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Southern Pacific Pond Turtle Project on the Kern River Preserve

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Capturing Turtles

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Turtles get a temporary new home

Gravid female, eggs and hatchlings

Biology of Southern Pacific Pond Turtles

Kern River Research Station Turtle Project

Male Southern Pacific Pond Turtle, notice the pale throat and thick tail.

A male hatching Southern Pacific Pond Turtle.

Female Southern Pacific Pond Turtle notice the thin tail and the spotted throat.

Photos courtesy Alison Sheehey NatureAli.org

  Winter 1997 Vol. 6, No. 1

 WESTERN POND TURTLES IN THE KERN VALLEY REGION

By 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. Dan 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.

Headstarting 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.

In 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 successfully.

Once 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.

Immediately 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.

The 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.

At 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.

A 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.

 Table 1. Pacific pond turtle Headstart Results at the Kern River Preserve by Year.

 Year         # of Gravid          # of Eggs          # Turtles        # Turtles
                Females                Incubated          Hatched         Released

  1992              4                         31                      23                  16
  1993              4                         21                      19                  19
  1995              5                         27                      18                  18
TOTAL            13                         79                      60                  53
 

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