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

Community-Based Conservation and Management of Chelonians in the Amazon

Chelonians represent an important resource in the Amazon, either as a source of protein at the base of the food chain of aquatic and transition ecosystems, or in the dispersion of seeds of plants from floodplains and flooded forests. The consumption and predatory exploitation of their meat and eggs by local populations has been, and still is, one of the main threats to these animals. Community-based conservation projects allied to official protection programs have been restoring populations of chelonians of the genus Podocnemis throughout the Amazon since 1974. In this study, we analyzed the historical time series of protection data of Podocnemis expansa, P. unifilis, P. sextuberculata and P. erythrocephala in areas protected by the government and communities in the Amazonas state and northwest of Pará state. Between 1974 and 2019, 230,444 nests and 21,350,201 hatchlings of P. expansa, 170,076 nests and 3,229,821 hatchlings of P. unifilis, 647,715 nests and 6,410,092 hatchlings of P. sextuberculata and 24,617 nests and 168,856 hatchlings of P. erythrocephala were protected. Community protection schemes emerged in 1990, and covered 80.7% of the areas and produced 64.2% of P. unifilis hatchlings and 44.6% of P. sextuberculata hatchlings. The areas with the highest production of P. expansa remain under government protection (57.4%). Using the time series of production of nests and hatchlings per beach, logistic growth curves were estimated, and the values of r and K were compared between the two protection systems (government and community). Beaches controlled by the government showed higher support capacity in the production of nests (1,910.7 ± 1,035) and hatchlings (211,513 ± 93,031) of P. expansa and P. sextuberculata (81,160 ± 34,924 hatchlings). However, the communities were more efficient in protecting nests (r = 0.102 ± 0.2315) and hatchlings (r = 0.282 ± 0.166) of P. unifilis. Community-based protection and monitoring programs are an important component that should be incorporated by the government’s environmental agencies for the management and conservation of turtles in the Amazon.

Evaluating the effect of expert elicitation techniques on population status assessment in the face of large uncertainty

Population projection models are important tools for conservation and management. They are often used for population status assessments, for threat analyses, and to predict the consequences of conservation actions. Although conservation decisions should be informed by science, critical decisions are often made with very little information to support decision-making. Conversely, postponing decisions until better information is available may reduce the benefit of a conservation decision. When empirical data are limited or lacking, expert elicitation can be used to supplement existing data and inform model parameter estimates. The use of rigorous techniques for expert elicitation that account for uncertainty can improve the quality of the expert elicited values and therefore the accuracy of the projection models. One recurring challenge for summarizing expert elicited values is how to aggregate them. Here, we illustrate a process for population status assessment using a combination of expert elicitation and data from the ecological literature. We discuss the importance of considering various aggregation techniques, and illustrate this process using matrix population models for the wood turtle (Glyptemys insculpta) to assist U.S. Fish and Wildlife Service decision-makers with their Species Status Assessment. We compare estimates of population growth using data from the ecological literature and four alternative aggregation techniques for the expert-elicited values. The estimate of population growth rate based on estimates from the literature (λmean = 0.952, 95% CI: 0.87-1.01) could not be used to unequivocally reject the hypotheses of a rapidly declining population nor the hypothesis of a stable, or even slightly growing population, whereas our results for the expert-elicited estimates supported the hypothesis that the wood turtle population will decline over time. Our results showed that the aggregation techniques used had an impact on model estimates, suggesting that the choice of techniques should be carefully considered. We discuss the benefits and limitations associated with each method and their relevance to the population status assessment. We note a difference in the temporal scope or inference between the literature-based estimates that provided insights about historical changes, whereas the expert-based estimates were forward looking. Therefore, conducting an expert-elicitation in addition to using parameter estimates from the literature improved our understanding of our species of interest.

