Population structure, life history, and terrestrial movements of western pond turtles (Actinemys marmorata) in lentic habitats along the Trinity River, California

Thesis (M.S.)--Humboldt State University, Biological Sciences, 2012As populations of a species decline, an understanding of habitat use and regional variation in population health can aid in focusing conservation efforts. Western Pond Turtle (Actinemys marmorata) populations have declined throughout much of their range as a result of habitat loss, overexploitation, introduced species, and water course alterations. The Trinity River, in northwestern California, has been modified from its natural state by damming and flow regulations; these alterations have decreased river quality for turtles. I investigated the health of Western Pond Turtle populations in lentic sites adjacent to the Trinity River and its tributaries using four indicators of population health: 1) age structure, 2) size structure, 3) body size, and 4) growth rate of young turtles. Of six lentic sites sampled, four were biased towards large, old turtles. These sites had prolific Bullfrog populations, while the other two sites lacked Bullfrogs. Given that Bullfrogs will eat hatchling turtles, Bullfrogs likely are inhibiting turtle recruitment. The four lentic sites with Bullfrogs also had turtles with faster growth rates and larger sizes, likely a result of warmer water temperatures. I also used radio telemetry to monitor the terrestrial movements of turtles within a complex of lentic habitats along the Trinity\ud iv\ud River. The majority of turtles used multiple aquatic resources within a year, indicating that their home range can include multiple water bodies separated by upland habitat. Overall, conservation efforts should focus on creating or preserving aquatic habitats free of Bullfrogs, and terrestrial corridors for turtles to move between them