Abundance and harvest proportion of river turtles in Missouri

Abstract

Freshwater turtle populations are declining worldwide, yet managers have little information about the effects of commercial turtle harvests. In Missouri, the snapping turtle (Chelydra serpentina), smooth softshell (Apalone mutica), and spiny softshell (Apalone spinifera) are harvested commercially in the Missouri River. In 2011 and 2012, we conducted markrecapture of these species to estimate abundance on the Missouri River and two unharvested tributaries, the Osage and Gasconade Rivers. We conducted mock harvests, applying capture methods of the state's primary commercial harvester, to estimate plausible expected harvest proportions. Snapping turtle abundance per 2 km was lower at harvested units (X = 15; SE = 7.1; unharvested: X = 90; SE = 40.3). Smooth softshell abundance was greater at harvested units (X = 59; SE = 7.9; unharvested: X = 14; SE = 28.1), although the difference was not significant. Mean unique spiny softshell captures were similar at harvested (X = 18; SE = 4.3) and unharvested (X = 17; SE = 9.7) units. Expected harvest proportions averaged 23% across species (SE = 5%; range = 6%-79%), exceeding sustainable rates reported for turtles. Our results suggest that on a small scale, using these methods, harvesters can remove a substantial portion of river turtle populations.