Many of the world’s turtle species have experienced population declines as commercial harvest pressure has increased to meet international market demand. Chinese consumption is considered the primary threat to global turtle populations following shifts from domestic harvest to international import. In the United States (US) demographic studies of turtle populations, after decades of commercial harvest, have been lacking. In the last 15 years snapping turtle (Chelydra serpentina) populations have experienced an exponential increase in the number of turtles harvested from US waters. To assess the current state of snapping turtle populations in Virginia we conducted a mark-recapture study in three waterways, each of which has historically experienced different levels of commercial harvest pressure. Using the robust design within Program MARK we estimated adult populations (greater than 20.32 cm curved carapace length (CCL)) for each river. We then constructed a 12 by 12 hybrid age/stage density-independent deterministic matrix model using demographic rates collected from this study and the literature to assess population response to recent harvest levels and to identify those life stages most critical to population viability.
Results/Conclusions
Over the duration of this study 181 snapping turtles were captured, marked, and released. Twenty-three were later recaptured, measured, and released for a recapture percentage of roughly 13%. The top model selected within Program MARK, based on model likelihood and AIC weight, is constant over the study period for survivability and immigration/emigration with capture and recapture probabilities varying over time depending on year. Mean population estimates for each site (in turtles per hectare) from this model are as follows: low harvest site 9.35 (±11.44SD), moderate harvest site 2.75 (±2.94SD), and high harvest site 2.5 (±3.46). Under recent harvest levels the matrix model predicts that only the no harvest site population is viable with a projected growth rate of 4% per annum. Both the moderate harvest and high harvest sites are projected to experience population declines of 2% and 6% per annum respectively. Sensitivity analyses indicate that for the no harvest site that legally harvestable adults (27.95 cm to 40.64 cm CCL) are most critical to population persistence and most in need of conservation. While these findings are preliminary the early indications are that the portion of the population most critical to overall viability are those individuals targeted for removal by current harvest size regulations. Without restricting harvest on larger mature adults (>27.95 cm CCL) the long term viability of these populations is in question.