Magdalena River turtle

Magdalena River turtles are iteroparous.[4] Males sexually mature at 3–4 years old, while females mature at 5–6 years old.[5] Females nest in the sandy riverbanks that result from areas of shallow water.[7] There are two nesting seasons: December–January and June–July.[7] It is unclear if individual females nest during both seasons in the same year.[3] Higher egg counts are observed in the June–July nesting season.[7] While average egg weight is significantly greater in the December–January nesting season.[7] Therefore, researchers have proposed it is equally vital to protect both seasons, as egg weight is positively correlated to hatching weight.[7] Average clutch size is 22 eggs.[3] The embryos within the eggs have temperature-dependent sex determination.[9] The species' pivotal temperature (T_piv), incubation temperature that produces 1:1 sex ratio, is 33.4 °C.[9] Incubation temperatures below the pivotal temperature produce a greater percentage of male hatchlings, while temperatures above produce a greater percentage of female hatchlings.[9] Concerns have been raised about the effects of climate change on this evolved developmental strategy.[9]

Among freshwater turtles, podocnemidids have among the longest aquatic migratory patterns, rarely leaving the water except to bask.[6] Their average home range spans between 0.3 to 14.6 ha.[5] Movement patterns are predicated on sex, body size, food availability, habitat quality, season, reproductive status, and life stage.[6] Seasonal movements are most prominent due to changing water levels.[6] Research has shown increased movement to deeper waters, likely as a result of climate change.[9]

As of 2018, 37% of all freshwater and terrestrial turtle species found in Colombia were classified as "Threatened".[10] Despite legislation passed in 1964 aimed at protecting these species (Ministry of Agriculture Resolution No. 0214-1964), their populations have continually decreased.[10] While many anthropogenic factors have contributed to the decline of Magdalena River turtles, over-harvest and climate change are the most prominent.[4] Over-harvest results from human demand for Magdalena River turtle consumption.[3] Locals believe that feeding on the turtles offer many medicinal qualities.[3] These include easing pregnancy recovery, curing diseases, boosting strength and longevity, and creating natural aphrodisiacs.[3] Climate change has led to discernible changes in temperature-dependent sex determination and movement patterns.[9][6] It has also contributed to nesting site flooding and other habitat alterations.[6]

While anthropogenic causes are most pronounced, several life history factors contribute to the Magdalena River turtles endangerment, as well.[4] High rates of mortality are seen in eggs, hatchlings, and juveniles.[4] Despite their high rates of survival as subadults and adults, their slow, r-selected growth means it takes a while for those stages to be reached.[4] They also require multiple habitats, one for nesting and another for feeding, which result in strenuous migrations.[4]

The most commonly used conservation approach for Magdalena River turtle conservation is "head-starting".[3] However, research efforts have been focused on finding more effective means on conservation, as understanding of the turtles' endangered nature is relatively novel.[10][5] A study that compiled 16 ecological knowledge criteria of Colombian freshwater and tortoise species suggested that the Magdalena River turtle should receive top conservation priority.[11] Studies are applying faster demographic modeling and surveying to better understand the species and establish practical conservation efforts.[4][10] Faster demographic modeling of the species' vital rates is focused on analyzing the contributions of each life stage and intrinsic growth rates (r).[4] Surveying has shown that local Magdalena River turtle consumption habits have changed and knowledge of their ecological role has improved.[10] This suggests that community-based strategies, including distribution of educational material, is proving effective in the conservation effort of Magdalena River turtles.[10]