Changes across a Decade in Size, Growth, and Body Condition of Western Pond Turtle (Actinemys marmorata) Populations on Free-flowing and Regulated Forks of the Trinity River in Northwest California

Abstract

Water diversions can disrupt flows and alter thermal regimes changing seasonal patterns that signal the onset of life-history functions of native organisms and compromise the fitness of their populations. We compared size, growth, relative mass, volumetric body condition, and reproductive status of Western Pond Turtles (Actinemys marmorata) across a decade on two forks of California’s Trinity River, one regulated and the other free-flowing. Turtles on the regulated fork experienced flows designed to accommodate anthropocentric demands, whereas those on the free-flowing fork experienced natural hydrologic cycles and seasonal warming. July water temperatures averaged 8.6°C colder on the regulated fork due to hypolimnetic releases. Turtles on the colder regulated fork grew more slowly and were smaller at similar ages compared with those on the free-flowing fork, a pattern that was exacerbated across the decade. Female relative mass (RM) across the decade did not differ between forks, whereas male RM was grea...