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The Northwestern Pond Turtle (Actinemys marmorata) ranges from Washington to the southern end of the Central Valley of California. Because of the extensive latitudinal range of the species, it is expected that several life-history traits will vary across the range. Most data on population structure and growth of A. marmorata have been gathered from southern Oregon and California, and reproductive data are sparse north of the southern end of the range. These data are important to a critical understanding of the species' biology and especially for making conservation judgments for a species some consider in need of protection. Thus, we collected key life-history information at the Luckiamute State Natural Area in the mid-Willamette Valley, Oregon. We found that the population structure, adult size, and growth were similar to southern Oregon sites. Clutch size from radiographs was 6.0 ± 1.18 SE (range = 5–8), smaller than sites at the southern end of the range. The slow growth rate of Luckiamute turtles may be explained by cooler temperature in the Willamette Valley compared to more southerly sites. Still, Luckiamute adults reach a slightly larger size than most turtles in more southerly sites. It just requires many more years to reach sexual maturity and achieve larger sizes in northern areas. [ABSTRACT FROM AUTHOR]

Although necessary for humans, agriculture can negatively affect populations of other species through direct and indirect means. This is true even for aquatic turtles, which require terrestrial areas in which to nest. The western pond turtle (Actinemys marmorata ; sensu lato) has lost most of its habitat in the Central Valley of California, USA, to agricultural activities, flood control, and urbanisation. Although a few areas still support this turtle, most habitats are now altered by humans. In 1999 and 2009, I trapped western pond turtles at a remnant slough surrounded by irrigated agricultural fields in the San Joaquin Valley portion of the Central Valley. In 1999, I caught 123 turtles in 2 days of trapping (4.39 turtles/trap night) and in 2009 I caught 216 turtles in 4 days of trapping (4.15 turtles/trap night). Both sexes grew fast, similar to other sites in the San Joaquin Valley. I caught significantly more turtles ≤5 years of age in 2009 than in 1999, but significantly fewer large adults. In 2009, I X-rayed females and the mean clutch size was 7.4 (n = 7). Although activities and vegetative cover associated with agriculture can impact aquatic turtles, the population of western pond turtles at the slough were reproducing well, but the marked decline in the number of large adults is of concern for the long-term sustainability of this population. Agriculture is pervasive throughout the world and can negatively affect species. I compared population attributes of western pond turtles at an agricultural site from 1999 to 2009 and found higher numbers of young but significantly fewer large adults in 2009. Loss of large adults could be a conservation concern. [ABSTRACT FROM AUTHOR]

We studied the population structure and growth of western pond turtles (Actinemys marmorata) at Vandenberg Air Force Base along the coast of central California in April 1995 and June 1996. We captured 179 individuals (115 males, 27 females) from 7 ponds during 26 days of trapping. Many turtles were adult-sized, but based on scute annuli, 74% were , 10 years of age, including many 2- to 3-year-olds. This population structure likely was due to a relatively fast growth rate, especially compared with closely related aquatic turtles in eastern North America. Mean clutch size was 5.2, but 66.7% of females were gravid, and 1 female produced 2 clutches. These reproductive data are similar to those reported for other populations in the southern portion of the species' range. Females reached reproductive maturity as early as 4 years of age. The relatively mild temperatures of California's Mediterranean climate, especially when compared to the seasonal extremes in more continental and northern regions of North America, may explain the different growth rates and population characteristics of freshwater turtles from these 2 regions of North America. [ABSTRACT FROM AUTHOR]