The Observation of a Red-Eared Slider

**In a Hydrology Study Site**

### Akira Ebisujima Kengo Isaki Tomoki Okada

Osaka Prefectural Higashisumiyoshi Technical High School

Japan

# **1.Abstract**

We selected our Hydrological Study Sites in both the *Ima-gawa* River
150 meters west of our school and in the *Yamato* River 1500 meters
south of our school. When we tested the water samples from these sites,
we often found red-eared sliders in the *Ima-gawa* River but seldom
found them in the *Yamato* River. Using the research methods of water
temperature and transparency according to GLOBE Protocols, line
censusing and marking-and-recapture method, we observed this turtle to
learn its behavior, population size at the site of the *Ima-gawa* River
and the reason why there are fewer red-eared sliders in the *Yamato*
River. We drew the following conclusions**:**

\(1\) Red-eared sliders at the site of the *Ima-gawa* River hibernate
when the water temperature drops below 10 degree centigrade.

\(2\) Using the marking-and-recapture method, about 100 red-eared
sliders are estimated to live at the site of the *Ima-gawa* River.

\(3\) The turbidity of the water in the *Yamato* River is much higher
than that of the *Ima-gawa* River. The high turbidity of the water
hinders the growth of the water plants in this area. Red-eared-sliders
are herbivorous as they grow into adults, and the Yamato River lacks the
food they need.

**2.Research Question/Hypothesis**

The red-eared slider, *Trachemys scripta elegans*, is native to the
United States, and a million red-eared sliders have been imported as
pets from the U.S. to Japan since the 1960's. So, we often found them in
the *Ima-gawa* River when we performed tests of the water samples from
this site, but seldom found them at the site of the *Yamato* River. We
decided to observe the dumped turtles as they adapted to their
circumstances.

We planned the following research:

(1) When do the red-eared sliders hibernate at the site of the
    *Ima-gawa* River?

> (In order to know the relationship between the water temperature and
> the hibernating behavior)

(2) How many turtles live at this site?

> (In order to estimate the population size of the red-eared sliders at
> the site of the *Ima-gawa* River)

(3) How much do the water temperatures and water transparency differ at
    the two sites?

> (In order to know the reason why there are fewer red-eared sliders at
> the site of the *Yamato* River)

**3.Research Method**

(1)We measured the temperature of water samples from the two sites
according to GLOBE Protocols.

(2)We measured water transparency using a turbidity tube. We tested
three samples and used the average of the measured values. The turbidity
tube we used was 1m in depth. If the bottom of the tube could be seen
when filled with the water sample we described it as being "over 100cm".

The temperature of the water sample was needed for studying the behavior
of the red-eared sliders, and to compare the water samples from the
sites of the *Ima-gawa* River and the *Yamato* River, so we could
discover why there are fewer red-eared sliders at the *Yamato* River.

(3)We used line censusing, in which we walked along the river at a
uniform velocity in order to count the number of individuals found in
this section.

Using this method, we learned the relation between the activity of the
turtles and the water temperature.

(4)We performed the "Marking-and-recapture method", in which we marked
the trapped turtles by making a small hole in the edge of their
carapace, and released them, then counted the number of recaptured
individuals.

Using this method, we were able to estimate the population size of the
red-eared sliders at the site of the *Ima-gawa* River.

**4.Data Summary**

**Table 1.** *Water Temperature and the Number of Turtles Found Using
the Line*

Censusing Method at the site of the Ima-gawa River.

+-----------------------------------------------------------------------+
| Number of                                                             |
|                                                                       |
| Air Water Number of Other Kinds                                       |
+-----------------------------------------------------------------------+

Date Temperature Temperature Red-eared sliders of Turtles

+-----------------------------------------------------------------------+
| \[degree \[degree                                                     |
|                                                                       |
| centigrade \] centigrade \]                                           |
+-----------------------------------------------------------------------+

11/06/02 10.5 12.0 0 3

11/15/02 12.0 14.0 13 1

11/22/02 14.5 14.0 4 0

12/02/02 11.5 10.0 16 0

01/09/03 8.0 9.5 2 0

02/05/03 6.5 8.0 1 0

02/26/03 11.0 10.5 1 0

03/13/03 - 11.5 11 0

03/27/03 - 18.5 13 0

  -----------------------------------------------------------------------
  The other kind of turtle was a reeves turtle*, Chinemys reevesii .*

