Demographics of Common Snapping Turtles (Chelydra serpentina): Implications for Conservation and Management of Long-lived Organisms

Abstract

SYNOPSIS. A study of common snapping turtles conducted from 1975 through 1992 in southeastern Michigan provided sufficient demographic data to examine how life history characteristics may constrain population responses of long-lived organisms. Females reached sexual maturity between 11 and 16 years of age. Minimum reproductive frequency was less than annual (0.85), and nest survivorship over 17 years ranged from 0 to 64% and averaged 23%. Survivorship of yearlings had to be estimated since hatchlings can pass through the mesh on traps. Actual survivorship of juveniles was over 0.65 by age 2 and averaged 0.77 between the ages of 2 and 12 years. Annual survivorship of adult females ranged from 0.88 to 0.97. A life table for the population resulted in a cohort generation time of 25 years. Population stability was most sensitive to changes in adult or juvenile survival, and less sensitive to changes in age at sexual maturity, nest survival or fecundity. An increase in annual mortality of 0.1 on adults over 15 years of age with no density-dependent compensation would halve the number of adults in less than 20 years. The results from the present study indicate that life history traits of long-lived organisms consist of co-evolved traits that severely constrain the ability of populations to respond to chronic disturbances. Successful management and conservation programs for long-lived organisms will be those that recognize that protection of all life stages is necessary. Without protection of adults and older juveniles, programs that protect nests and headstart hatchlings have a low probability of success. Carefully managed sport harvests of turtles or other long-lived organisms may be sustainable; however, commercial harvests will certainly cause substantial population declines