click on the photos below for captions and a slide show.
A baseline population study conducted by Wildlife Biologist Jeff Alvarez in 2009 revealed that some 90 to 120 adult western pond turtles depend on habitat provided by MVSD’s Moorhen Marsh. This 21-acre freshwater wetland was constructed in the 1970s to provide valuable aquatic habitat for native fish and wildlife. The marsh receives 1.2 million gallons daily of advanced secondarily treated effluent as its primary water source.
In 2011, MVSD recognized that to provide the best wildlife habitat possible, a new Management Plan was required for Moorhen Marsh. The plan was completed in 2013 and identified the need for pond dredging and levee stabilization. Kelly Davidson, District Biologist for MVSD, was concerned about how such activities would affect the pond turtle population. She wanted to know how the turtles were using the habitat throughout the year. Were they breeding and nesting on site? Were they overwintering in the ponds, on land, or off site? How the turtles used the wetland throughout the seasons would determine how and when the dredging, levee work, and other maintenance and enhancement activities would proceed. The best way to figure out what the turtles were doing, and when they were doing it, was a telemetry study.
The first attempt to answer some of these questions began in 2012. With grant funding from the Contra Costa Fish and Wildlife Committee, MVSD purchased five very high frequency (VHF) radio telemetry units to monitor the turtle’s activity. However, this method did not prove as successful as hoped, as the VHF units used to tag turtles proved unreliable. Though significantly more expensive, GPS is a more effective and efficient form of tracking compared with the VHF units, as long as the turtle is big enoughto carry the added weight of the larger GPS unit. Fortunately, Moorhen Marsh is home to some very large turtles!
Fisheries and Wildlife Biologist Bert Mulcahey at East Bay Municipal Utility District generously offered to loan MVSD the first five GPS units. These units were placed on one male and four female turtles in May and June of 2013. An additional four GPS units were placed on female turtles in May of 2014.
Thanks to the ongoing study, MVSD now knows that turtles are in fact, nesting in the limited upland habitat of the marsh. Sixteen pond turtle nests were detected in 2013 and 21 nests were found in 2014. Because female turtles do not incubate or tend to the nest after the eggs are laid, predation of nests is very common. Unfortunately, many of the nests in Moorhen Marsh were predated.
Through intense monitoring efforts, MVSD biologists and consultants were able to find five actively nesting females in June and July of 2014. To protect nests from predators, they were covered with special cages designed to allow hatchlings to get out once they emerged. The nests are incubated by the sun, and viable eggs could hatch in 80-100 days. Interestingly, most of the hatchlings will remain sequestered in the nests over the fall and winter and will not emerge until spring of the following year. For more information on turtle nest predation in Moorhen Marsh, CLICK HERE to read a short article published in the Herpetological Review.
The Western Pond Turtle was recently separated into two species, the Northern Pond Turtle (Actinemys marmorata) and the Southwestern Pond Turtle (Actinemys pallida). The southwestern pond turtle is in serious decline throughout its range, which likely includes Contra Costa County. Soon, MVSD hopes to determine which species calls Moorhen Marsh home. Check this site regularly for more updates on this and other aspects if the study!
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