Tracking Turtles
Rondeau
Provincial Park and Rondeau Bay are home to one of the few remaining
populations of Eastern Spiny Softshell turtles in Ontario. These turtles are unique
in that their shell is soft and leathery rather than hard and rigid like most other
turtles. The shell is quite flat, and brown to olive in colour with numerous
blotches. The blotches on males and juveniles are darker than the
overall shell colour and have a solid dark margin around them. On females the
blotches become lighter in colour and the margins fade and become incomplete as
they reach maturity. The “spiny” part of this turtles name comes from a series
of short spines found along the front edge of the shell.
The
Eastern Spiny Softshell is listed as Threatened by the Committee on the Status
of Endangered Wildlife in Canada (COSEWIC) and the Ministry of Natural
Resources, and has a fragmented distribution within the province. It is found
throughout most of the eastern United States, but is at the far northern extent
of its range in Ontario. Aside from Rondeau Bay, softshells can be found in the
Thames and Sydenham Rivers and in the Long Point Region.
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| From The Rondeau Watershed |
Previous studies within Rondeau Bay have indicated
that the south point of Rondeau Provincial Park is a significant nesting area
for softshells, and one of only a few locations in Ontario where there is
significant nesting success. Although a substantial amount of research had been
done on the nesting biology of this species at Rondeau, we knew little about
the species habits and range during the remainder of the year. For this reason,
a radio telemetry study was implemented in 2003. The goal of the study is to determine the daily,
seasonal and annual movements of Eastern Spiny Softshell turtles within Rondeau
Bay and surrounding Lake Erie (if they leave the Bay). Specifically, we wanted to
determine:
¨
Where softshells go during the summer – their
overall home range within Rondeau Bay and area, and any areas of concentration
¨
The extent to which these turtles are at risk to
boat collisions or other human induced risks and how we might be able to reduce
those threats
¨
Where softshells hibernate and whether hibernation
sites are adequately protected
How Did
We Do This?
Radio
tracking is done by attaching a small radio transmitter to the shell of each
turtle.
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| From The Rondeau Watershed |
The transmitter emits a constant signal that can be detected
by a receiver. Each transmitter works
on a different frequency which is set on the receiver when you want to find
that turtle. As you get closer to the turtle, the signal on the receiver gets stronger.
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| From The Rondeau Watershed |
During
the spring and early summer of 2003, biologists at Rondeau searched south
beach, the marsh and the shallow areas of the bay for softshells. Four male
softshells were captured along the edge of the marsh and four females were
captured on south beach after laying their eggs. Each of the turtles was then
tracked throughout the summer and fall. Every time a turtle was re-located, its
location was recorded and a description made about the location - such as water depth, water temperature and
the bottom substrate (mud, gravel, sand).
Turtles were tracked regularly until late fall when ice began to form and we could not travel by boat. We wanted to determine where the turtles were hibernating though, so in February 2004, when the ice was safe to travel on, we relocated some of the turtles. Once each turtle was located a hole was drilled in the ice as close to each turtle as could be determined using the radio telemetry equipment. Once the hole was drilled, we attempted to see the turtles by looking down through the hole. We placed a tarp over top of ourselves to try and reduce the amount of sunlight that was shining down the hole. All four of the turtles that we re-located were found in approximately 2m of water. We could clearly see the bottom, but could not see any turtles! Finally we did see the antenna from the radio transmitter of one of the turtles, which meant that the turtles had buried themselves beneath a few cm of sand. All four of these turtles were found within a very small area of less than one hectare.
What have we learned so
far?
Basking Habits
During
the early part of the season male softshells spent a great deal of time along
the edge of the marsh or the small islands out from the marshh. Quite often
they were associated with small mud flats. In these locations the turtles would
bury themselves under 2-5 cm of black mud. In some instances the radio antenna
could be seen above the mud, but in other instances nothing would be visible.
Without the radio transmitter they would have been impossible to find! The
reason for this behaviour appears to be related to basking, as the temperature
under the black mud was generally higher than the adjacent air temperature.
Females were not observed basking in this manner, but were seen basking on top
of mud flats (exposed) on one or two occasions. Females were not captured until
later in the season, however, and by the time females were captured males were
no longer basking in this manner either. Thus we are not certain whether
females basked in this manner earlier in the season. In 2004 further studies
will be done to investigate this habit, including the temperature benefit,
average temperature (air and water) when they stop basking in this manner, and
whether the females also bask in this manner.
Weed Mats
Once
the bay had warmed up, all of the turtles left the shoreline areas and tended
to spend the majority of their time in areas quite distant from shore. As the
summer progressed it became apparent that all of the softshells were utilizing
the extensive weed mats that formed in the middle of the bay. Other softshells
were occasionally observed basking on top of the weed mats, along with large
numbers of Map Turtles.
The
reason for this association with the weed mats is not yet clear, however, the
weed mats could provide cover, increased prey availability and warmer water
temperatures. Preliminary temperature
studies showed that water temperatures within the weed mats were often slightly
higher than in the adjacent open water areas. Further investigations into why
turtles utilize the weed beds will be conducted in 2004.
Overall Movement Within
Rondeau Bay
The
softshell’s tagged during this study utilized a large proportion of Rondeau
Bay. Males were all captured along
the edge of the marsh and females were all captured on south beach. Throughout
the summer, however, all of the tagged individuals traveled long distances
throughout Rondeau Bay. Overall north-south range in the bay ranged from 4-6 km
for the various tagged turtles. This distance is very large in comparison to
studies of softshells in stream environments, but only slightly larger than
that found by researchers studying softshells in Lake Champlain
(Quebec/Vermont).
All
of the female turtles followed a similar pattern of movement within the bay. As
the summer progressed, they all moved further and further north in the bay and
spent all of their time in the weed mats. The females were fairly spread out,
but all were in the north end of the bay. At the end of September, however, all
of the females moved to the south end of the bay and by October 7, all four
females were located within 50-100 meters of one another, and remained there
for the winter. All four remained in hibernation until late
April.
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| From The Rondeau Watershed |
We
were quite amazed to find all four of our tagged females hibernating in the
same location in the bay. In 2004 we hope to learn more about that particular
location in the bay and why it might be so important to the turtles for
hibernation.
It
is quite interesting to find out that Eastern Spiny Softshells in Rondeau Bay
do not appear to leave the bay itself. Other studies of softshells in lake environments
found that the turtles had small summer ranges, but moved significant distances
to hibernation sites. This is a good indication that Rondeau Bay is able to
provide all of the environmental conditions that they require on a year-round
basis, increasing the importance of protecting the bay itself for this rare and
interesting reptile.
Generous
funding for this project has been provided by the following organiztions:
- SWISH Environmental
Fund
- The Canada Ontario
Agreement (COA)
- OMNR Species at
Risk Funding
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