Population Dynamics and Biological Feasibility of Sustainable Harvesting as a Conservation Strategy for Tropical and Temperate Freshwater Turtles

Abstract

18Background: Conservation strategies are urgently needed for tropical turtles. Studies conducted 19 exclusively in the temperate zone have revealed that the suite of life history traits that 20 characterizes turtles and includes delayed sexual maturity and high adult survivorship makes 21 sustainable harvest programs an unviable strategy for turtle conservation. However, most turtles 22 are tropical in distribution and the tropics have higher, more constant and more extended ambient 23 temperature regimes that, in general, are more favorable for population growth. 24 Methods: To estimate the capacity of freshwater turtle species from temperate and tropical 25 regions to sustain harvest we synthesized life history traits from 165 freshwater turtle species in 26 12 families (Carettochelydae, Chelidae, Chelydridae, Dermatemydidae, Emydidae, 27 Geoemydidae, Kinosternidae, Pelomedusidae, Platysternidae, Podocnemididae, Staurotypidae 28 and Trionychidae). The influence of climate variables and latitude on freshwater turtle life 29 history traits (clutch size, clutch frequency, age at sexual maturity, and annual adult survival) 30were examined using Generalized Additive Models. The biological feasibility of sustainable 31 harvest in temperate and tropical species was evaluated using a sensitivity analysis of population 32 growth rates obtained from stage structured matrix population models. 33Results: Turtles at low latitudes (tropical zones) exhibit smaller clutch sizes, higher clutch 34 frequency, and earlier age at sexual maturity than those at high latitudes (temperate zone). Adult 35 survival increased weakly with latitude and declined significantly with increasing bioclimatic 36 temperature (mean temperature of warmest quarter). A modeling synthesis of these data indicates 37 that the interplay of life history traits does not create higher harvest opportunity in adults of 38 tropical species. Yet we found potential for sustainable exploitation of eggs in tropical species. 39 Conclusions: Sustainable harvest as a conservation strategy for tropical turtles appears to be as 40 biologically problematic as in temperature zones and likely only possible if the focus is on 41 limited harvest of eggs. Further studies are urgently needed to understand how the predicted 42 population surplus in early life stages can be most effectively incorporated into conservation 43 programs for tropical turtles increasingly threatened by unsustainable exploitation, climate 44 change and deforestation.45 46 47Vertebrate animals are important for human welfare and wellbeing 1-3 , particularly as food, 48 medicine, and cultural uses by rural and aboriginal communities 3-6 . Freshwater turtles are a good 49 example -they are frequently targeted for both subsistence and commercial harvest, primarily 50 by local communities that live in the vicinity of river and wetlands 7-9 . High biomass 10,11 , ease of 51 capture, and extended survival with minimal care in captivity make freshwater turtles a focus for 52 harvest 7-9 . 53Unsustainable harve...