Factors affecting the density of populations of common snapping turtles (Chelydra serpentina serpentina)

Abstract

Density, biomass, and sex ratio were measured in two populations of snapping turtles (Chelydra serpentina) in Ontario in 1984 and 1985. The more southern population inhabited a nutrient-enriched pond at an unusually high density and biomass density (66/ha, 340 kg/ha), and exhibited a significantly male-biased sex ratio (1.96:1) but no significant sexual dimorphism in adult size. The northern population inhabited dystrophic or oligotrophic ponds at a low density (2.4/ha, 16 kg/ha), did not show a significant bias in adult sex ratio, but did have a strong sexual dimorphism in adult size, males having approximately twice the mass of females. A comparison among several populations indicated that density was negatively correlated with latitude and with surface area of suitable habitat. Density and biomass density were significantly higher in habitats of relatively high primary productivity, which tended to be at relatively low latitudes. Therefore, important proximal factors affecting density of these turtles are likely to be primary productivity and recruitment history. Differences in sex ratio and sexual dimorphism in size between the two Ontario populations did not support the hypothesis that the latter is due to sexual selection.