Decadal change in a population of western pond turtles at an isolated agricultural site in the San Joaquin Valley, California, USA

Abstract

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.