Population dynamics and biological feasibility of sustainable harvesting as a conservation strategy for tropical and temperate freshwater turtles

Abstract

Background Conservation strategies are urgently needed for tropical turtles that are increasingly threatened by unsustainable exploitation. Studies conducted exclusively in temperate zones have revealed that typical turtle life history traits (including delayed sexual maturity and high adult survivorship) make sustainable harvest programs an unviable strategy for turtle conservation. However, most turtles are tropical in distribution and the tropics have higher, more constant and more extended ambient temperature regimes that, in general, are more favorable for population growth. Methods To estimate the capacity of temperate and tropical turtles to sustain harvest, we synthesized life-history traits from 165 predominantly freshwater turtle species in 12 families (Carettochelydae, Chelidae, Chelydridae, Dermatemydidae, Emydidae, Geoemydidae, Kinosternidae, Pelomedusidae, Platysternidae, Podocnemididae, Staurotypidae and Trionychidae). The influence of climate variables and latitude on turtle life-history traits (clutch size, clutch frequency, age at sexual maturity, and annual adult survival) were examined using Generalized Additive Models. The biological feasibility of sustainable harvest in temperate and tropical species was evaluated using a sensitivity analysis of population growth rates obtained from stage-structured matrix population models. Results Turtles at low latitudes (tropical zones) exhibit smaller clutch sizes, higher clutch frequency, and earlier age at sexual maturity than those at high latitudes (temperate zones). Adult survival increased weakly with latitude and declined significantly with increasing bioclimatic

Community based actions save Yellow-spotted river turtle (Podocnemis unifilis) eggs and hatchlings flooded by rapid river level rises

“…Although rigid eggshells can resist hydric changes, embryos are susceptible to changes in temperature associated with submersion. As P. unifilis only occurs within the tropics ( Norris et al, 2019 ; Rachmansah, Norris & Gibbs, 2020 ), temperature is likely to be a key determinant for the survival of all stages and it is unlikely that embryos have any adaptation to resist low temperatures such as those experienced under flowing rivers. The temperature range for successful incubation of P. unifilis nests is typically between 27–32 °C ( De Souza & Vogt, 1994 ; Ferreira Júnior & Castro, 2006 ; Páez & Bock, 1998 ; Páez & Bock, 2004 ).…”

“…Like many tropical species Amazonian freshwater turtles are threatened by deforestation (Fagundes et al, 2018), climate change (Eisemberg et al, 2016), and unsustainable exploitation (Rachmansah, Norris & Gibbs, 2020;Smith, 1979). Precautionary estimates suggest that populations of the once abundant Yellow-spotted river turtle (Podocnemis our results to discuss how management plans could include rescue of submerged eggs and premature hatchlings as part of species conservation and recovery actions.…”

“…Like many tropical species Amazonian freshwater turtles are threatened by deforestation ( Fagundes et al, 2018 ), climate change ( Eisemberg et al, 2016 ), and unsustainable exploitation ( Rachmansah, Norris & Gibbs, 2020 ; Smith, 1979 ). Precautionary estimates suggest that populations of the once abundant Yellow-spotted river turtle ( Podocnemis unifilis ) may experience severe (≥50%) and rapid (<50 years) future losses across 60% (5.3 M km 2 ) of the pan-Amazonian range ( Norris et al, 2019 ).…”

Peer Review #1 of "Community based actions save Yellow-spotted river turtle (Podocnemis unifilis) eggs and hatchlings flooded by rapid river level rises (v0.1)"

“…Manuscript to be reviewed Although rigid eggshells can resist hydric changes, embryos are susceptible to changes in temperature associated with submersion. As P. unifilis only occurs within the tropics Rachmansah et al 2020), temperature is likely to be a key determinant for the survival of all stages and it is unlikely that embryos have any adaptation to resist low temperatures such as those experienced under flowing rivers. The temperature range for successful incubation of P.…”

“…Like many tropical species Amazonian freshwater turtles are threatened by deforestation (Fagundes et al 2018), climate change (Eisemberg et al 2016), and unsustainable exploitation (Rachmansah et al 2020;Smith 1979). Precautionary estimates suggest that populations of the once abundant Yellow-spotted river turtle (Podocnemis unifilis) may experience severe (≥50%) and rapid (<50 years) future losses across 60% (5.3 M km 2 ) of the pan-Amazonian range (Norris et al 2019).…”