diagram [not provided here]. We retrieved the traps on June 16, 2017 at 10 AM. We found the following in each trap:
Trap 1: nothing was found
Trap 2: 3 Yellow-bellied Sliders (data collected on all)
Trap 3: 1 Yellow-bellied Sliders (data collected) and 1 large snapping turtle (released and no data collected)
Trap 4: 2 Musk Turtles and 5 fish (data collected on both turtles, fish released)
Trap 5: 1 Painted Turtle (data collected)
A Non-Trapping Option: Observing Basking Turtles
Select a pond, lake, or river to monitor. Basking turtles are most active in warm weather in the middle of the day. Upon arrival at the site, find a good position from which to observe. If some participants have binoculars, the search range can be wider. As participants observe turtles, have them describe to the rest of the group the distinguishing characteristics that identify this turtle species. Record the site’s GPS location.
Data Reporting to The HERP Project and HerpMapper
There are citizen science projects that provide a place to share findings. Species, location information, and pictures are needed to participate in this project. Through use of The HERP Project application (available for free download at http://theherpproject.uncg.edu/apps-collecting-data/), participants record data and upload it to an open source database found on The HERP Project website (http://nc-herps.appspot.com/). This enables us to compare our data with previous years, and we can our download data sets for further analysis. Data can be also uploaded to HerpMapper (https://www.herpmapper.org/).