The Magdalena River turtle or Rio Magdalena river turtle (Podocnemis lewyana) is a species of turtle in the family Podocnemididae,[3] which diverged from other turtles in the Cretaceous Period, 100 million years ago.[4] It is endemic to northern Colombia, where its home range consists of the Sinú, San Jorge, Cauca, and Magdalena river basins.[5]
| Magdalena River turtle | |
|---|---|
,_Medellin.jpg) | |
| From Medellin, Colombia | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Testudines |
| Suborder: | Pleurodira |
| Family: | Podocnemididae |
| Genus: | Podocnemis |
| Species: | P. lewyana |
| Binomial name | |
| Podocnemis lewyana Duméril, 1852 | |
 | |
| Range in red | |
| Synonyms | |
|
Podocnemis coutinhii Göldi, 1886 | |
The species has been classified as "Critically Endangered" by the IUCN in 2015 and is considered the most threatened species of the family Podocnemididae.[6][7] In less than 25 years, the species exhibited a population decline of over 80%.[4] The decline is attributed to habitat destruction, pollution, over-harvest, commercial exploitation, hydrological changes due to electrical generation facilities, and climate change.[5] While early conservation attempts were unsuccessful or unenforced, there has been a resurgence in studies aimed at discovering the most effective approaches.[8]
Description
Magdalena River turtles exhibit sexual dimorphism.[9] Both males and females have a shell composed of shield-like plates that are primarily brown in color.[4] Their necks extend to a robust head.[4]
Males have grayish-brown head scales, while females display head scales more reddish-brown in color.[9] Adult males, on average, weigh 1.6 kg and measure 24.6 cm in carapace length.[6] Whereas females, on average, weigh 5.6 kg and measure 37 cm in carapace length.[6]
The species is regarded as having a mostly herbivorous diet, however opportunistic insectivorous behavior has been observed.[9] At times, juveniles pursue piscivorous behavior.[9] Average life span is 10–15 years in the wild.[6]
Ecology
Reproduction
Magdalena River turtles are iteroparous.[5] Males sexually mature at 3–4 years old, while females mature at 5–6 years old.[6] Females nest in the sandy riverbanks that result from areas of shallow water.[8]
There are two nesting seasons: December–January and June–July.[8] It is unclear if individual females nest during both seasons in the same year.[4] Higher egg counts are observed in the June–July nesting season.[8]
While average egg weight is significantly greater in the December–January nesting season.[8] Therefore, researchers have proposed it is equally vital to protect both seasons, as egg weight is positively correlated to hatching weight.[8]
Average clutch size is 22 eggs.[4] The embryos within the eggs have temperature-dependent sex determination.[10] The species' pivotal temperature (Tpiv), incubation temperature that produces 1:1 sex ratio, is 33.4 °C.[10] Incubation temperatures below the pivotal temperature produce a greater percentage of male hatchlings, while temperatures above produce a greater percentage of female hatchlings.[10] Concerns have been raised about the effects of climate change on this evolved developmental strategy.[10]
Movement
Among freshwater turtles, podocnemidids have among the longest aquatic migratory patterns, rarely leaving the water except to bask.[7] Their average home range spans between 10.3 and 14.6 ha.[6] Movement patterns are predicated on sex, body size, food availability, habitat quality, season, reproductive status, and life stage.[7]
Seasonal movements are most prominent due to changing water levels.[7] Research has shown increased movement to deeper waters, likely as a result of climate change.[10]
Conservation
Threats
As of 2018, 37% of all freshwater and terrestrial turtle species found in Colombia were classified as "Threatened".[11] Despite legislation passed in 1964 aimed at protecting these species (Ministry of Agriculture Resolution No. 0214-1964), their populations have continually decreased.[11] While many anthropogenic factors have contributed to the decline of Magdalena River turtles, over-harvest and climate change are the most prominent.[5] Over-harvest results from human demand for Magdalena River turtle consumption.[4]
Locals believe that feeding on the turtles offer many medicinal qualities.[4] These include easing pregnancy recovery, curing diseases, boosting strength and longevity, and creating natural aphrodisiacs.[4] Climate change has led to discernible changes in temperature-dependent sex determination and movement patterns.[10][7] It has also contributed to nesting site flooding and other habitat alterations.[7]
While anthropogenic causes are most pronounced, several life history factors contribute to the Magdalena River turtles endangerment, as well.[5] High rates of mortality are seen in eggs, hatchlings, and juveniles.[5] 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.[5] They also require multiple habitats, one for nesting and another for feeding, which result in strenuous migrations.[5]
Conservation approaches
The most commonly used conservation approach for Magdalena River turtle conservation is "head-starting".[4] However, research efforts have been focused on finding more effective means on conservation, as understanding of the turtles' endangered nature is relatively novel.[11][6] 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.[12] Studies are applying faster demographic modeling and surveying to better understand the species and establish practical conservation efforts.[5][11] Faster demographic modeling of the species' vital rates is focused on analyzing the contributions of each life stage and intrinsic growth rates (r).[5] Surveying has shown that local Magdalena River turtle consumption habits have changed and knowledge of their ecological role has improved.[11] This suggests that community-based strategies, including distribution of educational material, is proving effective in the conservation effort of Magdalena River turtles.[11]
References
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