  -----------------------------------------------------------------------

***Table 2.** The Number of Captured and Recaptured Red-eared sliders by
Marking --*and- recapture Method

+-----------------------------------------------------------------------+
| Total Number of                                                       |
|                                                                       |
| Number of Number of Marked Estimated                                  |
|                                                                       |
| Captured Recaptured Individuals Population Individuals Individuals    |
| Before Trap Set Size                                                  |
+-----------------------------------------------------------------------+

Sample Date n m s N

  -----------------------------------------------------------------------
  1^st^ 09/25/02 13 - - -

  -----------------------------------------------------------------------

2^nd^ 11/06/02 7 1 13 91

3^rd^ 12/03/02 15 3 19 95

4^th^ 01/10/03 1 1 31 -

5^th^ 03/14/03 11 4 31 85

6^th^ 04/08/03 8 4 38 76

+-----------------------------------------------------------------------+
| We estimated the population size of the red-eared sliders using the   |
| following equation:                                                   |
|                                                                       |
| N = s \* n / m , N,s,n,m are shown in Table 2                         |
+-----------------------------------------------------------------------+

For example, according to the data of the 1^st^ and 2^nd^ samples,

N = 13 \* 7 / 1 = 91

***Table 3.*** The Water Temperature and Water Transparency of the
Samples from Both Sites of the Ima-gawa River and Yamato River.

+---------+-------------+---------------+------------+----------------+
|         | Water       |               | Water      |                |
|         | Temperature |               | Tr         |                |
|         | of the site |               | ansparency |                |
|         |             |               | of the     |                |
|         | \[degree    |               | site       |                |
|         | c           |               |            |                |
|         | entigrade\] |               | \[cm\]     |                |
+---------+-------------+---------------+------------+----------------+
| Date    | The Yamato  | The Ima-gawa  | The Yamato | The Ima-gawa   |
+---------+-------------+---------------+------------+----------------+
| 0       | 22.0        | 27.0          | 53         | Over 100       |
| 9/25/02 |             |               |            |                |
|         | 20.5        | 24.0          | 29         | Over 100       |
| 1       |             |               |            |                |
| 0/02/02 | 18.5        | 21.0          | 86         | Over 100       |
|         |             |               |            |                |
| 1       | 20.0        | 22.5          | 12         | Over 100       |
| 0/09/02 |             |               |            |                |
|         | 18.0        | 23.0          | 60         | Over 100       |
| 1       |             |               |            |                |
| 0/16/02 | 14.0        | 17.0          | 81         | Over 100       |
|         |             |               |            |                |
| 1       | 12.0        | 14.0          | 87         | Over 100       |
| 0/23/02 |             |               |            |                |
|         | 11.2        | 14.0          | 84         | Over 100       |
| 1       |             |               |            |                |
| 0/30/02 | 11.5        | 11.5          | 59         | Over 100       |
|         |             |               |            |                |
| 1       | 12.5        | 10.0          | 82         | Over 100       |
| 1/13/02 |             |               |            |                |
|         | 5.0         | 5.0           | 66         | Over 100       |
| 1       |             |               |            |                |
| 1/20/02 | 5.0         | 9.5           | 79         | Over 100       |
|         |             |               |            |                |
| 1       | 3.5         | 4.5           | 18         | Over 100       |
| 1/27/02 |             |               |            |                |
|         |             |               |            |                |
| 1       |             |               |            |                |
| 2/04/02 |             |               |            |                |
|         |             |               |            |                |
| 1       |             |               |            |                |
| 2/11/02 |             |               |            |                |
|         |             |               |            |                |
| 0       |             |               |            |                |
| 1/08/03 |             |               |            |                |
|         |             |               |            |                |
| 0       |             |               |            |                |
| 1/29/03 |             |               |            |                |
+---------+-------------+---------------+------------+----------------+

The transparency of the water samples from *the Ima-gawa* River is
measured almost always over 100cm.

