Nest removal by humans creates an evolutionary trap for Amazonian freshwater turtles

Abstract

Nest‐site selection exerts a fundamental maternal effect on offspring fitness in oviparous species. In many freshwater turtles, females do not care for their eggs after oviposition but rather rely on a nest's micro‐environment to incubate developing embryos although linkages between oviposition choices and overall fitness remain poorly evaluated. We tested predictions derived from multiple hypotheses to examine nesting patterns of the yellow‐spotted river turtle Podocnemis unifilis, a species imperiled by egg harvesting by humans throughout its range, based on data collected from 73 nesting sites along 118 km of river in the eastern Brazilian Amazon. Nesting area size largely explained nest‐site selection by turtles, but only weakly explained turtle egg harvesting by humans. Despite the wide availability of alternative nesting habitats, turtles do not appear to be capable of avoiding hazardous nesting sites associated with increased egg harvesting by humans. Because signals used by female turtles to select nesting areas are apparently not sufficient for avoiding nesting along rivers accessible to humans, direct conservation action will be vital for persistence of these and likely other Amazonian freshwater turtles.

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

“…Additionally, increasing survival of early stages via community-based protection of turtle nesting beaches has been shown to provide conservation success for local communities [94], target species [94][95][96][97] and also non-target vertebrate and invertebrate taxa [96]. Whilst promising, these results come from species of the South American Podocnemididae (P. expansa and P. unifilis) that remain widely distributed and nest in areas that are both relatively accessible and easy to find for humans [98] i.e. multiple females will lay nests in the same area [94][95][96][97].…”

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 2005; Escalona & Fa 1998;Ferreira Júnior & Castro 2010). Additionally, previous studies show that human harvest is also a major cause of nest loss in our area (Norris et al 2018b;Quintana et al 2019). As such the release of hatchlings from over half of the submerged eggs (that would otherwise have suffered 100% loss) is within the expected survival of natural nests.…”

“…1). Nesting of Podocnemis unifilis has been monitored since 2011 in the study area and here we present a brief summary of the previously described study area and P. unifilis nesting areas (Michalski et al 2020;Norris & Michalski 2013;Norris et al 2018a;Norris et al 2018b;Quintana et al 2019). Climate in the area is characterized as equatorial monsoon (Kottek et al 2006) with an annual rainfall greater than 2000 mm.…”

“…As part of a collaborative monitoring scheme with the local community, we monitored P. unifilis nesting areas from September to December 2018. This is a representative subset of the available nesting areas described previously (Norris et al 2018a;Quintana et al 2019) that were chosen in 2018 to encompass broad gradients (environmental and anthropogenic) and include areas with the majority of nests (including nesting areas with >90% nests recorded in previous years). Nesting areas were visited at least once a month to search for turtle nests and to monitor conditions of nests that were individually marked with a small stick.…”

“…Nesting areas were visited at least once a month to search for turtle nests and to monitor conditions of nests that were individually marked with a small stick. Nests were located by following turtle tracks on the sandy/gravel substrates and systematic substrate searches with blunt wooden sticks and fingertips (Escalona & Fa 1998;Norris et al 2018a;Quintana et al 2019). Searches were conducted by teams of two to three observers along lengthwise transects throughout each area at a standardized speed (mean 0.8, range 0.2 -1.3 km per hour); time spent searching nesting areas ranged from 10 to 97 minutes depending on the size of the area (Norris et al 2018a).…”