Winter 1997 Vol. 6, No. 1
POND TURTLES IN THE KERN VALLEY REGION
Lynn Overtree and Gary Collings, Research Associates
The Pacific pond turtle, Clemmys marmorata,
is California's only freshwater turtle. The species ranges from southern British
Columbia through Washington, Oregon, California, and into northern Baja
California. It is listed as endangered in Washington and Oregon and as a species
of special concern in California. It has declined by an estimated 95 % since the
early 1900's. The primary cause of decline is loss of habitat -wetlands. The
secondary cause is predation of hatch-lings by non-native species, especially
bullfrogs and large-mouth bass.
Holland, as a Ph.D. student at Southwestern Louisiana University, surveyed the
South Fork Kern River Valley from 1986-1994 and found no evidence of hatchling
survival. This lack of recruitment of hatchlings to the population means that,
as adults die, the species will disappear from the valley. Holland encouraged us
to try a "headstart" program for the Pacific pond turtles.
is a process by which hatchlings are raised in captivity until they are large
enough to avoid predators and then are released to the wild, While it has been
successful with other species of turtles, previous attempts with Western Pond
Turtles had failed.
spring 1992, we began collecting gravid (pregnant) females that we found looking
for nest sites on land. With the guidance of Dr. Frank Slavins and Paul Cowell
at Woodland Park Zoo in Seattle, WA, the eggs were collected and incubated
the females are collected from the wild, they are x-rayed to determine how many
eggs they are carrying. Labor is induced with oxytocin. A local veterinarian,
Dr. Thomas Jenkins, donated all the services and medicine needed to induce egg
laying. The females are released at their capture site soon after the eggs are
laid. The eggs are then incubated in a dry substrate for 80-100 days. In other
studies, attempts to incubate in moist substrates had led to failure. The gender
of the turtles is not determined by genetics, but by the temperature of the eggs
during incubation. We incubate the eggs at a relatively high temperature in
hopes of encouraging more females than males.
after hatching, the young turtles are set in plastic tubs with water and small
logs. The hatchlings weigh about 5 grams (a paperclip weighs 1 gram). Hatchlings
are identified by painting a code on their scales along the edge of the shell
(marginal scutes) with nail polish. The hatchlings do not hibernate during the
first winter. The lab is kept warm thermostatically and incandescent lights
provide focused heat under which the turtles can bask. Vitalites and black
lights provide critical light spectrums to the turtles. The hatchlings are
offered a variety of food items, including tubiflex worms, earthworms,
mealworms, night crawlers, fish, beef heart, and plants.
ability to consume a high quantity of food throughout the winter permits fast
growth that would take two to three years in nature. By the next summer many
hatchlings are large enough to release into the wild. At 50 grams, their scutes
are filed for permanent individual identification and the turtles are placed in
an outdoor pond within a predator-free enclosure for at least one month to
confirm that they can maintain their weight.
70 grams, the hatchlings are ready to be released. All hatchlings are being
released at ponds on the Kern River Preserve. The release site has an existing
population of adult turtles, a known nest site, a variety of microhabitats, and
basking sites. The pond is isolated from human and livestock disturbance, and
annual drying of the ponds limits the bass population. Bullfrogs, however, are
common and are removed in an eradication effort.
one-time trapping effort in 1993 caught four of the 12 turtles that had been
released earlier that season. They all appeared healthy and had gained weight. A
mark and recapture study is planned for the future. This will give us further
information on the demographics of this population, as well as information on
the survival rate, condition of the released juveniles, and long-term success of
our Pacific pond turtle Headstart Program.
1. Pacific pond turtle Headstart Results at the Kern River Preserve by Year.
# of Gravid # of Eggs