**5. Analysis**

(1) The relation of the water temperature and the activity of the red
    eared sliders:

> We often found red-eared sliders swimming in the water, but sometimes,
> basking in the sunshine on the water plants and on the banks of the
> river. As turtles are cold-blooded, they are sensitive to the changes
> of both air and water temperature. When the temperature dropped, the
> turtles burrowed into the sediment to be inactive. So, we could not
> observe them. (**Table 1**)

\(2\) The population size of red-eared sliders at the site of the
*Ima-gawa* River:

> We used the marking-and-recapture method to estimate the population
> size of the red-eared sliders at the site of the *Ima-gawa* River.
>
> This method can be used on the condition that the population size is
> unchanged. We learned that red-eared sliders are faithful to their
> home ranges, so we decided to use this method. The equation of the
> estimating population size is
>
> **N** = **s \* n** / **m** where **N** is the estimated population
> size
>
> **s** is the total number of marked individuals
>
> **n** is the number of captured individuals
>
> **m** is the number of marked-and-recaptured individuals
>
> The proportional equation is
>
> s / N = m / n
>
> So, N is read as follows
>
> N = s \* n / m
>
> We estimated the population size by using this equation. The numbers
> of population size are not exact, but we could make a rough
> estimate**. (Table 2)**

\(3\) We measure both the temperature and the transparency of the water
samples from the two sites according to GLOBE Protocols. The results of
the measurements are shown in **Table 3.**

We found the water temperature from the site of the *Ima-gawa* River was
higher than that from the site of the *Yamato* River almost every time
we tested it. The longer period of high water temperature gave the
red-eared sliders an advantage in their activities.

We also found the water transparency from the site of the *Ima-gawa*
River was much higher than that from the site of the *Yamato* River
every time we tested it. That is to say, the water of the *Yamato* River
has a high turbidity, so the sunlight could not reach the bottom of the
river. The growth of the water plants was hindered.

**6. Conclusions**

\(1\) Red-eared sliders at the site of the *Ima-gawa* River hibernate
when the water temperature drops below 10 degree centigrade. This is the
same temperature at which the red-eared sliders native to the U.S.
hibernate.

\(2\) Using the marking-and-recapture method, approximately 100
red-eared sliders are estimated to live at the site of the *Ima-gawa*
River.

\(3\) The turbidity of the water in the *Yamato* River is much higher
than that of the *Ima-gawa* River. The high turbidity of the water
hinders the growth of the water plants in this area. Red-eared-sliders
are herbivorous as they grow into adults; eating about 90% plant matter
and 10% animal matter. The *Yamato* River lacks the food they need.

**7. Discussion**

Red-eared sliders are one of the most popular turtles kept as pets. This
is obvious since five to ten million turtles have been exported around
the world. In Japan juvenile red-eared sliders were imported and sold at
pet shops. Some of their purchasers released them in rivers or ponds.
They felt it was difficult to breed adult sliders as they became fierce.
Red-eared sliders dumped at the *Ima-gawa* River succeeded in the
establishment of a colony. Why?

The *Ima-gawa* River runs through Osaka city which is densely populated.
The land is covered with concrete and asphalt that increase its
temperature. The water temperature of the *Ima-gawa* River is higher
than that of the *Yamato* River which runs through a suburban area. This
non-native turtle seems to prefer the urban ecosystem.

The reeves turtle, which is native to the far east including Japan, was
occasionally found when we performed line censusing. Is the relationship
of red-eared sliders and reeves turtles competitive? Do the red-eared
sliders at the *Ima-gawa* River push out the native turtles? We can't
precisely answer this question at this point..

But we hear that non-native turtles such as snapping turtles and
alligator snapping turtles were sometimes found at rivers and ponds in
Japan. We can say "Don't release your breeding non-native turtles. They
will be harmful to native turtles and will disturb the ecosystem
inhabited by many living things."

**8. Bibliography**

Odum,Eugene P.1970 *Fundamentals of Ecology, third edition.* Saunders
Co.166pp.

Grijalva, Lynna.2001.*The Biogeography of the Red-Eared
Slider*(*Trachemys scripta elegans*)

\[On-line\]. San Francisco State University Department of Geography.
Available:

[http://bss.sfsu.edu:224/courses/Fall01%20projects/reslider.htm](http://bss.sfsu.edu:224/courses/Fall01 projects/reslider.htm)
\[10/16/2002\]