The evolution of reproductive strategies in turtles

Optimal egg size theory assumes that changes in the egg and clutch are driven by selection, resulting in adjustments for the largest possible production of offspring with the highest fitness. Evidence supports the idea that large-bodied turtles tend to produce larger clutches with small and round eggs, while smaller species produce small clutches with large and elongated eggs. Our goals were to investigate whether egg and clutch size follow the predictions of egg size theory, if there are convergent reproductive strategies, and identify ecological factors that influence clutch and egg traits across all clades of living turtles. Using phylogenetic methods, we tested the covariance among reproductive traits, if they are convergent among different turtle lineages, and which ecological factors influence these traits. We found that both egg shape and size inversely correlate with clutch size, although with different evolutionary rates, following the predictions of the egg size theory. We also present compelling evidence for convergence among different turtle clades, over at least two reproductive strategies. Furthermore, climatic zone is the only ecological predictor to influence both egg size and fecundity, while diet only influences egg size. We conclude that egg and clutch traits in Testudines evolved independently several times across non-directly related clades that converged to similar reproductive strategies. Egg and clutch characteristics follow the trade-offs predicted by egg size theory and are influenced by ecological factors. Climatic zone and diet play an important role in the distribution of reproductive characteristics among turtles.

Blanding's Turtle Demography and Population Viability

In anticipation of U.S. federal status classification (warranted, warranted but precluded, not warranted), scheduled for 2023, we provide population viability analysis of the Blanding's turtle Emydoidea blandingii, a long-lived, late-maturing, semi-aquatic species of conservation concern throughout its range. We present demographic data from long-term study of a population in northeastern Illinois and use these data as the basis for viability and sensitivity analyses focused on parameter uncertainty and geographic parameter variation. We use population viability analysis to identify population sizes necessary to provide population resiliency to stochastic disturbance events and catastrophes, and demonstrate how alternative definitions of ‘foreseeable future' might affect status decisions. Demographic parameters within our focal population resulted in optimistic population projections (probability of extinction = 0% over 100 y) but results were less optimistic when catastrophes or uncertainty in parameter estimates were incorporated (probability of extinction = 3% and 16%, respectively). Uncertainty in estimates of age-specific mortality had the biggest impact on population viability analysis outcomes but uncertainty in other parameters (age of first reproduction, environmental variation in age-specific mortality, percent of females reproducing, clutch size) also contributed. Blanding's turtle demography varies geographically and incorporating this variation resulted in both mortality- and fecundity-related parameters affecting population viability analysis outcomes. Possibly, compensatory variation among demographic parameters allows for persistence across a wide range of parameter values. We found that extinction risk decreased and retention of genetic diversity increased rapidly with increasing initial population size. In the absence of catastrophes, demographic conservation goals could be met with a smaller initial population size than could genetic conservation goals; ≥20–50 adults were necessary for extinction risk <5%, whereas ≥50–110 adults were necessary to retain >95% of existing genetic diversity over 100 y. These thresholds shifted upward when catastrophes were included; ≥50–200 adults were necessary for extinction risk <5% and ≥110 to >200 adults were necessary to retain >95% of existing genetic diversity over 100 y. Impediments to Blanding's turtle conservation include an incomplete understanding of geographic covariation among demographic parameters, the large amount of effort necessary to estimate and monitor abundance, and uncertainty regarding the impacts of increasingly frequent extreme weather events.

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

The conservation and recovery of increasingly threatened tropical freshwater turtle populations depends on effective management plans and actions. Here we show that community-based actions saved Yellow-spotted river turtle (Podocnemis unifilis) eggs submerged by unseasonal flooding and ensured the release of hatchlings. We recovered 926 eggs and 65 premature hatchlings from 74 submerged nests at 16 flooded nesting areas along 75 km of waterways. The rescued eggs were transferred to a rearing center and incubated. Hatchlings emerged from eggs that had remained underwater for up to two days. Hatchlings were maintained in 250–500 L nursery tanks until yolk sac scars had closed. Healthy hatchlings were then immediately released around the original nesting areas. We released 599 hatchlings (60.4%) from 991 submerged eggs and hatchlings. Egg survival (61.7% (571/926)) was substantially less than hatchling survival (94.2% (599/636)) but within the expected range of values reported for this species. These findings suggest that Yellow-spotted river turtle eggs and embryos are resistant to short-term submersion, which could help explain the widespread distribution of this species across highly seasonal Amazonian rivers. Management plans should take the possible survival of submerged eggs into consideration as part of species conservation and recovery actions.